Alloparental care increases mating success

When individuals defend and care for young that are not their own (alloparental care), it raises the question of what benefits might lead to the evolution and persistence of such care. Here, we examine how male and female preferences affect the direct benefits of alloparental care. In the tessellated darter, alloparental care by some males often follows nest abandonment by others (Stiver KA, Wolff S, Alonzo SH, in preparation). We hypothesize that alloparental care may have evolved due to mating benefits: Alloparental care could be favored if females prefer to breed at nests that contain eggs. We found that, on average, males and females prefer nests with young eggs to those without eggs. Consequently, although young eggs increase the attractiveness of the nest, this positive effect is lost as the age of the eggs on the nest increases. We also found that alloparental care is costly in terms of future potential mating success as the amount of new eggs deposited in a nest decreases as nests become more filled. Therefore, alloparental males may initially increase their attractiveness to females by defending nests with another male's eggs but still potentially gain fewer eggs relative to those received by males defending empty nests. Our findings shed light on the evolution of alloparental care in the tessellated darter, suggesting that female mating preferences may underlie this well-documented cooperative relationship between males. Copyright 2011, Oxford University Press.