Featured Image Credit: Kentaro Morita
By Eva Gruber
Biologists studying a certain species of fish have confirmed a fascinating fact that confirms the discretion that female animals apply in choosing a mate to reproduce with. The females may mate up to 200 times over the course of the breeding season, with up to 10 different males. These marathon encounters actually take a lot of effort, and it wasn’t understood exactly what the benefit was for this tremendous use of their precious stores of energy.
Through careful observations, biologists determined that even though the females went through the motions of mating with all the different males, they did not always release their eggs to be fertilized. At some point in the courtship and spawning process, the females determined that this or that male was not worthy of fertilizing her eggs, and while she enacted the release of eggs while the male released his sperm, she did not actually release eggs. The males released their sperm regardless of whether the female released her eggs. In this way, she was saving her eggs “for the right one”.
This can all boil down to the base differences between male and females of almost all species. Males have a seemingly endless supply of sperm in which to produce offspring, while females have a very limited amount – even in groups of animals like fish or insects who may lay thousands of eggs at a time. The male of the species could, undoubtedly, fertilize the eggs of many individual females, although this only happens in mating systems where there is one aggressively dominant male.
This disparity in the amount of reproductive capabilities leads to differences in sexual behavior. Females often tend to be choosy – after all, they have a precious store of eggs, and they are often the ones who gestate the fertilized eggs (although in fish the gestation is external). This leads to the discretionary nature of females of most species. Males, on the other hand, have virtually unlimited reproductive capabilities, and it is in the interest of spreading their genes that they may try to fertilize as many females as possible.
In the Siberian brook lamprey, females appeared to engage in sham mating when surrounded by more males – which means that when presented with more choices of potential mates, the females become even choosier. The females can select the father of their offspring, based on whatever characteristics might signal to her that he is the healthiest and/or strongest of the bunch.
Hence, the Siberian brook lamprey continues the story of the evolutionary disparity between the sexes. This fascinating bit of information discovered through careful study and observation is added to the spread of knowledge we have as humans, and contributes to our understanding of the natural world.