The role of cultural divergence in reproductive isolation in a tropical bird, the rufous-collared sparrow (Zonotrichia capensis)
Danner, Julie Elizabeth
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In birds, song can evolve quickly through cultural transmission and due to errors in the learning process may result in regional dialects. A lack of dialectal recognition may be a critical component of reproductive isolation through female mate preference. I investigated the role of cultural divergence in reproductive isolation in a widespread Neotropical passerine the rufous-collared sparrow (Zonotrichia capensis). In Chapter II, I investigated, the role of female preference for and male territorial response towards, local and non-local dialects in two allopatric populations. Females in both populations preferred their local dialect to the dialect of an allopatric population only 25 km away. In contrast, males showed similar territorial response to all conspecific dialects. Premating reproductive isolation based on culture may exist among the study populations. In chapter III, I investigated if cultural divergence can drive population divergence by examining dialects and variable microsatellite loci among eight populations of Z. capensis. I investigated the presence of population divergence and then identified the mechanism that may be driving the pattern. Apart from culture, a geographic barrier (the Andean ridge), elevation, and geographic distance were potential mechanisms of population divergence that I considered. All sites exhibited localized dialects, except for two closest neighboring populations. Populations exhibited genetic differentiation with support for the presence of five genetic clusters. Culture does not appear to be driving population divergence because song dialects and genetic population structure were not correlated. Populations separated by an Andean ridge did not display higher genetic or song differences than distance would predict, suggesting that the ridge is not driving population divergence. Elevation was not correlated to song or genetic differentiation. Both song divergence and microsatellite allele frequency differentiation were correlated with geographic distance suggesting a pattern of isolation by distance. Overall, geographic distance is the best predictor of population divergence in this system. Cumulatively, I found that culture might promote assortative mating via female mate choice, perhaps generating partial reproductive isolation; however, song dialect differences among contiguous populations is not currently driving population divergence in this species.
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