# Neutral markers reveal complex population structure across the range of a widespread songbird

## TL;DR

This study explores how physical barriers affect gene flow in mountain bluebirds, revealing four distinct populations shaped by historical and current environmental factors.

## Contribution

The study identifies genetic population structure and selection patterns in mountain bluebirds, linking them to historical and contemporary environmental barriers.

## Key findings

- At least four genetically distinct mountain bluebird populations were detected using SNPs.
- Isolation-by-distance, the northern Rocky Mountains, and discontinuous habitat limit connectivity.
- Five candidate genes under balancing selection and three loci under diversifying selection were identified.

## Abstract

Understanding how both contemporary and historical physical barriers influence gene flow is key to reconstructing evolutionary histories and can allow us to predict species' resilience to changing environmental conditions. During the last glacial maximum (LGM), many high latitude North American bird species were forced into glacial refugia, including mountain bluebirds (Silia currucoides). Within their current breeding range, mountain bluebirds still experience a wide variety of environmental conditions and barriers that may disrupt gene flow and isolate populations. Using single nucleotide polymorphisms (SNPs) obtained through restriction site‐associated DNA sequencing, we detected at least four genetically distinct mountain bluebird populations. Based on this structure, we determined that isolation‐by‐distance, the northern Rocky Mountains, and discontinuous habitat are responsible for the low connectivity and the overall history of each population going back to the last glacial maximum. Finally, we identified five candidate genes under balancing selection and three loci under diversifying selection. This study provides the first look at connectivity and gene flow across the range of these high‐altitude and high latitude songbirds.

Understanding how both contemporary and historical physical barriers influence gene flow is key to reconstructing evolutionary histories and can allow us to predict species' resilience to changing environmental conditions. Using single nucleotide polymorphisms obtained through restriction site‐associated DNA sequencing, we detected at least four genetically distinct mountain bluebird populations. Based on this structure, we determined that isolation‐by‐distance, the northern Rocky Mountains, and discontinuous habitat are responsible for the low connectivity, and the overall history of each population going back to the last glacial maximum.