The kidney of tapirs: a macroscopical study

Area of Science:

• Comparative anatomy
• Renal morphology
• Mammalian evolution

Background:

• Tapirs, as primordial ungulates with semi-aquatic habits, possess unique physiological adaptations.
• Understanding their renal structure provides insights into evolutionary adaptations of kidney morphology in mammals.
• Previous studies on perissodactyl renal anatomy have not extensively detailed tapir kidney structure.

Purpose of the Study:

• To provide a detailed morphological description of the tapir kidney (Tapirus bairdi and T. pinchaque).
• To compare the renal structure of tapirs with other perissodactyl families (rhinoceri and equids).
• To investigate the functional implications of tapir renal morphology, particularly in relation to their aquatic environment.

Main Methods:

• Macroscopic and microscopic examination of tapir kidneys from adult and term-neonate specimens.
• Quantification of glomeruli number and size in different tapir species.
• Analysis of renal cortex, medulla, collecting duct system, and vascular architecture.

Main Results:

• Tapir kidneys exhibit a continuous, nonlobed renal cortex comprising approximately 70-80% of renal mass.
• A high number of moderately mature glomeruli were observed, even in neonates, with species-specific variations in number and size.
• The medulla is a simple crest-type, with terminal collecting ducts opening separately at the crest and unique vascular patterns traversing the cortico-medullary border.

Conclusions:

• The tapir kidney's structure, characterized by a large cortex, numerous glomeruli, and a simple crest-type medulla, is distinct among perissodactyls.
• The observed renal morphology suggests adaptations for efficient filtration and potentially water balance in their semi-aquatic niche.
• The unique vascular arrangement bypassing the outer medulla highlights a divergence from other eutherian mammals with medullary crests.