Osmoregulation in marine mammals

Area of Science:

• Comparative Physiology
• Marine Mammal Biology
• Renal Function

Background:

• Osmoregulation in marine mammals is crucial for survival in high-salinity environments.
• A century of research necessitates a review of current understanding regarding water and electrolyte balance.
• Key aspects include kidney structure, water sources, feeding/fasting/diving effects, and hormonal influences.

Purpose of the Study:

• To review recent advances in marine mammal osmoregulation, focusing on water and electrolyte balance.
• To synthesize current knowledge on renal function in diverse marine mammal groups.
• To identify gaps and suggest future research directions in marine mammal physiology.

Main Methods:

• Literature review of studies on kidney structure, urine concentrating ability, and water sources.
• Analysis of physiological responses to feeding, fasting, diving, and saline infusions.
• Examination of hormonal regulation, including the renin-angiotensin-aldosterone system and vasopressin.

Main Results:

• Marine mammal kidneys (pinnipeds, cetaceans) are reniculate but do not offer superior concentrating ability compared to terrestrial mammals.
• Pinnipeds and sea otters can produce urine with electrolyte concentrations similar to seawater, potentially enabling seawater drinking.
• Water balance is primarily maintained via metabolic and dietary water; hormonal systems like renin-angiotensin-aldosterone show sensitivity to sodium availability.

Conclusions:

• Marine mammals employ diverse strategies for osmoregulation, relying on metabolic water and specialized renal capabilities.
• While some species can tolerate seawater, drinking is not universal; dietary water and salt balance are critical.
• Further research is needed on the roles of vasopressin and atrial natriuretic peptide in marine mammal osmoregulation.