Meeting Abstract
P3.80 Saturday, Jan. 5 Regulation of kidney-like function in freshwater land-crabs: a study of the Christmas Island Blue Crab, Discoplax hirtipes TURNER, Lucy M; MORRIS, Steve*; WEBSTER, Simon G; University of Bristol, UK; University of Bristol, UK; University of Wales – Bangor, UK Steve.Morris@bristol.ac.uk
The gecarcinid land crab Discoplax hirtipes is distributed throughout the tropical Indo-Pacific including on Christmas Island, Indian Ocean. D. hirtipes exhibits a dichotomous distribution depending on rainfall: in the dry season these crabs are restricted to areas of freshwater seepages and springs. However, once the wet season begins the crabs disperse over a wider area and when the rains are well established they undertake their breeding migration to the ocean. D. hirtipes has evolved to a terrestrial-amphibious existence with adaptations including the development of lungs and the utilisation of the gills as a kidney analogue to reclaim urinary salts. The seasonally variable ecology is accompanied by important changes in underlying mechanisms of ionic and osmotic regulation. Neuropeptides of the Crustacean Hyperglycaemic Hormone family (CHH) were initially identified as important in carbohydrate metabolism but have recently been implicated in osmoregulation. Gecarcinids produce relatively large amounts of CHH and this hormone is a prime contender for controlling the seasonally variable physiological state and specifically the regulation of salt balance in D. hirtipes. Initial molecular work (e.g. HPLC, DNA and Edman sequencing and MALDI-TOF mass spectrometry) show two forms of CHH to be present in D. hirtipes sharing a common central amino acid sequence (so far identified in few crustacean species). Bioassays have confirmed the hyperglycaemic response to these two forms and we are investigating the role these play in osmoregulation. Field and laboratory studies of gill function as a kidney analogue have determined how unidirectional ion influx (22Na tracer) and branchial pumps (Na+/K+-ATPase activity) respond to, and are controlled by, the expression and release of CHH.
