Speciation, gene flow, and seasonal migration in Catharus thrushes (Aves:Turdidae).

New World thrushes in the genus Catharus are small, insectivorous or omnivorous birds that have been used to explore several important questions in avian evolution, including the evolution of seasonal migration and plumage variation. Within Catharus, members of a clade of obligate long-distance migrants (C. fuscescens, C. minimus, and C. bicknelli) have also been used in the development of heteropatric speciation theory, a divergence process in which migratory lineages (which might occur in allopatry or sympatry during portions of their annual cycle) diverge despite low levels of gene flow. However, research on Catharus relationships has thus far been restricted to the use of small genetic datasets, which provide limited resolution of both phylogenetic and demographic histories. We used a large, multi-locus dataset from loci containing ultraconserved elements (UCEs) to study the demographic histories of the migratory C. fuscescens-minimus-bicknelli clade and to resolve the phylogeny of the migratory species of Catharus. Our dataset included more than 2000 loci and over 1700 variable genotyped sites, and analyses supported our prediction of divergence with gene flow in the fully migratory clade, with significant gene flow among all three species. Our phylogeny of the genus differs from past work in its placement of C. ustulatus, and further analyses suggest historic gene flow throughout the genus, producing genetically reticulate (or network) phylogenies. This raises questions about trait origins and suggests that seasonal migration and the resulting migratory condition of heteropatry is likely to promote hybridization not only during pairwise divergence and speciation, but also among non-sisters.

Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals.

Assessing the physiological impact of stressors in pinnipeds is logistically challenging, and many hormones are altered by capture and handling, limiting the utility of metabolically active tissues. Hair is increasingly being used to investigate stress-related and reproductive hormones in wildlife populations due to less-invasive collection methods, being metabolically inert once grown and containing multiple biomarkers of ecological interest. We validated enzyme immunoassays for measuring aldosterone, cortisol, corticosterone, and testosterone in lanugo (natal hair grown in utero) samples collected from Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus). We applied laboratory validation methods including recovery of added mass, parallelism and dilution linearity. We found no effects due to differences in alcohol- versus detergent-based cleaning methods. Further, there were no significant differences in hormone concentrations in hair samples collected immediately after the molt and the subsequent samples collected over 1 year, indicating steroid hormones are stable once deposited into pinniped hair. We found no sex differences in any hormone concentrations, likely due to the lanugo being grown in utero and influenced by maternal hormone concentrations. For Steller sea lion and California sea lion pups, we found hormone concentrations significantly differed between rookeries, which warrants future research. Hair provides a novel tissue to explore the intrinsic or extrinsic drivers behind hormone measurements in otariids, which can be paired with multiple health-related metrics to further investigate possible drivers of physiological stress.