Male snakes evolved larger eyes to find mates

A new study has revealed that the male sea snakes underwent a variety of strange adaptations, which included changes in size and increased dimorphism.

The study, published in the journal Royal Society Open Science, while emphasising their sex lives said that the female aipysurine sea snakes turned increasingly larger compared to their male counterparts and the males started developing larger eyes than females in order to find their mate.

“Males had larger eyes, compared to head length, in all six species. It was statistically significant in three of those species. One reason for larger eyes in males may be that they have shifted to vision to find mates, because (unlike land snakes), they can’t follow a scent trail laid onto the ground by a female as she moves along,” said a study author Richard Shine, a professor of biology at Australia’s Macquarie University, while speaking to Newsweek.

The researchers added that although the males evolved to become smaller in comparison to the females, their eyes started becoming much larger in comparison to their entire bodies.

Sea snakes undergo modification in watery environment
As per the theory, these changes took place to help the male snakes spot the females as they tried to adjust to the watery environment. The watery environment was making it difficult for them to follow a scent trail.

“Sexual selection on mate-finding ability offers a plausible selective advantage for larger relative eye size in males,” wrote the authors, in the paper.

“Unlike their terrestrial counterparts, male sea snakes cannot locate reproductive females by following substrate-deposited pheromonal trails; and instead, may rely upon visual cues to find mates until the other snake is close enough for chemosensory sampling. The resulting difficulty in finding mates may have imposed strong selection on visual acuity in male sea snakes,” they added.

As per alternative theories, the smaller males had eyes which were too small to properly see and this led to evolvement of disproportionally larger eyes. It was also suggested that the eye size may have changed due to differing foraging habits of the males and females.

It was also suggested in the paper that the females had evolved larger to have more babies because of the loss of male-male fighting for females.