Abstract

Dominance hierarchies typically develop in social organisms with competitive mating systems where resources are limiting. Facilitating cohabitation in these systems involves antagonistic interactions, such as physical aggression which can be costly. Gambusia affinis, commonly known as the western mosquito fish, exhibits dominance hierarchies and sexual dimorphism in that the males have a gonopodium rather than bright coloration. The gonopodium is a sex organ that is used to transfer sperm to females. Theoretically, males form dominance hierarchies that are based on aggressive behaviors and relative body size in this species. We are interested in how the particular morphologies contribute to dominance rank. We tested behavioral and morphological characteristics in male G. affinis that may contribute to dominance when multiple competing males are present. More specifically, we measured gonopodial thrusts and displays, and pigmentation changes. We predicted that dominant males would have darker body pigmentation, including the tear-drop pigment around the eye, and a longer gonopodium. We grouped similar sized males into sets of 5 (33 groups), marked each with one of five marks with fin clips (including “no mark”), and acclimated them for 24 hours before beginning trials. We observed male interactions with and without a female present by noting thrusts, displays, and pigmentation changes across 5 days. We currently are in the process of analyzing data, and will use regression analyses to determine if dominant males exhibit more body pigmentation and longer gonopodia. These findings will contribute to the body of literature on evolution and systems in freshwater species.

Authors

• Ciara Crochet, St Edward's University

• Dylan J Wichman, St. Edward's University

• Raelynn Deaton Haynes, St. Edward's University