Male Sea Snakes Evolve To Be Smaller With Bigger Eyes Than Female Counterparts [Study]

Sea snakes evolve surprisingly - males are becoming smaller than females. A theory said evolution helped males spot females for sexual selection.

Sea Snakes Evolution

A new study reveals that male aipysurine sea snakes started to develop larger eyes than their female counterparts to find a mate, and females grew progressively larger than males. Males were evolving to be smaller than females, but their eyes were growing significantly bigger than the rest of their bodies.

"Females averaged larger than males in all taxa, and generally were wider-bodied with shorter and wider tails and smaller eyes," the authors wrote.

According to one theory, this occurred to aid male snakes in locating females as they transitioned to the ocean, as the wet environment prevents them from following a smell trail, which would have occurred on land.

"Sexual selection on mate-finding ability offers a plausible selective advantage for larger relative eye size in males," they added.

Unlike their terrestrial counterparts, male sea snakes may rely on visual cues to discover mates until the other snake is close enough for chemosensory sampling. They cannot locate reproductive females by following substrate-deposited pheromonal trails. Additionally, they may have experienced a strong selection in their visual acuity because of their difficulty finding partners.

Alternatively, it's possible that the smaller males' eyes were too small to see well, which caused them to evolve into disproportionately larger eyes. This also indicates that the different feeding behaviors of the males and females may have contributed to the variation in eye size.

Another theory suggests that females got bigger to have more offspring, or maybe because there was no longer any male-to-male competition for females. In species where males compete for female access, larger males frequently have a major advantage over smaller males. Males will no longer have an evolutionary incentive in size in the absence of male-to-male combat.

Interestingly, no male-to-male conflict has appeared in aquatic snakes; this may be because tactics such as ramming a rival's head into the substrate are useless in a three-dimensional aquatic environment.

"The apparent ubiquity of female-larger size dimorphism in sea snakes thus may reflect an evolutionary loss of male-male combat, reducing the benefit to larger body size in males," the researchers added.

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New Snake Species Named After Harrison Ford

In related news, in August, a new snake species was discovered in Peru, and it was named Tachymenoides harrisonfordi after "Indiana Jones" star Harrison Ford.

Ford serves as vice chair of Conservation International, a nonprofit organization. In response to the recent honor, he said it was "humbling."

He told Conservation International in jest that the kids were afraid of the animals that bore his name. In real life, Ford enjoys leisurely cross-stitching and even lulling his basil plants to sleep. He said that, unlike the "Indiana Jones" character he portrayed, he liked snakes and "fell in love" with them.