Eumelanic Coloration Impacts Mating Behavior, Stress Response, and Predator Preference in the Polymorphic Eastern Mosquitofish

The expression of melanic or black coloration is ubiquitous and has significant behavioral and ecological relevance. Although black coloration is common, melanic morphs within populations are often considered rare. The mechanism for the maintenance of rare melanic morphs is often associated with differences in morph behavior, predator preference, or the interaction of both. Mechanistically, the genetic loci associated with black coloration in rare morphs can also influence behaviors, and these pleiotropic effects may provide some benefit to black morphs. We predicted that different mating behaviors, antipredator responses, and stress response, as well as predator preference influenced the maintenance of a rare black morph in freshwater Eastern mosquitofish. We created predator and control treatments to measure differences in melanic and silver mosquitofish behavior and cortisol levels. We also measured predator approach and attack of melanic and silver morphs. Overall, melanic morphs exhibited a higher number of mating behaviors compared to silver morphs and returned to mating attempts quicker than silver morphs after predator exposure. Melanic males also exhibited higher baseline cortisol levels, but silver males produced more cortisol after predator exposures compared to melanic males. These specific responses may provide the mechanism by which melanic males continue to persist in populations where they are rare.