MAMMALIAN SPERM MORPHOMETRY

Understanding the adaptive significance of sperm form and function has been a challenge to biologists because sperm are highly specialized c ells operating at a microscopic level in a complex environment. A frui tful course of investigation has been to use the comparative approach. This comparative study attempts to address some fundamental questions of the evolution of mammalian sperm morphometry. Data on sperm morpho metry for 445 mammalian species were collated from published sources. I use contemporary phylogenetic analysis to control for the inherent n on-independence of species and explore relationships between the morph ometric dimensions of the three essential spermatozoal components: hea d, mid-piece and flagellum. Energy for flagellar action is metabolized by the mitochondrial-dense mid-piece and these combine to propel the sperm head, carrying the male haplotype, to the ovum. I therefore sear ch for evolutionary associations between sperm morphometry and body ma ss, karyotype and the duration of oestrus. In contrast to previous fin dings, there is no inverse correlation between body weight and sperm l ength. Sperm mid-piece and flagellum lengths are positively associated with both head length and area, and the slopes of these relationships are discussed. Flagellum length is positively associated with mid-pie ce length but, in contrast to previous research and after phylogenetic control, I find no relationship between flagellum length and the volu me of the mitochondrial sheath. Sperm head dimensions are not related to either genome mass or chromosome number, and there are no relations hips between sperm morphometry and the duration of oestrus.