Protandrous arrival timing to breeding areas: a review

Yolanda E. Morbey* and Ronald C. Ydenberg Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada. *Correspondence: Department of Zoology, Ramsay Wright Zoological Laboratories, University of Toronto, 25 Harbord St., Toronto, Ont., M5S 3G5, Canada. E-mail: [email protected] Abstract 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 insects, ®sh, amphibians, reptiles, birds and mammals). The adaptive signi®cance of protandry is not fully understood and, since the 1970s, at least seven hypotheses for protandry have been proposed. We describe each of these hypotheses and summarize what is known about each. In three of these hypotheses, the relative arrival timing of males and females has no direct ®tness consequences for males or females, but selection for different timing in each sex indirectly produces protandry. In the other four hypotheses, the difference between male and female timing has ®tness consequences for males or females and selection directly maintains the ®tness-maximizing degree of sex-biased timing. The hypotheses are not mutually exclusive, and the degree of multiple mating by males and the occurrence of male territoriality seem to determine the relative importance of each hypothesis. In order to understand the adaptive signi®cance of sex-biased timing, future studies need to consider all the alternatives and to assess the costs and bene®ts to males of early arrival relative to calendar date, to other males and to females.