For conservation purposes islands are considered safe refuges for many species, particularly in r... more For conservation purposes islands are considered safe refuges for many species, particularly in regions where introduced predators form a major threat to the native fauna, but island populations are also known to possess low levels of genetic diversity. The New Zealand archipelago provides an ideal system to compare genetic diversity of large mainland populations where introduced predators are common, to that of smaller offshore islands, which serve as predator-free refuges. We assessed microsatellite variation in South Island robins (Petroica australis australis), and compared large mainland, small mainland, natural island and translocated island populations. Large mainland populations exhibited more polymorphic loci and higher number of alleles than small mainland and natural island populations. Genetic variation did not differ between natural and translocated island populations, even though one of the translocated populations was established with five individuals. Hatching failure was recorded in a subset of the populations and found to be significantly higher in translocated populations than in a large mainland population. Significant population differentiation was largely based on heterogeneity in allele frequencies (including fixation of alleles), as few unique alleles were observed. This study shows that large mainland populations retain higher levels of genetic diversity than natural and translocated island populations. It highlights the importance of protecting these mainland populations and using them as a source for new translocations. In the future, these populations may become extremely valuable for species conservation if existing island populations become adversely affected by low levels of genetic variation and do not persist.
High rates of extra-pair paternity (EPP) can be relatively common in passerines whereas low rates... more High rates of extra-pair paternity (EPP) can be relatively common in passerines whereas low rates or absence of EPP are often associated with taxa that are long-lived and exhibit obligatory paternal care. We examined EPP in an under-represented category: passerine species with relatively long life spans (or low annual mortality rates). Specifically, we studied EPP in New Zealand saddlebacks Philesturnus carunculatus and robins Petroica australis, two species with unusually low annual mortality rates (6.5–11% and 10–20% respectively). No EPP (0%) was detected in saddlebacks (39 pairs, 202 offspring) and only one case of EPP (1.9%) was detected in robins (54 pairs, 198 offspring). Genetic monogamy in these passerine species supports the hypothesis that low annual mortality rates play an important role in explaining variation in rates of EPP across species.
Populations established with a small number of founders are thought to have a high risk of extinc... more Populations established with a small number of founders are thought to have a high risk of extinction due to Allee effects, demographic stochasticity, inbreeding and reduced genetic variation. We tested whether the initial number of birds released was related to persistence in reintroductions of saddlebacks (Philesturnus carunculatus) and robins (Petroica australis) to New Zealand offshore islands. Data were analysed for 31 populations that had been observed for at least 3 years since reintroductions. The numbers released ranged from 5-188. Most of the populations (26) survived and grew, including five from less than 15 founders, and four out of the five extinctions were attributable to introduced mammalian predators. The number of individuals released did not significantly affect extinction probability. The ability of these small releases to establish populations can be attributed to the closed nature of the islands (allowing birds to find mates), low mortality rates following release and high growth rates at low density. Stochastic simulation models based on data from two reintroduced populations suggested that populations with four founders (two male, two female) would have a negligible chance of extinction through demographic stochasticity and would be able to grow even if there were high rates of egg failure through inbreeding.
For conservation purposes islands are considered safe refuges for many species, particularly in r... more For conservation purposes islands are considered safe refuges for many species, particularly in regions where introduced predators form a major threat to the native fauna, but island populations are also known to possess low levels of genetic diversity. The New Zealand archipelago provides an ideal system to compare genetic diversity of large mainland populations where introduced predators are common, to that of smaller offshore islands, which serve as predator-free refuges. We assessed microsatellite variation in South Island robins (Petroica australis australis), and compared large mainland, small mainland, natural island and translocated island populations. Large mainland populations exhibited more polymorphic loci and higher number of alleles than small mainland and natural island populations. Genetic variation did not differ between natural and translocated island populations, even though one of the translocated populations was established with five individuals. Hatching failure was recorded in a subset of the populations and found to be significantly higher in translocated populations than in a large mainland population. Significant population differentiation was largely based on heterogeneity in allele frequencies (including fixation of alleles), as few unique alleles were observed. This study shows that large mainland populations retain higher levels of genetic diversity than natural and translocated island populations. It highlights the importance of protecting these mainland populations and using them as a source for new translocations. In the future, these populations may become extremely valuable for species conservation if existing island populations become adversely affected by low levels of genetic variation and do not persist.
When dispersal options are limited and encounters with relatives are likely, individuals need to ... more When dispersal options are limited and encounters with relatives are likely, individuals need to recognize and avoid mating with kin to avoid the fitness costs of close inbreeding. New Zealand robins and saddlebacks are genetically monogamous and possess life-history traits that predict they should show zero tolerance of close inbreeding. However, of 11 population-years of pedigree data, there was evidence of inbreeding avoidance in only 1 year. We also found no indication that incestuous pairings were avoided or that individuals were choosing genetically dissimilar mates based on microsatellite DNA analysis. Furthermore, a review of the literature revealed that inbreeding avoidance via kin recognition is common in cooperatively breeding birds, but pairbreeding birds such as robins and saddlebacks mate randomly with respect to relatedness. A model that incorporates encounter rates with close kin for various degrees of mate-searching effort shows that inbreeding avoidance is beneficial at intermediate to high levels of encounter rates with close kin (as found in cooperative breeders), but that random mating is more beneficial at low or extremely high encounter rates. We conclude that random mating normally results in such low rates of close inbreeding that it exerts negligible selection pressure to evolve kin recognition. Consequently, many threatened species are unlikely to have a natural ''built-in'' mechanism for avoiding close inbreeding, and the assumption of random mating built into many population viability models may be appropriate.
Successful founders of new populations may represent a non-random sample of potential founding in... more Successful founders of new populations may represent a non-random sample of potential founding individuals. Using a recent Saddleback Philesturnus carunculatus translocation as a natural experiment, we related morphology, parasite load and genetic variation of translocated individuals to subsequent survivorship to assess the traits of successful founders. We also included capture location and holding time in our models to account for variables particular to translocations. Generalized linear model results suggest that, in addition to capture location, poor body condition (males) and the presence of ectoparasites (females) significantly reduced survivorship. Despite recent claims in the literature, we found no evidence that genetic variation was associated with survivorship or parasite load.
Repeated population bottlenecks can lead to loss of genetic variation and normally should be avoi... more Repeated population bottlenecks can lead to loss of genetic variation and normally should be avoided in threatened species to preserve evolutionary potential. We examined the effect of repeated bottlenecks, in the form of sequential translocations, on loss of genetic variation in a threatened passerine, the saddleback (Philesturnus carunculatus carunculatus), a species that has recovered from a remnant population with historically low levels of genetic variation. Although a slight but nonsignificant loss of alleles may have occurred between the first-order translocation and the extirpated source population, first-, second-, and third-order translocated populations had very similar levels of genetic variation to each other. The most obvious difference among the seven island populations appeared to lie in allele frequencies with little or no loss of alleles among extant populations. Although sequential translocations are known to cause loss of variation in genetically diverse species, our study indicates that genetically depauperate species may be less sensitive to loss of genetic variation through founder events presumably because the few remaining alleles are well represented in founding individuals. These results show that ancient bottlenecks may have a long-term effect on genetic variation, to the extent that contemporary population bottlenecks may leave no appreciable genetic signature. Our results suggest that subjecting genetically depauperate endangered species to sequential translocations could be used to rapidly establish new populations without further eroding genetic variation.
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