《Nature》：竞争压力与亲缘关系

Aggression by polyembryonic wasp soldiers correlates with kinship but not resource competition

Kin selection theory predicts that individuals will show less aggression and more altruism towards relatives. However, recent theoretical developments suggest that with limited dispersal, competition between relatives can override the effects of relatedness. The predicted and opposing influences of relatedness and competition are difficult to approach experimentally because conditions that increase average relatedness among individuals also tend to increase competition. Polyembryonic wasps in the family Encyrtidae are parasites whose eggs undergo clonal division to produce large broods. These insects have also evolved a caste system: some embryos in a clone develop into reproductive larvae that mature into adults, whereas others develop into sterile soldier larvae that defend siblings from competitors. In a brood from a single egg, reproductive altruism by soldiers reflects clone-level allocation to defence at the cost of reproduction, with no conflict between individuals. When multiple eggs are laid into a host, inter-clone conflicts of interest arise. Here we report that soldier aggression in Copidosoma floridanum is inversely related to the genetic relatedness of competitors but shows no correlation with the level of resource competition.

Figure 1 Life cycle of C. floridanum in its host T. ni. The schematic shows a host larva and the developmental stages of C. floridanum. Below the schematic are the host's life stages in relation to time (days). After parasitism, the host egg hatches and the larva develops to a fifth instar over 14 days. The C. floridanum egg develops initially into a primary morula. The primary morula then clonally proliferates to form a polymorula of more than 1,000 embryos during the host first to fourth instar period. Soldier larvae eclose during this period. Reproductive larvae eclose in the host fifth instar.

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