From commensalism to parasitism in Carapidae (Ophidiiformes): heterochronic modes of development?

Abstract

Phenotypic variations allow a lineage to move into new regions of the adaptive landscape. The purpose of this study is to analyse the life history of the pearlfishes (Carapinae) in a phylogenetic framework and particularly to highlight the evolution of parasite and commensal ways of life. Furthermore, we investigate the skull anatomy of parasites and commensals and discuss the developmental process that would explain the passage from one form to the other. The genusCarapusforms a paraphyletic grouping in contrast to the genusEncheliophis, which forms a monophyletic cluster. The combination of phylogenetic, morphologic and ontogenetic data clearly indicates that parasitic species derive from commensal species and do not constitute an iterative evolution from free-living forms. Although the head morphology ofCarapusspecies differs completely fromEncheliophis,C. homeiis the sister group of the parasites. Interestingly, morphological characteristics allowing the establishment of the relation betweenCarapus homeiandEncheliophisspp. concern the sound-producing mechanism, which can explain the diversification of the taxon but not the acquisition of the parasite morphotype.Carapus homeialready has the sound-producing mechanism typically found in the parasite form but still has a commensal way of life and the corresponding head structure. Moreover, comparisons between the larval and adult Carapini highlight that the adult morphotype “Encheliophis” is obtained by going beyond the adult stage reached byCarapus. The entrance into the new adaptive landscape could have been realised by at least two processes: paedomorphosis and allometric repatterning.