Abstract
Defense against enemies is a type of natural selection considered fundamentally equivalent between the sexes. In reality, however, whether males and females differ in defense strategy is unknown. Multiparasitism necessarily leads to the problem of defense for a parasite (parasitoid). The polyembryonic parasitic wasp Copidosoma floridanum is famous for its larval soldiers’ ability to kill other parasites. This wasp also exhibits sexual differences not only with regard to the competitive ability of the soldier caste but also with regard to host immune enhancement. Female soldiers are more aggressive than male soldiers, and their numbers increase upon invasion of the host by other parasites. In this report, in vivo and in vitro competition assays were used to test whether females have a toxic humoral factor; if so, then its strength was compared with that of males. We found that females have a toxic factor that is much weaker than that of males. Our results imply sexual complementarity between host humoral toxicity and larval soldiers. We discuss how this sexual complementarity guarantees adaptive advantages for both males and females despite the one-sided killing of male reproductives by larval female soldiers in a mixed-sex brood.
Highlights
Defense against enemies is a type of natural selection considered fundamentally equivalent between the sexes
This study provided the first evidence of the existence of humoral toxic factors produced by female C. floridanum, which were weaker than male factors
The current findings indicate that sexual complementarity exists between the two types of defense systems: (1) soldier larvae and (2) toxic factors of the sexes
Summary
Defense against enemies is a type of natural selection considered fundamentally equivalent between the sexes. The polyembryonic parasitoids of the genus Copidosoma and other closely related encyrtid genera have sterile larval soldiers that provide a unique defense against heterospecific and conspecific competitors. In a mixed-sex brood, which is derived from female and male eggs laid in the same host egg, the sex ratio is often extremely female-biased because most male embryos are killed by female soldier larvae. Note that those male embryos were to grow to male reproductive if not killed. Sex differences in the level of aggressiveness between female and male soldier larvae likely evolved because of sexual conflict[7,11,12,13]. The sex difference in aggressiveness in soldier larvae should increase the protective ability of both sexes against heterospecific competitors[10]
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