Phylogenetics and population genetics of the Eurasian parasitoid Macrocentrus cingulum based on mitochondrial and nuclear loci

Correspondence and present address: Benjamin Pélissié, CIRAD, BIOS,UR-106, TA A-50/D, Campus de Baillarguet, 34398 Montpellier Cedex 5, France. E-mail: [email protected] audienceSpecifying species boundaries is often tricky, because advanced biomolecular analyses can reveal that morphologically similar individuals in fact belong to distinct species. This is frequently the case when populations previously considered as a single polyphagous taxon prove to consist of several genetically distinct taxa using different resources, e.g., among insect parasitoids. Macrocentrus cingulum Brischke (Hymenoptera: Braconidae), a parasitoid of the genus Ostrinia (Lepidoptera: Crambidae) feeding on various host plants across the world, is one of them. In Western Europe, M. cingulum has never been found in Ostrinia nubilalis (Hubner) populations feeding on maize, although it heavily parasitizes sympatric Ostrinia scapulalis Walker populations feeding on mugwort. In contrast, it contributes to pest control of Ostrinia furnacalis Guenee feeding on maize in Asia and O. nubilalis feeding on maize in America, suggesting that European and Asian M. cingulum populations might form two distinct taxa. We tested this hypothesis by conducting phylogenetic and population genetic analyses based on two mitochondrial and two nuclear genes, on 97 M. cingulum individuals sampled in Asia, USA, and Europe. Our analyses not only suggest that all sampled M. cingulum probably belong to the same species, but also show a significant genetic differentiation between individuals originating from Europe on the one hand and Asia/USA on the other, which correlates with infestation patterns. Moreover, they show that American specimens are closely related to Asian ones, consistent with historical records about M. cingulum introductions into the USA in the 1920s and 1930s to control expanding O. nubilalis populations. Combining these results with what is known about the evolutionary history within the genus Ostrinia, we offer a candidate evolutionary scenario that is amenable to future empirical testing

Bateman gradients in hermaphrodites : an extendes approach to quantify sexual selection

Sexual selection is often quantified using Bateman gradients, which represent sex-specific regression slopes of reproductive success on mating success and thus describe the expected fitness returns from mating more often. Although the analytical framework for Bateman gradients aimed at covering all sexual systems, empirical studies are biased toward separate-sex organisms, probably because important characteristics of other systems remain incompletely treated. Our synthesis complements the existing Bateman gradient approach with three essential reproductive features of simultaneous hermaphrodites. First, mating in one sex may affect fitness via the opposite sex, for example, through energetic trade-offs. We integrate cross-sex selection effects and show how they help characterizing sexually mutualistic versus antagonistic selection. Second, male and female mating successes may be correlated, complicating the interpretation of Bateman gradients. We show how to quantify the impact of this correlation on sexual selection and propose a principal component analysis on male and female mating success to facilitate interpretation. Third, self-fertilization is accounted for by adding selfed progeny as a separate category of reproductive success to analyses of Bateman gradients. Finally, using a worked example from the snail Biomphalaria glabrata, we illustrate how the extended analytical framework can enhance our understanding of sexual selection in hermaphroditic animals and plants