Digging ability and digging performance in a hyporheic gravel-dwelling crayfish, the hairy crayfish Cambarus friaufi (Hobbs 1953) (Decapoda: Astacidae: Cambaridae)

Abstract Crayfishes are known for their ability to construct burrows, although there is intra- and interspecific variation in the complexity and reliance on such burrows. Crayfishes historically have been classified into ecological groupings based on their reliance on their burrow and the burrows connection to the water table. These ecological classifications, however, do not completely account for the behavioral diversity throughout crayfishes. One group of crayfishes that do not necessarily fit into these ecological classifications are members of the invalid subgenus Glareocola of Cambarus Erichson, 1846, which includes four species: C. brachydactylus (Hobbs, 1953), C. friaufi (Hobbs, 1953), C. polypilosus (Loughman & Williams, 2018), and C. williami (Bouchard & Bouchard 1995). All four species inhabit streams characterized by loose chert gravel, which creates ample interstitial spaces and potential access to the streambed’s hyporheic zone. We studied how one member of the Glareocola group, C. friaufi, exhibits unique morphological and behavioral adaptations that enable individuals to dig into the hyporheic zone of their natural chert substrate. We found that C. friaufi was sexually monomorphic regarding the relationship between body size and claw size, which contrasts findings from other stream-dwelling crayfish species. By evaluating the digging ability and digging performance of C. friaufi and sand, pea gravel, and their natural chert substrate, we also demonstrate how their digging ability is highly adapted to their natural chert substrate. Individuals of C. friaufi were either unable to dig or rarely dig underneath substrates other than chert. We discuss our results considering the behavioral ecology and natural history of the crayfishes within this enigmatic group.