Meeting Abstract
Many vertebrate groups have weaponized their skulls and, though some cranial weaponry aids defense, intraspecific combat appears to drive the evolution of these structures in most terrestrial cases. Equally impressive weaponry adorns aquatic vertebrates, such as the sculpins in superfamily Cottoidea. The skulls of these diverse fishes bear antler-like preopercular spines of remarkable variation, and the males of many species show intraspecific agonistic behavior during the breeding season. Do the evolutionary trends in weapon morphology of these fishes follow those observed in ungulates, beetles, and other fighting fauna? If so, we predicted that their spine shape would show ontogenetic change, sexual dimorphism, and asymmetry. We tested these predictions in members of the sculpin subfamily Oligocottinae by quantifying spine shape with 3D geometric morphometric techniques applied to reconstructions from micro-CT scans of members of each species. We found that sexual dimorphism is not apparent in the preopercular spine shape of oligocottines but ontogenetic change in shape is evident in several species and that asymmetry is common in all species. Interestingly, the direction of change across ontogeny is inconsistent across species, with the spines of some species becoming proportionally larger and more complex with age, while in others the spines become reduced. Asymmetry also showed higher than expected variation, with ~48% of preopercles having a shape more similar to the preopercle of a different individual than to the other side of their own body. Taken together, these results suggest that sculpins use their spines at least partially for agonism and combat, but also for defensive purposes, with possible trade-offs in some species across ontogeny.
