Temperature and relative humidity effects on water loss and hemolymph osmolality of Littoraria angulifera (Lamarck, 1822)



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Desiccation stress is considered to be one of the more significant determining factors that influence how organisms are distributed in the marine littoral. Gastropods living above the high tide mark, referred to as eulittoral fringe gastropods are not wetted as regularly and face unpredictable and prolonged periods of emersion. Consequently, adaptations displayed by eulittoral fringe gastropods are aimed at minimizing water loss and surviving prolonged periods of desiccation stress. Littoraria angulifera, is a tropically distributed marine eulittoral fringe gastropod. Because L. angulifera spends a majority of its time emersed there was interest in studying how the weight loss and hemolymph osmolality of this species changed over a period of time in response to varying environmental conditions. Hypotheses were that weight loss and hemolymph osmolality would be dependent upon temperature and relative humidity with weight loss and hemolymph osmolality being highest at high temperatures and low relative humidities. Additionally, it was predicted that this species should also exhibit some form of regulation of either weight loss or osmolality. Specimens ranging in size from 15.24 to 28.40 mm were collected from concrete marina bulkheads in Port Isabel, Texas. Weight loss rate and hemolymph osmolality were examined at test temperatures of 15°, 25°, and 35°C and relative humidities (RH) of <5%, 33%, 53%, 75%, and >95%. Weight loss rates were tracked for 5 individuals in each temperature/RH treatment. Hemolymph osmolality of was determined at 0, 5, 10, and 15 days in each of the temperature/RH treatments. The weight loss rates were significantly affected by test temperature and relative humidity and varied significantly across each test temperature/RH combination. Hemolymph osmolality was not significantly affected by test temperature but was affected by RH. Results indicated that weight loss increased as temperatures increased and RH decreased and hemolymph osmolalities generally increasing as relative humidity decreased. Specimens did not seem to display any signs of osmoregulation, but this may have been due to an experimental shortcoming. Behavioral responses to emersion that were observed were consistent with the responses displayed by other eulittoral fringe species displaying how this species’ is well adapted to life in its exacting habitat.
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