Unseen Opportunity: Do Hermaphrodite Cues Influence Male-Male Aggression in Mangrove Rivulus Fish.

Aggressive contests in fish often occur in the presence of an audience, which can affect contest dynamics and outcomes. These so-called "Audience Effects" can vary depending on the sex of the audience members. For example, a female audience can elicit increased use of low-intensity displays and decreased use of high-intensity attacks between the male combatants. Mangrove rivulus (Kryptolebias marmoratus) fish occur naturally as either self-fertilizing, simultaneous hermaphrodites or functional males. Male rivulus' reproductive success thus depends on their ability to obtain outcrossing opportunities with hermaphrodites. Our study's aim is to examine if hermaphroditic chemical cues in the absence of visual cues influence the intensity of male-male rivulus contests and if unequal access to these cues provides a competitive advantage. We dosed focal individuals with either DI water (control) or water laced with hermaphroditic cues (treated). Following, we created size-matched pairings that resulted in three combinations of contestants; control-control, control-treated, and treated-treated. We found that untreated, control-control contests were more likely to escalate to high-intensity behaviors compared to treated-treated contests. Further, dosed individuals pitted against untreated individuals did not have a competitive advantage. Our findings show that male rivulus do modulate their aggressive behavior dependent on presence of an audience [ABSTRACT FROM AUTHOR]