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Small populations establishing on colonization fronts have to adapt to novel environments with limited genetic variation. The pace at which they can adapt, and the influence of genetic variation on their success, are key questions for understanding intraspecific diversity. To investigate these topics, we performed a reciprocal transplant experiment between two recently founded populations of brown trout in the sub-Antarctic Kerguelen Islands. Using individual tagging and genetic assignment methods, we tracked the fitness of local and foreign individuals, as well as the fitness of their offspring over two generations. In both populations, although not to the same extent, gene flow occurred between local and foreign gene pools. In both cases, however, we failed to detect obvious footprints of local adaptation (which should limit gene flow) and only weak support for genetic rescue (which should enhance gene flow). In the population where gene flow from foreign individuals was low, no clear differences were observed between the fitness of local, foreign, and F1 hybrid individuals. In the population where gene flow was high, foreign individuals were successful due to high mating success rather than high survival, and F1 hybrids had the same fitness as pure local offspring. These results suggest the importance of considering sexual selection, rather than just local adaptation and genetic rescue, when evaluating the determinants of success in small and recently founded populations.

The genus Telestes primarily comprises freshwater fish distributed mostly in the Mediterranean area. Recent investigation of the evolutionary history of this genus revealed that it originated in southern Europe, where the most ancient Telestes species are still present. The isolation of rivers in the karstic region facilitated allopatric speciation, resulting in a high number of Telestes species and a great portion of endemic species in freshwater systems of Croatia and Bosnia and Herzegovina. Most of the endemic Telestes species have very small distribution areas, inhabiting a single river or a few water bodies in a single karstic field, making them extremely vulnerable to anthropogenic changes. In order to contribute to practical conservation of the endemic Telestes species through the design of conservational measures that are likely to be the most effective in ensuring the future viability and undisturbed evolutionary course of those species, we have investigated their population genetic structure and estimated their viabilities. Population viability analyses were carried out based on the current state of populations and their habitats, as well as recognized threats. Several scenarios also included potential threats. Our results show that invasive species pose the biggest threat to the future survival of the endemic Telestes species. Contrary to previous opinions that a reduced genetic diversity is characteristic for small populations, high intraspecific genetic diversity was revealed inside most of the investigated species, which might enable most of the populations to cope with future changes and mitigate negative effects. [ABSTRACT FROM AUTHOR]

Reduced fitness through genetic drift and inbreeding is a major threat to small and isolated populations. Although previous studies have generally used genetically verified pedigrees to document effects of inbreeding and gene flow, these often fail to capture the whole inbreeding history of the species. By assembling a draft arctic fox (Vulpes lagopus) genome and resequencing complete genomes of 23 additional foxes born before and after a well‐documented immigration event in Scandinavia, we here look into the genomic consequences of inbreeding and genetic rescue. We found a difference in genome‐wide diversity, with 18% higher heterozygosity and 81% lower FROH in immigrant F1 compared to native individuals. However, more distant descendants of immigrants (F2, F3) did not show the same pattern. We also found that foxes with lower inbreeding had higher probability to survive their first year of life. Our results demonstrate the important link between genetic variation and fitness as well as the transient nature of genetic rescue. Moreover, our results have implications in conservation biology as they demonstrate that inbreeding depression can effectively be detected in the wild by a genomic approach. [ABSTRACT FROM AUTHOR]

Isolation of small populations can reduce fitness through inbreeding depression and impede population growth. Outcrossing with only a few unrelated individuals can increase demographic and genetic viability substantially, but few studies have documented such genetic rescue in natural mammal populations. We investigate the effects of immigration in a subpopulation of the endangered Scandinavian arctic fox (Vulpes lagopus), founded by six individuals and isolated for 9 years at an extremely small population size. Based on a long-term pedigree (105 litters, 543 individuals) combined with individual fitness traits, we found evidence for genetic rescue. Natural immigration and gene flow of three outbred males in 2010 resulted in a reduction in population average inbreeding coefficient ( f ), from 0.14 to 0.08 within 5 years. Genetic rescue was further supported by 1.9 times higher juvenile survival and 1.3 times higher breeding success in immigrant first-generation offspring compared with inbred offspring. Five years after immigration, the population had more than doubled in size and allelic richness increased by 41%. This is one of few studies that has documented genetic rescue in a natural mammal population suffering from inbreeding depression and contributes to a growing body of data demonstrating the vital connection between genetics and individual fitness. [ABSTRACT FROM AUTHOR]

Small, isolated populations risk extinction through inbreeding depression, chance loss of beneficial variation, and reduced adaptability to changing environments. Genetic rescue via gene flow from genetically diverse sources is the most effective way to improve fitness of such populations. However, when the only potential source of immigrants is a different subspecies that diverged long ago and occupies a different environment, genetic rescue may lead to reduced fitness of admixed offspring through outbreeding depression or maladaptation. Test cases are needed to evaluate how to manage such potentially risky rescues to deliver enhanced population fitness. The helmeted honeyeater Lichenostomus melanops cassidix is a critically endangered subspecies of the yellow-tufted honeyeater. The sole remaining natural wild population experiences strong inbreeding depression for lifetime reproductive fitness. Captive genetic rescue trials are underway using a neighbouring subspecies, gippslandicus , which diverged from cassidix thousands of years ago and differs in morphology, mobility and preferred habitat. We evaluated short-term reproductive fitness for captive cassidix - cassidix pairs, first- and second-generation intersubspecific crosses and backcrosses to cassidix , while accounting for breeding season, sex, age at breeding, and wild/captive origin of each bird. Most admixed pair-types more readily engaged in breeding, raised more nestlings per nest, and had less male-biased chick sex-ratios than did cassidix - cassidix pairs, with negligible evidence of outbreeding depression. Continuing monitoring of fitness after releases into the wild is recommended, to ensure local adaptation is retained. With potentially riskier rescue increasingly becoming the only option for many populations, our study provides an encouraging test case. [Display omitted] • Gene flow from another subspecies is perceived as risky and often avoided. • Such gene flow is needed to save critically endangered helmeted honeyeaters. • Captive trials revealed gene flow between subspecies improved fitness. • Gene flow between subspecies also resulted in less male-biased offspring. • Releases of admixed birds into the wild should benefit population recovery. [ABSTRACT FROM AUTHOR]

Big tree rhododendron ( Rhododendron protistum var. giganteum ) is an extremely endangered plant with only two remnant populations distributed in the Gaoligong Mountains of northwestern Yunnan Province, China. However, the genetic structure, demographic history, and the population dynamics of this species have been rarely described. In the present study, data from 14 polymorphic nuclear microsatellite loci were used to assess the levels of genetic diversity, genetic structure, and demographic history of big tree rhododendron remnant populations. Results suggested that renmants maintained a moderate level of genetic diversity ( N E = 2.86, A R = 5.726, H o = 0.510, H e = 0.602, I = 1.174) despite their small population. Bayesian clustering and principal coordinate analysis indicated that sampled individuals were clustered into two distinct genetic groups. Demographic history analysis revealed high historical and low contemporary gene flow between two remnant populations. BOTTLENECK analysis under a two-phase mutation model showed that the populations could have experienced a recent historical bottleneck. The effective population sizes of the two populations were smaller than 30. Therefore, in situ conservation of this species should be prioritized. Furtheremore, ex situ cultivation of field collected seeds and introduction of saplings into the source site might be considered for the future conservation and restoration of big tree rhododendron. [ABSTRACT FROM AUTHOR]

Background: Small, genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness. Fragmentation can intensify these genetic adversities and, therefore, dispersal and gene flow among subpopulations within an isolated population is often essential for maintaining its viability. Using microsatellite and mtDNA data, we examined genetic diversity, spatial differentiation, interregional gene flow, and effective population sizes in the critically endangered Saimaa ringed seal (Phoca hispida saimensis), which is endemic to the large but highly fragmented Lake Saimaa in southeastern Finland. Results: Microsatellite diversity within the subspecies (HE = 0.36) ranks among the lowest thus far recorded within the order Pinnipedia, with signs of ongoing loss of individual heterozygosity, reflecting very low effective subpopulation sizes. Bayesian assignment analyses of the microsatellite data revealed clear genetic differentiation among the main breeding areas, but interregional structuring was substantially weaker in biparentally inherited microsatellites (FST = 0.107) than in maternally inherited mtDNA (FST = 0.444), indicating a sevenfold difference in the gene flow mediated by males versus females. Conclusions: Genetic structuring in the population appears to arise from the joint effects of multiple factors, including small effective subpopulation sizes, a fragmented lacustrine habitat, and behavioural dispersal limitation. The fine-scale differentiation found in the landlocked Saimaa ringed seal is especially surprising when contrasted with marine ringed seals, which often exhibit near-panmixia among subpopulations separated by hundreds or even thousands of kilometres. Our results demonstrate that population structures of endangered animals cannot be predicted based on data on even closely related species or subspecies. [ABSTRACT FROM AUTHOR]

Small populations establishing on colonization fronts have to adapt to novel environments with limited genetic variation. The pace at which they can adapt, and the influence of genetic variation on their success, are key questions for understanding intraspecific diversity. To investigate these topics, we performed a reciprocal transplant experiment between two recently founded populations of brown trout in the sub-Antarctic Kerguelen Islands. Using individual tagging and genetic assignment methods, we tracked the fitness of local and foreign individuals, as well as the fitness of their offspring over two generations. In both populations, although not to the same extent, gene flow occurred between local and foreign gene pools. In both cases, however, we failed to detect obvious footprints of local adaptation (which should limit gene flow) and only weak support for genetic rescue (which should enhance gene flow). In the population where gene flow from foreign individuals was low, no clear differences were observed between the fitness of local, foreign, and F1 hybrid individuals. In the population where gene flow was high, foreign individuals were successful due to high mating success rather than high survival, and F1 hybrids had the same fitness as pure local offspring. These results suggest the importance of considering sexual selection, rather than just local adaptation and genetic rescue, when evaluating the determinants of success in small and recently founded populations. [ABSTRACT FROM AUTHOR]