Understanding the energetic costs of living in saline environments: effects of salinity on basal metabolic rate, body mass and daily energy consumption of a long-distance migratory shorebird

Abstract

SUMMARYMany migratory vertebrates typically move between habitats with varying salinities during the annual cycle. These organisms clearly exhibit a remarkable phenotypic flexibility in their 'osmoregulatory machinery', but the metabolic consequences of salinity acclimatization are still not well understood. We investigated the effects of salinity on basal metabolic rate (BMR), body mass and daily energy consumption of a long-distance migratory shorebird, the dunlin (Calidris alpina), outside the breeding season. Masscorrected BMR and daily energy consumption increased significantly by 17 and 20% between freshwater (0.3‰ NaCl) and saltwater (33.0-35.0‰ NaCl), respectively. Body mass in both captive and wild dunlins was lower (9-16%) in saline than in freshwater environments. These changes on BMR and body mass were quickly reversed by returning the birds to freshwater, suggesting that metabolic adjustment to saltwater and metabolic readjustment to freshwater are both processes that occur in a few days. Our findings support empirically that the processes of developing and maintaining an active osmoregulatory machinery are energetically expensive, and they could help to explain diet and/or habitat selection patterns along the flyway. Finally, we discuss whether body mass loss in saltwater may be a strategy to reduce maintenance cost in osmotically stressful conditions such as overwintering in marine habitats, and raise some methodological implications for studies of BMR-related outcomes using captive birds captured in saline environments.

Salt tolerance's toll: prolonged exposure to saline water inflicts damage to the blood cells of dice snakes (<i>Natrix tessellata</i>)

“…A fundamental challenge for the cell is a change in the osmolarity of the surrounding medium (Pastor et al, 2009). Osmoregulation is a major physiological challenge for numerous vertebrates that are subject to extensive changes in the salinity of their environment (Gutiérrez et al, 2011). Our data suggest that disintegration of the cell membranes was a result of the osmotic pressure gradient following prolonged dwelling in waters with increased conductivity.…”

Physiological, Morphological and Behavioural Responses of Self-Feeding Precocial Chicks Copying with Contrasting Levels of Water Salinity during Development

“…Shorebirds inhabiting hypersaline habitats rely on hypo-osmotic prey such as brine shrimp and diptera larvae and adults, whose body water content is about 78–87% of body mass [11]. The water content of fly larvae provided in our experiment was 73.3 ± 0.5% [17]. The food and water were replaced three times a day, and salinity levels of residual and fresh water were measured using a conductivity meter (HI 98402).…”

“…In birds, this flexible physiological trait is known to show physiological adaptations to ecological conditions [15,16]. A recent study showed that adult individuals of a shorebird species, the Dunlin ( Calidris alpina ) increased their BMR and daily energy consumption by 17% and 20%, respectively, between freshwater and saltwater [17]. This finding provided strong support that maintaining functional osmoregulatory machinery to excrete excess salt imposes significant energy costs, probably owing to the increased size and metabolic intensity of supraorbital saltglands [17,18], the key organ used by air-breathing animals such as many waterbirds, seabirds and some reptiles to ensure survival in saline environments [5].…”

“…This set of physiological variables were measured because they may reflect saline stress in birds [18]. In particular, we measured Hsp70, which is assumed to be the major family of heat shock proteins in vertebrates, and has been used as an index of a range of environmental stressors including salinity (see [17] and references therein).…”

Crying a river: how much salt-laden jelly can a leatherback turtle really eat?

“…In the best-studied group (marine fish, which have large surface areas of highly permeable gills) estimates are below 10% of routine metabolic rate (Evans, 2009), even as low as 0.5%. However, shore birds (dunlin, Calidris alpina) showed increases of 17% in basal metabolic rate when their water supply was changed from freshwater to seawater but much of this cost was probably due to an upregulation of osmoregulatory machinery rather than the costs of salt pumping per se (Gutierrez et al, 2011). An alternative approach is to estimate feasible metabolic rates of salt gland tissue.…”