University of Cambridge > Talks.cam > Evolution and Development Seminar Series > Isolated branches in the phylogeny of Platyhelminthes

Isolated branches in the phylogeny of Platyhelminthes

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Flatworms number among the most diverse invertebrate phyla and represent the most biomedically significant branch of the major bilaterian clade Spiralia, but to date, deep evolutionary relationships within this group have been studied using only a single locus (the rRNA operon), leaving the origins of many key groups unclear. In this study, using a survey of genomes and transcriptomes representing all free-living flatworm orders, we provide resolution of platyhelminth interrelationships based on hundreds of nuclear protein-coding genes, exploring phylogenetic signal through concatenation as well as recently developed consensus approaches. These analyses robustly support a modern hypothesis of flatworm phylogeny, one which corroborates several long-held morphological hypotheses which had not previously seen support in molecular studies (e.g. Trepaxonemata, Cercomeromorpha), several hypotheses also found in rRNA studies (e.g. Euneoophora, Adiaphanida), and several hypotheses not previously discussed (e.g. a sister-group relationship between Prorhynchida and Polycladida). Perhaps most notably, these data also introduce a novel scenario for the interrelationships between free-living flatworms and the vertebrate-parasitic Neodermata, providing new opportunities to shed light on the origins and biological consequences of parasitism in these iconic invertebrates. We also present evidence for previously unrecognized deep phylogenetic diversity within the clade Adiaphanida, showing that the enigmatic crustacean-parasitic genus Genostoma, previously considered a member of Fecampiida, represents its own deeply branching lineage. Finally, using a related RNA -seq based phylogenetic datset spanning the diversity of protostomes, we recover evidence for a sister-group relationship between Platyhelminthes and Gastrotricha, and for a placement of this clade as well as the similarly meiofaunal clade Gnathifera as separate early branches within Spiralia. We conclude with a synoptic discussion of the status of deep flatworm phylogeny to date, highlighting those areas of the tree most in need of continued investigation, and emphasizing the crucial role of continued morphological and developmental research in testing and ultimately conferring biological meaning to the tree topology encoded in the genomes of these remarkable invertebrate animals.

This talk is part of the Evolution and Development Seminar Series series.

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