Osmoregulatory response to acute diet change in an avian nectarivore: rapid rehydration following water shortage

摘要: Nectarivores may be required to switch between water conservation and excretion as rapidly they change food plants in nature. We examined the rehydration response Whitebellied Sunbirds (Nectarinia talatala) that had been fed a concentrated sucrose diet (2.5 mol/l) for 2 days then were switched 10 x less (0.25 on morning of third day. measured gain well cloacal fluid (CF) volume hourly over 12 h, analysed CF osmolality calculated osmotic excretion. was also assayed osmoregulatory hormone aldosterone (ALDO). As most water-deprived birds, whitebellied sunbirds cope with shortage when sugar by almost completely ceasing void CF. Although is high, volumes are not sufficient maintain steady rate birds retain osmolytes. Immediately upon switching dilute diet, produce copious elevated maintained at high levels first 6 h rehydration. This stabilises afternoon expected hydrated birds. Some 2-3 after peak excretion, there discrepancy intake output, mirrored an increase ALDO output. These data suggest retained osmolytes undertaken soon available, changes body composition occurring subsequently. study vindicates use obtain repeated measurements steroid small