Environment and phylogeny influence scale shape variation in Etheostomatinae darters
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Abstract
Variation in scale number and type has been well studied in Teleost fishes however, variation in scale shape has received less attention. Given the well-documented role of environment and phylogeny on multiple aspects of phenotype, we evaluated the impact of both on scale shape variation in darters (Percidae: Etheostomatinae). We predicted that darters with close phylogenetic relationships and/or shared ecologies would have more similar scale shapes, but this relationship would be mediated by their use of the boundary layer. We used geometric morphometrics and seven homologous scale landmarks from 30 individuals each for 92 species of darters representing all genera and terminal clades. Variables describing habitat, spawning mode, maximum body size (Size), and phylogeny were summarized from the literature. We used ordinations to examine scale shape variation among phylogenetic and ecological groups. To test for relationships between scale shape and ecological characteristics we conducted Partial Least Squares and Phylogenetic Generalized Least Squares analyses. Scale shape variation occurred within and among darter clades, and was significantly related to phylogeny, suggesting some variation is evolutionarily constrained. However, after accounting for phylogenetic signal, size and water column position (WCP) were related to scale shape such that extra-large, midwater species had longer, narrower scales that may decrease laminar drag, and sub-benthic darters had scales that were narrower at the anterior insertion, had longer scale bodies and longer, wider ctenial margins that may facilitate burying. Among benthic darters, size was significantly related to scale shape but other results may indicate that boundary layer use reduces selective pressures of drag. Consistency between our results and others from the literature provide support for environmental
influences on scale shape in Teleost fishes.