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Abstract
Across taxa, morphological and behavioral traits can correlate within individuals. Eastern Mosquitofish (Gambusia holbrooki) exhibit a discrete color polymorphism. Males are either the common silver morph or the uncommon mottled morph, unpigmented with black blotches. I first reviewed and synthesized literature about the biology and correlated phenotypes of this color pattern in Poeciliidae. This review revealed conflicting results about the social behavior of mosquitofish morphs. I subsequently studied how behavior was affected by the focal male’s morph and by indirect genetic effects, specifically the phenotypes of interacting individuals. I investigated how social behavior differed across three social contexts: with a group of females, in a male-male dyad, and in a mix-sex group. Mottled males are more assertive towards female groups than silver males, but not in mix-sex contexts. In dyads and mix-sex groups, mottled males dominate silver males, which results from silver males altering their behavior based on the opponent male’s morph. In silver mosquitofish, size usually predicts social dominance, but its effect on the dominance of mottled males was unknown. Arranging social dyads of every color morph-combination across a range of size differences, I found that larger relative body size predicts dominance in within-morph conflicts, but morph is more important in between-morph conflicts. Mottled males dominate silver males, regardless of size differences. Finally, to determine potential genetic mechanisms for phenotypic correlations within mosquitofish morphs, I used whole-brain transcriptomics of mottled and silver males following interactions with a silver male. Morphs show distinct differences in their neuromolecular responses. I identify three differentially expressed transcripts that correlate with social behavior, including GIPC1 (GIPC PDZ domain containing family, member 1), which was previously determined to have a Y-chromosome linked allele associated with the mottled pattern. In conclusion, social behavior depends both on the male’s morph and on the phenotypes of conspecific interacting individuals, but mottled males dominate silver males across size differences and social contexts. Future studies should examine whether and how the differentially expressed transcripts identified here affect the expression of color pattern and social dominance in male mosquitofish.