Behavioral Ecology Advance Access originally published online on September 10, 2007
Behavioral Ecology 2007 18(6):1106-1115; doi:10.1093/beheco/arm083
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Sex ratio schedules in a dynamic game: the effect of competitive asymmetry by male emergence order
a Department of Systems Sciences, University of Tokyo, Meguro, Tokyo 153-8902, Japan b Faculty of Applied Biological Sciences, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan c Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK d Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan
Address correspondence to Jun Abe. E-mail: jun.abe{at}ed.ac.uk.
| Abstract |
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Studies of sex allocation have provided some of the most successful tests of theory in behavioral and evolutionary ecology. For instance, local mate competition (LMC) theory has explained variation in sex allocation across numerous species. However, some patterns of sex ratio variation remain unexplained by existing theory. Most existing models have ignored variation in male competitive ability and assumed all males have equal opportunities to mate within a patch. However, in some species experiencing LMC, males often fight fiercely for mates, such that male mating success varies with male fighting ability. Here, we examine the effect of competitive ability on optimal sex allocation schedules using a dynamic programming approach. This model assumes an asymmetric competitive ability derived from different mortalities according to the timing of male emergence. If the mortality of newly emerging males is larger than that of already emerged males, our model predicts a more female-biased sex ratio than expected under traditional LMC models. In addition, females are predicted to produce new males constantly at a low rate over the offspring emergence period. We show that our model successfully predicts the sex ratios produced by females of the parasitoid wasp Melittobia, a genus renowned for its vigorously fighting males and lower than expected sex ratios.
Key words: dynamic game model, lethal male combat, local mate competition, Melittobia, parasitoid wasps, sex allocation.
Received 26 September 2006; revised 6 May 2007; accepted 10 August 2007.