Welcome to the American Ornithological Society 2018 Annual Conference. We are pleased to have you join us at the lovely Hilton El Conquistador Resort in Tucson, AZ.
The role of adaptation to divergent environments – or ecological speciation – in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms' adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline-freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here we sequence 20 whole genomes of two avian sister species endemic to tidal marshes – the Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson's Sparrow (A. nelsoni) – to evaluate the influence of selective and demographic processes in shaping genome-wide patterns of divergence. Genome-wide divergence between these two recently diverged sister species was notably high (genome-wide FST = 0.32). Divergent regions were widespread across the genome, as opposed to focused within islands of differentiation; these patterns may in part be the result of genetic drift acting during past tidal marsh colonization events. We identified several candidate genes that exhibited elevated divergence between Saltmarsh and Nelson's sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism – all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.
