Sperm and eggs can be unbelievably tiny, far smaller than those made by people, or they can be unexpectedly enormous. The sperm is the smallest cell in human biology, but also one of the most complex. The egg meanwhile is the largest cell and similarly intricate. Looking further out into the natural world, the diversity of these sex cells, or gametes, is truly remarkable. To be good at both is a challenge, because the two jobs create opposing drives across a size-number trade-off," explains Matthew Gage from the University of East Anglia, UK.
Etheostoma is a genus of North American darter fish whose species have similar habitats and breeding seasons, yet hybridization is rare. Behavioral barriers have been demonstrated to play a key role in maintaining species boundaries. Further, conspecific same species sperm precedence has also been observed when the gametes of two different species come into contact. In this study, we investigated if physical characteristics of sperm could be a mechanism for the lower fertilization success of heterospecific different species males when eggs are simultaneously exposed to conspecific and heterospecific sperm. We chose to examine the sperm of two closely related species, E. Using toluidine blue and immunofluorescent labeling methods, we compared head diameter and tail length of sperm cells between the two species.
Sperm competition is now recognised as a potent selective force shaping many male reproductive traits. While the influence of sperm competition on sperm number is widely accepted, its effects upon sperm size remain controversial. It had been traditionally assumed that there is a trade-off between sperm number and sperm size, so that an increase in sperm number would result in a decrease in sperm size, under conditions of sperm competition.