Genetic footprints of adaptive divergence in the bracovirus of Cotesia sesamiae identified by targeted resequencing

Abstract

The African parasitoid wasp Cotesia sesamiae is a generalist species structured in locally adapted populations showing differences in host range. The recent discovery of Cotesia typhae, a specialist, sister species to C. sesamiae, provides a good framework to study the genetic determinants of parasitoid host range. To investigate the genomic bases of divergence between these populations and species, we used a targeted sequencing approach on 24 samples. We targeted the bracovirus genomic region encoding virulence genes involved in the interaction with the lepidopteran hosts of the wasps. High sequencing coverage was obtained for all samples, allowing the study of genetic variation between wasp populations and species. By combining population genetic estimations, such as nucleotide diversity (π), relative differentiation (F ) and absolute divergence (d ), with branch-site dN/dS measures, we identified six of 98 bracovirus genes showing significant divergence and evidence of positive selection. These genes, belonging to different gene families, are potentially involved in host adaptation and in the specialization process. Fine-scale analyses of genetic variation also revealed mutations and large deletions in certain genes inducing pseudogenization and loss of function. The image emerging from these results is that adaptation mediated by bracovirus genes happens through selection of particularly adaptive alleles and loss of nonadaptive genes. These results highlight the central role of the bracovirus in the molecular interactions between the wasps and their hosts and in the evolutionary processes of specialization.

The Parasitic Wasp, Cotesia congregata (Say), Consists of Two Incipient Species Isolated by Asymmetric Reproductive Incompatibility and Hybrid Inability to Overcome Host Defenses

“…Future studies should include a larger number of BV genes across a broader array of host-foodplant sources of C. congregata. Further, comparative genome-scale sequencing studies, similar to those conducted by Jancek et al (2013) and Gauthier et al (2018) for C. sesamiae and other Cotesia species isolates, as well as analysis of population structure, are required to understand the genetic relationships among sympatric host-foodplant sources of C. congregata.…”

Editorial 2019

“…The third section probed the evolution of symbiotic relationships and how they shape host adaptation (Engl et al, 2018;Gauthier et al., 2018;Vanderpool, Bracewell, & McCutcheon, 2018) and the fourth section looked into the resilience of these relationships in the changing environment of the Anthropocene (Deveautour, Donn, Power, Bennett, & Powell, 2018;Doremus et al, 2018;Ramsby, Hoogenboom, Whalan, & Webster, 2018).…”

Western European Populations of the Ichneumonid Wasp Hyposoter didymator Belong to a Single Taxon

“…The role of polydnaviruses in parasitoid local adaptation has previously been reported for the braconid Cotesia sesamiae. Although C. sesamiae was initially considered as a generalist species developing on several lepidopteran hosts, two taxa of C. sesamiae were identified in Kenya that vary in their capacity to overcome the resistance of the lepidopteran host, a feature that was linked to allelic variations in viral genes (Branca et al, 2011;Kaiser et al, 2017;Gauthier et al, 2018). Although not differentiated in several genetically differentiated taxa, H. didymator probably does not parasitize all noctuid species indifferently and part of this specialization might be due, like C. sesamiae, to polydnaviruses, explaining a higher level of genetic differentiation at Hdiv loci.…”