Inconsistent genetic structure among members of a multitrophic system: did bruchid parasitoids (Horismenusspp.) escape the effects of bean domestication?

Abstract

AbstractAnthropogenic range expansion and cultural practices have modified the distribution, abundance and genetic diversity of domesticated organisms, thereby altering multitrophic assemblages through space and time. The putative Mesoamerican domestication centre of the common bean,Phaseolus vulgarisL., in Mexico allows investigating the effects of plant domestication on the genetic structure of members of a multitrophic system. The aim of this study was to compare the evolutionary history ofHorismenusparasitoids (Hymenoptera: Eulophidae) to those of their bruchid beetle hosts (Coleoptera: Bruchidae) and their domesticated host plant (P. vulgaris), in the context of traditional agriculture in Mexico. We analyzed the population genetic structure of fourHorismenusspecies in Mexico using mitochondrialCOIhaplotype data. The two most abundant parasitoid species wereHorismenus depressusandHorismenus missouriensis. Horismenus missouriensiswere infected byWolbachiaendosymbionts and had little to no population differentiation (FST = 0.06). We suspect the mitochondrial history ofH. missouriensisto be blurred byWolbachia, because differentiation among infected vs. non-infected individuals exists (FST = 0.11). Populations ofH. depressuswere found to be highly differentiated (FST = 0.34), but the genetic structuring could not be explained by tested spatial components. We then compared the genetic structure observed in this parasitoid species to previously published studies on bruchid beetles and their host plants. Despite extensive human-mediated migration and likely population homogenization of its twoAcanthoscelidesbruchid beetle hosts,H. depressuspopulations are structured like its host plant, by a recent dispersal from a diverse ancestral gene pool. Distinct evolutionary dynamics may explain inconsistent patterns among trophic levels. Parasitoids likely migrate from wild bean populations and are poorly adapted to bean storage conditions similar to their bruchid beetle hosts. Integrating several trophic levels to the study of evolutionary history has proven to be fruitful in detecting different ecological responses to human-mediated disturbances and host parasite interactions.