Phylogenomic analyses of a Mediterranean earthworm family (Annelida: Hormogastridae)

- Phylogenomics of hormogastrid earthworms was investigated.
- Hemigastrodrilus was recovered as the basal group of the family.
- Ailoscolex, formerly included within Ailoscolecidae, clustered within Hormogastridae.
- Results reinforced the hypothesis of the family origin near Southern France.
- Gene tree vs concatenated dataset conflicts confounded the internal relationships.

Earthworm taxonomy and evolutionary biology remain a challenge because of their scarce distinct morphological characters of taxonomic value, the morphological convergence by adaptation to the uniformity of the soil where they inhabit, and their high plasticity when challenged with stressful or new environmental conditions. Here we present a phylogenomic study of the family Hormogastridae, representing also the first piece of work of this type within earthworms. We included seven transcriptomes of the group representing the main lineages as previously-described, analysed in a final matrix that includes twelve earthworms and eleven outgroups. While there is a high degree of gene conflict in the generated trees that obscure some of the internal relationships, the origin of the family is well resolved: the hormogastrid Hemigastrodrilus appears as the most ancestral group, followed by the ailoscolecid Ailoscolex, therefore rejecting the validity of the family Ailoscolecidae. Our results place the origin of hormogastrids in Southern France, as previously hypothesised.

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