Sexual dimorphism in fin size and shape in North American Killifish

Sexual dimorphism is intriguing because it suggests that males and females
differ in phenotypic optima for traits and that sex-specific trait values
can evolve despite a shared genome. Differences in sexual dimorphism
across populations or species suggest that the nature of sexual selection
and/or genetic constraints differs among species. Here, we measured sexual
dimorphism in 20 species of North American killifish (Fundulidae) in size
and shape of dorsal, anal, and caudal fins. We observed profound sexual
dimorphism in anal and dorsal fin size and shape across all species,
suggesting a common direction of selection. Sexual dimorphism was also
present in caudal fin size and shape but was much lower in magnitude, with
several species not differing from a null expectation of zero. There was
little evidence for a phylogenetic signal in the levels of sexual
dimorphism in dorsal and anal fin traits. We also found a strong
phylogenetic correlation between sexual dimorphism in anal and dorsal fin
shape but no phylogenetic correlation between fin area, base length, or
ray length across different fins. Our results indicate that there is
pronounced sexual dimorphism in anal and dorsal fin size and shape across
fundulids. Similar patterns of sexual dimorphism in anal and dorsal fin
properties have been documented in other groups, including gars, bichirs,
graylings, minnows, and many species in the Atherinomorpha, suggesting
that this pattern may be common across Actinopterygii.