The importance of forest patch networks for the conservation of the Thorn-tailed Rayaditos in central Chile

Heterozygosity-Fitness Correlations in a Continental Island Population of Thorn-Tailed Rayadito

Heterozygosity-fitness correlations (HFCs) have been used to monitor the effects of inbreeding in threatened populations. HFCs can also be useful to investigate the potential effects of inbreeding in isolated relict populations of long-term persistence and to better understand the role of inbreeding and outbreeding as drivers of changes in genetic diversity. We studied a continental island population of thorn-tailed rayadito (Aphrastura spinicauda) inhabiting the relict forest of Fray Jorge National Park, north-central Chile. This population has experienced a long-term, gradual process of isolation since the end of the Tertiary. Using 10 years of field data in combination with molecular techniques, we tested for HFCs to assess the importance of inbreeding depression. If inbreeding depression is important, we predict a positive relationship between individual heterozygosity and fitness-related traits. We genotyped 183 individuals at 12 polymorphic microsatellite loci and used 7 measures of reproductive success and estimates of apparent survival to calculate HFCs. We found weak to moderate statistical support (P-values between 0.05 and 0.01) for a linear effect of female multi-locus heterozygosity (MLH) on clutch size and nonlinear effects on laying date and fledging success. While more heterozygous females laid smaller clutches, nonlinear effects indicated that females with intermediate values of MLH started laying earlier and had higher fledging success. We found no evidence for effects of MLH on annual fecundity or on apparent survival. Our results along with the long-term demographic stability of the study population contradict the hypothesis that inbreeding depression occurs in this population.

Range-wide genetic structure in the thorn-tailed rayadito suggests limited gene flow towards peripheral populations

Understanding the population genetic consequences of habitat heterogeneity requires assessing whether patterns of gene flow correspond to landscape configuration. Studies of the genetic structure of populations are still scarce for Neotropical forest birds. We assessed range-wide genetic structure and contemporary gene flow in the thorn-tailed rayadito (Aphrastura spinicauda), a passerine bird inhabiting the temperate forests of South America. We used 12 microsatellite loci to genotype 582 individuals from eight localities across a large latitudinal range (30°S–56°S). Using population structure metrics, multivariate analyses, clustering algorithms, and Bayesian methods, we found evidence for moderately low regional genetic structure and reduced gene flow towards the range margins. Genetic differentiation increased with geographic distance, particularly in the southern part of the species’ distribution where forests are continuously distributed. Populations in the north seem to experience limited gene flow likely due to forest discontinuity, and may comprise a demographically independent unit. The southernmost population, on the other hand, is genetically depauperate and different from all other populations. Different analytical approaches support the presence of three to five genetic clusters. We hypothesize that the genetic structure of the species follows a hierarchical clustered pattern.

Variation in fine-scale genetic structure and local dispersal patterns between peripheral populations of a South American passerine bird

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.