Korpach, A. M. | Search bioRxiv

bioRxiv2023

Migration distance and mating system are not associated with genetic diversity and differentiation among bats (Chiroptera)

Genetic variation is critical for evolutionary responses to environmental change. Links between genetic variation and behavioural or life history traits may reveal how varied strategies influence evolutionary trends in speciation and adaptation. Traits associated with movement typically correlate with population genetic structure and could help predict populations vulnerability to geographic processes such as habitat fragmentation and disease spread. With their wide diversity in behaviours and ecologies, bats provide a useful testing ground for hypotheses about population structure related to species-specific movement patterns. We used a global sample of microsatellite data (n=233 sites from 17 bat species) associated with published studies to examine potential links between genetic variation and migration and mating strategies. The genetic measures we tested were population-specific differentiation, gene diversity, and allelic richness. Using Bayesian models that accounted for phylogenetic distances among species, we identified no correlations between migration or mating strategy and genetic variation. Our results do not support long-standing hypotheses about dispersal-mediated genetic structure, and contrast with prior studies on bat genetic diversity and differentiation. We discuss the need for continued research into the complex association of ecological, biogeographical, and behavioural factors that facilitate gene flow among populations, especially in species with diverse movement patterns.

zoology↗

bioRxiv2023

Assessing an age-old ecogeographical rule in nightjars across the full annual cycle

Bergmanns rule states that homeotherms are larger in colder climates (which occur at higher latitudes and elevations) due to thermoregulatory mechanisms. Despite being perhaps the most extensively studied biogeographical rule across all organisms, consistent mechanisms explaining which species or taxa adhere to Bergmanns rule have been elusive. Furthermore, evidence for Bergmanns rule in migratory animals has been mixed, and it was difficult to assess how environmental conditions across the full annual cycle impact body size until the recent miniaturization of tracking technology. Nightjars (Family Caprimulgidae), nocturnal birds with physiological and behavioral adaptations (e.g., torpor) to cope with the environmental extremes they often experience, offer a unique opportunity to elucidate the mechanisms underpinning Bergmanns rule. Many nightjar species are strongly migratory and have large breeding ranges, offering the opportunity to look at variation in potential drivers within and across seasons of the annual cycle. Furthermore, variation in migration strategy within the family provides an opportunity to separate adaptations for migration strategy from adaptations for thermal tolerance. In this study, we use cross-continental data from three species of nightjars (Common nighthawk, Eastern whip-poor-will, and European nightjar) to assess 1) whether migratory species in this clade adheres to Bergmanns rule, 2) which environmental factors are the best predictors of body size, and 3) the extent to which environmental conditions across the full annual cycle determine body size. For each species, we use breeding and winter location data from GPS tags to compare competing hypotheses explaining variation in body size: temperature regulation, productivity, and seasonality (during both the breeding and wintering periods), and migration distance. We found that Common nighthawk and Eastern whip-poor-will exhibit Bergmannian patterns in body size while European nightjar does not, although the spread of tag deployment sites on the breeding grounds was minimal for the European nightjar. Predictor variables associated with nightjar breeding locations more often explained body size than did variables on the wintering grounds. Surprisingly, models representing the geography hypothesis were best represented among important models in our final data set. Latitude and longitude correlated strongly with environmental variables and migratory distance; thus, these geographical variables offer a composite variable of sorts, summarizing many factors that likely influence body size in nightjars. Leveraging multi-species and cross-continental data across the full annual cycle, along with global environmental data, can provide insight into long-standing questions and will be important for understanding the generalizability of Bergmanns rule.

zoology↗