Smaller squid make up for their size by producing bigger sperm than their larger competitors. Scientists believe the bigger sperm, in combination with an unorthodox mating tactic, provide a way for these modestly-sized squid to pass on their genes.
Male spear squid, also known as Bleeker's squid, come in two sizes. The larger males are known as "consorts," while the more diminutive members of the species are known as "sneakers." Whether you're a sneaker or a consort determines how you go about wooing, and ultimately mating with, a female spear squid.
Consorts aim to impress females by engaging in grandiose shows of bravado, flashing bright and colorful displays across their bodies. The glitziest of the consort squid gets to mate with the female and deposit his sperm inside her oviduct. Then, as his designation of "consort" implies he should, he guards her until she spawns her eggs to ensure that his sperm will fertilize them as they're laid.
Why is the consort squid so vigilant? As it turns out, "sneaker" squid aren't called sneakers for nothing. Severely lacking in the sense of tact possessed by their larger competitors, sneakers will forego trying to impress a female in favor of guerilla mating tactics.
Right when a female begins to lay her eggs, a sneaker squid will dash in head first and deposit his sperm on the outside of the female's body, just below her mouth. If he times it just right, the female's eggs will pass over the sneaker's sperm and be fertilized by him, rather than his larger competitor.
But a study by researchers from London and Japan reveals that the sperm of the sneaker squid are also larger than those of the consorts, as this image clearly demonstrates. According Dr Yoko Iwata, a research member from the University of Tokyo:
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.
In other words, the researchers believe that the smaller sperm likely work better within the female's oviduct, while the larger sperm function better outside the body. So while the larger males wind up producing more offspring, the smaller sneakers still have a fighting chance at passing on their genetic information.