Available at: https://digitalcommons.calpoly.edu/theses/2741
Date of Award
MS in Biological Sciences
College of Science and Mathematics
College of Science and Mathematics
Eavesdropping occurs when a receiver extracts information from an interaction without directly engaging with the signaler. Eavesdropping has been shown to be an effective way of evaluating the quality of potential mates and their abilities in male-male competition, without having to directly interact with them, thereby reducing energy costs and mating harassment. Girardinus metallicus is a livebearing poeciliid fish endemic to Cuba whose mating system is dominated by mating harassment in the form of sneak copulations, persistent displaying, and male-male aggression. G. metallicus has a male specific polymorphism in both melanin coloration and behavior. Males with melanin coloration are known as black morphs. Black morph males show persistent displaying and higher aggression, whereas plain morph males, the most common morph, do not have pronounced melanin patches and mate solely by sneak copulation. Plain morph males exhibit lower levels of aggression than black morph males.
In Chapter 1, we created groups consisting of a female and two males differing in body size and exposed them to dichotomous choice tests of female preference before and after the females witnessed the males interacting with each other. We hypothesized that: 1) male morphological traits are sexually selected via female choice in G. metallicus because these traits indicate quality; 2) female G. metallicus eavesdrop on male aggression to make mate choice decisions because aggression may indicate the quality of the male and his propensity to harass females; and 3) male size classes differ in behavior and morphology (saturation, brightness, and gonopodium size), consistent with other poeciliid studies showing that body size influences phenotype and that these traits are intercorrelated. We predicted 1) females will associate more with more colorful males, males with shorter gonopodia, and the larger male, before eavesdropping on male-male interactions, after, or both; 2) females will spend more time associating with males that subsequently delivered more chases and bites to a competitor male; and 3) larger males would be more active, more persistent in mating attempts, be more aggressive, and have a larger gonopodium size, and greater saturation and brightness of their posterior, ventral, and dorsal body regions. We found that females prefer to associate with males whose body regions are highly saturated, before eavesdropping on the two males interacting, but females did not prefer saturation after eavesdropping. We also found that females had a preference for smaller gonopodia relative for a males’ body size after eavesdropping. We also found that as male size increases, gonopodium length is proportional to their standard length. This study is the first to show female preference for coloration traits within any morph of G. metallicus, suggesting that plain morph males are not as plain to females as their name suggests.
Individual animals consistently vary in the average level of behavior exhibited across a range of contexts, which is also known as personality. Behavioral syndromes are correlations among personalities grouping them together. Personality traits have implications for mate choice, fitness, and predator avoidance. In Chapter 2, we addressed behavioral traits and personality in females and whether they influence how males respond to different degrees of boldness, activity, and aggression. We assessed female latency time to emerge from a refuge chamber, activity level, and aggressiveness to another female, on three successive days. We then quantified the degree of mating harassment each female experienced, when tested with a male. We hypothesized the following: 1) female G. metallicus exhibit personality across behavioral contexts (risk, activity, and resource competition), consistent with findings in other poeciliids including male G. metallicus; 2) the rank orders of boldness, activity, and aggression are positively correlated, consistent with other poeciliid studies that found evidence for behavioral syndromes; and 3) female personality traits mitigate male harassment because females that exhibit those personality traits are better at avoiding/retaliating against male harassment. We predicted that: 1) behavioral traits (latency time to emerge, boxes entered, and chases, bites, and fin flares delivered to a female competitor) measured within each context would be repeatable; 2) female rank orders of boldness, activity, and aggression personalities would be positively correlated with each other; 3) that larger females would experience less harassment; and 4) when females directly interact with a male, females that are bolder, more active, and more aggressive (bites and chases delivered to the male) are better able to mitigate male harassment. We found support for the hypothesis that some behavioral traits are repeatable in females; however, we found no evidence for behavioral syndromes. We found evidence to suggest that females that are less bold and less aggressive received less mating harassment from males, possibly because those females are of lower quality and not as attractive to males. Our most novel finding in this study was that activity and aggression were both consistent behavioral traits in females, and therefore constitute personalities; however, these personalities did not have a correlation grouping them together into a behavioral syndrome. Maybe there is a tradeoff: good females are bold and aggressive and get more food, but receive more mating harassment, whereas bad females are submissive and get less food, but avoid mating harassment.