Biology Essay on Sperm Competition

Sperm competition is the physical process of trying to be the first to fertilise a
Female’s eggs with you’re sperm. Sperm competition is very common in many evolutionary processes. Many species, like the waterfowl duck species have adapted certain behaviours and morphologies that help to promote their sperm competition and result in their sperm being the most favourable and their genes passed into the gene pool.

Some of the waterfowl species have elaborate morphology that promotes sperm competition. The female has a lot of say in who fathers her young, she can control the length of her vagina and is more likely to pick the male with the best shaped penis, the longest penis or the stiffest. This way she can have the best genes for her offspring. Through co-evolution the female has been able to mirror the shape of the male’s penis with her vagina. The female can control the males sperm content inside of her because of her blind ending pouches and therefore reduces forced copulation. The female ducks have certain behavioural characteristics that indicate they are ready for copulation. Certain muscles in the vagina show signs that they are preparing to mate including relaxing (Patricia L. R. Brennan 2009).

The male gentalia found in waterfowl is very uncommon among birds. (Patricia L. R. Brennan 2009). Fertilisation partners can be influenced by certain bodily functions and structures. The penis is generally located, inverted, in the Phallic sack. When the penis is erect it is still adaptable and is not limited to stiff movements, this is because of the arrangement of the axial orthogonal arrays. Mechanical barriers were tested to see if ejaculation would still continue if the female’s vagina did not mirror penis shape, ejaculation is still possible if the penis is not fully inverted. The penis has a rough texture that contributes to the spiral shaped (Patricia L. R. Brennan 2009). The penis shape, size and inversion are all adaptions resulting from competition between the males, female’s will pick the bird with the biggest, stiffest penis to pass the best genes on to her offspring, this is called natural selection and is an evolution pressure that has promoted sperm competition.

Natural selection is a naturalistic process where certain phenotypes are selected for to make it easier for the species to adjust to the environment and excel in reproductive and environmental situations (Biology online 2001). Natural selection has brought the importance of having the biggest penis in male Waterfowls. For a male to get the sperm closest to the females eggs, he will need to have a bigger and stiffer penis than the other males. It is natural for a male to want his genes to be passed on to the offspring, where the young will inherit his gene’s. Choosing a male with better penis and sperm adaptions could ensure higher survival or reproduction success. If the male’s have superior features or adaptions that will benefit survival for a species they will be chosen for mate selection by the females (Evolution and natural selection 2010). A bigger penis is an evolutionary adaption that will help a male to reproduce and therefore is a trait selected for in natural selection.

The Damselfly, Enallagma Hageni is an example of sperm competition. One male fertilizes ninety five percent of the eggs that are first laid. Multiple mating partners create the other five percent. If the female does not deposit her eggs after copulation another male is still able to fertilize her eggs. He does this by inserting his penis and removing the sperm that is stored in the females storage organs. Copulation then begins and he replaces the sperm with his own. This can happen up to four times before the female deposits the eggs. This creates competition within males to deposit their sperm in each female. Forced copulation is not possible because the female has to contract her abdomen for the male’s penis to be fully inserted inside her. The female benefits from this relationship with the male because he will watch over her and protect her as she oviposits her eggs under water, where she is more exposed to pray. The female will be encouraged to mate with other males in order to find a better ovipositing site among the pond (Ola M. Fincke, 1983).