Papers by Carla S. Pimentel
Oikos
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Interactions between pinewood nematodes and the fungal community of pine trees
Fungal Ecology
Abstract The pinewood nematode Bursaphelenchus xylophilus, is the pathogenic agent of pine wilt d... more Abstract The pinewood nematode Bursaphelenchus xylophilus, is the pathogenic agent of pine wilt disease and a globally notable pine pest. Despite being a plant pathogen, B. xylophilus has a mycophagous phase during its life cycle. We assessed the capacity for polyphagy of mycetophagous pinewood nematodes, testing which of the common species of fungi in pine trees provide better food and higher population growth rates. B. xylophilus performed particularly well on airborne fungi, namely the endophytes Botrytis cinerea and Cladosporium herbarum, and the pathogens Sirococcus conigenus and Sphaeropsis sapinea. Surprisingly, growth performance was not as good on the blue stain species (Ophiostoma spp. and Leptographium spp.) which are considered natural associates of B. xylophilus in the wild. Most of the fungi nonetheless permitted positive population growth of B. xylophilus, which is polyphagous and capable of feeding on numerous fungal species with diverse ecological niches.
Methods to obtain and maintain cultures of pinewood nematodes, <i>Bursaphelenchus xylophilus</i>
The pinewood nematode <i>Bursaphelenchus xylophilus</i>, native from North America, i... more The pinewood nematode <i>Bursaphelenchus xylophilus</i>, native from North America, is the causal agent of the pine wilt disease, being considered one of the most important invasive pests in Eurasian pine forests. The establishment of laboratory isolates of <i>B. xylophilus</i> has been crucial to research on this important pathogen of pine trees. However, studies on the effects of <i>in vitro</i> serial passage on the pathogen evolution, and suitability of standard culture media to the wild populations have been surprisingly few. In the present work, we tested the suitability of different culture media for obtaining <i>B. xylophilus</i> lab populations from dauer larvae that have been isolated from pine sawyer beetles (<i>Monochamus</i> spp.), which serve as their vector. We conducted studies in North America and Portugal. Results showed that adding groundwood (xylem from pine trees) to standard agar medium dramatically im...
Disentangling the effects of climate and defoliation on forest growth: The case of an outbreak of a Thaumetopoea pityocampa population with a shifted phenology in a Pinus pinaster monoculture
Forest Ecology and Management, 2021
Abstract Forests are widely affected by disturbances, both abiotic, climate related, and biotic, ... more Abstract Forests are widely affected by disturbances, both abiotic, climate related, and biotic, like insect outbreaks. However, the impact of the interaction of these disturbances on tree growth is still not well understood. On the present work the impact of climatic and long-term defoliation by Thaumetopoea pityocampa (Dennis and Schiff.) during summer on Pinus pinaster growth was evaluated. At the National Pine Forest of Leiria, in Portugal, we sampled defoliated and non-defoliated forest plots covered by monocultures of young P. pinaster trees. Growth was assessed using dendrochronological techniques, and its relationship with climatic variability, including severe droughts, and defoliation, was analysed using hierarchical partitioning models. Results suggest that long term defoliation result in trees not being able to take advantage of favourable climatic conditions, leading to a reduced radial and height growth. Droughts were the major climatic disturbance, causing growth reduction as well, although the impacts of both disturbances did not act synergistically. Additionally, models showed that previous year climatic conditions have a significant effect on annual growth, namely, previous year annual precipitation and temperature. Yet, the best model obtained include a positive effect of the previous year annual precipitation and a negative effect of the interaction between this climatic parameter and defoliation. This work illustrates the potential of defoliation and climate to reduce forest productivity and the importance of water availability for tree development in Mediterranean climates. In addition, our results also emphasise the need to simultaneously evaluate the effects of different disturbances, particularly in a time of global change when an increase in forests disturbances is expected. This approach will certainly contribute to a more informed management of production forests.
Life-history strategies and virulence in the pinewood nematode
Physiological and Molecular Plant Pathology, 2021
Sublethal infection of different pine species by the pinewood nematode
Plant Pathology, 2020
Bursaphelenchus xylophilus, the pinewood nematode and causal agent of pine wilt disease (PWD), is... more Bursaphelenchus xylophilus, the pinewood nematode and causal agent of pine wilt disease (PWD), is a globally destructive pine pest. PWD is favoured by high temperatures and drought, but B. xylophilus can also persist in symptomless hosts in areas not prone to PWD. We compared seedlings of different Pinus species that were inoculated with B. xylophilus when well‐watered and under moderate temperatures, conditions that favour sublethal infections. We compared isolates of B. xylophilus in south‐west Europe (Portugal) and south‐east USA (Louisiana). P. pinea, P. pinaster, and P. radiata were challenged in both areas with inoculations of local B. xylophilus. P. sylvestris in Portugal and P. palustris in Louisiana were also tested. Seedling mortality was low, as expected, but nematode establishment was common. There were higher nematode densities and more damage in seedlings of P. sylvestris and P. radiata, followed by P. pinaster, with P. pinea and P. palustris proving to be more tolerant. Life history of hosts was a better predictor of resistance to B. xylophilus than geographical origin, even under sublethal conditions. Fast‐growing species (P. radiata and P. pinaster) appeared most likely to be symptomless carriers in areas not prone to the development of PWD. Cold‐adapted species (P. sylvestris) may still be suitable hosts for the pathogen, even at the sublethal conditions of their distribution areas. There were more nematodes per gram of host using nematode isolates from Portugal. Nonetheless, our results opposed the hypothesis that North American pinewood nematodes have such low virulence that they are obligatorily saprophytic.
Journal of Forest Research, 2020
The pinewood nematode Bursaphelenchus xylophilus, native from North America, is the causal agent ... more The pinewood nematode Bursaphelenchus xylophilus, native from North America, is the causal agent of the pine wilt disease, being considered one of the most important invasive pests in Eurasian pine forests. The establishment of laboratory isolates of B. xylophilus has been crucial to research on this important pathogen of pine trees. However, studies on the effects of in vitro serial passage on the pathogen evolution, and suitability of standard culture media to the wild populations have been surprisingly few. In the present work, we tested the suitability of different culture media for obtaining B. xylophilus lab populations from dauer larvae that have been isolated from pine sawyer beetles (Monochamus spp.), which serve as their vector. We conducted studies in North America and Portugal. Results showed that adding groundwood (xylem from pine trees) to standard agar medium dramatically improves the survival and growth of wild populations of B. xylophilus in the laboratory. Further, malt extract agar proved to be more suitable than potato dextrose agar. Once in culture, B. xylophilus grew well feeding on either of two fungus species: Botrytis cinerea or Ophiostoma minus. Growth rates were highest on B. cinerea, the most widely used fungus to maintain lab cultures of B. xylophilus, but O. minus has the advantage of being a natural associate and putative diet of wild populations. There remains a need for better understanding of how to obtain and maintain laboratory populations of this pathogen such that their natural characteristics are maintained.
Journal of Thermal Biology, 2018
Direct effects of temperature on plant pathogens can be crucial to determine the onset and epidem... more Direct effects of temperature on plant pathogens can be crucial to determine the onset and epidemiology of disease. The pinewood nematode Bursaphelenchus xylophilus, the causal agent of the pine wilt disease (PWD), has a wide geographical distribution in Eurasia and East Asia, and local temperatures are considered determinant for the onset of the PWD. However, direct effects of temperature on this pathogen are never considered when forecasting its distribution and impact. On the present study we assessed: 1) at which temperatures is the development of wild populations of the pinewood nematode optimized; 2) if there is niche divergence on different populations from its wide distribution area. For this we studied two populations originated from different latitudes in eastern NA, and used multi-model inference to evaluate the contributions of temperature, diet, and nematode population toward the growth rates of B. xylophilus. Although population origin had some effect on the predictive models, there seems to be niche conservatism, with temperatures of 28-29°C optimizing the growth rates of the pathogen. Thus, the use of the number of days in the summer with temperatures around 28-29°C would probably help to improve models forecasting B. xylophilus dispersion and PWD. The present work highlight the importance of considering adaptations to temperatures in forest pathogens with large geographical distributions, when building models forecasting the impact of climate on these organisms.
Forest Ecology and Management, 2019
The pinewood nematode, Bursaphelenchus xylophilus, has been identified as being responsible for t... more The pinewood nematode, Bursaphelenchus xylophilus, has been identified as being responsible for the decline of pine forests in Portugal, since its detection in the territory about 20 years ago. Forest decline due to disease and/or pests is a complex phenomenon, and a knowledge of the spatial patterns of tree mortality is important for providing an understanding of forest susceptibility and pest dynamics. Objectives: The aim of the present study was to investigate the relationship between the spatial structure of pine mortality and that of different climatic, edaphic and landscape variables in an area of Portugal where B. xylophilus is known to have spread during the last decade. Methods: Pine mortality was assessed in the field, in a large, complex area of Central-North Portugal. An ArcGis database with a range of environmental variables was created for the study area. Spatial autocorrelation of the different variables was investigated by means of Moran's I and Mantel r analysis. The relationship between pine decline and the different variables was analyzed using bivariate Moran's I. Results: Environmental descriptors exhibit a clear spatial pattern, influenced by an undulating landscape. Pine mortality is spatially aggregated; warm, dry locations with higher evapotranspiration present high values, and in areas of extensive pine occupancy in a diverse landscape mortality decreases. Conclusions: Forest mortality attributed to infestation by a non-native forest pathogen cannot be dissociated from the effects of climate and landscape diversity associated with pine forests. The analysis of landscape patterns appears to be crucial for gaining an understanding of forest pathology and decline.
Spatial patterns at host and forest stand scale and population regulation of the pine processionary moth Thaumetopoea pityocampa
Agricultural and Forest Entomology, 2016
Different spatial processes are likely to generate variability at different scales. Thus, the exp... more Different spatial processes are likely to generate variability at different scales. Thus, the explanation of patterns may be facilitated by knowledge about the spatial scales where variation in patterns occurs. In the present study, the link between spatial patterns of the pine processionary moth Thaumetopoea pityocampa Den. & Schiff. (Lepidoptera, Notodontidae) at two different scales, as well as its population dynamics, was assessed. First, the spatial patterns of T. pityocampa population were assessed at the forest stand scale by surveying the distribution of larval colonies within the pine forest, indicative of adult dispersion. Second, egg‐laying patterns across individual host‐plants, indicative of female oviposition choices, were assessed, as well as their impact on the survival of immature stages. It was found that T. pityocampa presents a gregarious distribution in homogeneous pine forests, over distances of a few dozen metres. At the pine tree scale, females tend to aggregate their egg batches, whereas aggregation increases with population density. Natural enemies such as parasitoids do not appear to play an important role in regulating the population dynamics of the species. At the same time, aggregation in individual hosts leads to increased mortality in the period from hatching to the third instar, which is notable at high population densities. A patchy distribution in the landscape over short distances has a potentially positive effect on population dynamics of the species, avoiding the Allee effect, and allowing for a rapid increase in population, even where initial numbers are low, leading to localized outbreaks. At the same time, increased mortality as a result of egg‐batch clumping at high population densities is a potential density‐dependent mechanism of population regulation.
Ecology and Evolution, 2016
Plant Pathology, 2016
The pinewood nematode, Bursaphelenchus xylophilus, originating from North America (NA), is a majo... more The pinewood nematode, Bursaphelenchus xylophilus, originating from North America (NA), is a major invasive pine pest in Eurasia. It was first detected in Portugal in 1999 associated with maritime pine, Pinus pinaster, and has been differently affecting the main local pine species, P. pinaster and P. pinea. Field studies and direct inoculation experiments in Pinus spp. seedlings, under controlled conditions, were performed to assess whether the differences in constitutive and inducible defences are determining the different susceptibility of pine host species to B. xylophilus. Host co-evolution with the pathogen was also assessed, including the NA P. radiata, widely used in forestry in the northeast of the Iberian peninsula. Pine mortality in the field was positively related with the abundance of B. xylophilus, and concentration of phenolics and condensed tannins in pines. In the greenhouse assay, seedling tissues were analysed for constitutive investment in defences, as well as the potential inducibility of those defences as driven by B. xylophilus inoculation. Slower growing P. pinea presented higher levels of constitutive defences than faster growing P. pinaster, with only P. pinaster being affected by B. xylophilus. Furthermore, co-evolution with the pathogen is important, with the fast-growing NA P. radiata presenting an inducible and effective response to B. xylophilus. Results point to the importance of integrating data on pine life history traits, including growth rate, and production of constitutive and inducible defences, into predictive models for this invasive forest pest.
Ecology and evolution, 2014
Nests are structures built to support and protect eggs and/or offspring from predators, parasites... more Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose nest sites and to build optimally sized nests, yet our current understanding of clutch size-nest size relationships is limited to small-scale studies performed over short time periods. Here, we quantified the relationship between clutch size and nest size, using an exhaustive database of 116 slope estimates based on 17,472 nests of 21 species of hole and non-hole-nesting birds. There was a significant, positive relationship between clutch size and the base area of the nest box or the nest, and this relationship did not differ significantly between open nesting and hole-nesting species. The slope of the relationship showed significant intr...
Methods in Ecology and Evolution, 2014
1. Secondary hole-nesting birds that do not construct nest holes themselves and hence regularly b... more 1. Secondary hole-nesting birds that do not construct nest holes themselves and hence regularly breed in nest boxes constitute important model systems for field studies in many biological disciplines with hundreds of scientists and amateurs involved. Those research groups are spread over wide geographic areas that experience considerable variation in environmental conditions, and researchers provide nest boxes of varying designs that may inadvertently introduce spatial and temporal variation in reproductive parameters. 2. We quantified the relationship between mean clutch size and nest box size and material after controlling for a range of environmental variables in four of the most widely used model species in the Western Palaearctic: great tit Parus major, blue tit Cyanistes caeruleus, pied flycatcher Ficedula hypoleuca and collared flycatcher F. albicollis from 365 populations and 79 610 clutches. 3. Nest floor area and nest box material varied non-randomly across latitudes and longitudes, showing that scientists did not adopt a random box design. Clutch size increased with nest floor area in great tits, but not in blue tits and flycatchers. Clutch size of blue tits was larger in wooden than in concrete nest boxes. 4. These findings demonstrate that the size of nest boxes and material used to construct nest boxes can differentially affect clutch size in different species. The findings also suggest that the nest box design may affect not only focal species, but also indirectly other species through the effects of nest box design on productivity and therefore potentially population density and hence interspecific competition.
Biological Journal of the Linnean Society, 2011
The present study aimed to investigate the relationship between growth rate, final mass, and larv... more The present study aimed to investigate the relationship between growth rate, final mass, and larval development, as well as how this relationship influences reproductive trade-offs, in the context of a gregarious lifestyle and the need to keep an optimal group size. We use as a model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, which occur in different seasons and thus experience different climatic conditions. Thaumetopoea pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However, in 1997, a population in which larval development occurs during the summer was discovered in Portugal, namely the summer population (SP), as opposed to the normal winter population (WP), which coexists in the same forest feeding on the same host during the winter. Both populations were monitored over 3 years, with an assessment of the length of the larval period and its relationship with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality at different life stages. The SP larval period was reduced as a result of development in the warmer part of the year, although it reached the same final mass and adult size as the WP. Despite an equal size at maturity, a trade-off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This contrasts with the findings obtained in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro-geographical scale for T. pityocampa, with females from northern latitudes and a colder environment producing more (and smaller) eggs. The results demonstrate the importance of the number of eggs in cold environments as a result of an advantage of large colonies when gregarious caterpillars develop in such environments, and these findings are discussed in accordance with the major theories regarding size in animals.
Biological Journal of the Linnean Society, 2010
The present study aimed to investigate how the impact of several factors linked to geography woul... more The present study aimed to investigate how the impact of several factors linked to geography would shape life-history traits in a gregarious species, using the pine processionary moth (PPM) Thaumetopoea pityocampa as a model system. PPM has a wide geographical distribution over the Mediterranean Basin, and it is a strictly gregarious species throughout larval development, where the total reproductive output of each female forms a colony. We reviewed both published and unpublished data on PPM from all over its distribution in the Mediterranean Basin and extracted data on fecundity, egg size, egg parasitoid mortality, flight period, and development time. These life-history traits were then related to location, expressed as latitude and altitude, local average temperatures, and host tree species. We found that PPM fecundity increaseed with latitude, concomitant with an increase in the length of development and an earlier onset of adult flight. These results are the opposite of that found in other Lepidoptera species with a wide geographical distribution, as well as in insects in general. We propose that a large colony size in PPM is important at higher latitudes because this confers an advantage for thermoregulation and tent building in areas where larvae have to face harsher conditions during the winter, thus shifting the optimal trade-off between the number and size of eggs with latitude. However, host tree species also affected the relationship between egg number and size and the optimal outcome of these traits is likely a compromise between different selection pressures.
Agricultural and Forest Entomology, 2014
Bursaphelenchus xylophilus (Steiner & Buhrer) (Nematoda: Aphelenchoididae), the pinewood nematode... more Bursaphelenchus xylophilus (Steiner & Buhrer) (Nematoda: Aphelenchoididae), the pinewood nematode and the causal agent of the pine wilt disease, is a globally important invasive pathogen of pine forests. It is phoretic in woodborer beetles of the genus Monochamus (Megerle) (Coleoptera, Cerambycidae) and has been able to exploit novel indigenous species of Monochamus (but only Monochamus) in newly-invaded areas. North America (NA) is the continent of origin for the B. xylophilus/Monochamus spp. phoretic system. NA also contains the largest number of Monochamus species known to act as vectors for B. xylophilus. Understanding this phoretic system in its native geographical area helps to explain the evolutionary ecology of pine wilt disease. 2 In the present study, we measured the flight phenology, size, sex ratios and species identity of Monochamus species in five geographically distant forests in NA. We also measured phoresy by B. xylophilus. 3 We found the nematode to be abundant across eastern NA but rare or absent in western NA. In eastern forests, nematode phoresy was highest on the Monochamus species that flew earliest in the year. However, in the southeast, where Monochamus is most likely multivoltine with a long flight season, we found vectors with high nematode loads throughout the season, indicating that B. xylophilus can be transmitted to new hosts during most part of the year. The frequency distribution of nematode dauers on Monochamus was highly aggregated. Bursaphelenchus xylophilus in NA appears to be able to use all available Monochamus species as vectors. 4 In native NA pine forests, the pinewood nematode appears to have an ecology that is sufficiently flexible to exploit different species (and both genders) of Monochamus, and disperse at different times of the year. This flexibility may contribute to its recent success in invading Eurasian pine forests. Keywords Biological invasions, flight phenology, North America, pine forests, plant parasitism, zero-inflated negative binomial distribution.
Impact of climatic variation on populations of pine processionary moth Thaumetopoea pityocampa in a core area of its distribution
Agricultural and Forest Entomology, 2011
There is growing appreciation of climatic effects on insect population dynamics at the margins of... more There is growing appreciation of climatic effects on insect population dynamics at the margins of distribution limits. Climatic effects might be less important and/or involve different drivers and processes near the centre of distributions.
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Papers by Carla S. Pimentel