Divergent evolutionary pathways and host shifts among the commensal pontoniine shrimps: a preliminary analysis based on selected Indo-Pacific species

As the most species-rich subfamily of Caridea, Pontoniinae Kingsley, 1878 is well-known for its great diversity in morphology, lifestyle and habitat. However, the phylogeny of Pontoniinae has been poorly studied since it was erected, and there are many taxonomic and evolutionary controversies remained unresolved. Among these controversies, the relationship between the commensal pontoniine shrimps and their hosts is the issue of most concern. Herein, a total of 26 Indo-Pacific pontoniine species from 23 genera, including both free-living and commensal taxa associated with different marine organisms from five phyla, are selected to preliminarily explore the differentiation process accompanied with the reciprocal natural selections between them and their hosts. Based on the molecular phylogenetic analyses, two major clades, representing the ‘primitive groups’ and ‘derived groups’, and several subgroups related to the hosts are well recovered, which are also supported in morphology. Additionally, several possible evolutionary pathways of those commensal pontoniine shrimps with similar hosts or niches are identified, with a host-shifting hypothesis proposed for cavity-inhabiting pontoniines based on molecular data in conjunction with morphological and ecological evidence.