Evolutionary divergence and adaptive capacity in morphologically distinct song sparrow subspecies

Spatial variation in the environment can affect population fitness and individual phenotype by facilitating natural selection and local adaptation, and thereby enhance the diversity and adaptive capacity and persistence of species at regional to continental scales. The song sparrow subspecies complex endemic to the San Francisco Bay region, which has received over a century of close study, presents an opportunity to evaluate the adaptive potential of distinct subspecies faced with habitat loss, population decline, and threats of future environmental change. We used whole-genome sequences from 39 individuals representing five morphologically distinct song sparrow subspecies to evaluate the role of neutral and adaptive evolutionary processes in driving divergence within physiologically challenging habitats across multiple environmental clines. We found that natural selection for traits explained by ecological variables, including temperature and salinity, are drivers of adaptive genetic variation in these song sparrows. Differentiation was highest for candidate loci under selection (compared to neutral markers), as predicted if local ecological processes are at least partially responsible for the rapid radiation of these subspecies. Our findings inform management aimed at conserving and prioritizing population-level diversity in species displaying local adaptation and inhabiting a diverse range of environments.

Automated summary

Spatial variation in the environment can have significant impacts on population fitness and individual phenotype by driving natural selection and local adaptation, which can contribute to the diversity and adaptability of species at large scales. This study focused on the song sparrow subspecies complex in the San Francisco Bay region to assess the adaptive potential of different subspecies facing habitat loss and future environmental changes. By analyzing whole-genome sequences from 39 individuals, the researchers demonstrated that natural selection driven by ecological variables such as temperature and salinity plays a key role in shaping adaptive genetic variation in these song sparrows. The findings contribute valuable insights for conservation management strategies aimed at preserving population-level diversity in species with local adaptation across diverse environments.