Quantitative studies on variation in sperm head morphology of the hopping mouse, Notomys alexis

Abstract

AbstractSpermatozoa from the Australian conilurine rodent, Notomys alexis, display a remarkable degree of variability in head morphology. This variation was quantified by differential counting (n=18 animals) and image analysis (n=4 animals) of spermatozoa recovered from the cauda epididymidis and vasa deferentia. Variability in sperm morphology was exhibited in all individuals examined regardless of age. Sperm heads examined by phase contrast microscopy could be classified into four main types, and in addition, often bizarre forms occurred that ranged in shape from having a small dorsocaudal projection to being ovoid or dome‐shaped. Measured by image analysis, sperm nuclear size for Notomys alexis ranged from 2.21 to 6.94 μm2 (mean 4.34 ± 0.94 μm2) as compared with a range of 4.53–5.82 μm2 (mean 5.33 ± 0.26 μm2) for spermatozoa from Pseudomys australis, a closely related species. The acrosome of Notomys alexis spermatozoa also exhibited considerable morphological variation as detected by immunolocalisation with a monoclonal antibody to a mammalian acrosomal antigen.This variability exhibited by both the acrosome and the nucleus of the sperm head in Notomys alexis may relate to low levels of intermale sperm competition that probably occurs in these animals.