Modeling male reproductive strategies and optimal mate number in an orb-web spider

Abstract

It is widely accepted that males maximize their reproductive success by maximizing their number of mates. However, empirical evidence shows that males, like females, may use complex strategies to allocate their reproductive investment, and optimize, rather than maximize, their mate number. We use a dynamic state model to evaluate male mating strategies and mate number in the golden orb-web spider Nephila clavipes. In this spider, males move among female webs and compete to copulate with the web owner. Pre- and postcopulatory competition for fertilizations is a function of female age and mated status. Thus, males experience a heterogeneous mating environment. In addition, because males have very limited sperm, there is strong selection on males to optimize their mating strategies. We determine the major factors that limit male mate number and assess whether males use size-based strategies to maximize their reproductive success. Results suggest that there is more than one mate number optimum for males. Male reproductive success from mating monogynously with a virgin female is similar to reproductive success from mating promiscuously. Mean reproductive success decreases over the course of the season. Mate guarding and mating multiply are traded-off by males depending on potential reproductive rate and male size. Variation in female quality favors multiple mating but not choosiness unless the costs of reproduction are extreme. Finally, males of different sizes achieve similar reproductive success but employ size-dependent strategies