Rapid Loss of Genetic Variation in Large Captive Populations of Drosophila Flies: Implications for the Genetic Management of Captive Populations

Levels of variation in eight large captive populations of D. melanogaster (census sizes ∼ 5000) that had been in captivity for periods from 6 months to 23 years (8 to 365 generations) were estimated from allozyme heterozygosities, lethal frequencies, and inversion heterozygosities and phenotypic variances, additive genetic variances ( V _A), and heritabilities ( h ²) for sternopleural bristle numbers. Correlations between all measures of variation except lethal frequencies were high and significant. All measures of genetic variation declined with time in captivity, with those for average heterozygosities, V _A, and h ² being significant. The effective population size ( N _e) was estimated to be 185–253 in these populations, only 0.037–0.051 of census size (N). Levels of allozyme heterozygosities declined rapidly in two large captive populations founded from another wild stock, being reduced by 86% and 62% within 2.5 years in spite of being maintained at sizes of approximately 1000 and 3500. Estimates of N _e/ N for these populations were only 0.016 and 0.004. Two estimates of N _e/ N for captive populations of D. pseudoobscura from data in the literature were also low at 0.036 and 0.012. Consequently, the rate of loss of genetic variation in captive populations and endangered species may be more rapid than hitherto recognized. Merely maintaining captive populations at large census sizes may not be sufficient to maintain essential genetic variation.     

Effective Population Size and Maintenance of Genetic Diversity in Captive-Bred Populations of a Lake Victoria Cichlid

Abstract: We used microsatellite DNA markers to investigate the maintenance of genetic diversity within and between samples of subpopulations (spanning five captive-bred generations) of the haplochromine cichlid Prognathochromis perrieri . The subpopulations are maintained as part of the Lake Victoria Cichlid species survival plan. Changes in the frequencies of 24 alleles, over four polymorphic loci, were used to estimate effective population size (   N _e   ). Point estimates of N _e ranged from 2.5 to 7.7 individuals and were significantly smaller than the actual census size (   N _obs  ) for all subpopulations (32–243 individuals per generation), with the corresponding conservative N _e   /  N _obs ratios ranging from 0.01 to 0.12. Approximately 19% of the initial alleles were lost within the first four generations of captive breeding. Between-generation comparisons of expected heterozygosity showed significant losses ranging from 6% to 12% per generation. Seven private alleles were observed in the last sampled generation of four subpopulations, and analysis of population structure by F _ST indicated that approximately 33% of the total genetic diversity is maintained between the subpopulations from different institutions. To reduce the loss of genetic variation, we recommend that offspring production be equalized by periodically removing dominant males, which will encourage reproduction by additional males. Consideration should also be given to encouraging more institutions to maintain populations, because a significant fraction of the genetic variation exists as among-population differences resulting from random differentiation among subpopulations.     

Unprecedented Low Levels of Genetic Variation and Inbreeding Depression in an Island Population of the Black-Footed Rock-Wallaby

Abstract: It has been argued that demographic and environmental factors will cause small, isolated populations to become extinct before genetic factors have a significant negative impact. Islands provide an ideal opportunity to test this hypothesis because they often support small, isolated populations that are highly vulnerable to extinction. To assess the potential negative impact of isolation and small population size, we compared levels of genetic variation and fitness in island and mainland populations of the black-footed rock-wallaby ( Petrogale lateralis [Marsupialia: Macropodidae]). Our results indicate that the Barrow Island population of P. lateralis has unprecedented low levels of genetic variation (  H _e = 0.053, from 10 microsatellite loci) and suffers from inbreeding depression (reduced female fecundity, skewed sex ratio, increased levels of fluctuating asymmetry). Despite a long period of isolation ( ∼ 1600 generations) and small effective population size (  N _e ∼ 15), demographic and environmental factors have not yet driven this population to extinction. Nevertheless, it has been affected significantly by genetic factors. It has lost most of its genetic variation and become highly inbred (  F _e = 0.91), and it exhibits reduced fitness. Because several other island populations of P. lateralis also exhibit exceptionally low levels of genetic variation, this phenomenon may be widespread. Inbreeding in these populations is at a level associated with high rates of extinction in populations of domestic and laboratory species. Genetic factors cannot then be excluded as contributing to the extinction proneness of small, isolated populations.     

Application of Reproduction Technologies to the Conservation of Genetic Resources

Abstract: Maintaining the levels of genetic variability in captive populations of endangered species is an important objective of conservation biology. Because of the generally low sizes of captive populations, genetic drift is the main cause of loss of diversity. Several simple management rules, such as equalization of contributions from parents to the next generation, are recommended for minimizing genetic drift, but it cannot be removed completely because of the unavoidable random segregation of heterozygotes. Recent advances in reproductive technology, particularly developed for mammals, are now making a reality of the possibility of using more than one cell from a single meiosis in reproduction. With this technology it is possible to reduce or even completely cancel the genetic drift caused by segregation of heterozygotes. We evaluated the theoretical benefits of the use of such technologies to conservation biology. The effective population size can be increased enormously and, consequently, the amount of drift can be greatly reduced if manipulations in reproduction are made.     

Lineage Loss in Serengeti Cheetahs: Consequences of High Reproductive Variance and Heritability of Fitness on Effective Population Size

Abstract: In natural populations, many breeders do not leave surviving offspring, and as a result many potential genetic lineages are lost. I examined lineage extinction in Serengeti cheetahs ( Acinonyx jubatus ) and found that 76% of matrilines were lost over a 25-year period. Production of future breeders was nonrandom and generally confined to a few families. Five out of 63 matrilines accounted for 45% of the total cheetah population over the course of the study. Lineage persistence is perhaps best illustrated by the variance in lifetime reproductive success ( LRS) and heritability in this parameter. In female cheetahs, variance in LRS was high, and new data show that this LRS was heritable. Variance in LRS and heritability in LRS have dramatic consequences for effective population size, N _e. I calculated N _e for cheetahs, taking into account fluctuating population size, unequal sex ratio, non-Poisson distribution of reproductive success, and heritability of fitness. The N _e was most strongly affected by variance in reproductive success and especially heritability in reproductive success. The variance N _e was 44% of the actual population size, and the inclusion of heritability further reduced N _e to only 15% of the actual population, a ratio similar to that of a social carnivore with reproductive suppression. The current cheetah population in the Serengeti is below numbers suggested by N _e estimates as sufficient to maintain sufficient genetic diversity.     

Genetic Diversity, Population Size, and Fitness in Central and Peripheral Populations of a Rare Plant Lychnis viscaria

Abstract: Genetic diversity is expected to decrease in small and isolated populations as a consequence of bottlenecks, founder effects, inbreeding, and genetic drift. The genetics and ecology of the rare perennial plant Lychnis viscaria (Caryophyllaceae) were studied in both peripheral and central populations within its distribution area. We aimed to investigate the overall level of genetic diversity, its spatial distribution, and possible differences between peripheral and central populations by examining several populations with electrophoresis. Our results showed that the level of genetic diversity varied substantially among populations (  H _exp = 0.000–0.116) and that the total level of genetic diversity (mean H _exp = 0.056) was low compared to that of other species with similar life-history attributes. The peripheral populations of L. viscaria had less genetic variation (mean H _exp = 0.034) than the central ones (0.114). Analysis of genetic structure suggested limited gene flow (mean F _ST = 0.430) and high differentiation among populations, emphasizing the role of genetic drift (  N _e m = 0.33). Isolation was even higher than expected based on the physical distance among populations. We also focused on the association between population size and genetic diversity and possible effects on fitness of these factors. Population size was positively correlated with genetic diversity. Population size and genetic diversity, however, were not associated with fitness components such as germination rate, seedling mass, or seed yield. There were no differences in the measured fitness components between peripheral and central populations. Even though small and peripheral populations had lower levels of genetic variation, they were as viable as larger populations, which emphasizes their potential value for conservation.     

Genetic Effects of Habitat Fragmentation on Common Species of Swiss Fen Meadows

Abstract:  The area of Caricion davallianae alliance in Switzerland has been considerably reduced and fragmented during the last 150 years. We assessed the genetic variability, inbreeding level, and among-population differentiation of two common habitat-specific plant species, Carex davalliana SM. and Succisa pratensis Moench, in 18 Caricion davallianae fen meadows subjected to fragmentation. We used a spatial field design of fen systems (six systems total), each consisting of one large habitat island and two small habitat islands. We used allozyme electrophoresis to derive standard genetic parameters ( A, P, H_O, H_E, F_IS, F_ST ). In Carex we identified a consistently lower A in isolated habitat islands; furthermore, H_E was lower in small habitat islands than in large habitat islands. In Succisa we identified a lower H_O in small habitat islands than in larger ones. Small habitat islands were marginally significantly differentiated (  F_ST ) from large islands for Succisa . For both species, no effects were evident for F_IS ; therefore, we argue that genetic drift rather than inbreeding is the main cause of the observed differences. The genetic structure of Carex and Succisa in small habitat islands differed from that in large habitat islands, but differences were small. It appears that the observed differences in genetic variability among fen meadows correspond to observed differences in fitness and demographic traits. We show that habitat fragmentation affects not only the rare species in an ecosystem but also reduces the survival probabilities of common species. One of the main goals of conservation should be to mitigate fragmentation of natural habitats in order to increase population sizes and connectivity.     

Relationship of Effective to Census Size in Fluctuating Populations

Abstract: The effective size of a population (    N _e   ) rather than the census size (    N ) determines its rate of genetic drift. Knowing the ratio of effective to census size, N _e  /   N , is useful for estimating the effective size of a population from census data and for examining how different ecological factors influence effective size. Two different multigenerational ratios have been used in the literature based on either the arithmetic mean or the harmonic mean in the denominator. We clarify the interpretation and meaning of these ratios. The arithmetic mean N _e  /   N ratio compares the total number of real individuals to the long-term effective size of the population. The harmonic mean N _e  /   N ratio summarizes variation in the N _e  /   N ratio for each generation. In addition, we show that the ratio of the harmonic mean population size to the arithmetic mean population size provides a useful measure of how much fluctuation in size reduced the effective size of a population. We discuss applications of these ratios and emphasize how to use the harmonic mean N _e  /   N ratio to estimate the effective size of a population over a period of time for which census counts have been collected.     

Genetic Effects of Multiple Generations of Supportive Breeding

Abstract: The practice of supporting weak wild populations by capturing a fraction of the wild individuals, bringing them into captivity for reproduction, and releasing their offspring into the natural habitat to mix with wild ones is called supportive breeding and has been widely applied in the fields of conservation biology and fish and wildlife management. This procedure is intended to increase population size without introducing exogenous genes into the managed population. Previous work examining the genetic effects of a single generation of supportive breeding has shown that although a successful program increases the census population size, it may reduce the genetically effective population size and thereby induce excessive inbreeding and loss of genetic variation. We expand and generalize previous analyses of supportive breeding and consider the effects of multiple generations of supportive breeding on rates of inbreeding and genetic drift. We derived recurrence equations for the inbreeding coefficient and coancestry, and thereby equations for inbreeding and variance effective sizes, under three models for selecting captive breeders: at random, preferentially among those born in captivity, and preferentially among those born in the wild. Numerical examples indicate that supportive breeding, when carried out successfully over multiple generations, may increase not only the census but also the effective size of the supported population as a whole. If supportive breeding does not result in a substantial and continuous increase of the census size of the breeding population, however, it might be genetically harmful because of elevated rates of inbreeding and genetic drift.     

Inbreeding and Loss of Genetic Variation in a Reintroduced Population of Mauritius Kestrel

Abstract:  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.     

Translating effects of inbreeding depression on component vital rates to overall population growth in endangered bighorn sheep

Evidence of inbreeding depression is commonly detected from the fitness traits of animals, yet its effects on population growth rates of endangered species are rarely assessed. We examined whether inbreeding depression was affecting Sierra Nevada bighorn sheep (Ovis canadensis sierrae), a subspecies listed as endangered under the U.S. Endangered Species Act. Our objectives were to characterize genetic variation in this subspecies; test whether inbreeding depression affects bighorn sheep vital rates (adult survival and female fecundity); evaluate whether inbreeding depression may limit subspecies recovery; and examine the potential for genetic management to increase population growth rates. Genetic variation in 4 populations of Sierra Nevada bighorn sheep was among the lowest reported for any wild bighorn sheep population, and our results suggest that inbreeding depression has reduced adult female fecundity. Despite this population sizes and growth rates predicted from matrix-based projection models demonstrated that inbreeding depression would not substantially inhibit the recovery of Sierra Nevada bighorn sheep populations in the next approximately 8 bighorn sheep generations (48 years). Furthermore, simulations of genetic rescue within the subspecies did not suggest that such activities would appreciably increase population sizes or growth rates during the period we modeled (10 bighorn sheep generations, 60 years). Only simulations that augmented the Mono Basin population with genetic variation from other subspecies, which is not currently a management option, predicted significant increases in population size. Although we recommend that recovery activities should minimize future losses of genetic variation, genetic effects within these endangered populations-either negative (inbreeding depression) or positive (within subspecies genetic rescue)-appear unlikely to dramatically compromise or stimulate short-term conservation efforts. The distinction between detecting the effects of inbreeding depression on a component vital rate (e.g., fecundity) and the effects of inbreeding depression on population growth underscores the importance of quantifying inbreeding costs relative to population dynamics to effectively manage endangered populations.     

Relationship of Breeding System to Rarity in the Lakeside Daisy (Hymenoxys acaulis var. glabra)

The breeding system of a rare Great Lakes endemic, the lakeside daisy ( Hymenoxys acaulis var. glabra ), was investigated when plants from a remnant Illinois population produced no seeds for over 15 years. To determine if the Lakeside daisy was self-incompatible, 20 plants from two populations, Illinois and Ohio, were selfed and outcrossed. Seed/ovule ratios were compared among the different treatments and the location of the incompatibility reaction was identified. Lakeside daisy was found to be self-incompatible (sporophytic). The last Illinois population was effectively extinct because the remaining plants belonged to the same mating type ( N _e = 1) and only produced seeds when outcrossed to the Ohio plants. Cross-incompatibility was also observed among Ohio plants, suggesting that within large populations, compatible mating types may be rare locally. In addition, inbreeding depression (lower seed/ovule ratios in inbred than in outcrosses) was observed after one generation of inbreeding. Small populations of self-incompatible species are vulnerable to extinction if the number of self-incompatibility alleles, either as a result of a bottleneck or of genetic drift, falls below tbe number needed for the breeding system to function. Recovery protocols based on these genetic considerations were developed and implemented in 1988 when Lakeside daisy populations were established at three Illinois nature preserves.     

Risk Assessment of Inbreeding and Outbreeding Depression in a Captive‐Breeding Program

Captive‐breeding programs can be implemented to preserve the genetic diversity of endangered populations such that the controlled release of captive‐bred individuals into the wild may promote recovery. A common difficulty, however, is that programs are founded with limited wild broodstock, and inbreeding can become increasingly difficult to avoid with successive generations in captivity. Program managers must choose between maintaining the genetic purity of populations, at the risk of inbreeding depression, or interbreeding populations, at the risk of outbreeding depression. We evaluate these relative risks in a captive‐breeding program for 3 endangered populations of Atlantic salmon (Salmo salar). In each of 2 years, we released juvenile F₁ and F₂ interpopulation hybrids, backcrosses, as well as inbred and noninbred within‐population crosstypes into 9 wild streams. Juvenile size and survival was quantified in each year. Few crosstype effects were observed, but interestingly, the relative fitness consequences of inbreeding and outbreeding varied from year to year. Temporal variation in environmental quality might have driven some of these annual differences, by exacerbating the importance of maternal effects on juvenile fitness in a year of low environmental quality and by affecting the severity of inbreeding depression differently in different years. Nonetheless, inbreeding was more consistently associated with a negative effect on fitness, whereas the consequences of outbreeding were less predictable. Considering the challenges associated with a sound risk assessment in the wild and given that the effect of inbreeding on fitness is relatively predictable, we suggest that risk can be weighted more strongly in terms of the probable outcome of outbreeding. Factors such as genetic similarities between populations and the number of generations in isolation can sometimes be used to assess outbreeding risk, in lieu of experimentation. Evaluación del Riesgo de Depresión por Endogamia y Exogamia en un Programa de Reproducción en Cautiverio     

A Reassessment of Homozygosity and the Case for Inbreeding Depression in the Cheetah, Acinonyx jubatus: Implications for Conservation

Preservation of genetic diversity within declining populations of endangered species is a major concern in the discipline of conservation biology. The endangered cheetah, Acinonyx jubatus , exhibits relatively little genetic variability (polymorphism = 0.02–0.04, heterozygosity = 0.0004–0.014). Since the discovery of the cheetah's relative homozygosity, this species has been frequently cited as an example of one whose survival may be compromised by the loss of genetic diversity. The cheetah's genetic uniformity is generally believed to be the result of an historical population bottle-neck followed by a high level of inbreeding. Evidence offered in support of this hypothesis includes the cheetah's present low level of genetic variability and symptoms of inbreeding depression in captive populations. Using available data on fluctuating asymmetry and genetic variation in other carnivores, I question the assumption that the present level of genetic diversity in the cheetah is indicative of a loss of former variability. Carnivores exhibit significantly lower levels of genetic variation than other mammals, and several carnivores for which data are available exhibit lower levels of heterozygosity and polymorphism than the cheetah does. Measures of fluctuating asymmetry do not support the hypothesis that the cheetah is suffering an increased level of bomozygosity due to genetic stress. Many of the phenotypic effects attributed to inbreeding depression, such as infertility, reduced litter sizes, and increased susceptibility to disease, are limited to captive individuals and may be explained as physiological or behavioral artifacts of captivity. In sum, the genetic constitution of the cheetah does not appear to compromise the survival of the species. Conservation efforts may be more effectively aimed at a real, immediate threat to the cheetah's future: the loss of its natural habitat.     

Application of the One-Migrant-per-Generation Rule to Conservation and Management

Abstract:  Endangered species are commonly found in several (partially) isolated populations dispersed on different fragments of a habitat, natural reserve, or zoo. A certain level of connectivity among such populations is essential for maintaining genetic variation within and between populations to allow local and global adaptation and for preventing inbreeding depression. A rule of thumb widely accepted by the conservation community is that one migrant per generation (OMPG) into a population is the appropriate level of gene flow. This rule is based on Wright's study of his island model under a long list of simplifying assumptions. I examined the robustness of the OMPG rule to the violation of each of the many assumptions, quantifying the effect with population genetics theory. I showed that, when interpreted as one effective migrant per generation, OMPG is generally valid for real populations departing from the ideal model in the discrepancies of actual (  N ) and effective (  N_e  ) population sizes and actual ( m ) and effective ( m_e  ) migration rates. I also addressed the issue of converting the effective number of migrants (  M_e= N_em_e  ) into the actual number of migrants ( M = Nm  ) of a certain age and sex. In particular, N_e < N , a case common for natural populations, did not necessarily require M > M_e to maintain a certain level of differentiation among populations. Rather, translating the elusive M_e into the manageable M depends on the specific causes (e.g., biased sex ratio, reproductive skew) that lead to N_e < N .     

Effect of Migration or Inbreeding Followed by Selection on Low-Founder-Number Populations: Implications for Captive Breeding Programs

Using the housefly, Musca domestica (L), as a model system, we tested the ability of two extremes in the range of possible captive breeding protocols to yield sustainable populations following founding with low founder numbers. The protocols tested included two levels of migration as well as inbreeding followed by selection, each with appropriate controls. Each low-founder-number population was founded with two pairs of flies. The maximum migration scheme had 50% migration per generation, and the minimum migration populations experienced a migration rate of 2.5% per generation. The control level of migration was 0%. A fourth low-founder-number treatment was designed to test the effect of inbreeding followed by selection. Two sets of high-founder-number control groups were also derived from the stock population. Two fitness measures, viability and productivity of the populations, were recorded at the fifth generation. Populations in the minimum-migration and zero migration treatment groups had lower fitness than populations in any other treatment for both measures. Populations that experienced inbreeding and selection for high fitness levels, high levels of migration, or large high-founder-number populations were equally fit. These results demonstrate that a captive-breeding scheme that contains substantial levels of migration or inbreeding followed by selection can yield highly adapted populations.     

Inbreeding Depression in the Speke's Gazelle Captive Breeding Program

Abstract: The Speke's gazelle ( Gazella spekei ) captive breeding program has been presented as one of the few examples of selection reducing the genetic load of a population and as a potential model for the captive breeding of endangered species founded from a small number of individuals. In this breeding program, three generations of mate selection apparently increased the viability of inbred individuals. We reanalyzed the Speke's gazelle studbook and examined potential causes for the reduction of inbreeding depression. Our analysis indicates that the decrease in inbreeding depression is not consistent with any model of genetic improvement in the herd. Instead, we found that the effect of inbreeding decreased from severe to moderate during the first generation of inbreeding, and that this change is responsible for almost all of the decline in inbreeding depression observed during the breeding program. This eliminates selection as a potential explanation for the decrease in inbreeding depression and suggests that inbreeding depression may be more sensitive to environmental influences than is usually thought.     

Genetic Structure of a Mimosoid Tree Deprived of Its Seed Disperser, the Spider Monkey

Abstract: To assess the genetic consequences for a Neotropical tree of the loss of its main seed disperser, we compared the genetic structure of Inga ingoides in a site where the spider monkey (Ateles paniscus) was abundant and a site where it had been eliminated by subsistence hunting. Gene flow should be reduced in the site where the spider monkey is absent, and there should be a corresponding subpopulation differentiation of seedlings within the spatial range of the movements of these primates in the absence of between-site differences in allelic frequencies. At the microhabitat (  family) scale, seedlings growing under parent plants should be genetically more related in the absence of the spider monkey than in its presence. Subpopulation differentiation was smaller where the spider monkey was present (  four loci, F_ST = 0.011) than where it was absent (  four loci, F_ST = 0.053) for the first year of study, but not for the second year (three loci, F_ST = 0.005 vs. 0.003). The number of alleles in common among seedlings growing under parent plants was smaller in the presence of the spider monkey than in its absence, showing family genetic structure in the first generation for both years of study ( Mann-Whitney, z = −2.17, p = 0.03 and z = −2.72, p = 0.006 for 1996 and 1997, respectively). This family genetic structure in the first generation should accelerate the development of population genetic structure. Development of genetic structure might result in demographic changes, one of which would be a fitness reduction if the species were self-incompatible, as suggested for Inga by available evidence. Large birds and mammals are the main targets of subsistence hunting in the Neotropics. Extinction of seed-dispersing frugivores may result in pronounced changes in the demographic and genetic structure of tree species in Neotropical forests.     

Inbreeding Depression Accumulation across Life‐History Stages of the Endangered Takahe

Abstract: Studies evaluating the impact of inbreeding depression on population viability of threatened species tend to focus on the effects of inbreeding at a single life‐history stage (e.g., juvenile survival). We examined the effects of inbreeding across the full life‐history continuum, from survival up to adulthood, to subsequent reproductive success, and to the recruitment of second‐generation offspring, in wild Takahe ( Porphyrio hochstetteri ) by analyzing pedigree and fitness data collected over 21 breeding seasons. Although the effect size of inbreeding at individual life‐history stages was small, inbreeding depression accumulated across multiple life‐history stages and ultimately reduced long‐term fitness (i.e., successful recruitment of second‐generation offspring). The estimated total lethal equivalents (2B) summed across all life‐history stages were substantial (16.05, 95% CI 0.08–90.8) and equivalent to an 88% reduction in recruitment of second‐generation offspring for closely related pairs (e.g., sib–sib pairings) relative to unrelated pairs (according to the pedigree). A history of small population size in the Takahe could have contributed to partial purging of the genetic load and the low level of inbreeding depression detected at each single life‐history stage. Nevertheless, our results indicate that such “purged” populations can still exhibit substantial inbreeding depression, especially when small but negative fitness effects accumulate across the species’ life history. Because inbreeding depression can ultimately affect population viability of small, isolated populations, our results illustrate the importance of measuring the effects of inbreeding across the full life‐history continuum.