Cross-context behavioral correlations and signals of aggression in females of a livebearing fish

Behaviors may be adaptively correlated with each other and with other aspects of phenotype. We investigated behavior across foraging, mating, and risk contexts in females of the poeciliid fish, Girardinus metallicus. We quantified relationships between these behaviors and aggression signals, body size, and reproductive output. Behaviors describing aggression and boldness, some of which were repeatable, were correlated in females. Aggression was signaled by the darkening of a black spot on the extended dorsal fin or by fin flaring. Spot darkening occurred during intra- and intersexual interactions and was positively correlated with inter-female aggression and negatively correlated with time females spent following males, suggesting that it honestly indicates motivational state. In contrast, fin flaring was only directed at females and occurred more frequently in the foraging context. Larger females had fewer offspring and received fewer courtship displays, possibly because they were more aggressive to males. In contrast to studies of males, we found a negative relationship between rank order of boldness and aggression, consistent with either a tradeoff or with selection favoring the negative relationship. Our results highlight the importance of studying females in model systems to uncover novel patterns and potentially meaningful departures from what is typically seen in males.

Methods
Data were collected by counting offspring for life history variables, measurement from images for morphology, direct observation for behaviors, and water-borne collection for cortisol. Data analysis was performed using JMP 16.