Study Explains Why Sea Snakes are Evolving Smaller Heads

A new study from Australia has shown why some species of sea snakes have developed smaller heads than related species of sea snakes.

There are about 60 species of highly venomous sea snakes in the world. In an adaptation to life in water, these snakes have flat bodies and an oar-like tail.

The shrinking of heads in a species of sea-snakes puzzled researchers, as large heads would have enabled snakes to catch bigger prey. However, these snakes have evolved small heads which help them look for sand eels.

The study has shown that the snakes have evolved these small heads rapidly and have split into different species due to this trait. Researchers also say that the population of the snakes with smaller heads is relatively small and that these don't interbreed with snakes that have larger heads.

"A team led by my colleague Dr Kate Sanders (University of Adelaide) has been investigating genetic differences across all sea snakes, and we noticed that the blue-banded sea snake (Hydrophis cyanocinctus) and the slender-necked sea snake (Hydrophis melanocephalus) were almost indistinguishable genetically, despite being drastically different in size and shape," Dr. Mike Lee from the South Australian Museum said in a press release.

Lee said that the slender-necked sea snake has a much smaller head and is about half the size of the blue-banded sea snake.

"This suggested they separated very recently from a common ancestral species and had rapidly evolved their different appearances," Lee added.

One possible explanation for this change in the snakes' head is that a population of large head sea snake rapidly evolved into snakes with smaller heads to aid eel-hunting. Subsequently, these small head sea snakes stopped interbreeding with snakes with larger heads, researchers said.

"Our results highlight the viviparous sea snakes as a promising system for studies of speciation and adaptive radiation in marine environments," said Dr Kate Sanders from the University of Adelaide, lead author of the study.

The study is published in the journal Molecular Ecology.