Morphological Description and Analysis of Octopus rubescens Testis and Sperm

Abstract

The male reproductive system in cephalopods is a topic rarely studied in the field of fertilization biology. The changes the sperm cell undergoes during spermiogenesis varies slightly across the animal kingdom and unravelling the process as it occurs in individual species is vitally important for understanding evolution and fertilization strategies. This study aims to describe the structures involved in the spermiogenesis process of the cephalopod Octopus rubescens. To test the hypothesis that there will be a maturity gradient in the morphology of sperm developmental stages and overall sperm structure in O. rubescens, we dissected the testis of a male O. rubescens in senescence and divided the samples into 4 categories based on our proposed level of sperm maturity. After fixing the samples in glutaraldehyde and dehydrating them in ethanol (EtOH), we divided each sample in half. In one half, we stained the nucleus and microtubules to be imaged with fluorescent microscopy and dried and sputter-coated the other half to be imaged with scanning electron microscopy (SEM). The results of the fluorescent microscopy and SEM indicate a gradient of sperm maturity throughout the testis and that all maturation stages are present throughout the entire testis. The individual sperm were also observed to have considerably long tails which can be associated with sperm competition and selective pressures by the female during fertilization. This study broadens our understanding of the developmental biology of O. rubescens and cephalopods overall.