Commensalism used by freshwater crayfish species to survive drying in seasonal habitats

摘要

Gramastacus insolitus is a very small non-burrowing Australian freshwater crayfishwith a restricted distribution, occurring almost exclusively in seasonal habitats throughout itsrange. It is listed as a threatened species but its strategy for surviving dry periods was unknown.Eight seasonal surveys of crayfish distribution showed that members of G. insolitus were neverfound at sites that were outside the distribution of two larger burrowing freshwater crayfishspecies, Geocharax falcata and Cherax destructor. Excavation of 80 burrows of members ofG. falcata and C. destructor in three different seasonal habitats in the Grampians NationalPark, Victoria, Australia, revealed that individuals of G. insolitus found refuge from drying byestivating in cracks and shallow depressions at the side of the main burrow tunnels constructedby larger species. Members of G. insolitus were not found estivating at the surface, such as underfallen wood, nor was it usually found in crayfish burrows unoccupied by the host crayfish. Thisstudy indicates that members of G. insolitus are commensal upon larger crayfish species, usingtheir burrows to survive the seasonal drying of their habitat. Conservation strategies forpopulations of G. insolitus will need to consider co-existing species of burrowing crayfish.