Origins of divergence – The causes of pre- and post-zygotic isolation barriers in Spodoptera frugiperda

• Applicants: Professor Dr. David G. Heckel; Dr. Sabine Hänniger
• Subject Area: Evolution, Anthropology ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446441643

Speciation is the evolutionary process by which new biological species arise. There has been increasing acceptance of sympatric speciation models, where reproductive isolation and incompatibility between populations evolve in the face of gene flow; yet documenting this process remains challenging since gene flow reduction most likely results from a combination of factors. The reproductive barriers can be initiated either by divergent selection (i.e., ‘ecological’ or sexual selection) or by the evolution of genetic incompatibilities, i.e. through genetic drift, as an indirect consequence of selection, or through genomic conflict.This project aims at deciphering the factors at play in the divergence of the two sympatric strains of the fall armyworm (FAW, Spodoptera frugiperda). This noctuid moth is an ideal model organism to investigate different isolation barriers in incipient species. While morphologically indistinguishable, the two strains can be differentiated on the basis of genetic haplotypes, and they exhibit a number of phenotypic differences that can function as pre-or post-zygotic isolation barriers. The objectives of the project are:1) Identification and characterization of diverging genetic loci between the strains.Using a new population genomics approach, all loci diverging between the strains will be identified. The variants will be classified according to the hypothetical contribution to speciation: timing, oviposition preference, pheromones, female hybrid frigidity larval preference, larval performance, female hybrid fertility. They will be functionally characterized using CRISPR/CAS9.2) Determination of the origin of post-zygotic reproductive isolation in invasive populations.Preliminary data of invasive populations in Africa suggests fitness costs for corn-collected larvae on rice and vice versa, illustrating FAWs adaptive potential in invaded areas. We will analyze the genomic differentiation of these invasive populations.3) To investigate the causes of strain-specific host plant differentiationThe differential distribution of the strains on different host plants in native habitats likely result from different oviposition choices or from differences in egg quality. We will determine the genetic basis of these traits by GWAS.4) To determine the ultimate causes of the strain-specific timing differentiationThe strains differ by their mating time at night. We will test experimentally if these differences can be related to variation in biotic factors connected to different habitats, e.g parasitoids or predator occurrence or plant defense rhythms.This unique integrative study is based on the combination of various approaches: The study of phenotypes in natura and forward genetics in Germany and reverse genetics and functional genomics in France. It will clarify evolutionary status of the FAW strains and is thus a prerequisite to understand the success of the invasive populations in their new environment.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Dr. Emmanuelle D' Alencon; Dr. Ki-Woong Nam