Social network analysis resolves temporal dynamics of male dominance relationships

Social organization is often studied through point estimates of individual association or interaction patterns, which does not account for temporal changes in the course of familiarization processes and the establishment of social dominance. Here, we present new insights on short-term temporal dynamics in social organization of mixed-sex groups that have the potential to affect sexual selection patterns. Using the live-bearing Atlantic molly (Poecilia mexicana), a species with pronounced male size polymorphism, we investigated social network dynamics of mixed sex experimental groups consisting of eight females and three different-sized males over a period of 5 days. Analyzing association-based social networks as well as direct measures of spatial proximity, we found that large males tended to monopolize most females, while excluding small- and medium-bodied males from access to females. This effect, however, emerged only gradually over time, and different-sized males had equal access to females on day 1 as well as day 2, though to a lesser extent. In this highly aggressive species with strong social dominance stratifications, the observed temporal dynamics in male-female association patterns may balance the presumed reproductive skew among differentially competitive male phenotypes when social structures are unstable (i.e., when individual turnover rates are moderate to high). Ultimately, our results point toward context-dependent sexual selection arising from temporal shifts in social organization. © 2014 Springer-Verlag Berlin Heidelberg

Female mating preferences for male morphological traits used in species and mate recognition in the Mexican sailfin mollies, Poecilia velifera and Poecilia petenensis

We tested whether sexually selected morphological traits in the sailfin mollies, Poecilia velifera and Poecilia petenensis, are also used in species recognition. Our first experiment, using live males as stimuli and providing females with olfactory as well as visual cues, found that females of both sailfin species preferred conspecific males to males of shortfin species. However, neither species preferred conspecific males when compared with heterospecific sailfin males, suggesting that premating reproductive isolation is not well developed between them. Our second experiment, providing females with only visual cues when distinguishing between live males, found that females of P. velifera preferred the larger of 2 stimulus males, regardless of whether the larger male was a conspecific or an heterospecific sailfin male. Such a preference for the larger sized male was not found in P. petenensis. To further investigate the role of the dorsal "sailfin" in species recognition, we used model males that varied only in the species identity of their dorsal fins. Females of both sailfin species preferred conspecific models with conspecific sailfins to those with dorsal fins of the shortfin species. In addition, females of P. velifera preferred the model with the largest sailfin, regardless of species identity. Similarly to the live male experiments, females of P. petenensis did not distinguish between conspecific and heterospecific sailfins. Overall, our study suggests that females of P. velifera have a generalized preference for larger males and that species-specific differences in sailfin shape do not lead to premating reproductive isolation between these 2 sailfin species. Copyright 2008, Oxford University Press.