Host choice strategies in micro-sympatric Nasonia species

Background/Question/Methods

To understand how the amazing diversity we see originated and is maintained, biologists study the evolutionary and ecological aspects of species interactions. Ecological interactions can lead, through selection, to morphological or behavioural adaptations increasing an individual’s fitness. Parasitoids are very well suited for studying adaptive behaviour due to the direct link between behaviour and fitness. Usually the community context is ignored in such studies, but species might show different responses when studied under a multi-species context than when studied alone. Here we focus on oviposition, one largely studied adaptive behaviour in parasitoids. Optimal oviposition theory predicts that a female will choose to oviposit on the host in which larvae perform best, as this will maximise her own fitness. We experimentally tested the host preference of two Nasonia vitripennis and one N. giraulti strain, which are gregarious parasioids of cycloraphous fly pupae. One N. vitripennis strain coexists microsympatrically with the N. giraulti strain in North America. The other is an allopatric strain from Corsica, France. We measured a number of behavioural traits associated with host exploration and acceptance for oviposition in a choice situation where females can choose between an unparasitized and a preparasitized host.

Results/Conclusions

Our results show that females randomly choose a pupa for exploration and probing, and that they change hosts more often after probing the pupae. This suggests that they get most of the cues of the quality of the host once they have drilled into the host. We find that N. vitripennis lines change significantly more often when they are on the preparasitized pupae, while N. giraulti shows consistently the opposite trend, although it is often not statistically significant. N. vitripennis spends most of its time on the unparasitized pupae while N. giraulti spends most of its time on preparasitized one. This is the first time such a preference is reported in the Nasonia system. We discuss our results in the context of their natural environment and possible competition and species coexistence.