Populations forced through bottlenecks typically lose genetic variation and exhibit inbreeding depression. 'Genetic rescue' techniques that introduce individuals from outbred populations can be highly effective in reversing the deleterious effects of inbreeding, but have limited application for the majority of endangered species, which survive only in a few bottlenecked populations. We tested the effectiveness of using highly inbred populations as donors to rescue two isolated and bottlenecked populations of the South Island robin (Petroica australis). Reciprocal translocations significantly increased heterozygosity and allelic diversity. Increased genetic diversity was accompanied by increased juvenile survival and recruitment, sperm quality, and immunocompetence of hybrid individuals (crosses between the two populations) compared with inbred control individuals (crosses within each population). Our results confirm that the implementation of 'genetic rescue' using bottlenecked populations as donors provides a way of preserving endangered species and restoring their viability when outbred donor populations no longer exist.
The distribution of suitable habitat influences natal and breeding dispersal at small spatial scales, resulting in strong microgeographic genetic structure. Although environmental variation can promote interpopulation differences in dispersal behavior and local spatial patterns, the effects of distinct ecological conditions on within‐species variation in dispersal strategies and in fine‐scale genetic structure remain poorly understood. We studied local dispersal and fine‐scale genetic structure in the thorn‐tailed rayadito (Aphrastura spinicauda), a South American bird that breeds along a wide latitudinal gradient. We combine capture‐mark‐recapture data from eight breeding seasons and molecular genetics to compare two peripheral populations with contrasting environments in Chile: Navarino Island, a continuous and low density habitat, and Fray Jorge National Park, a fragmented, densely populated and more stressful environment. Natal dispersal showed no sex bias in Navarino but was female‐biased in the more dense population in Fray Jorge. In the latter, male movements were restricted, and some birds seemed to skip breeding in their first year, suggesting habitat saturation. Breeding dispersal was limited in both populations, with males being more philopatric than females. Spatial genetic autocorrelation analyzes using 13 polymorphic microsatellite loci confirmed the observed dispersal patterns: a fine‐scale genetic structure was only detectable for males in Fray Jorge for distances up to 450 m. Furthermore, two‐dimensional autocorrelation analyzes and estimates of genetic relatedness indicated that related males tended to be spatially clustered in this population. Our study shows evidence for context‐dependent variation in natal dispersal and corresponding local genetic structure in peripheral populations of this bird. It seems likely that the costs of dispersal are higher in the fragmented and higher density environment in Fray Jorge, particularly for males. The observed differences in microgeographic genetic structure for rayaditos might reflect the genetic consequences of population‐specific responses to contrasting environmental pressures near the range limits of its distribution.
In several bird species, the period around dawn seems important for extrapair behavior. For example, a study on great tits (Parus major) showed that females that emerged earlier from their roosting place during the peak of their fertile period were more likely to have extrapair young in their brood. We investigated the potential effect of female emergence times on extrapair behavior in the blue tit (Cyanistes caeruleus). First, we tested the relationship between natural female emergence times from the nest-box and the presence or frequency of extrapair offspring in the brood, using 4 years of data. Females progressively emerged earlier from the nest-box as egg laying approached, with the earliest emergence 2 days before the start of laying. However, we found no relationship between female emergence time and the occurrence of extrapair young in the brood. Secondly, in 2 breeding seasons, we experimentally advanced female emergence times by supplying the roosting females with additional light in the early morning. Although the experiment had inconsistent effects on the occurrence of extrapair young in the brood, we found no evidence that female emergence time during peak fertility is directly linked to extrapair paternity. Interestingly, females exposed to artificial light were more likely to return to breed in the next year.
We have characterized a set of 106 microsatellite markers in 26-127 individual blue tits (Cyanistes caeruleus), and assigned their location on the zebra finch (Taeniopygia guttata) and on the chicken (Gallus gallus) genome on the basis of sequence homology. Thirty-one markers are newly designed from zebra finch EST (expressed sequence tags) sequences, 22 markers were developed by others from EST sequences using different methods and the remaining 53 loci were previously designed or modified passerine markers. The 106 microsatellite markers are distributed over 26 and 24 chromosomes in the zebra finch and in the chicken genome respectively and the number of alleles varies between 2 and 49. Eight loci deviate significantly from Hardy-Weinberg equilibrium and show a high frequency of null alleles, and three pairs of markers located in the same chromosome appear to be in linkage disequilibrium. With the exception of these few loci, the polymorphic microsatellite markers presented here provide a useful genome-wide resource for population and evolutionary genetic studies of the blue tit, in addition to their potential utility in other passerine birds.
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