Cooperative Fish and Wildlife Research Units Program: South Carolina
Education, Research and Technical Assistance for Managing Our Natural Resources

Grady, J. T., Bower, L. M., Gienger, C. M., & Blanton, R. E. (2022). Fish scale shape follows predictable patterns of variation based on water column position, body size, and phylogeny. Evolutionary Ecology, 36(1), 93-116.


The influence of environment and phylogeny on morphological characteristics of organisms is well documented. However, little is known about how these factors influence scale shape in fishes, a feature which may be important for drag reduction. We evaluated the impact of both on scale shape variation in the primarily benthic, riverine darter clade (Percidae: Etheostomatinae) of fishes. 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 use of the substrate boundary layer. We used geometric morphometrics and seven homologous landmarks for 92 species of darters representing all genera and 37 terminal clades within genera to measure scale shape. Phylogenetic relationships and ecological categories describing habitat, spawning mode, and maximum body size of each species were summarized from the literature. We used ordinations to examine scale shape variation among phylogenetic and ecological groups. We conducted Phylogenetic Generalized Least Squares analyses to test for relationships between scale shape and ecological characteristics. Scale shape variation occurred within and among darter clades, and was significantly related to phylogeny. However, we found divergent scale shapes between close relatives and similar scale shapes between distantly related species. After accounting for phylogenetic signal, size and water column position were related to scale shape. Extra-large, hyperbenthic species had longer, narrower scales that may decrease laminar drag. Sub-benthic darters had scales that were narrower at the insertion, and with enlarged ctenial margins that may facilitate burying. Among benthic darters, size was significantly related to scale shape though a lack of clustering among many taxonomic and ecological groups may indicate that boundary layer use has reduced selective pressures from drag. Our results are consistent with others that have found both environment and phylogeny influence Teleost fish morphology.