Higher establishment success in specialized parasitoids: support for the existence of trade-offs in the evolution of specialization

Most animals do not feed on all the resources available to them, but the mechanisms behind the evolution of dietary specialization are still debated. A central but unanswered question is whether specialists generally gain fitness advantages on their resource compared to generalists, experiencing a trade-off between the ability to use a broad range of resources and the fitness reached on each single one.Empirical tests so far suffered from difficulties in measuring fitness; they were restricted to few species, and results were equivocal. This lack of support for the importance of trade-offs gave rise to theories explaining the evolution of specialization without such trade-offs.Using a large dataset of intentional biological control introductions of 254 species of parasitoids from 15 families to locations outside their native range, we show that establishment success, a measure of total fitness, is higher in specialized species. This result holds when controlling for possible confounding factors such as the number of introduced individuals (propagule pressure).The outcome of this study provides robust evidence that dietary specialization implies fitness advantages in an entire species-rich taxon, indicating that trade-offs might be widely involved in the evolution of specialization

A solitary ground‐nesting wasp truncates its parental investment in response to detection of parasites

1. Parental investment by solitary nest-building wasps and bees is predicted to be plastic, responding to variation in the sex of the offspring, the availability of food used as provisions ('resource limitation'), the female's inventory of mature oocytes ('egg limitation'), and risk imposed by nest parasites. 2. I observed nest provisioning by Ammophila dysmica, a solitary, ground-nesting wasp that provisions its nest with one or two caterpillar prey to evaluate the hypotheses that provisioning is shaped by caterpillar size, offspring sex, the hunting time required to capture prey, a female's egg load, and penetration of nests by the parasites Argochrysis armilla and Hilarella hilarella. 3. Ammophila dysmica were more likely to add a second provision to the nest when the first prey item was relatively small and when provisioning daughters. 4. Neither the hunting time required to capture the first caterpillar prey nor the female's inventory of oocytes predicted a female's likelihood of adding a second caterpillar to a nest. Variation in oocyte inventory across females was minimal; all females examined had a mature or nearly mature oocyte remaining in the ovaries immediately after laying an egg. 5. Ammophila dysmica were much less likely to add a second caterpillar to nests that were penetrated by parasites during the first provisioning. 6. Although many nest parasites have evolved adaptations to avoid detection by their hosts, oviposition by A. armilla often appears to reveal its presence, eliciting an abrupt truncation of investment by the host in that nest.All needed metadata are included with the data files (see metadata tabs). Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: Funding provided by: University of California BerkeleyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006978Award Number: Funding provided by: Sigma XiCrossref Funder Registry ID: http://dx.doi.org/10.13039/100011084Award Number: Funding provided by: University of Hawai'iCrossref Funder Registry ID: http://dx.doi.org/10.13039/100008782Award Number:All data were collected by direct observations in the field