Abstract

The Rhynchocinetidae (binge-beak' shrimps) is a family of marine caridean decapods with considerable variation in sexual dimorphism, male weaponry, mating tactics, and sexual systems. Thus, this group is an excellent model with which to analyse the evolution of these important characteristics, which are of interest not only in shrimps specifically but also in animal taxa in general. Yet, there exists no phylogenetic hypothesis, either molecular or morphological, for this taxon against which to test either the evolution of behavioural traits within the Rhynchocinetidae or its genealogical relationships with other caridean taxa. In this study, we tested (1) hypotheses on the phylogenetic relationships of rhynchocinetid shrimps, and (2) the efficacy of different (one-, two-, and three-phase) methods to generate a reliable phylogeny. Total genomic DNA was extracted from tissue samples taken from 17 species of Rhynchocinetidae and five other species currently or previously assigned to the same superfamily (Nematocarcinoidea); six species from other superfamilies were used as outgroups. Sequences from two nuclear genes (H3 and Enolase) and one mitocliondrial gene (12S) were used to construct phylogenies. One-phase playlogenetic analyses (SATe-II) and classical two- and three-phase playlogenetic analyses were employed, using both maximum likelihood and Bayesian inference methods. Both a two-gene data set (H3 and Enolase) and a three-gene data set (H3, Enolase, 12S) were utilized to explore the relationships amongst the targeted species. These analyses showed that the superfamily Nematocarcinoidea, as currently accepted, is polyphyletic. Furthermore, the two major clades recognized by the SATe-II analysis are clearly concordant with the genera Rhynchocinetes and Cinetorhynchus, which are currently recognized in the morphological-based classification (implicit phylogeny) as composing the family Rhynchocinetidae. The SATe-II method is considered superior to the other phylogenetic analyses employed, which failed to recognize these two major clades. Studies using more genes and a more complete species data set are needed to test yet unresolved inter- and intrafamilial systematic and evolutionary questions about this remarkable clade of caridean shrimps.