Underwater vision has evolved in sea snakes for 15 million years. In a new study led by the University of Plymouth, researchers have determined that sea snakes have been refining their ability to see underwater ever since they entered the marine environment 15 million years ago.
The study is the first of its kind to describe when, where, and how frequently a species has adapted its ability to see in color.
The evidence suggests that the vision of sea snakes has evolved over millions of years as the snakes adapted to new environments. Genetic modifications helped the snakes spot their prey, as well as predators, in the deep sea.
Surprisingly, the researchers also discovered that sea snakes have the same adaptive properties as some fruit-eating primates.
“In the natural world, species obviously have to adapt as the environment around them changes. But to see such a rapid change in the sea snakes’ vision over less than 15 million years is truly astonishing,” said study lead author Dr. Bruno Simões.
“The pace of diversification among sea snakes, compared to their terrestrial and amphibious relatives, is perhaps a demonstration of the immensely challenging environment they live in and the need for them to continue to adapt in order to survive.”
Dr. Simões said the study also shows that snake and mammal vision has evolved very differently in the transition from land to sea.
“Sea snakes have retained or expanded their color vision compared to their terrestrial relatives, whereas pinnipeds and cetaceans underwent a further reduction in the dimensions of their color vision. This contrast is further evidence of the remarkable evolutionary diversity of snake eyesight.”
The researchers explained that despite being descended from highly visual lizards, snakes have limited color vision that is attributed to the dim-light lifestyle of their early snake ancestors.
The family of venomous front-fanged snakes, known as elapids, includes around 300 terrestrial species and 63 fully marine sea snakes.
To investigate the evolution of spectral sensitivity in elapids, the team analyzed the genes that produce visual pigments, retinal photoreceptors, and eye lenses of various terrestrial and marine species.
The analysis showed that the visual pigments of sea snakes had diversified much more rapidly in response to their surroundings compared to terrestrial and amphibious snakes.
For example, one particular lineage of sea snake had expanded its UV-Blue sensitivity, which would help the snakes navigate the variable light conditions of the ocean water column.
The study also suggests that sea snakes had two slightly different copies of the same gene, or alleles, just like fruit-eating primates. In sea snakes, this mechanism was used to expand their underwater vision with both UV sensitive and blue-sensitive alleles.
“Different alleles of the same gene can be used by organisms to adapt to new environmental conditions,” said study senior author Dr. Kate Sanders. “The ABO blood types in primates are a result of different alleles of the same gene.”
“However, despite being very important for the adaptation of species this mechanism is still poorly reported. For vision, it has been only reported on the long-wavelength opsin of some primates but our study suggests an intriguing parallel with diving sea snakes.”
The study is published in the journal Current Biology.
By Chrissy Sexton, Earth.com Staff Writer