In The Belly of the Beast: a cophylogenetic study of the pitcher plant flies (Fletcherimyia) and their carnivorous hosts (Sarracenia)
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Date
2021-08-12
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Authors
Kann, Peter T
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Publisher
East Carolina University
Abstract
Sarcophagidae, commonly known as the flesh flies, comprises one of the more behaviorally diverse families among the insects. In addition to carrion feeding, sarcophagids have evolved life history strategies that include predation, parasitism, and kleptoparasitism. Most kleptoparasitic species specialize on solitary hymenopterans, but one genus, Fletcherimyia, has developed a relationship with unlikely hosts—the North American pitcher plants (Sarracenia, Sarraceniaceae). Well known for their carnivory, Sarracenia paradoxically supports an ecologically distinct arthropod community, several members of which are obligate associates. For example, Fletcherimyia flies undergo larval development exclusively within pitchers and feed on captured insect prey. Eight species are currently recognized within Fletcherimyia, all morphologically-defined constructs based largely on genital morphology; the species have yet to be confirmed genetically and have never been placed in any phylogenetic context. Previous studies have characterized Fletcherimyia-Sarracenia interactions: five of the eight fly species appear to be restricted to a single host species, whereas the remaining three fly species affiliate with multiple pitcher species. However, fly-pitcher affiliations are largely based on limited observation with narrow geographic scope. The evolutionary history of the Fletcherimyia-Sarracenia system as a whole has yet to be addressed.
We conducted the most comprehensive ecological sampling of Fletcherimyia to date to 1) examine the status of species constructs; 2) present the first phylogeny for the genus; and 3) conduct a cophylogenetic analysis of the flies and their pitcher hosts. To do so, we generated two molecular datasets (mitochondrial cox1, 2bRADseq) for all eight fly species across their respective geographic ranges and hosts. We provide strong molecular support for each species and present the first phylogeny for the genus based on our 2bRAD data, providing evolutionary insight and context to original species descriptions. Our results demonstrate the efficacy of 2bRAD— a recent modification of RADseq protocol—for phylogenetic analysis of recently diverged taxa.
To reevaluate host plant usage, we defined Fletcherimyia-Sarracenia interactions by larval presence, as larvae are bound by pitcher deposition whereas adults potentially visit multiple pitcher species. In the absence of diagnostic larval morphology, we typed larval specimens genetically, using cox1 as a genetic marker for species identification. For cophylogenetic analysis of the fly-pitcher system, we compared a recent phylogeny of Sarracenia to our 2bRAD phylogeny. We found evidence for early cospeciation and subsequent host-switching between eastern and western pitcher species, indicating a protracted coevolutionary history between Fletcherimyia and Sarracenia lineages.