Protandrous arrival timing to breeding areas: a review

Protandry, the earlier arrival of males to breeding areas than females, is a common pattern of sex-biased timing in many animal taxa (e.g. some insect s, fish, amphibians, reptiles, birds and mammals). The adaptive significanc e of protandry is not fully understood and, since the 1970s, at least seven hypotheses for protandry have been proposed. We describe each of these hyp otheses and summarize what is known about each. In three of these hypothese s, the relative arrival timing of males and females has no direct fitness c onsequences for males or females, but selection for different timing in eac h sex indirectly produces protandry. In the other four hypotheses, the diff erence between male and female timing has fitness consequences for males or females and selection directly maintains the fitness-maximizing degree of sex-biased timing. The hypotheses are not mutually exclusive, and the degre e of multiple mating by males and the occurrence of male territoriality see m to determine the relative importance of each hypothesis. In order to unde rstand the adaptive significance of sex-biased timing, future studies need to consider all the alternatives and to assess the costs and benefits to ma les of early arrival relative to calendar date, to other males and to femal es.