Physiological capacity and environmental tolerance in two sandhopper species with contrasting geographical ranges: Talitrus saltator and Talorchestia ugolinii
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We investigated the physiological plasticity and environmental tolerance of two phylogenetically closely related, ecologically similar and co-occurring species of supralittoral amphipods differing drastically in the size of their geographical ranges. A series of physiological traits were characterised for the Corsican-endemic Talorchestia ugolinii Bella-Santini and Ruffo and the widespread Talitrus saltator Montagu. The effect of body mass, temperature and salinity on heart rate (used as proxy for metabolic activity and stress), the effect of temperature on oxygen consumption and the tolerance to salinity exposure were investigated in both species, together with the characterisation of haemolymph osmoregulation in T. ugolinii. Our results showed that there is a clear difference in the resting metabolic rates and physiological capacity, as well as environmental tolerance, between T. saltator and T. ugolinii, with T. saltator overall showing a broader physiological niche. Although T. ugolinii showed a relatively good ability to regulate its haemolymph osmotic concentration (similar to that previously described for T. saltator), it demonstrated a lower tolerance to exposure to hypo-osmotic stress. In addition, a consistent picture emerged between the ability to control the cardiac function and the capacity to actively respond to osmotic stress. The physiological findings are discussed in relation to the known ecology and geographical distribution of T. ugolinii.
KeywordsDecapod Crustacean Environmental Tolerance Physiological Capacity Osmotic Concentration Hyposaline
We are grateful to two anonymous reviewers for their useful comments. This research was financially supported by the Young Researcher Fund 2001 (Università di Firenze) assigned to P. Calosi and by local funds of the Università di Firenze assigned to A. Ugolini. Work at RHUL was, in part, supported by equipment purchased with a University of London Central Research Fund grant. We wish to thank R Ciotti, F Parrini and M Tanganelli for their help in collecting animals. The experiments comply with the regulations of the countries where this research was undertaken.
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