Ultramorphology of the ventriculus of nectarivorous, granivorous and omnivorous species of passerine birds

Abstract

The objective of this study was to investigate the effect of disparate diets on the ventriculi of three species of similar sized granivorous, nectarivorous and omnivorous passerine birds. A total of twelve birds were captured with mist net under license and ventriculi from these birds were processed for light and electron microscopy. Nectarivorousventriculus had thin, poorly developed muscle and sac-like in shape while the granivorous gizzard had the thick, well developed muscle with the classical shape of biconvex lens and the omnivorous gizzard was intermediate. The wall of the ventriculus consisted of mucosal, submucosal , muscularis and inconspicuous serosal layers. Tunica muscularis, the most prominent layer of the wall was thickest in granivore, thinnest in nectarivore , and intermediate in omnivore. The mucosal glands were individual, tubular units with slightly expanded basal ends, demarcated from each other by dense connective tissue and opened individually into the lumen of the organ. Each glandular unit consisted of basal, chief, endocrine, neck and surface epithelial cells.The chief cells of the glandular units produced the "tubular” portion of the cuticle while the neck and surface epithelial cells produced the "surface” portion of the cuticle and the merger of these two portions formed the gastric cuticle, a protein mucopolysaccharide complex. The overlaying gastric cuticle (luminal cuticle) of the ventriculus was hard, tough, and sieve-like in the granivore, soft and jelly-like in the nectarivore and intermediate in the omnivore. The structural adaptations of the ventriculi of these three species to their various diets are discussed. There is need for more studies to be done on composition and functional morphology of the cuticle in aves.

Keywords: Morphology, Ventriculus, Gizzard, Passerine Birds