[Adaptive evolution of osmoregulation in rodents with different ecologies]

Area of Science:

• Comparative physiology
• Renal physiology
• Rodent osmoregulation

Background:

• Osmoregulation is crucial for survival in varying water availability.
• Rodents exhibit diverse adaptations to water scarcity.
• Understanding species-specific osmoregulatory mechanisms is key to ecological specialization.

Purpose of the Study:

• To investigate osmoregulation differences in aquatic rats (Arvicola terristris), cotton rats (Sigmodon hispidus), and Wistar albino rats.
• To analyze the effects of water deficiency on blood constants and kidney function.
• To elucidate the mechanisms behind varying osmotic concentrating abilities in rodents.

Main Methods:

• Comparative analysis of blood serum constants (sodium, urea, osmolarity) under normal and dehydrated conditions.
• Measurement of antidiuretic activity in blood serum.
• Assessment of the urine to plasma osmolarity ratio (U/Posm) as an index of kidney concentrating ability.

Main Results:

• Water deficiency caused significant changes in blood constants related to osmotic homeostasis in all studied rodents.
• Wistar albino rats exhibited increased antidiuretic activity and a high osmotic concentrating index (7.4 +/- 0.2).
• Aquatic and cotton rats showed increased antidiuretic activity but no significant increase in U/Posm (2.7 +/- 0.2 and 4.8 +/- 0.3, respectively), indicating lower concentrating effectiveness.

Conclusions:

• Water-loving rodents possess a less effective kidney concentrating mechanism compared to albino rats.
• Structural and functional kidney adaptations, leading to decreased intrarenal sodium and urea gradients, underlie the low concentrating effectiveness in aquatic and cotton rats.
• These osmoregulatory peculiarities are integral to the ecological specialization of these rodent species.