Competition for territories does not explain allopaternal care in the tessellated darter

Abstract

Extensive research has focused on understanding the evolution of parental care, with fishes providing important model systems for understanding patterns of variation within and between species. Classic theory predicts that individuals will care for offspring when the fitness benefits through increased offspring survival and growth outweigh the cost to the parents through decreased future reproductive opportunities. Yet, a puzzling observation not explained by this basic theory is the fact that in some species individuals defend and provision unrelated offspring and thus exhibit alloparental care. The tessellated darter, Etheostoma olmstedi, represents one of the first known examples of allopaternal care in fishes. In this species, males often clean and guard eggs fertilized but deserted by other males. Allopaternal care has been argued to occur in the tessellated darter because of competition for a limited number of mating sites where less dominant males accept territories with eggs when other breeding sites are not available. Here, we test this hypothesis using male territory choice experiments. When allowed to choose between two otherwise identical territories either containing eggs fertilized by another male or with no eggs, males spent significantly more time at territories with eggs. This demonstrates that competition for mating territories is not the primary factor explaining the existence of allopaternal care in the tessellated darter. Instead, males of this species may exhibit allopaternal care to dilute predator pressure on their own eggs or because females prefer to mate with males whose territories contain eggs.