Abstract
The Dwarf crayfish or Cambarellinae, is a morphologically singular subfamily of decapod crustaceans that contains only one genus, Cambarellus. Its intriguing distribution, along the river basins of the Gulf Coast of United States (Gulf Group) and into Central México (Mexican Group), has until now lacked of satisfactory explanation. This study provides a comprehensive sampling of most of the extant species of Cambarellus and sheds light on its evolutionary history, systematics and biogeography. We tested the impact of Gulf Group versus Mexican Group geography on rates of cladogenesis using a maximum likelihood framework, testing different models of birth/extinction of lineages. We propose a comprehensive phylogenetic hypothesis for the subfamily based on mitochondrial and nuclear loci (3,833 bp) using Bayesian and Maximum Likelihood methods. The phylogenetic structure found two phylogenetic groups associated to the two main geographic components (Gulf Group and Mexican Group) and is partially consistent with the historical structure of river basins. The previous hypothesis, which divided the genus into three subgenera based on genitalia morphology was only partially supported (P = 0.047), resulting in a paraphyletic subgenus Pandicambarus. We found at least two cases in which phylogenetic structure failed to recover monophyly of recognized species while detecting several cases of cryptic diversity, corresponding to lineages not assigned to any described species. Cladogenetic patterns in the entire subfamily are better explained by an allopatric model of speciation. Diversification analyses showed similar cladogenesis patterns between both groups and did not significantly differ from the constant rate models. While cladogenesis in the Gulf Group is coincident in time with changes in the sea levels, in the Mexican Group, cladogenesis is congruent with the formation of the Trans-Mexican Volcanic Belt. Our results show how similar allopatric divergence in freshwater organisms can be promoted through diverse vicariant factors.
Highlights
The freshwater crayfish subfamily Cambarellinae is comprised of the unique genus Cambarellus, with 17 recognized species and a disjunctive distribution across the freshwater streams of the Gulf Cost of the United States and North and Central Mexico (Fig. 1) [1]
Cytochrome Oxidase subunit I (COI)-like sequences were found in seven cases, identified by the occurrence of one or several stop-codons along the sequence and an unusual sequence divergence, which affected position in the tree and divergence regarding the other sequences coming from the same population
The combination of mitochondrial and nuclear markers provide sufficient information to resolve the relationships between highly supported clades, namely the Gulf (Pandicambarus/Dirigicambarus) and Mexican (Cambarellus) Groups and included clades (Figure 3)
Summary
The freshwater crayfish subfamily Cambarellinae is comprised of the unique genus Cambarellus, with 17 recognized species and a disjunctive distribution across the freshwater streams of the Gulf Cost of the United States and North and Central Mexico (Fig. 1) [1]. The subfamily is unique because of the exceptionally small body size of its species They typically reach only 4 cm compared to most crayfish averaging a maximum body size of .5 cm; the reference to the genus as the ‘‘Dwarf’’ crayfishes. Their distribution goes from the Swanee River in northern Florida, eastward through the southern Mississippi River watershed to southern Illinois and continues southwest to the Nueces River in Texas [2,3].
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