Coevolution of Retrovarium n. gen. (Digenea: Cryptogonimidae) in Lutjanidae and Haemulidae (Perciformes) in the Indo-West Pacific.

We describe 11 new species of cryptogonimids belonging to Retrovarium n. gen., from eight species of Lutjanidae and one species of Haemulidae, from the Great Barrier Reef, French Polynesia and the Maldives. We also transfer Neoparacryptogonimus saccatus (Manter, 1963) and Neoparacryptogonimus sphericus Nahhas, Sey & Nishimoto, 1998 to Retrovarium. The morphologically based taxonomic approach was augmented with DNA sequence data from three nuclear ribosomal DNA regions (28S, ITS1 and ITS2) to explore the species integrity, biogeographic distribution and evolution of the species recognised here. Sequencing included multiple replicates and revealed 11 distinct genotypes which corroborated our morphologically based hypotheses of putative species present in the system. There was no intraspecific variation and all three rDNA regions differed between every combination of species. Two species exhibited wide geographic ranges, having identical rDNA sequences between the Great Barrier Reef and the Maldives, localities separated by over 9600 km. One host species, Symphorus nematophorus, proved to be exceptionally rich, harbouring six species. Minimum evolution analyses were conducted on each of the rDNA datasets independently; minimum evolution, maximum likelihood and Bayesian inference analyses were conducted on a combined (28S, ITS1 and ITS2) dataset for sequence comparison purposes and to explore the evolutionary history of these parasites. To examine the coevolutionary history of this complex, assessment of phylogenetic relationships between the 23 species of Lutjanidae and two species of Haemulidae collected during this survey was performed with data from 16S and cytochrome b mtDNA using Bayesian inference analysis. Despite the high host specificity observed in most of the species, mapping of the parasites on the host phylogeny revealed an absence of strict coevolution or co-descent within this complex. Overall, Retrovarium appears to have had an exceptionally patchy radiation, failing to infect many taxa, infecting species with no readily discernible pattern, and radiating dramatically within one species.