Starvation in subterranean species versus surface-dwelling species: Crustaceans, fish, and salamanders

Abstract

Subterranean habitats are characterized by constant abiotic factors usually, including darkness, humidity, and temperature; yet these habitats also exhibit high temporal and spatial patchiness of food availability. Therefore, hypogean organisms often cope with periods of starvation that can last a few weeks to a few months. Subterranean species generally exhibit specific adaptations to long-term food deprivation and show a higher resistance to starvation than their epigean counterparts. The effects of long-term fasting and subsequent refeeding on behavior, locomotory and ventilatory activities, oxygen consumption, digestive physiology, and energy stores were investigated in subterranean aquatic crustaceans, fishes, and amphibians and then compared with responses observed among closely related or morphologically similar surface-dwelling species. When possible epigean and hypogean populations of the same species were compared. The remarkable resistance to long-term fasting showed by subterranean organisms may be partly explained by (1) lower metabolic demands and larger body stores in their nourished state, (2) the ability to undergo starvation-induced hypometabolism, and (3) a prolonged state of glycogen- and protein-sparing, permitted by extensive lipid catabolism. In addition, these groundwater species display high recovery abilities during refeeding, showing an optimal utilization of available food and a rapid restoration of their body reserves. Such responses are adaptive for life in harsh and unpredictable subterranean environments. The first part of this review focuses on the food status of subterranean ecosystems (especially caves and groundwaters'). The second part examines the sensitivity and responses of hypogean organisms to prolonged starvation.