Search

Decreased genome-wide heterozygosity of inbred individuals can result in reduced survival and reproductive fitness (i.e. inbreeding depression). However, showing such heterozygosity-fitness correlations in endangered species, especially those that are already genetically impoverished, has proven to be difficult. New Zealand's kakapo ( S trigops habroptilus) is a critically endangered, flightless parrot that now survives only on islands free of introduced predators. The recent population bottleneck of 51 individuals, lek mating system (where only females care for eggs and young) and the fact that all but one of the population's founders came from the same insular population, render them particularly susceptible to inbreeding depression. The present study uses 25 microsatellite loci to derive estimates of relatedness to investigate heterozygosity-fitness correlations in kakapo. After accounting for the effects of co-variables, there was no evidence that male heterozygosity affected variation in egg fertility, but there was evidence that female heterozygosity affected fecundity (i.e. clutch size) and hatching success; that is, more homozygous females lay smaller clutches and had lower hatching success. The present study detected significant heterozygosity-fitness correlations and demonstrates that inbreeding is a contributing factor towards relatively low hatching success, which in turn reduces population growth in this highly endangered, flightless parrot. [ABSTRACT FROM AUTHOR]

Preserving genetic health is an important aspect of species conservation. Allelic diversity is particularly important to conserve, as it provides capacity for adaptation and thus enables long-term population viability. Allele retention is difficult to predict beyond one generation for real populations with complex demography and life-history traits, so we developed a computer model to simulate allele retention in small populations. Allele Retain is an individual-based model implemented in r and can be applied to assess management options for conserving allelic diversity in small populations of animals with overlapping generations. Allele Retain remedies the limitations of similar existing software, and its source code is freely available for further modification. Allele Retain and its supporting materials can be downloaded from https://sites.google.com/site/alleleretain/ or CRAN (http://cran.r-project.org). [ABSTRACT FROM AUTHOR]

Continuous inbreeding exposes deleterious recessive alleles to selection and can thereby lead to partial purging of the genetic load and reduced inbreeding depression. Purging has been well documented in experimental laboratory populations, but evidence of reduced inbreeding depression due to purging in wild populations is largely lacking. This study examines the inbreeding load associated with juvenile survival at a protected island site of a bottlenecked population of the Stewart Island robin Petroica australis rakiura. Based on a complete pedigree of the island population, we found little evidence that inbreeding coefficients explained any additional variation in juvenile survival, once demographic factors such as the effects of density, timing of fledging and age of mother were taken into account. Lethal equivalents, a standardized measure of the strength of inbreeding depression, were close to zero ( B=0.24, 95% CI=−1.92-1.04, n=326) and lower than that documented for an island population of a widespread congener ( B=6.71, 95% CI=−0.66-14.08, n=238) and for several other species for which significant inbreeding depression was detected ( B=1.30-7.47). There are several reasons as to why studies can fail to detect pedigree-based inbreeding depression in wild populations, but evidence presented here of low lethal equivalents and relatively high survival of both inbred and non-inbred juveniles are consistent with a population that has undergone partial purging of its genetic load during historical population bottlenecks. Although our study does not imply a complete absence of inbreeding depression, it is one of the first studies of a wild population where weak inbreeding depression for juvenile survival appears to be associated with a prolonged bottleneck. [ABSTRACT FROM AUTHOR]

Reintroductions of threatened species are increasingly common in conservation. The translocation of a small subset of individuals from a genetically diverse source population could potentially lead to substantial inbreeding depression due to the high genetic load of the parent population. We analysed 12 years of data from the reintroduced population of North Island robins Petroica longipes on Tiritiri Matangi Island, New Zealand, to determine the frequency of inbreeding and magnitude of inbreeding depression. The initial breeding population consisted of 12 females and 21 males, which came from a large mainland population of robins. The frequency of mating between relatives ( f>0; 39%, n=82 pairs) and close relatives ( f=0.25; 6.1%) and the average level of inbreeding ( f=0.027) were within the range reported for other small island populations of birds. The average level of inbreeding fluctuated from year to year depending on the frequency of close inbreeding (e.g. sib–sib pairs). We found evidence for inbreeding depression in juvenile survival, with survival probability estimated to decline from 31% among non-inbred birds ( f=0) to 11% in highly inbred juveniles ( f=0.25). The estimated number of lethal equivalents based on this relationship (4.14) was moderate compared with values reported for other island populations of passerines. Given that significant loss of fitness was only evident in highly inbred individuals, and such individuals were relatively rare once the population expanded above 30 pairs, we conclude that inbreeding depression should have little influence on this robin population. Although the future fitness consequences of any loss of genetic variation due to inbreeding are uncertain, the immediate impact of inbreeding depression is likely to be low in any reintroduced population that expands relatively quickly after establishment. [ABSTRACT FROM AUTHOR]

South Island SaddlebacksPhilesturnus carunculatus carunculatuswere once found throughout the South Island of New Zealand, but by the early 1960s were confined to the island of Big South Cape, in the extreme south of the country. All subsequent reintroduced populations of South Island Saddlebacks are derived from 36 surviving birds from this relict population. The aim of this study was to compare the breeding success of three recently reintroduced populations of Saddlebacks relative to their distance from, and habitat similarity to, the relict population. The three study islands show a latitudinal cline with Ulva, Breaksea and Motuara Islands located 60, 190 and 810 km north of Big South Cape, respectively. Saddlebacks on Ulva and Breaksea appeared to prefer to establish breeding territories in coastal scrub, the dominant habitat feature of Big South Cape. The area of coastal scrub habitat was much smaller on Motuara, where breeding territories were instead scattered through broadleaf forest habitat. Nesting success, calculated using Mayfield's method, was significantly greater on Ulva (73%) than on Breaksea (32%) or Motuara (19%) owing primarily to higher egg fertility and hatching success. Although egg failure rates were highest on Motuara, the island least similar to Big South Cape, they were also relatively high on Breaksea where the habitat was similar to Ulva and Big South Cape. Therefore, the results only partially support the hypothesis that nesting success should decrease with increasing habitat difference associated with increasing latitudinal distance from the source population. The data from this 1-year study lay the groundwork for examining further hypotheses on the effects of reintroducing endangered species outside their contemporary range, but within their historical range. [ABSTRACT FROM AUTHOR]

Many of New Zealand's endangered birds have been transferred from the 'mainland' of the North and South Islands to smaller coastal islands free from introduced predators and competitors. The transfer of Takahe Porphyrio mantelli (Plate 1) to offshore islands is unique because these highly endangered, flightless rails are being moved from alpine-tussock habitat of Fiordland, the last remaining natural population, to substantially different lowland habitat on island refuges. Despite the fact that 30% of the approximately 160 Takahe left in the wild now live on coastal islands, a detailed analysis on the success of the island populations has never been undertaken. Using data available from New Zealand's Department of Conservation, we found that while adult survivorship of Takahe on islands is high, reproductive success is significantly lower than in Fiordland. Most factors examined, including inbreeding and nutrient deficiency, had no significant effect on reproductive success of Takahe breeding on islands. Island pairs produced fewer eggs and juveniles in the first year of their pair bond relative to all other years. Hence the large number of transfers of birds between islands during the initial stages of the relocation program may have resulted in a higher frequency of pair formation and thus may have contributed to the islands' lower reproductive success. Why first clutches did so poorly (four juveniles from 43 clutches) compared with second (11 from 36) and third (six from 13) clutches is not known but was one of the main contributing factors for island pairs making greater nesting effort but significantly lower returns than birds breeding in Fiordland. In addition, some individual birds have been very successful in producing young relative to other birds, suggesting that important differences in quality of some breeders may also exist. We expect island productivity will improve over time as the number of interisland transfers of Takahe decreases and as the proportion of breeding birds raised in the island environment increases. [ABSTRACT FROM AUTHOR]