Spermatogenesis and Spermiogenesis, Birds

Abstract

Spermatogenesis in birds and mammals is generally similar, and therefore the mammalian terminology is adopted generally. The number of ‘cellular associations’ and ‘steps of spermiogenesis’ is variable in birds. A transverse section of the seminiferous tubular epithelium displays small, multiple ‘cellular associations’. Spermatogenesis is more rapid in birds than in mammals. Spermatid differentiation in non-passerine birds produces conical acrosomes that may possess a perforatorium, vermiform nuclei with dense chromatin, mitochondrial sheaths, and long flagella with the typical microtubular conformation. Passerine spermatids differentiate into considerably elongated, spiral-shaped, spermatozoa, comprising acrosomes as long or longer than the nuclei, and unlike non-passerine birds, five helical structures develop, viz. acrosomal, nuclear, mitochondrial, granular, and microtubular helices; the latter two structures being absent in non-passerine birds.