A qualitative analysis of the kidney structure of Meliphagid honeyeaters from wet and arid environments.

The qualitative ultrastructural renal anatomy was examined in 4 species of honeyeater (parvorder Corvi) inhabiting 2 distinctly different environments. The kidneys of the wet zone New Holland honeyeater Phylidonyris novaehollandiae and little wattlebird Anthochaera lunulata were compared with those of the arid zone white-fronted honeyeater Phylidonyris albifrons and spiny-cheeked honeyeater Acanthogenys rufogularis. The size and structure of glomeruli were similar between species. In all species, except in P. novaehollandiae, the proximal tubule cells contained wide intercellular spaces filled with basolateral cell membrane interdigitations. Medullary nephron tubules were arranged in a sequential manner in all species. Thick and thin limbs of Henle were separated by the collecting ducts and extended the entire length of the medulla, a situation not found in muscicapid passerines. This tubular arrangement is not entirely consistent with the proposed single-effect countercurrent multiplier theory. The thin limb of Henle consisted of only one epithelium type, which had wide intercellular spaces. The thick limb of Henle consisted of 2 types of epithelial cells, each having narrow intercellular spaces, but with varying degrees of cell membrane infoldings. The ultrastructural morphology of the limbs of Henle in honeyeaters differed from those of muscicapid passerines. The ultrastructure of the distal nephron was similar in each species studied. All of the above nephron characteristics are considered to enable honeyeaters to absorb a large proportion of solutes and water from the glomerular filtrate.