Behavioral Regulation of Hemolymph Osmolarity Through Selective Drinking in Land Crabs, Birgus latro and Gecarcoidea lalandii

Abstract

Drinking behavior in Birgus latro and Gecarcoidea lalandii was videotaped under controlled laboratory conditions. B. latro displayed the drinking behavior typically observed in nature, spooning up water with the chelae (Lister, 1888; Gross, 1955). G. lalandii is documented for the first time displaying this same behavior; however it obtained water primarily through immersion. Under normal hydrated conditions (hemolymph osmolarities < 1050 mOsm) B. latro showed no preference for drinking fresh or seawater. When dehydrated (hemolymph osmolarities > 1050 mOsm) B. latro altered its drinking behavior and showed a distinct preference for freshwater. This strategy resulted in restoration of original hemolymph osmolarities and wet weights and was accomplished through periods of intensive drinking activity. Conversely, G. lalandii never experienced true dehydration; rather, the hemolymph became hyperosmotic compared with control animals. This species preferred freshwater both under normal and hemoconcentrated conditions. G. lalandii was also able to osmoregulate behaviorally and was able to restore hemolymph osmolarities to normal concentrations via immersion in freshwater following experimentally induced hemoconcentration. Possible physiological and ecological reasons for the differences in water uptake strategies and preferences are discussed.

Terrestrial adaptations in the Anomura (Crustacea: Decapoda)

“…In situations where B. latro has access to both dilute and saline drinking water, e.g. on small islands and atolls, it too can regulate its body fluid concentration by differential drinking (Gross, 1955;Combs et al, 1992).…”

Role of Behavior in Meeting Osmotic Challenges1

“…This phenomenon has been particularly thoroughly studied in land crabs, which often occur in habitats containing both seawater and freshwater. Robber crabs Birgus latro drink by spooning up water with their chelae (Combs et al, 1992;Taylor et al, 1993). When hydrated, they select freshwater and seawater in about equal volumes.…”

“…Christmas Island red crabs Gecarcoidea lalandii, when hemoconcentrated by evaporative losses, similarly prefer freshwater in which to partially immerse themselves, thereby bringing down hemolymph concentration (Combs et al, 1992). Hemodilution also can occur because urine flow and ion fluxes are fairly high despite mechanisms to conserve ions.…”

Modificações esqueletais e apendiculares torácicas para captação de água do solo em caranguejos semiterrestres (Crustacea: Brachyura: Grapsoidea:Ocypodoidea)

“…Quando ingerida diretamente, a água, do mar ou doce, é transportada pelos quelípodes até os maxilípedes e bebida. É um método frequentemente adotado por espécies que permanecem em regiões de solo seco mas não é suficiente para suprir a necessidade de absorção de água, o que faz com que essas espécies também utilizem alguma outra fonte, normalmente a imersão em um corpo d'água (Combs et al, 1992;Dela-Cruz & Morris, 1997).…”