Burrowing constrains the phenotypic diversity of fossorial crayfish.

Strong selective pressure on phenotype can arise when habitat transitions fundamentally alter the physical media in which animals live, such as the invasion of land by lobe-finned fishes and insects. When environmental gradients differ drastically among habitats and multiple lineages transition between these habitats, we expect phenotypic convergence to be prevalent. One transition where widespread convergence has been observed is the shift from aboveground to subterranean environments in fossorial animals. Subterranean environments are low-light, confined spaces and tend to be hypoxic or anoxic, not to mention that the act of burrowing itself demands morphological specializations for excavation. Research suggests burrowing promotes morphological convergence in crayfish, with non-burrowing forms having a dorsoventrally compressed carapace and long, slender claws (chelae) while primary burrowing forms have a dorsolaterally compressed carapace and shorter, more powerful claws. However, earlier ecomorphological comparisons relied on qualitative, rather than quantitative assessments of phenotypic differences. This study tested for convergence in North American crayfishes using a geometric morphometric approach. We photographed the carapace and claw for representative species across thirteen North American genera. We hypothesized that crayfishes which occur in similar habitats and exhibit similar burrowing behaviors will converge in their carapace and claw shapes. We found evidence for convergence in carapace and claw morphologies in burrowing crayfishes. However, claw phenotypes did not converge as strongly as carapace shape, an example of "imperfect" or "incomplete" convergence we attribute to the multiple competing demands on claw form and function. We argue that nuances in habitat characteristics, like soil type or compaction, make complete convergence unlikely for range- and dispersal-limited fossorial crayfishes.

Redescription and circumscription of the Acuminate Crayfish, Cambarus acuminatus Faxon, 1884 (Decapoda: Cambaridae).

Cambarus acuminatus was described by Walter Faxon in 1884 from three specimens collected from the Saluda River in northwestern South Carolina, USA. Cambarus acuminatus sensu lato has since been acknowledged to comprise a species complex. This complex, also known as Cambarus sp. C, spans a range across much of the Piedmont Plateau and Coastal Plain from central South Carolina north to Maryland and southeastern Pennsylvania. A primary impediment to a much-needed thorough taxonomic assessment and revision of C. sp. C is the absence of taxonomically useful type material of C. acuminatus coupled with the lack of a detailed description of the species. Here we provide a redescription of C. acuminatus based on modern standards for astacoidean crayfishes in the genus Cambarus and emend the circumscription of the species, thereby laying the groundwork necessary for future taxonomic and phylogenetic work within, and involving, the C. sp. C complex.