In a research published in journal BMC Evolutionary Biology, researchers demonstrate that the evolution of different sperm sizes in the Male squid (Loligo bleekeri) can be attributed to the divergent mating behavior. The body size of the squid urges the animal to utilize diverse reproductive strategies.
Large male squid demonstrate their flashy skin color-change technique to contend for females for courtship. Once the partner has been selected by the female, the male places his sperm within the oviduct of the female by mating in an above and below position. The male ascertains that his own sperm fertilizes the eggs and ensures that no other males mate with the female by remaining with her until spawning. At the very instant the eggs are laid, tiny ‘sneaker’ males make an entry and mate with the female head on. As these small males leave the female’s body, they place bundles of sperm by the female’s mouth in anticipation that their sperm may have an opportunity to fertilize the eggs.
When British and Japanese researchers examined the sperm produced by the tiny sneaker males and compared it with that of large consort males, they discovered that the sperm produced by the latter was smaller than that of the larger consorts. Dr Yoko Iwata from University of Tokyo said, “Sperm size is likely to be an adaptation to fertilization environment, either inside the female or externally, rather than competition between sperm, because the fertility and motility of sneaker and consort sperm were the same.”
The strategy employed by the larger males definitely resulted in higher paternity rates. However, the behavior of being sneaky facilitates the passing on of genes by small sneaker males, who fail to win over a female fair and square.