Testing Phylogenetic Hypotheses of the Subgenera of the Freshwater Crayfish Genus Cambarus (Decapoda: Cambaridae)

Abstract

BackgroundThe genus Cambarus is one of three most species rich crayfish genera in the Northern Hemisphere. The genus has its center of diversity in the Southern Appalachians of the United States and has been divided into 12 subgenera. Using Cambarus we test the correspondence of subgeneric designations based on morphology used in traditional crayfish taxonomy to the underlying evolutionary history for these crayfish. We further test for significant correlation and explanatory power of geographic distance, taxonomic model, and a habitat model to estimated phylogenetic distance with multiple variable regression.Methodology/Principal FindingsWe use three mitochondrial and one nuclear gene regions to estimate the phylogenetic relationships for species within the genus Cambarus and test evolutionary hypotheses of relationships and associated morphological and biogeographical hypotheses. Our resulting phylogeny indicates that the genus Cambarus is polyphyletic, however we fail to reject the monophyly of Cambarus with a topology test. The majority of the Cambarus subgenera are rejected as monophyletic, suggesting the morphological characters used to define those taxa are subject to convergent evolution. While we found incongruence between taxonomy and estimated phylogenetic relationships, a multiple model regression analysis indicates that taxonomy had more explanatory power of genetic relationships than either habitat or geographic distance.ConclusionsWe find convergent evolution has impacted the morphological features used to delimit Cambarus subgenera. Studies of the crayfish genus Orconectes have shown gonopod morphology used to delimit subgenera is also affected by convergent evolution. This suggests that morphological diagnoses based on traditional crayfish taxonomy might be confounded by convergent evolution across the cambarids and has little utility in diagnosing relationships or defining natural groups. We further suggest that convergent morphological evolution appears to be a common occurrence in invertebrates suggesting the need for careful phylogenetically based interpretations of morphological evolution in invertebrate systematics.

The marbled crayfish (Decapoda: Cambaridae) represents an independent new species

“…Genetic analysis can be used to reveal independent species in the absence of distinctive morphological features (Bickford et al, 2007). Furthermore, convergent evolution of morphological characters appears to be common in cambarids (Breinholt et al, 2012), which further illustrates the value of genetic information for crayfish taxonomy (Owen et al, 2015). Complete mitochondrial genome sequencing of marbled crayfish from diverse sources revealed their genetic homogeneity and strongly suggested a single origin of the known marbled crayfish population (Vogt et al, 2015).…”

Molecular phylogenetics of the burrowing crayfish genus Fallicambarus (Decapoda: Cambaridae)

“…1999)), as well as two nuclear gene regions 28S [∼800–1000 bp; with primers 28s‐rd3a and 28s‐rD5b (Whiting et al. 2000, 1997) or with 28sF‐cray and 28sR‐cray (Breinholt et al. 2012)] and H3 [∼328; with H3AF and H3AR (Colgan et al.…”

Unrecognized diversity in New Guinean crayfish species (Decapoda, Parastacidae): The evidence from molecular data

“…A similar situation with the validity of Cambarus subgenera classifications based on morphological characteristics is currently being intensely debated among the North American community of crayfish researchers (e.g. Breinholt et al 2012). We are afraid that only advanced morphometric methods, combined with molecular evidence using already mentioned nuclear markers, will help to elucidate this incongruence in Cherax species relative to 2 different subgenera of Cherax and justify or omit their usage in future taxonomic works.…”

“…Most of these descriptions, except for C. subterigneus and C. gherardiae, were based only on morphometrics, although it is well known that crayfish show substantial variability in many morphological characters which can be associated with habitat variation (Austin & Knott 1996). A genetic analysis would help in species identification and clarification of phylogenetic relationships (Mathews et al 2008;Breinholt et al 2012;Thoma & Loughman 2014). In this study, we focused on phylogenetic analysis of recently described Cherax species from New Guinea and available Cherax sequences from the GenBank database.…”