ABSTRACT
Freshwater crayfish (Astacidea) serve as model organisms for many diverse disciplines, from neurology to toxicology, and have been the focus of many physiological, ecological, and molecular-based studies. Although much of the recent work has focused on the evolutionary history, phylogeography, and conservation biology of freshwater crayfishes, estimations of their divergence times and radiations have never been made. Recently, divergence time estimations for decapods provided the first proposed molecular-timing hypothesis involving freshwater crayfish. In this study we focus specifically on estimating divergence among Astacidea. We employ a Bayesian method implemented in multidivtime for timing estimation, calibrated with multiple fossils including a Parastacoidea fossil newly discovered in Australia. With our narrow taxonomic focus, we increase the accuracy and provide divergence estimations more specific to freshwater crayfish. Our molecular time estimation supports a late Permian to early Triassic divergence from Nephropoidea with radiation and dispersal before the breakup of Pangaea, as well as subsequent speciation and radiation prior to or directly associated with Gondwana and Laurasia disassembly. The breakup of Gondwana and Laurasia resulted in the separation of Parastacoidea and Astacoidea during the Jurassic. The hypothesized divergence and radiation of these two superfamilies are also supported by our molecular time estimations. For the three families of crayfish, we estimate the Astacidae radiation at ∼153 million years ago (MYA), the Cambaridae radiation at ∼90 MYA, and diversification of Parastacidae at ∼161 MYA.
