Variation in the Venom of Parasitic Wasps, Drift, or Selection? Insights From a Multivariate QST Analysis

Hugo Mathé-Hubert,Marylène Poirié,Dominique Colinet,Jean-Luc Gatti,Émilie Delava,Laurent Kremmer,Joan Van Baaren

doi:10.3389/fevo.2019.00156

Abstract

Differentiation of traits among populations can evolve by drift when gene flow is low relative to drift or selection when there are different local optima in each population (heterogeneous selection), whereas homogeneous selection tends to prevent evolution of such a differentiation. Analyses of geographical variations in venom composition have been done in several taxa such as wasps, spiders, scorpions, cone snails and snakes, but surprisingly never in parasitoid wasps, although their venom should constrain their ability to succeed on locally available hosts. Such a study is now facilitated by the development of an accurate method (quantitative digital analysis) that allows analyzing the quantitative variation of large sets of proteins from several individuals. This method was used here to analyse the venom-based differentiation of four samples of Leptopilina boulardi and five samples of L. heterotoma from populations along a 300 km long south-north gradient in the Rhone-Saone valley (South-East of France). A major result is that the composition of the venom allows to differentiate the populations studied even when separated by few kilometers. We further analyzed these differentiations on the populations (reared under similar conditions to exclude environmental variance) with a QST analysis which compared the variance of a quantitative trait (Q) among the subpopulations (S) to the total variance (T). We also used random forest clustering analyses to detect the venom components the most likely to be adapted locally. The signature of the natural selection was strong for L. heterotoma and L. boulardi. For the latter, the comparison with the differentiation observed at some neutral markers revealed that differentiation was partly due to some local adaptation. The combination of methods used here appears to be a powerful framework for population proteomics and for the study of eco-evolutionary feedbacks between proteomic level and population and ecosystem levels. This is of interest not only for studying field evolution at an intermediate level between the genome and phenotypes, or for understanding the role of evolution in chemical ecology, but also for more applied issues in biological control.

Highlights

Local adaptation, the fact that populations are more adapted to their own local environment than to another environment, has long been the searched signature of an ongoing natural selection in the field (Futuyma and Moreno, 1988; Kawecki and Ebert, 2004; Poisot et al, 2011)
We tentatively identified the proteins present in these reference bands by matching these bands with the bands on the 1D electrophoresis gels used for L. boulardi and L. heterotoma venom proteomics (Colinet et al, 2013a)
Our field sampling design was well-suited for such analysis since the distance between populations varied wildly

Summary

Introduction

The fact that populations are more adapted to their own local environment than to another environment, has long been the searched signature of an ongoing natural selection in the field (Futuyma and Moreno, 1988; Kawecki and Ebert, 2004; Poisot et al, 2011). Traits involved in the antagonistic interactions can be subject to such local adaptations, but with the particularity that the interacting species each represent the environment of the other, which can produce local adaptations induced by coevolution. Local adaptation induced by coevolution is expected between species whose interactions involve resistancevirulence traits, as is the case for host-parasite or host-parasitoid interactions. Parasitoids are insects which develop at the expense of the host, usually leading to its death For such interactions, Gandon (2002) has shown that the localized coevolution is more likely when the fitness cost to the host and the specificity of the parasite are high. The ability to select its host combined with the specificity of virulence may explain the tendency of similar parasitoid genotypes to parasitize similar host genotypes under certain environmental conditions (Lavandero and Tylianakis, 2013)

Methods

Results

Discussion

Conclusion