Meeting Abstract
Sexual selection acts on an organism’s ability to successfully obtain mates, either through intersexual selection, generally via female choice of males, or intrasexual selection, where males compete against each other for access to females. Male competition for mates can occur both before and after copulation, but the relationship between these two types of competition is unclear. Stronger pre-copulatory male competition generally leads to greater sexual size dimorphism (SSD), with males growing to larger body sizes than females, while the strength of post-copulatory selection is often associated with testis and sperm morphology. To better understand the dynamics between these pressures when they are both present within the same individuals, we examined nine species of Anolis lizards from the Dominican Republic. Using cryosectioned testis tissues, we measured the cross-sectional area of the testis and the seminiferous tubules to assess the relationship between these measures with SSD and the gonadosomatic index (GSI, the ratio of testis mass to body mass). Our findings show that bigger lizards have bigger testes (R2 = 0.60; p = 0.005) and that bigger testes have larger seminiferous tubules, regardless of body size (p = 0.005). Additionally, we found preliminary evidence suggesting that lizards with greater SSD have a smaller GSI (R2 = 0.238, p = 0.104), indicating a tradeoff between the resources allocated to pre- and post-copulatory selection. To better understand how sexual selection influences the evolution of reproductive morphologies in lizards, we will include additional measures of testis morphology (lumen area, seminiferous epithelial thickness, and cell-type ratios) with the morphology of mature sperm across our species.
