Phenotypic Plasticity

Trematomus newnesi inhabited inshore (<20 m) subzero waters in McMurdo Sound where it fed in the water column on Euphausia crystallorophias and fishes. This sample included the largest reported specimens of this species. The length–weight relationship was Weight = 3.17 × 10−6 (Standard Length)3.34, n = 67, r2 = 0.95. The population was phenotypically plastic, with two distinct morphs easily separated by visual inspection – the typical morph and a large mouth/broad headed morph comprising 28% of the sample. The large mouth morph had a wider and blunter head, longer upper jaw, wider gape, more heavily ossified jaws and darker colouration. To document this morphology, four views of the head are illustrated. Inference from morphology and measurements suggested that the large mouth morph was more benthic than the typical semipelagic morph. Museum specimens from Cape Adare confirmed the presence of the large mouth morph 700 km north of McMurdo Sound. This is the first clear example of ...

Evolution of bacteria to selective chemical pressure (e.g. antibiotics) is well studied in contrast to the influence of physical stressors. Here we show that instantaneous physical stress in a homogeneous environment (without concentration gradient) induces fast adaptation of Escherichia coli. We exposed E. coli to a large number of collisions of around 105 per bacterium per second with sharp ZnO nanorods. The pressure exerted on the bacterial cell wall was up to 10 GPa and induced phenotype changes. The bacteria’s shape became more spherical, the density of their periplasm increased by around 15% and the average thickness of the cell wall by 30%. Such E. coli cells appeared almost as Gram-positive bacteria in the standard Gram staining. Additionally, we observed a combination of changes occurring at the genomic level (mutations identified in form of single nucleotide polymorphisms) and down-regulation of expression of 61 genes encoding proteins involved in β-oxidation of fatty acid...

Diatoms are well known for their regularly patterned siliceous cell walls (frustules) and the apparent fidelity with which wall construction is replicated at each cell division, yet it is also known that morphological changes can occur as cell size decreases, following successive vegetative divisions. In addition, examples of heterovalvy, when the two halves (valves) of a single frustule differ morphologically (apart from the monoraphid diatoms, which are inherently heterovalvate), can be found in the literature

In dioecious species, sex-related adaptive strategies, influenced by natural and sexual selection, allow each sex to meet the specific demands of reproduction. Differences in ecophysiological traits between males and females may rely on innate differences in secondary sex traits such as structural and functional leaf traits. We tested structural sexual leaf dimorphism in Pistacia vera L. and the intersexual differences in sun–shade acclimation processes expected from the different adaptive strategies of males and females. Fifteen structural and functional leaf traits were compared in 50-year-old trees between females with low fruit load and males under sun and shade conditions. Despite the low additional energy investment in reproduction in females, remarkable sex effects in leaf structure and function were observed. Male trees had smaller leaves with significantly lower total conducting petiole area (TCA) and higher stomatal density, water use efficiency and concentration of phenol...

Climate change-induced elevated temperatures and drought are considered to be serious threats to forest ecosystems worldwide, negatively affecting tree growth and viability. We studied nine European beech (Fagus sylvatica L.) provenances located in two provenance trial plots with contrasting climates in Central Europe. Stomata play a vital role in the water balance of plants by regulating gaseous exchanges between plants and the atmosphere. Therefore, to explain the possible adaptation and acclimation of provenances to climate conditions, stomatal (stomatal density, the length of guard cells, and the potential conductance index) and leaf morphological traits (leaf size, leaf dry weight and specific leaf area) were assessed. The phenotypic plasticity index was calculated from the variability of provenances’ stomatal and leaf traits between the provenance plots. We assessed the impact of various climatic characteristics and derived indices (e.g., ecodistance) on intraspecific differen...

Knowledge about the root system structure and the uptake efficiency of root orders is critical to understand the adaptive plasticity of plants towards salt stress. Thus, this study describes the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe NaCl stress on the level of root orders. Phenotypic root traits known to influence uptake processes, for example frequency of root orders, specific root area, cortical thickness, and xylem traits, did not change homogeneously throughout the root system, but changes after 6 months under 90 mM NaCl stress were root order specific. Chloride accumulation significantly increased with decreasing root order, and the Cl 2 concentration in lower root orders exceeded those in leaves. Water flux densities of firstorder roots decreased to <20% under salinity and did not recover after stress release. The water flux densities of higher root orders changed marginally under salinity and increased 2-to 6-fold in second and third root orders after short-term stress release. Changes in root order frequency, morphology, and anatomy indicate rapid and major modification of C. volkameriana root systems under salt stress. Reduced water uptake under salinity was related to changes of water flux densities among root orders and to reduced root surface areas. The importance of root orders for water uptake changed under salinity from root tips towards higher root orders. The root order-specific changes reflect differences in vulnerability (indicated by the salt accumulation) and ontogenetic status, and point to functional differences among root orders under high salinity.

Clinal variation in life histories can be genetically based, resulting from selection imposed by different environments, or it may be due to the differential expression of phenotypically plastic traits. We examined the cline in voltinism in the egg-diapausing cricket Allonemobius socius, with populations spanning the switch from a univoltine to a bivoltine phenology. A common garden experiment was employed, using environments that mimicked photoperiod and temperature conditions found in the field. There were only small differences in development time among populations, and the difference in phenology observed in the field is likely due to clinal variation in the length of the growing season. We found large genetically-based differences in the reaction norm for egg diapause that were further magnified by environmental cues. The synergism of genetic and environmental effects was an example of cogradient selection. In the zone of transition between phenologies, voltinism appeared to be a conditional strategy, rather than a genetic polymorphism. First-generation females from this area can lay either direct-developing or diapause eggs depending on the likelihood that a second generation will have sufficient time to develop. For this species, the cline in voltinism is the result of a combination of environmental effects on development, and genetic and environmental influences on egg diapause propensity.

Local climate is an important source of selection on thermal reaction norms that has been well investigated in cline studies, where populations sampled along altitudinal or latitudinal gradients are compared. Several biotic factors vary with climate but are rarely integrated as alternative agents of selection to climatic factors. We tested the hypothesis that habitat may select for thermal reaction norms and magnitude of phenotypic plasticity in a drosophila parasitoid, independently of the climate of origin. We sampled populations of Leptopilina boulardi, a Drosophila parasitoid in two different habitats, orchards and forests. Orchards offer laying opportunities over small distances for parasitoids, with a low variability in the number of hosts per patch, while forests offer more dispersed and more variable patches. The sampling was realised in a temperate and a Mediterranean climate. We measured egg load, volume of eggs, longevity and lipid content for parasitoids reared at two temperatures. Reaction norms were opposite for populations from forests and orchards for investment in reproduction, independently of the climate of origin. The maximal investment of resources in reproduction occurred at the lower temperature in orchards and the higher temperature in forests. Host distribution differences between habitats may explain these opposite reaction norms. We also observed a flatter reaction norm for egg load in forests than in orchards. This relative canalization may have been selected in response to the higher variability in laying opportunities observed in forests. Our results demonstrate the potential role of resource distribution in evolution of thermal plasticity.

Understanding the speed of and the type of mechanisms that species use to adapt to rapid change is a central question in evolutionary biology. Classically, the two mechanisms denoted in the literature that allow individuals to address these environmental changes are either phenotypic plasticity or rapid evolutionary changes. However, phenotypic plasticity itself can evolve rapidly. In this study, we investigated the genetic differentiation between marginal and core populations of a high-trophic level insect,Leptopilina boulardi, aDrosophilaparasitoid, which has exhibited a very rapid progression northward of its geographical range. Several life history traits have been investigated in different populations according to four fluctuating thermal regimes that mimic the thermal conditions in the field. We found that at low developmental temperature, the two northern marginal populations that have to face a colder winter, survive longer than the two core populations. In addition, the nor...

Bateson & Brindley (1892) reported that males of the rhinoceros beetle Xylotrupes gideon are dimorphic (i.e. occurring in two distinct forms) with respect to size of the prominent cephalic horn. This claim was based on a comparison of frequency distributions for size of the horn (bimodal) and size of the body (unimodal). Bateson and Brindley did not realize, however, that a bivariate plot of horn length against body size follows a steep, S-shaped trajectory, or that steepness of such a curve-and not dimorphism-underlies the bimodal frequency distribution for size of the horn. The bivariate distribution for horn size vs. body size is continuous and without breaks or interruptions, so the beetles merely exhibit a pattern of allometric variation that went unrecognized at the time. Other species of dynastine beetle also display patterns of sigmoid allometry, but only those with the steepest slopes for the allometric curve also have bimodal frequency distributions for size of the horn. The concept of male dimorphism in X. gideon and other dynastine beetles needs to be reconsidered in the light of findings reported here and elsewhere.

I used linear and nonlinear regression to reexamine the allometric relationship between length of the cephalic horn and width of the pronotum (a measure of body size) for males of 28 species of rhinoceros beetle (Coleoptera, Scarabaeidae, Dynastinae). An earlier investigation reported that variation in relative size of the horn conforms in most of the 28 species to a pattern of discontinuous, loglinear allometry, which implies, in turn, that two different power equations are needed to describe the full range in untransformed data. My analyses indicate, however, that allometric variation is continuous in all 28 species and that pattern in each of the original bivariate distributions is well described by a single mathematical function. Allometric variation on the original, arithmetic scale is linear for some species; either linear or slightly sigmoidal for other species; and decidedly sigmoidal in still other species. So-called major and minor morphs merely represent the extremes in absolute and relative size for the horn on animals drawn from the same, continuous distribution. The different findings reported in the earlier investigation resulted from insidious problems introduced by logarithmic transformation of the original bivariate data coupled with an overly complex statistical protocol for classifying individual males as either "major" or "minor." Attempts at classification lead inevitably to oversimplification and misrepresentation of the pattern of allometric variation. Focus needs to return to describing and interpreting pattern in untransformed observations because the relationship between the original variables is the relationship of interest.

An organism’s reaction to environmental changes is mediated by coordinated responses of multiple tissues. Additionally, parental priming may increase offsprings’ acclimation potential to changing environmental conditions. As acidification of oceans continues to intensify it is critical to assess the acclimation potential of species at the whole organismal scale. To do this we need to understand the cross-talk between tissues in regulating and responding to pH changes. Here by using a multi-tissue approach we determine the influence of 1) variation in parental behavioural tolerance and 2) parental environment, on molecular responses of their offspring in a coral reef fish. The gills and liver showed the highest transcriptional response to OA conditions in juvenile fish regardless of the parental environment, while the brain and liver showed the greatest signal of intergenerational acclimation. Key functional pathways that were altered in the brain and liver upon within-generational C...

Intraspecific morphological variation in the wild penaeid shrimps was studied in four estuarine and two shallow-water study sites in Malindi-Ungwana Bay. Three morphometric characteristics, body length, carapace length and total length describing shape of penaeid shrimps were used. Total length, the explanatory variable, brings out significant information in shrimps, while groups of population that varied significantly in terms of morphometric variations were easily differentiated (P < 0.05) across the sample stations. Generally, Principle Component Analysis dimensions for all shrimps except the Penaeus canaliculatus indicated an inversely correlation between body length and carapace length and a good correlation of carapace length and total length. Several species displayed intraspecific morphological variability where shape variations increased with size and postlarva were closer to each other than adults along the first axis of Principle Component Analysis. The present study concludes that the variability among individual species within each population indicates the presence of high genetic diversity among the populations of different shrimps that give rise to genetically panmictic populations within the Malindi-Ungwana Bay.

PremiseSpecies delimitation in parasitic organisms is challenging because traits used to identify species are often plastic and vary depending on the host. Here, we use species from a recent radiation of generalist hemiparasitic Euphrasia to investigate trait variation and trait plasticity. We tested whether Euphrasia species show reliable trait differences, investigated whether these differences correspond to life history trade‐offs between growth and reproduction, and quantified plasticity in response to host species.MethodsCommon garden experiments were used to evaluate trait differences between 11 Euphrasia taxa grown on a common host, document phenotypic plasticity when a single Euphrasia species is grown on eight different hosts, and relate observations to trait differences recorded in the wild.ResultsEuphrasia exhibited variation in life history strategies; some individuals transitioned rapidly to flowering at the expense of early season growth, while others invested in veget...

ABSTRACTPremise of the studyParasite lifetime reproductive success is determined by both genetic variation and phenotypically plastic life history traits that respond to host quality and external environment. Here, we use the generalist parasitic plant genus Euphrasia to investigate life history trait variation, in particular whether there is a trade-off between growth and reproduction, and how life history traits are affected by host quality.MethodsWe perform a common garden experiment to evaluate life history trait differences between eleven Euphrasia taxa grown on a common host, document phenotypic plasticity when a single Euphrasia species is grown on eight different hosts, and relate our observations to trait differences recorded in the wild.Key resultsEuphrasia exhibit a range of life history strategies that differ between species that transition rapidly to flower at the expense of early season growth, and those that invest in vegetative growth and delay flowering. Many life h...

Objetivos: el objetivo del estudio fue evaluar la respuesta al tratamiento y seguridad del alendronato de sodio en una presentación de cápsulas blandas de gelatina (Neobon 70 ®), en mujeres posmenopáusicas con osteoporosis u osteopenia. Métodos: estudio clínico multicéntrico abierto a un año de tratamiento en mujeres postmenopáusicas. Las pacientes fueron asignadas a recibir 70 mg cada semana de alendronato sódico en presentación de cápsulas de gelatina blanda. Los desenlaces primarios fueron la densidad mineral ósea medida por DEXA y el valor plasmático del C-Telopéptido. La condición ósea fue evaluada por densitometría al inicio del estudio, al mes 6 y a los 12 meses de tratamiento. La resorción ósea fue evaluada por los niveles de C-Telopéptido basal, a los 3, 6 y 12 meses de tratamiento. Como desenlace secundario se evaluó la presentación de eventos adversos secundarios. Resultados: el estudio incluyó 146 mujeres reclutadas en diez centros de consulta externa de reumatología en cuatro ciudades de Colombia, que tuvieran diagnóstico de osteoporosis u osteopenia. La media de edad fue de 67±8 años (rango entre 45,7 y 92,8 años), y el promedio de tiempo transcurrido desde el inicio de la menopausia fue de 16±7,8 años. Treinta pacientes (20,54%) tenían

The ability to form symbiotic associations with soil microorganisms and the consequences for plant growth were studied for three woody legumes grown in five different soils of a Portuguese coastal dune system. Seedlings of the invasive Acacia longifolia and the natives Ulex europaeus and Cytisus grandiflorus were planted in the five soil types in which at least one of these species appear in the studied coastal dune system. We found significant differences between the three woody legumes in the number of nodules produced, final plant biomass and shoot 15 N content. The number of nodules produced by A. longifolia was more than five times higher than the number of nodules produced by the native legumes. The obtained 15 N values suggest that both A. longifolia and U. europaeus incorporated more biologically-fixed nitrogen than C. grandiflorus which is also the species with the smallest distribution. Finally, differences were also found between the three species in the allocation of biomass in the different studied soils. Acacia longifolia displayed a lower phenotypic plasticity than the two native legumes which resulted in a greater allocation to aboveground biomass in the soils with lower nutrient content. We conclude that the invasive success of A. longifolia in the studied coastal sand dune system is correlated to its capacity to nodulate profusely and to use the biologically-fixed nitrogen to enhance aboveground growth in soils with low N content.

Animals plastically adjust their physiological and behavioural phenotypes to conform to their social environment-social niche conformance. The degree of sexual competition is a critical part of the social environment to which animals adjust their phenotypes, but the underlying genetic mechanisms are poorly understood. We conducted a study to investigate how differences in sperm competition risk affect the gene expression pro les of the testes and two brain areas (posterior pallium and optic tectum) in breeding male zebra nches (Taeniopygia castanotis). In this pre-registered study, we investigated a large sample of 59 individual transcriptomes. We compared two experimental groups: males held in single pairs (low sexual competition) versus those held in two pairs (elevated sexual competition) per breeding cage. Using weighted gene co-expression network analysis (WGCNA), we observed signi cant effects of the social treatment in all three tissues. However, only the treatment effects found in the pallium were con rmed by an additional randomisation test for statistical robustness. Likewise, the differential gene expression analysis revealed treatment effects only in the posterior pallium (ten genes) and optic tectum (six genes). No treatment effects were found in the testis at the single gene level. Thus, our experiments do not provide strong evidence for transcriptomic adjustment speci c to manipulated sperm competition risk. However, we did observe transcriptomic adjustments to the manipulated social environment in the posterior pallium. These effects were polygenic rather than based on few individual genes with strong effects. Our ndings are discussed in relation to an accompanying paper using the same animals, which reports behavioural results consistent with the results presented here.

Traits that promote the maintenance of body temperatures within an optimal range provide advantages to ectothermic species. Pigmentation plasticity is found in many insects and enhances thermoregulatory potential as increased melanization can result in greater heat retention. The thermal melanism hypothesis predicts that species with developmental plasticity will have darker pigmentation in colder environments, which can be an important adaptation for temperate species experiencing seasonal variation in climate. The harlequin bug (Murgantia histrionica, Hemiptera: Pentatomidae, Hahn 1834) is a widespread invasive crop pest with variable patterning where developmental plasticity in melanization could affect performance. To investigate the impact of temperature and photoperiod on melanization and size, nymphs were reared under two temperatures and two photoperiods simulating summer and fall seasons. The size and degree of melanization of adults were quantified using digital imagery. T...

The analysis of phenotypic change is important for several evolutionary biology disciplines, including phenotypic plasticity, evolutionary developmental biology, morphological evolution, physiological evolution, evolutionary ecology and behavioral evolution. It is common for researchers in these disciplines to work with multivariate phenotypic data. When phenotypic variables exceed the number of research subjects-data called &#39;high-dimensional data&#39;-researchers are confronted with analytical challenges. Parametric tests that require high observation to variable ratios present a paradox for researchers, as eliminating variables potentially reduces effect sizes for comparative analyses, yet test statistics require more observations than variables. This problem is exacerbated with data that describe &#39;multidimensional&#39; phenotypes, whereby a description of phenotype requires high-dimensional data. For example, landmark-based geometric morphometric data use the Cartesian co...

Many evolutionary studies require an understanding of phenotypic change. However, while analyses of phenotypic variation across pairs of evolutionary levels (populations or time steps) are well established, methods for testing hypotheses that compare evolutionary sequences across multiple levels are less developed. Here we describe a general analytical procedure for quantifying and comparing patterns of phenotypic evolution. The phenotypic evolution of a lineage is defined as a trajectory across a set of evolutionary levels in a multivariate phenotype space. Attributes of these trajectories (their size, direction, and shape), are quantified, and statistically compared across pairs of taxa, and a summary statistic is used to determine the extent to which patterns of phenotypic evolution are concordant across multiple taxa. This approach provides a direct quantitative description of how patterns of phenotypic evolution differ, as well as a statistical assessment of the degree of repeatability in the evolutionary responses to selection among taxa. We describe how this approach can quantify phenotypic trajectories from many ecological and evolutionary processes, whose data encode multivariate characterizations of the phenotype, including: phenotypic plasticity, ecological selection, ontogeny and growth, local adaptation, and biomechanics. We illustrate the approach by examining the phenotypic evolution of several fossil lineages of Globorotalia.

Analyses of two-state phenotypic change are common in ecological research. Some examples include phenotypic changes due to phenotypic plasticity between two environments, changes due to predator/non-predator character shifts, character displacement via competitive interactions, and patterns of sexual dimorphism. However, methods for analyzing phenotypic change for multivariate data have not been rigorously developed. Here we outline a method for testing vectors of phenotypic change in terms of two important attributes: the magnitude of change (vector length) and the direction of change described by trait covariation (angular difference between vectors). We describe a permutation procedure for testing these attributes, which allows non-targeted sources of variation to be held constant. We provide examples that illustrate the importance of considering vector attributes of phenotypic change in biological studies, and we demonstrate how greater inference can be made than by evaluating variance components with MANOVA alone. Finally, we consider how our method may be extended to more complex data.

Population divergence in antipredator defence and behaviour occurs rapidly and repeatedly. Genetic differences, phenotypic plasticity or parental effects may all contribute to divergence, but the relative importance of each of these mechanisms remains unknown. We exposed juveniles to parents and predators to measure how induced changes contribute to shoaling behaviour differences between two threespine stickleback species (benthics and limnetics: Gasterosteus spp). We found that limnetics increased shoaling in response to predator attacks, whereas benthics did not alter their behaviour. Care by limnetic fathers led to increased shoaling in both limnetic and benthic offspring. Shoaling helps limnetics avoid trout and avian predation; our results suggest that this adaptive behaviour is the result of a combination of paternal effects, predator‐induced plasticity and genetic differences between species. These results suggest that plasticity substantially contributes to the rapid diverge...

Organisms are faced with variable environments and one of the most common solutions to cope with such variability is phenotypic plasticity, a modification of the phenotype to the environment. These modifications are commonly modelled in evolutionary theories as adaptive, influencing ecological and evolutionary processes. If plasticity is adaptive, we would predict that the closer to fitness a trait is, the less plastic it would be. To test this hypothesis, we conducted a meta-analysis of 213 studies and measured the plasticity of each reported trait as a coefficient of variation. Traits were categorized as closer to fitness—life-history traits including reproduction and survival related traits, and farther from fitness—non-life-history traits including traits related to development, metabolism and physiology, morphology and behaviour. Our results showed, unexpectedly, that although traits differed in their amounts of plasticity, trait plasticity was not related to its proximity to f...

Understanding the evolution of reaction norms remains a major challenge in ecology and evolution. Investigating evolutionary divergence in reaction norm shapes between populations and closely related species is one approach to providing insights. Here we use a meta-analytic approach to compare divergence in reaction norms of closely related species or populations of animals and plants across types of traits and environments. We quantified mean-standardized differences in overall trait means (Offset) and reaction norm shape (including both Slope and Curvature). These analyses revealed that differences in shape (Slope and Curvature together) were generally greater than differences in Offset. Additionally, differences in Curvature were generally greater than differences in Slope. The type of taxon contrast (species vs. population), trait, organism, and the type and novelty of environments all contributed to the best-fitting models, especially for Offset, Curvature, and the total differences (Total) between reaction norms. Congeneric species had greater differences in reaction norms than populations, and novel environmental conditions increased the differences in reaction norms between populations or species. These results show that evolutionary divergence of curvature is common and should be considered an important aspect of plasticity, together with slope. Biological details about traits and environments, including cryptic variation expressed in novel environmental conditions, may be critical to understanding how reaction norms evolve in novel and rapidly changing environments.

Plants offer a habitat for a range of interactions to occur among different stress factors. Epigenetics has become the most promising functional genomics tool, with huge potential for improving plant adaptation to biotic and abiotic stresses. Advances in plant molecular biology have dramatically changed our understanding of the molecular mechanisms that control these interactions, and plant epigenetics has attracted great interest in this context. Accumulating literature substantiates the crucial role of epigenetics in the diversity of plant responses that can be harnessed to accelerate the progress of crop improvement. However, harnessing epigenetics to its full potential will require a thorough understanding of the epigenetic modifications and assessing the functional relevance of these variants. The modern technologies of profiling and engineering plants at genomewide scale provide new horizons to elucidate how epigenetic modifications occur in plants in response to stress conditions. This review summarizes recent progress on understanding the epigenetic regulation of plant stress responses, methods to detect genome-wide epigenetic modifications, and disentangling their contributions to plant phenotypes from other sources of variations. Key epigenetic mechanisms underlying stress memory are highlighted. Linking plant response with the patterns of epigenetic variations would help devise breeding strategies for improving crop performance under stressed scenarios.

As global climates change, alien species are anticipated to have a growing advantage relative to their indigenous counterparts, mediated through consistent trait differences between the groups. These insights have largely been developed based on interspecific comparisons using multiple species examined from different locations. Whether such consistent physiological trait differences are present within assemblages is not well understood, especially for animals. Yet, it is at the assemblage level that interactions play out. Here, we examine whether physiological trait differences observed at the interspecific level are also applicable to assemblages. We focus on the Collembola, an important component of the soil fauna characterized by invasions globally, and five traits related to fitness: critical thermal maximum, minimum and range, desiccation resistance and egg development rate. We test the predictions that the alien component of a local assemblage has greater basal physiological t...

Most studies of predator-induced plasticity have focused on documenting how prey species respond to predators by modifying phenotypic traits and how traits correlate with fitness. We have previously shown that Pleurodema thaul tadpoles exposed to the dragonfly Rhionaeschna variegata responded strongly by showing morphological changes, less activity, and better survival than non-exposed tadpoles. Here, we tested whether there is a functional link between morphological plasticity and increased survival in the presence of predators. Tadpoles that experienced predation risk were smaller, less developed, and much less active than tadpoles without this experience. Burst speed did not correlate significantly with morphological changes and predator-induced deeper tails did not act as a lure to divert predator strikes away from the head. Although we have previously found that tadpoles with predator-induced morphology survive better under a direct predator threat, our results on the functional link between morphology and fitness are not conclusive. Our results suggest that in P. thaul tadpoles (1) burst speed is not important to evade predators, (2) those exposed to predators reduce their activity, and (3) morphological changes do not divert predator attacks away from areas that compromise tadpole survivalEE. Our results show that morphological changes in P. thaul tadpoles do not explain burst speed or lure attraction, although there was a clear reduction of activity, which itself reduces predation. We propose that changes in tadpole activity could be further analyzed from another perspective, with morphological change as an indirect product of behavior mediated by physiological mechanisms.

A challenge to ecologists and evolutionary biologists is predicting organismal responses to the anticipated changes to global ecosystems through climate change. Most evidence suggests that short-term global change may involve increasing occurrences of extreme events, therefore the immediate response of individuals will be determined by physiological capacities and life-history adaptations to cope with extreme environmental conditions. Here, we consider the role of hormones and maternal effects in determining the persistence of species in altered environments. Hormones, specifically steroids, are critical for patterning the behaviour and morphology of parents and their offspring. Hence, steroids have a pervasive influence on multiple aspects of the offspring phenotype over its lifespan. Stress hormones, e.g. glucocorticoids, modulate and perturb phenotypes both early in development and later into adulthood. Females exposed to abiotic stressors during reproduction may alter the phenot...

Lakes in Vuoksi drainage area in eastern Finland are inhabited by four salmonid species: the grayling (Thymallus thymallus), the Atlantic salmon (Salmo salar m. sebago), the brown trout (Salmo trutta m. lacustris), and the arctic charr (Salvelinus alpinus). We studied second-generation hatchery-reared juveniles of these freshwater salmonids from two age groups: (0+)-year-old fish, and (1+)-year-old fish; and compared their morphology in order to assess both intra-and interspecific variation in morphometric characters, and changes associated with growth. We observed that the (0+)-year-old salmonids are morphologically very similar, but as they grow, the interspecific differences become more pronounced. The characters that best discriminate among the studied species are body height and head dimensions as well as pectoral fin length. The grayling and the arctic charr are streamlined, whereas the salmon and the brown trout are more robust in their body shape. The shape of the studied species reflects also their adaptation to their native habitats. years of life. The arctic charr and the studied grayling stock live and reproduce in lakes (there are also river-reproducing stocks of the grayling), and the juveniles spend their first summer in the littoral area. All the species spawn in autumn except the grayling, that spawns in spring, but the eggs of all these species hatch in spring. They all thrive in cool or cold, clean, well-oxygenated water, but due to waterway constructions, and other manmade changes in their native environment as well as overfishing these species have became locally endangered. Phylogenetically salmonids are con-

Lakes in Vuoksi drainage area in eastern Finland are inhabited by four salmonid species: the grayling (Thymallus thymallus), the Atlantic salmon (Salmo salar m. sebago), the brown trout (Salmo trutta m. lacustris), and the arctic charr (Salvelinus alpinus). We studied second-generation hatchery-reared juveniles of these freshwater salmonids from two age groups: (0+)-year-old fish, and (1+)-year-old fish; and compared their morphology in order to assess both intra-and interspecific variation in morphometric characters, and changes associated with growth. We observed that the (0+)-year-old salmonids are morphologically very similar, but as they grow, the interspecific differences become more pronounced. The characters that best discriminate among the studied species are body height and head dimensions as well as pectoral fin length. The grayling and the arctic charr are streamlined, whereas the salmon and the brown trout are more robust in their body shape. The shape of the studied species reflects also their adaptation to their native habitats. years of life. The arctic charr and the studied grayling stock live and reproduce in lakes (there are also river-reproducing stocks of the grayling), and the juveniles spend their first summer in the littoral area. All the species spawn in autumn except the grayling, that spawns in spring, but the eggs of all these species hatch in spring. They all thrive in cool or cold, clean, well-oxygenated water, but due to waterway constructions, and other manmade changes in their native environment as well as overfishing these species have became locally endangered. Phylogenetically salmonids are con-

Vascular endothelial cells are characterized by a high degree of functional and phenotypic plasticity, which is controlled both by their pericellular microenvironment and their intracellular gene expression programs. To gain further insight into the mechanisms regulating the endothelial cell phenotype, we have compared the responses of lymphatic endothelial cells (LECs) and blood vascular endothelial cells (BECs) to vascular endothelial growth factors (VEGFs). VEGFR-3-specific signals are sufficient for LEC but not BEC proliferation, as shown by the ability of the specific ligand VEGF-C156S to stimulate cell cycle entry only in LECs. On the other hand, we found that VEGFR-3 stimulation did not induce LEC cell shape changes typical of VEGFR-2-stimulated LECs, indicating receptor-specific differences in the cytoskeletal responses. Genes induced via VEGFR-2 also differed between BECs and LECs: angiopoietin-2 (Ang-2) was induced via VEGFR-2 in BECs and LECs, but the smooth muscle cell (SMC) chemoattractant BMP-2 was induced only in BECs. Both BECs and LECs were able to promote SMC chemotaxis, but contact with SMCs led to down-regulation of VEGFR-3 expression in BECs in a 3-dimensional coculture system. This was consistent with the finding that VEGFR-3 is down-regulated in vivo at sites of endothelial cell-pericyte/smooth muscle cell contacts. Collectively, these data show intrinsic cell-specific differences of BEC and LEC responses to VEGFs and identify a pericellular regulatory mechanism for VEGFR-3 down-regulation in endothelial cells.

The effect of phenotypic plasticity in an evolutionary process, the so-called Baldwin effect, has been studied extensively for more than 100 years. Plasticity has been found to influence the speed of evolution towards an optimal genetic configuration, but whether or not plasticity can cause evolution to veer towards a different genetic configuration from what pursued by evolution alone, is still an open question. Here, this question is investigated analytically and experimentally, by means of an agent-based simulation of a foraging task, in an environment where the distribution of resources follows seasonal cycles. Foraging is limited by a trade-off that forces agents to either specialize to one specific resource type or generalize over all resource types at a lower success rate. Experiments demonstrate that in such an environment the introduction of learning, one of many instances of phenotypic plasticity, leads evolution to a different genetic configuration. Specifically, learning...

The lack of bone morphological markers associated with the human control of wild animals has prevented the documentation of incipient animal domestication in archaeology. Here, we assess whether direct environmental changes (i.e. mobility reduction) could immediately affect ontogenetic changes in long bone structure, providing a skeletal marker of early domestication. We relied on a wild boar experimental model, analysing 24 wild-born specimens raised in captivity from 6 months to 2 years old. The shaft cortical thickness of their humerus was measured using a 3D morphometric mapping approach and compared with 23 free-ranging wild boars and 22 pigs from different breeds, taking into account sex, mass and muscle force differences. In wild boars we found that captivity induced an increase in cortical bone volume and muscle force, and a topographic change of cortical thickness associated with muscular expression along a phenotypic trajectory that differed from the divergence induced by ...

Deciphering the plastic (non-heritable) changes induced by human control over wild animals in the archaeological record is challenging. We hypothesized that changes in locomotor behaviour in a wild ungulate due to mobility control could be quantified in the bone anatomy. To test this, we experimented with the effect of mobility reduction on the skeleton of wild boar ( Sus scrofa ), using the calcaneus shape as a possible phenotypic marker. We first assessed differences in shape variation and covariation in captive-reared and wild-caught wild boars, taking into account differences in sex, body mass, available space for movement and muscle force. This plastic signal was then contrasted with the phenotypic changes induced by selective breeding in domestic pigs. We found that mobility reduction induces a plastic response beyond the shape variation of wild boars in their natural habitat, associated with a reduction in the range of locomotor behaviours and muscle loads. This plastic signa...

Wheat (Triticum aestivum L.) growth habit traits, such as prostrate and erect growth, play a significant role in determining plant competitiveness, water-use efficiency, and resilience to environmental stress. To find significant marker trait associations (MTAs), a panel of 105 diverse spring wheat genotypes, previously genotyped with 15 K Infinium SNP array, was used to perform Genome-Wide Association Study (GWAS) of prostrate/erect growth habit (GH); flag leaf angle (FLA); plant height (PH), and tiller number per plant (TNPP). The phenotypic data was collected consistently over three consecutive years (2019-2020, 2020-2021, and 2021-2022). GWAS was conducted using five different models, including two single-locus models (GLM and MLM) and three multi-locus models (BLINK, FarmCPU, and MLMM), with a statistical significance threshold of-log10 (p) > 3. This rigorous analysis unveiled a total of 284 significant MTAs for all four traits across different environments and as well as from combined environment (CE). The highest number of MTAs putatively related to the traits was found on chromosomes 2D, 5B, 2B, and 3B. Subsequently, we used these MTAs to pinpoint 55 candidate genes (CGs) linked to the four studied traits. Zinc-finger transcription factors, such as C2H2 and CCCH; ABC transporter; glycoside hydrolase; ankyrin repeat protein and F-Box domain, known to be involved in studied traits were found as among the most likely CGs. Furthermore, an in silico expression analysis of these CGs was performed in various plant tissues and at different developmental stages. The results can contribute to a better understanding of the mechanisms that control prostrate and erect growth habits in wheat, and enhance its potential to adapt to resource-constrained environments. Keywords Triticum aestivum L. • GWAS • MTAs • Growth habit • Plant height • Flag leaf angle • Tiller number per plant * Shailendra Sharma

Wild and farmed animals are key elements of natural and managed ecosystems that deliver functions such as pollination, pest control and nutrient cycling. They are submitted to global changes with a profound impact on natural range and viability of animal species, emergence and spatial distribution of pathogens, land use, ecosystem services and farming sustainability. We urgently need to improve our understanding of how animal populations can respond adaptively and therefore sustainably to these new selective pressures. In this context, we explored the common points between animal production science and animal ecology to identify promising avenues of synergy between communities through the transfer of concepts and/or methodologies, focusing on seven concepts that link both disciplines. Animal adaptability, animal diversity, selection, animal management, animal monitoring, agroecology and viability risks were identified as key concepts that should serve the cross-fertilization of both...

Honey bee behavioral maturation exemplifies phenotypic plasticity, the ability of a single genotype to produce multiple phenotypes in response to environmental conditions . Behavioral maturation in honey bees is characterized by a socially regulated transition of adult worker bees from brood caring ("nursing") to foraging outside hives . It involves a suite of behavioral and physiological changes regulated by multiple environmental and internal factors. With the sequenced honey bee genome (Honey Bee Genome Sequencing Consortium, 2006), and development of genomic techniques, honey bee behavioral maturation provides a platform to understand molecular mechanisms underlying phenotypic plasticity. It has been demonstrated that phenotypic plasticity is associated with massive gene expression changes (Aubin-Horth & Renn, 2009). Therefore, it is essential to understand mechanisms of transcriptional regulation related to alternative phenotypes. This thesis focuses on two important aspects of transcriptional regulation: DNA methylation and transcription regulation by a nuclear receptor, Ultraspiracle (USP). Chapter 2 presents results that demonstrate that there is a functional CpG methylation system in honey bees, the first well-characterized functional DNA methylation system in insects. Catalytically active orthologs of vertebrate DNA methyltransferase (Dnmts) were identified along with methylated genes. Compared to vertebrate genomes, DNA methylations in honey bees are sparse, and all of the identified methylations are intragenic, similar to results shown in other invertebrates. Differences in DNA methylation density and positions suggest possibly different functions of DNA methylation in vertebrates and invertebrates. The characterization of a DNA methylation iii system in honey bees paves the way to study its function in honey bee behavioral maturation. This paper was published in 2006 in Science 314: 645-647. Chapter 3 presents a review of nutritional regulation of honey bee behavioral maturation and propose systems biology approaches to reveal the gene regulatory networks (GRNs) underlying behavioral maturation. It was published in 2010 in Wiley Interdisciplinary Reviews: Systems Biology and Medicine (published online in advance of print). Chapter 4 presents results on transcriptional regulation related to behavioral maturation in the context of fat bodies gene expression change. As a first step, we focus on transcription regulation by USP, a nuclear receptor implicated in JH signaling. USP was first demonstrated to regulate behavioral maturation. usp knockdown in honey bee workers' fat bodies significantly delayed onset of foraging. Genome-wide USP binding sites were then mapped in the fat bodies of nurses and foragers respectively. No difference of USP binding was detected, suggesting USP regulates gene expression depending on the availability of co-factors or ligands and chromatin environments. Functional analysis of USP putative genes reveals several genes involved in multiple signaling pathways in behavioral maturation, raising the possibility that USP works as a master regulator to integrate different signals during honey bee behavioral maturation. Graduate school has been a wonderful and transforming experience for me thanks to many great people I met at the University of Illinois, Urbana-Champaign. I would like to express my gratitude to my advisers, Gene Robinson and Craig Mizzen, for being always enthusiastic, patient and encouraging. I am especially thankful for their great advice and solid support to my career choice. I would like to thank other members of my committee, David Clayton, Hugh Roberson, Peter Jones and Christopher Schoenherr, for their special interest, excellent advice, and effort to make time for me. Peter Jones deserves special thanks. He taught me essential lab skills, and his optimism always cheers me up. I also want to thank other faculty members in the department of Cell and Developmental Biology especially Brian Freeman, and Lisa Stubbs for their interest and support. Thomas Newman and Karen Pruiett offered many forms of assistance and advice in Robinson lab and bee lab, without which my research projects could not go smoothly. My colleagues in Robinson lab are fun, hard-working and intelligent, who stimulated, helped, and entertained me. I would like to thank Miguel Corona and Zhengzheng Liang for their company in late night experiments, and Seth Ament for his brilliance and non-stop challenges. My friends and housemates in Brooks co-op offered delicious food, interesting conversation and valuable friendship, which were essential for my sanity in graduate school. Last but not least, I would like to thank my mother and grandparents for their loving and enthusiastic support through all these years. v

Elevated atmospheric carbon dioxide (eCO 2 ) often enhances rates of photosynthesis leading to increased productivity in trees. In their native habitats in Australia, eucalypts display considerable phenotypic plasticity in response to changes in environmental conditions. Little is known whether this plasticity can be harnessed effectively under future atmospheric eCO 2 conditions and be used to identify provenances with superior growth. Here, we report two experiments that assessed the physiological and growth responses of Eucalyptus grandis-one of the world's most important hardwood plantation species-to eCO 2 . We used 11 provenances from contrasting climates. Our selection was based on site-specific information of long-term temperature and water availability. In Experiment 1, four provenances exhibited significant variation in light-saturated photosynthetic rates (A sat ), stomatal conductance (g s ), and concentrations of non-structural carbohydrates in leaves, stems and roots when grown under ambient CO 2 (aCO 2 ). Biomass of leaves, stems and roots varied significantly and were negatively correlated with mean annual temperature (MAT) at seed origin, indicating that provenances from cooler, wetter climates generally produced greater biomass. Yet, stem growth of these provenances was not stimulated by eCO 2 . Given the vast environmental gradient covered by provenances of E. grandis, we expanded the selection from four to nine provenances in Experiment 2. This allowed us to validate results from Experiment 1 with its small selection and detailed measurements of various physiological parameters by focusing on growth responses to eCO 2 across a wider environmental gradient in Experiment 2. In Experiment 2, nine provenances also exhibited intraspecific differences in growth, but these were not related to climate of origin, and eCO 2 had little effect on growth traits. Growth responses under eCO 2 varied widely across provenances in both experiments, confirming phenotypic plasticity in E. grandis, though responses were not systematically correlated with climate of origin. These results indicate that selection of provenances for improved stem growth of E. grandis under future eCO 2 cannot be based solely on climate of origin, as is common practice for other planted tree species.

We aimed at exploring the plant functional traits whose stress-induced plasticity is altered by the presence of AM fungi, considering the direction of their changes. We also sought for a coordinated variation of plant biomass and functional traits, during plant adaptation to environmental stressors, and the role of AM status on the variation. We performed a meta-analysis across 114 articles spanning 110 plant species or cultivars. We quantified the size effect of AM symbiosis on the stress-induced plasticity of several reported and calculated functional traits, and using linear mixed model analysis (LMM). Correlation between traits plasticity and total biomass variation were also performed through LMM. The literature search and further selection yielded seven functional traits, extracted from 114 laboratory studies, including 888 observations and 110 plant species/cultivars. Evidence for significant effects of predictor variables (type of stress, AM symbiosis and/or their interaction) on plasticity were found for three of these functional traits: leafarea ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio. Our results provided evidence to accept the hypothesis that AM fungal inoculation may reduce the phenotypic plasticity of important plant functional traits leaf area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio, by decreasing its magnitude. We also found a weak correlation between traits plasticity and total biomass variation. Although our literature search and data collection were intensive and our results robust, the scope of our conclusions is limited by the agronomical bias of plant species targeted by the meta-analysis. Further knowledge on non-cultivable plant species and better understanding of the mechanisms ruling resources allocation in plants would allow more generalized conclusions.

Our hypothesis is that Lotus glaber (a glycophytic species, highly tolerant to saline-alkaline soils) displays a plastic root phenotypic response to soil salinity that may be influenced by mycorrhizal and rhizobial microorganisms. Uninoculated plants and plants colonised by Glomus intraradices or Mesorhizobium loti were exposed to either 150 or 0 mM NaCl. General plant growth and root architectural parameters (morphology and topology) were measured and phenotypic plasticity determined at the end of the salt treatment period. Two genotypes differing in their salt tolerance capacity were used in this study. G. intraradices and M. loti reduced the total biomass of non-salinised, sensitive plants, but they did not affect that of corresponding tolerant ones. Root morphology of sensitive plants was greatly affected by salinity, whereas mycorrhiza establishment counteracted salinity effects. Under both saline conditions, the external link length and the internal link length of mycorrhizal saltsensitive plants were higher than those of uninoculated control and rhizobial treatments. The topological trend (TT) was strongly influenced by genotype × symbiosis interaction. Under non-saline conditions, nodulated root systems of the sensitive plant genotype had a more herringbone architecture than corresponding uninoculated ones. At 150 mM NaCl, nodulated root systems of tolerant plants were more dichotomous and those of the corresponding sensitive genotype more herringbone in architecture. Notwithstanding the absence of a link between TTs and variations in plant growth, it is possible to predict a dissimilar adaptation of plants with different TTs. Root colonisation by either symbiotic microorganisms reduced the level of root phenotypic plasticity in the sensitive plant genotype. We conclude that root plasticity could be part of the general mechanism of L. glaber salt tolerance only in the case of non-symbiotic plants.

Metamorphosis has intrigued biologists for a long time as an extreme form of complex life cycles that are ubiquitous in animals. While investigated from a variety of perspectives, the ecological focus has been on identifying and understanding the ecological factors that aVect an individual's decision on when, and at what size, to metamorphose. Predation is a major factor that aVects metamorphic decisions and a recent review by Benard (Annu Rev Ecol Evol Syst 35:651-673, 2004)) documented how predator cues induce metamorphic changes relative to model predictions. Importantly, however, real predators aVect larval prey via several mechanisms beyond simple induction. In this paper, I contrast the leading models of metamorphosis, provide an overview of the multiple ways that predators can directly and indirectly aVect larval growth and development (via induction, thinning, and selection), and identify how each process should aVect the time to and size at metamorphosis. With this mechanistic foundation established, I then turn to the well-studied model system of larval amphibians to synthesize studies on: (1) caged predators (which cause only induction), and (2) lethal predators (which cause induction, thinning, and selection). Among the caged-predator studies, the chemical cues emitted by predators rarely induce a smaller size at metamorphosis or a shorter time to metamorphosis, which is in direct contrast to theoretical predictions but in agreement with Benard's (Annu Rev Ecol Evol Syst 35:651-673, 2004) review based on a considerably smaller dataset. Among the lethal-predator studies, there is a diversity of outcomes depending upon the relative importance of induction versus thinning with the relative importance of the two processes appearing to change with larval density. Finally, I review the persistent eVects of larval predators after metamorphosis including both phenotypic and Wtness eVects. At the end, I outline a number of future directions to allow researchers to continue gaining insight into how predators aVect the metamorphic decisions of their prey.

This study presents a detailed anatomical and histological investigation of the sea urchin Echinometra mathaei, emphasizing unique morphological structures and site-specific variations. In March 2023, echinoids were collected from two sites in the northern Red Sea at depths ranging from 0 to 5 meters. Various soft tissues, including the peritoneum, peristome, gills, podium, ampulla, and food canal, were extracted and preserved in 10% formalin. Sections of five microns were prepared and stained using the haematoxylin and eosin technique, followed by examination under a light microscope. The study concentrated on the external anatomy revealed distinct oral and aboral structures, including spines, pedicellariae, tube feet, and gills, with measurements indicating notable size and weight differences between specimens from the two collection sites. Internally, the digestive, nervous, and water vascular systems, as well as Aristotle's lantern and gonads, were described in detail. Histological analysis highlighted cellular arrangements in key structures such as the peristome, esophagus, stomach, and intestines, with unique features identified in connective tissues and epithelial layers. A key finding of this study is the observation of tricephalous pedicellariae, expanding the taxonomic understanding of E. mathaei. Morphological variations in tube feet ossicles between collection sites suggest environmental or genetic influences. Additionally, the ultrastructure of spines and stereom provided new insights into their composition and function. This comprehensive analysis enhances the knowledge of E. mathaei's anatomy, contributes to echinoid systematics, and underscores its ecological adaptations across varying habitats.

Rice germplasm investigated as completely randomized design under flooding and deficit irrigation conditions. The results of the association analysis indicated that RM29, RM63, and RM53 could be used for rice breeding programs to improve yields under deficit irrigation. The highest accuracy of rice performance prediction was 98.36 for the RFA (RFA) for panicle length, flag leaf length, and width, and the number of primary branches, after that, the MLP algorithm had better prediction power than other algorithms. When a genotypes code was considered as a criterion to classify the genotypes under the drought stress at the reproductive stage, the random forest algorithm (RFA) was the best algorithm based on the predictive accuracy (67.93), kappa value (0.514) and root mean square error (0.293). Based on the artificial intelligence methods, the RFA presented the best results to predict the response of genotypes to deficit irrigation using the microsatellite molecular data.

Large differences in the sea urchin Paracentrotus lividus (Lamarck) population structure have been observed in the NW Mediterranean. Differences have been attributed to removal of predatory fish through human f~shing activities. This study attempted to determine the effect of predation by fishes on sea urchin population structure. Three infralittoral areas (2 within a marine reserve with a high density of predatory fish, and 1 within an unprotected area with a low density of predatory fish) were studied to compare population structure differences attributable to differing fish predation pressure. P lividus populations were 3 to 4x denser and predation rates were -5x lower in the unprotected site than in the protected sites. Within the reserve, fish accounted for 100% of the predation. P lividus individual mean size was lower within the protected sites than in the unprotected site. Size-frequency distributions showed a negative exponential pattern for P llividus within the reserve, and a bimodal pattern outside the reserve. The urchins showed a crevice-dwelling behaviour in response to the intense predation in the marine reserve. Within the reserve, P lividus population structure appears to be determined by predation by fish. In contrast, in the unprotected area, where the predation rate is much lower, P lividus population structure appears to be determined by recruitment rate. We suggest that a recent increase in P lividus abundance on infralittoral rocky bottoms in the NW Mediterranean, where urchins are not harvested, is caused by human fishing activities. Since P lividus is the major benth~c herbivore in the NW Mediterranean, fishing level may, due to cascading effects, determine the structure of benthic infralittoral con~munities.

Genotype by environment interactions (GEI) play a major part in shaping the genetic architecture of quantitative traits and are confounding factors in genetic studies, for example, in attempts to associate genetic variation with disease susceptibility. It is generally not known what proportion of phenotypic variation is due to GEI and how many and which genes contribute to GEI. Behaviors are complex traits that mediate interactions with the environment and, thus, are ideally suited for studies of GEI. Olfactory behavior in Drosophila melanogaster presents an opportunity to systematically dissect GEI, since large numbers of genetically identical individuals can be reared under defined environmental conditions and the olfactory system of Drosophila and its behavioral response to odorants have been well characterized. We assessed variation in olfactory behavior in a population of 41 wild-derived inbred lines and asked to what extent different larval-rearing environments would influence...

Pulmonary alveolar type I cells (TI cell) are very large (~5400 μm 2 in surface area) squamous cells that cover more than 98% of the internal surface area of rodent lungs. In the past, TI cells were believed to serve only passive barrier functions, with no active functional properties in the lung. The fairly recent development of methods to isolate TI cells has permitted investigation of functions of this cell type for the first time. Resolvable by electron microscopy, TI cells contain microvilli and organelles typically associated with metabolic functions, such as mitochondria, abundant smooth and rough endoplasmic reticulum and Golgi apparatus. TI cells contain the molecular machinery necessary for ion transport and take up Na + , K + , and Cl -, from which one can infer that it is likely that they play a role in ion and fluid transport in vivo. Because the abundance/ μm 2 of highly selective Na + channels (HSC channels, consisting of all three ENaC subunits) is the same in TI and TII cells and because TI cells cover the majority of the lung internal surface, TI cells may play the major role in bulk transport of Na + . In vitro, TI cells can proliferate and exhibit phenotypic plasticity, raising the question of whether this cell type may play a role in development and lung repair after injury. From gene expression analysis of TI cells, one can infer a variety of other possible functions for TI cells. The development of techniques to administer transgenes specifically to TI cells will permit direct study of this cell type in vivo.