A QUALITATIVE-ANALYSIS OF THE KIDNEY STRUCTURE OF MELIPHAGID HONEYEATERS FROM WET AND ARID ENVIRONMENTS

The qualitative ultrastructural renal anatomy was examined in 4 specie s of honeyeater (parvorder Corvi) inhabiting 2 distinctly different en vironments. The kidneys of the wet zone New Holland honeyeater Phylido nyris novaehollandiae and little wattlebird Anthochaera lunulata were compared with those of the arid zone white-fronted honeyeater Phylidon yris albifrons and spiny-cheeked honeyeater Acanthogenys rufogularis. The size and structure of glomeruli were similar between species. In a ll species, except in P. novaehollandiae, the proximal tubule cells co ntained wide intercellular spaces filled with basolateral cell membran e interdigitations. Medullary nephron tubules were arranged in a seque ntial manner in all species. Thick and thin limbs of Henle were separa ted by the collecting ducts and extended the entire length of the medu lla, a situation not found in muscicapid passerines. This tubular arra ngement is not entirely consistent with the proposed single-effect cou ntercurrent multiplier theory. The thin limb of Henle consisted of onl y one epithelium type, which had wide intercellular spaces. The thick limb of Henle consisted of 2 types of epithelial cells, each having na rrow intercellular spaces, but with varying degrees of cell membrane i nfoldings. The ultrastructural morphology of the limbs of Henle in hon eyeaters differed from those of muscicapid passerines. The ultrastruct ure 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.