Abstract
Intertidal crustaceans have a high degree of physiological plasticity, which allows them to withstand periods of water emersion. In this study we examine the physiological constraints that determine the distribution and abundance of the intertidal porcellanid crabs Petrolisthes laevigatus and Petrolisthes violaceus . This study evaluates the distribution and abundance of the two species at different tidal heights, in relation to haemocyanin concentration and LDH activity, resistance to air desiccation, thermal tolerance, and resistance to hypoxic water. The results showed that Petrolisthes laevigatus was more abundant at the high tide level than Petrolisthes violaceus , which was more abundant at the low tide level. Petrolisthes laevigatus showed greater tolerance to high temperatures and lower tolerance to desiccation when exposed to air than P. violaceus , which was also more tolerant to hypoxia during prolonged exposure. No differences were found in haemocyanin concentration and LDH activity. These findings support the idea of an evolutionary gradient towards terrestrial adaptations. Of the two species, Petrolisthes laevigatus showed the most advanced physiological features for semi-terrestrial specialization.
Highlights
Organisms inhabiting the intertidal zone are routinely exposed to environmental changes due to the tidal cycles and may sometimes spend 50% of their lives in semi-terrestrial conditions (Stillman and Somero, 1996)
Abiotic factors are considered to be more important in the upper intertidal zone, whereas biotic factors are more relevant in the lower intertidal zone (Hofmann and Somero, 1995; Stillman and Somero, 1996; Somero, 2002; Stillman, 2002)
To test if differences in physiological responses are associated with their position in the intertidal zone, we evaluated differences in abundance of Petrolisthes laevigatus and P. violaceus at different intertidal heights in relation to their resistance to desiccation and the effects of high temperatures, the concentration of oxygen in the water, and haemolymph physiology (LDH activity, haemocyanin concentration)
Summary
Organisms inhabiting the intertidal zone are routinely exposed to environmental changes due to the tidal cycles and may sometimes spend 50% of their lives in semi-terrestrial conditions (Stillman and Somero, 1996). These conditions may include hours of air exposure, increased temperatures, and ambient hypoxia (Allen and Burnet, 2008). Abiotic factors are considered to be more important in the upper intertidal zone, whereas biotic factors are more relevant in the lower intertidal zone (Hofmann and Somero, 1995; Stillman and Somero, 1996; Somero, 2002; Stillman, 2002). In spite of these generalizations, there is only limited information on the physiological specializations that have allowed species with similar evolutionary histories to inhabit different positions in the intertidal zone
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