Inbreeding and Extinction in Island Populations: a Cautionary Note (original) (raw)
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Environmental Evidence, 2015
Background: Threatened species often have small and isolated populations where mating among relatives can result in inbreeding depression increasing extinction risk. Effective management is hampered by a lack of syntheses summarising the magnitude of, and variation in inbreeding depression. Here we describe the nature and scope of the literature examining phenotypic/fitness consequences of inbreeding, to provide a foundation for future syntheses and management. Methods: We searched the literature for articles documenting the impact of inbreeding in natural populations. Article titles, abstracts and full-texts were assessed against a priori defined criteria, and information relating to study design, quality and other factors that may influence inbreeding responses (e.g. population size) was extracted from relevant articles.
Inbreeding and extinction: The effect of environmental stress and lineage
Conservation Genetics, 2002
Human activities are simultaneously decreasing the size of wildlife populations (causing inbreeding) and increasing the level of stress that wildlife populations must face. Inbreeding reduces population fitness and increases extinction risk. However, very little information on the impact of stressful environments on extinction risk under inbreeding is available. We evaluated the impact of full sib inbreeding on extinction risk, using
Realistic levels of inbreeding depression strongly affect extinction risk in wild populations
Biological Conservation, 2006
The role of inbreeding depression in the extinction of wild populations is controversial, largely because there are no quantitative estimates of its impact using realistic levels of inbreeding depression. To address this deficiency, this study (1) provides a comprehensive estimate of the impact of inbreeding depression on wild, mammalian and avian species via a meta-analysis, and (2) determines the impact of this level of inbreeding depression on extinction risk over a broad taxonomic range via stochastic computer projections with and without inbreeding depression for populations with carrying capacities of 100, 500 and 2000 individuals. An average overall effect of 12 diploid lethal equivalents was found across the life-history of the species in the meta-analysis. In the stochastic computer projections, 12 diploid lethal equivalents of inbreeding depression (with purging) decreased median times to extinction by an average of 37%. These decreases were significant and of very similar magnitude, regardless of the carrying capacity modelled. Disregarding the influence of inbreeding depression on extinction risk will lead to serious overestimates of the survival prospects of threatened mammalian and avian taxa. Further, inappropriate recovery plans may be instituted if the causes of extinction risk and their relative contributions are not recognized.
Inbreeding and Loss of Genetic Variation in a Reintroduced Population of Mauritius Kestrel
Conservation Biology, 2008
Many populations have recovered from severe bottlenecks either naturally or through intensive conservation management. In the past, however, few conservation programs have monitored the genetic health of recovering populations. We conducted a conservation genetic assessment of a small, reintroduced population of Mauritius Kestrel (Falco punctatus) to determine whether genetic deterioration has occurred since its reintroduction. We used pedigree analysis that partially accounted for individuals of unknown origin to document that (1) inbreeding occurred frequently (2.6% increase per generation; N eI = 18.9), (2) 25% of breeding pairs were composed of either closely or moderately related individuals, (3) genetic diversity has been lost from the population (1.6% loss per generation; N eV = 32.1) less rapidly than the corresponding increase in inbreeding, and (4) ignoring the contribution of unknown individuals to a pedigree will bias the metrics derived from that pedigree, ultimately obscuring the prevailing genetic dynamics. The rates of inbreeding and loss of genetic variation in the subpopulation of Mauritius Kestrel we examined were extreme and among the highest yet documented in a wild vertebrate population. Thus, genetic deterioration may affect this population's long-term viability. Remedial conservation strategies are needed to reduce the impact of inbreeding and loss of genetic variation in this species. We suggest that schemes to monitor genetic variation after reintroduction should be an integral component of endangered species recovery programs.
Molecular Ecology, 2011
In nonpedigreed wild populations, inbreeding depression is often quantified through the use of heterozygosity-fitness correlations (HFCs), based on molecular estimates of relatedness. Although such correlations are typically interpreted as evidence of inbreeding depression, by assuming that the marker heterozygosity is a proxy for genome-wide heterozygosity, theory predicts that these relationships should be difficult to detect. Until now, the vast majority of empirical research in this area has been performed on generally outbred, nonbottlenecked populations, but differences in population genetic processes may limit extrapolation of results to threatened populations. Here, we present an analysis of HFCs, and their implications for the interpretation of inbreeding, in a free-ranging pedigreed population of a bottlenecked species: the endangered takahe (Porphyrio hochstetteri). Pedigree-based inbreeding depression has already been detected in this species. Using 23 microsatellite loci, we observed only weak evidence of the expected relationship between multilocus heterozygosity and fitness at individual life-history stages (such as survival to hatching and fledging), and parameter estimates were imprecise (had high error). Furthermore, our molecular data set could not accurately predict the inbreeding status of individuals (as 'inbred' or 'outbred', determined from pedigrees), nor could we show that the observed HFCs were the result of genome-wide identity disequilibrium. These results may be attributed to high variance in heterozygosity within inbreeding classes. This study is an empirical example from a free-ranging endangered species, suggesting that even relatively large numbers (>20) of microsatellites may give poor precision for estimating individual genome-wide heterozygosity. We argue that pedigree methods remain the most effective method of quantifying inbreeding in wild populations, particularly those that have gone through severe bottlenecks.
Genomes retain evidence of the demographic history and evolutionary forces that have shaped populations. Across island systems, contemporary patterns of genetic diversity reflect complex population demography, including colonisation events, bottlenecks, gene flow and genetic drift. Here, we investigate whether island founder events have prolonged effects on genome-wide diversity and runs of homozygosity (ROH) distributions, using whole genome resequencing from six populations across three archipelagos of Berthelot’s pipit (Anthus berthelotii) - a passerine which has undergone island speciation relatively recently. Pairwise sequential Markovian coalescent (PSMC) analyses estimated divergence from its sister species approximately two million years ago. Results indicate that all Berthelot’s pipit populations had shared ancestry until approximately 50,000 years ago, when the Madeiran archipelago populations were founded, while the Selvagens were colonised within the last 8,000 years. We...
Conservation Biology, 2003
Although the negative effects of close inbreeding in captive populations are well known, inbreeding in small, free-ranging populations is less well understood. During the mid-1980s, small numbers of the flightless Takahe (Porphyrio hochstetteri) were successfully translocated from the last remaining population in mountainous Fiordland to four island refuges. Previous research has shown that introduced island Takahe and their descendents lay significantly more infertile eggs and raise fewer juveniles per egg than Takahe in their native habitat in Fiordland. Here we first show that the remnant population of Takahe in Fiordland was likely to have been severely inbred. From this we hypothesize that further, recent inbreeding (based on four generations of pedigree data) by Takahe on islands should have negligible fitness consequences. This hypothesis is only partially supported. Mean hatching and fledging success has remained consistently low (Ͻ 40% and 77%, respectively) and was not correlated with the rapid increase in the average inbreeding coefficient of island Takahe since 1991. Neither the inbreeding coefficient of a pair's offspring nor the inbreeding status of the breeding male had a significant effect on hatching or fledging success. Similarly, the inbreeding status of the breeding female had no significant effect on hatching success. However, the inbreeding status of the female did negatively affect fledging success. Why poor reproductive success was further exacerbated by inbreeding in females but not in males or pairs is unknown, although a similar pattern has been reported in an island population of Song Sparrows (Melospiza melodia). We speculate that the generally lower reproductive success that most island Takahe exhibit is a result of environment-dependent inbreeding depression. We conclude from our pedigree analysis that island Takahe are undergoing further inbreeding depression, but the reduction in fitness appears to be expressed in inbred females only.