Feeding Mechanics and Functional Morphology in the Jaws of Sculpins

Abstract

Species with overlapping geographic ranges, similar morphology, and ecological roles often vie for the same resources and therefore face competitive exclusion. This competition can be reduced if species vary in skeletal and muscular anatomy, because it changes biomechanical performance across species. We examined biomechanical variation of feeding structures in a group of nineteen sculpins (Cottoidea) that co-occur in the marine habitat around the San Juan Islands. We quantified evolutionary correlations of skeletal morphology and muscle morphology by conducting phylogenetic independent contrasts using a phylogeny constructed from published molecular data. We hypothesized that skeletal leverage (mechanical advantage) and muscle architecture (gearing) could either display a positive evolutionary correlation (changing over evolutionary time to perform inversely of each other), or the features could display a negative correlation (changing over evolutionary time to perform in the same way). We found a positive correlation between evolutionary shifts of out-lever length and adductor muscle length, but no correlation between evolutionary shifts of in-lever length and adductor muscle length or adductor muscle length and lever ratio. Our results demonstrate that skeletal leverage and muscle architecture evolve independently in individual species of sculpins. These results also suggest that these two functional units (skeletal morphology and muscle morphology) both contribute to biomechanical diversity in closely related, geographically co-occurring sculpin species, indicating their importance as metrics of ecomorphological diversity.