Meeting Abstract
Among animals that use displays for courtship and competition, visual signals incorporating gesture— or body movements used specifically for communication—are widespread. These displays vary widely in complexity, from simple limb movements to downright acrobatic performances. However, this is seldom studied on an evolutionary basis. Here we address this by exploring why species use a more or less diverse range of movements in their display repertoire. One factor that should influence how displays evolve is latitudinal biogeography, which indirectly influences sexual selection. This is because the high-latitude temperate breeding season offers a restricted time frame for reproduction, and increasing display complexity is one way to expedite mating decisions. At the same time, a species’ social mating system may also influence display evolution, because males of polygynous species undergo more intense competition for mates than monogamous species. In this study, we use the New World blackbirds to explore how biogeography and social mating system each shape gestural complexity. We first find that temperate species evolve more complex gestures than their tropical counterparts, which we attribute to differences in breeding seasonality. Interestingly, these species also evolved in the midst of repeated glaciation events, which can serve as a mechanism for isolation, divergence, and reinforcement. However, social mating system alone does not explain differences in complexity. Altogether, these data offer a first look at how surprising macroevolutionary patterns in an overlooked display mode reveal evolutionary mechanisms at work.
