Meeting Abstract
Alternative Reproductive Tactics (ARTs) are discrete variations in the reproductive phenotypes of members of the same sex within a species. When shared traits between ARTs have a common genetic basis, but different fitness optima, the resulting antagonistic selection can generate Intralocus Tactical Conflict (IATC). Studies on IATC can greatly improve our understanding of how ARTs evolve. The evolution of tactical dimorphism is one of the mechanisms that can resolve IATC, and can also be used as an indicator for traits experiencing disruptive selection. Using the two male ARTs in the high-backed pygmy swordtail fish, Xiphophorus multilineatus, we employed geometric morphometrics to examine the extent of body shape dimorphism between the tactics. Courter males, that use only courtship to attract females, were significantly less dorsal-ventrally compressed than sneaker males, that alternate between courtship displays and forced copulation. Sneaker males switch from courtship to forced copulation in the presence of a competitor, but will engage in both behaviors even when alone with a female. Therefore, we also investigated if a sneaker male’s morphology predicts the mating behavior it will most likely use in the absence of a competitor. Sneakers with a narrower body shape were more likely to use force copulatory behavior when alone with a female, suggesting that this may be the optimal morphology for this behavior. Future work will investigate the criteria necessary to demonstrate IATC in Xiphophorus mulitlineatus: shared traits are genetically correlated, opposing phenotypic optima for those traits, and that the tactics are currently not at their optima for those traits.
