Alternative Reproductive Tactic Frequencies Vary with Stream Size for an Appalachian Salamander

AbstractSpatial variation in allele frequencies can provide clues about the mechanisms responsible for the maintenance of genetic polymorphisms. In some populations of two-lined salamanders, males exhibit two alternative reproductive tactics determined by a Y-linked genetic polymorphism: searching males locate and court females in terrestrial habitats, and guarding males defend mates at aquatic nesting sites. Here, we study the fine-scale spatial variation in the frequency of these tactics by genotyping >1,000 total larvae from five pairs of small and large stream reaches in the Appalachian Mountains. We found strong evidence that tactic frequency varies with stream size-with searching males accounting for >80% of male larvae in small stream reaches and only 50% of male larvae in large stream reaches. We discuss several hypotheses that may explain this pattern of fine-scale variation and highlight the utility of this tractable study system for understanding the mechanisms that maintain polymorphisms in wild populations.