Asymmetric discrimination of geographical variation in song in a migratory passerine

Abstract

Variation in sexual signals across populations is a common phenomenon, and most research to date has found that individuals discriminate against nonlocal signals. However, the strength of nonlocal signal discrimination can vary asymmetrically across populations, a possibility that has received less attention. Such asymmetries can be due to recognition errors in some populations, variation across populations in the [`]quality' of local individuals, such that populations with high-quality individuals respond more strongly, and/or variation in the perception of signals, with signals from some populations being perceived as more intimidating or aggressive. Here, we examine song differences and male responsiveness to local and nonlocal songs in two populations of the black-throated blue warbler, Dendroica caerulescens, and also explore possible reasons for geographical variation in responsiveness. In the northern population, male responses were stronger to local songs than to nonlocal songs, whereas in the southern population, male responses to local and nonlocal songs did not differ. Overall responsiveness did not differ between the populations, and songs from one population were not responded to more weakly (or strongly) across populations. Overall, our results fit best with a model of asymmetric recognition error. Asymmetries in nonlocal responsiveness across populations may be a common phenomenon, and can have profound effects on patterns of dispersal, mate choice and gene flow.