Abstract
Non‐sex‐linked color polymorphism is common in animals and can be maintained in populations via balancing selection or, when under diversifying selection, can promote divergence. Despite their potential importance in ecological interactions and the evolution of biodiversity, their function and the mechanisms by which these polymorphisms are maintained are still poorly understood. Here, we combine field observations with life history and molecular data to compare four sympatric color morphs of the coral reef fish Paracirrhites forsteri (family Cirrhitidae) in the central Red Sea. Our findings verify that the color morphs are not sex‐limited, inhabit the same reefs, and do not show clear signs of avoidance or aggression among them. A barcoding approach based on 1,276 bp of mitochondrial DNA could not differentiate the color morphs. However, when 36,769 SNPs were considered, we found low but significant population structure. Focusing on 1,121 F ST outliers, we recovered distinct population clusters that corresponded to shifts in allele frequencies with each color morph harboring unique alleles. Genetic divergence at these outlier loci is accompanied by differences in growth and marginal variation in microhabitat preference. Together, life history and molecular analysis suggest subtle divergence between the color morphs in this population, the causes for which remain elusive.
Highlights
Color polymorphism is common among animals and serves a number of critical functions in communication, crypsis, mate signaling, and mimicry (McLean & Stuart-Fox, 2014; Nosil & Crespi, 2006; Roulin, 2004; White & Kemp, 2016)
Non-sex-linked color polymorphism can be maintained by balancing selection, but when under the influence of divergent selection, it can promote speciation
Unique color morphology can be used to distinguish allopatric populations diverging through neutral processes
Summary
Color polymorphism is common among animals and serves a number of critical functions in communication, crypsis, mate signaling, and mimicry (McLean & Stuart-Fox, 2014; Nosil & Crespi, 2006; Roulin, 2004; White & Kemp, 2016). Theoretical models predict that balancing selection can maintain color polymorphisms in a population under a number of scenarios (Gray & McKinnon, 2006). Color polymorphism has been observed within and among populations of reef fishes and has been linked to sex, life history stage, or behavior (Thresher, 1984; Thresher & Moyer, 1983). Of particular interest is color polymorphism in fish that is not linked to sex or ontogeny, but instead may represent intraspecific variation or unrecognized evolutionary partitions (Violi, Gaither, Burns, Hoelzel, & Neat, 2018; Whitney, Bowen, & Karl, 2018). Where color morphs are geographically isolated, molecular evidence often indicates recent divergence that may not relate to ecologically or behaviorally driven evolution (Drew, Allen, & Erdmann, 2010; Drew, Allen, Kaufman, & Barber, 2008; Taylor & Hellberg, 2003). Color morphology can fail to translate into genetic partitions (Lin, Sánchez-Ortiz, & Hastings, 2009; Messmer, van Herwerden, Munday, & Jones, 2005), implicating a mechanism other than geographic isolation in their maintenance (Messmer et al, 2005; Munday, Eyre, & Jones, 2003)
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