Life-history adaptations and reproductive costs associated with specialization in predacious insects

1. A diverse array of predatory insects has evolved restricted prey associations, and yet life-history determinants of prey specialization have been examined in very few species. In a comparative experimental study, a pair of generalist and specialist sister-species showed significant developmental and reproductive responses to each other's prey. The results reveal evolutionary adaptations, as well as trade-offs, associated with predator-prey specialization. 2. Hatchlings of the generalist Chrysopa quadripunctata suffered very high mortality in the presence of woolly alder aphids. the stout-bodied, colonial aphid species that constitutes the prey of its specialist sister-species C. slossonae. In contrast, the characteristically larger and more robust hatchlings of the specialist, and older larvae of both species, survived well on this prey. It appears that the evolution of large hatchlings and an associated set of traits (large adults, reduced fecundity, large eggs, reduced developmental rates) underlies the specialized prey association between C. slossonae and the woolly alder aphid. 3. The woolly alder aphid diet of the specialist caused four of the generalist's life-history traits to tend towards those of the specialist, i.e. size of adults and eggs increased, and rates of oviposition and preimaginal development decreased. Such diet-based phenotypic plasticity in the sister-species' ancestor could have helped facilitate the early evolutionarg stages of C. slossomae's association with the woolly alder aphid. 4. In comparison, the generalist's prey did not negatively affect either survival or development of the specialist's immatures, but the resulting adults had significant reductions in body size, survival, oviposition and egg fertility. Thus, we conclude that oc a drastic diminution in the ability to reproduce on the presumed ancestral-like prey accompanied specialization on the woolly alder aphid. Although the physiological basis for the specialist's reduced ability to use the generalist's prey is unknown, it may contribute to a very stable dietary association with the woolly alder aphid.