Reproduction Abstracts

Introduction: Testes investment plays a major role in male reproductive success because larger testes are expected to produce higher sperm number and quality. In birds, comparative studies have shown that testis size – a proxy measure of postcopulatory sexual selection – is negatively related with the intraspecific variation of sperm design. By contrast, links between the intramale variation of sperm morphometry and testicular size in mammals are unknown. Here, for the first time, we test the hypothesis that intramale variation in sperm morphometry is negatively associated with testes investment in red deer.

Materials and methods: Samples were collected from 17 adult red deers during the breeding season. Testicular mass was calculated averaging the values from the right and left testes. Spermatozoa were collected from the epididymal cauda and fixed in glutaraldehyde solution. Sperm head and flagellum morphometry were assessed by phase contrast microscopy on 25 spermatozoa/male using the Software ImageJ.

Results and discussion: Testicular mass showed a high variability between males ranging from 23.74 to 82.75 g. Overall, high testis mass was associated with low intramale variation of sperm design. Indeed, we found that testicular mass was negatively related with intramale coefficient of variation of total sperm length (P=0.015), head width and area (P=0.001 and P=0.041 respectively). The same trend of correlations was also found for the remaining morphometric parameters, although not significant. In conclusion, our results suggest that a low intramale variation in sperm morphometry indicates a high efficiency of sperm machinery.