Size-dependent ejaculation strategies and reproductive success in the yellow dung fly, Scathophaga stercoraria

Theory predicts that sperm competition will favour the production of larger ejaculates. However, because the benefits of greater reproductive investment are balanced by the costs of spermatogenesis, expenditure should depend on male physiology, mating rate and the relationship between additional investment and fertilization gains. In the yellow dung fly, Scathophagastercoraria, males adopt size-dependent alternative mating tactics that are associated with discrete ecological resources (foraging and oviposition substrates), although males switch between these environments throughout their lives. By copulating on foraging substrate (fruit or flowers), males can bypass intense mate competition that occurs at oviposition sites (cow dung), but as a consequence, must occupy a disfavoured mating role (i.e. face a greater risk that their ejaculate will be displaced from storage prior to fertilization). Small males often mate on foraging substrate, whereas large males mate in this environment on...