Host shifting and host sharing in a genus of specialist flies diversifying alongside their sunflower hosts

Authors: HIPPEE, ALAINE C. - University Of Iowa

Submitted to: Journal of Evolutionary Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2020
Publication Date: 11/15/2020
Citation: Hippee, A. 2020. Host shifting and host sharing in a genus of specialist flies diversifying alongside their sunflower hosts. Journal of Evolutionary Biology. 34:364-379. https://doi.org/10.1111/jeb.13740.
DOI: https://doi.org/10.1111/jeb.13740

Interpretive Summary: Fruit flies are pests of numerous commercial fruits and vegetables and attack numerous crops, including cultivated sunflower. The pest of commercial sunflower belongs to a complex of extremely morphologically similar, or cryptic, species that also breed in other sunflowers. The taxonomy of these species, including how to distinguish them, has been problematic. This study utilizes molecular methods to distinguish these species and analyze their evolutionary relationships. This information will be useful to APHIS-PPQ and other regulatory agencies as well as scientists interested in the ecology, evolution or control of these insects.

Technical Abstract: Congeneric parasites are unlikely to specialize on the same tissues of the same host species, likely because of strong multifarious selection against niche overlap. Exceptions where multiple congeneric species overlap on the same tissues may therefore reveal important insights into the ecological factors underlying the origins and maintenance of diversity. Larvae of sunflower maggot flies in genus Strauzia feed on the pith of plants in the family Asteraceae. Although Strauzia tend to be host specialists, some species overlap in their host use. To resolve the origins of host sharing among these specialist flies, we used reduced representation genomic sequencing to infer the first multi-locus phylogeny of genus Strauzia. Our results show that Helianthus tuberosus and Helianthus grosseserratus each host three different fly species, and that the flies co-occurring on a host are not one another’s closest relatives. Though this pattern implies that host sharing is most likely the result of host shifts, these may not be host shifts in the conventional sense of an insect moving onto an entirely new plant. Many hosts of Strauzia belong to a young (1-2 MYA) clade of perennial sunflowers noted for their frequent introgression and hybrid speciation events. In at least one case, flies may have converged upon a host after their respective ancestral host plants hybridized to form a new sunflower species (H. tuberosus). Broadly, we suggest that rapid and recent adaptive introgression and speciation in this group of plants may have instigated the rapid diversification of their phytophagous fly associates, including the convergence of >1 species onto the same shared host plants.