Meeting Abstract

P3-147   -   Head shape variation in darters is driven by allometry and modularity Goodwin, MR*; Arbour, JH; Middle Tennessee State University; Middle Tennessee State University goodwinmaris@gmail.com

Darters are a speciose group of freshwater fish endemic to North America. They display a wide range of morphological differences, most notably in their head shape. This study aimed to address a few questions: (1) whether head shape in darters varies by size, (2) if darter species exhibit differing allometric slopes, and (3) if shape variation is partitioned across the darter head. We collected geometric morphometric landmarks from eight different species (n = 146) spread across the darter phylogeny. We used the R package “geomorph” to test for evidence of allometric shifts, namely a multivariate regression to determine the influence of size, species, and the interaction between the two on head shape. In addition, we used the covariance ratio function to quantify the degree of modularity between the preorbital and postorbital regions of the darter head. We found that different species have unique allometric slopes and that closely related darter species tend to show ontogenetic divergence, suggesting that as darters grow larger, they may develop more diverse head shapes to inhabit specific ecological niches. For a majority of the species tested, modularity was present, implying that shape variation is partitioned across the head. Overall, our work suggests that ontogenetic relationships may have been important to the evolution of head shape in darters, particularly in the preorbital module, allowing species a developmental pathway to adapt to needs specific to their environment.