Sea snakes are fascinating reptiles with evolutionary adaptations that help them hunt and live predominantly in the fast reef systems in the ocean. They can breathe through their skin, have flattened tails adapted to swimming and large saccular lungs that take up the length of their entire bodies.
But little else is known about the behaviour of these fascinating creatures and the extent of social bonds, interactions and reproductive behaviour. But a new study has shed some light on the incredible courting ritual that shows us how these oft-misunderstood serpents’ softer side.
In a new study published in the Biological Journal of the Linnean Society, researchers at the University of Adelaide have identified how male turtle-headed sea snakes (Emydocephalus annulatus) locate and court females in the ocean.
In the study, researchers examined 59 specimens collected from offshore reefs in the Timor Sea, and accessed from the Australian Museum, the Art Gallery of Northern Territory, and the Western Australian Museum. The study was co-authored by researchers at the University of Melbourne and the University of New Caledonia.
This sea snake species have developed enlarged touch receptors that look like freckles scattered across their face and reproductive organs. Research has found that these receptors play a crucial role in identifying a potential partner, alignment of sex organs and even stimulation before intercourse.
Sea snakes’ tongues are not as effective as their land-dwelling counterparts. They also have poor eyesight making it hard to locate potential mates in reef systems. But these touch receptors, known as a scale sensillum, on male turtle-headed snakes counters the inefficiency of using their tongues or eyesight and helps them locate and court females in aquatic environments.
Lead author, Jenna Crowe-Riddell, PhD graduate at the University of Adelaide’s School of Biological Sciences, said in a media release that “on land, snakes use tongue-flicking to sense and follow sex pheromones left by other snakes, but in the water, these chemicals are diluted.”
A 2005 study on turtlehead sea snakes, published in the Journal of Behavioral Ecology and Sociobiology, found that during courtship, 20 of the 31 males observed lost contact with the female while trying to maintain buoyancy underwater. They would then try and mate with other black creatures like sea cucumbers or some fish.
“What’s more, turtle-headed sea snakes can’t see very clearly underwater; they’ve been known to court anything long and dark, including sea cucumbers. To make matters worse, once a female is found the male must overcome buoyancy force so he doesn’t float away from his potential mate, she added.”
These touch receptors are present across several species of snakes, both on land and in the sea. But male turtlehead sea snakes sport much larger spots and in much greater density around the mouth, face and cloaca (reproductive/ excretory duct). These receptors that look like freckles are used to sense vibrations made by swimming mates, prey or predators.
“When we took a closer look at museum specimens, we discovered male turtle-headed sea snakes have larger touch receptors overall than females. We also found mature males have enlarged scale structures on their snout and chin, and their cloaca – an all-purpose hole used for reproduction and excretion.”
The study concluded that these receptors serve a very specific function in turtle-headed sea snakes. They help males find a potential mate and align their respective cloacal regions to successfully reproduce. They help the male identify the direction the female is facing and also the alignment of the snake to navigate their ‘rostral spine’ used to stimulate the female.
The team of researchers have found that the rostral spine, present neat the snout of males, is used for courting. Males are often seen rubbing and prodding the back of females with the snout. This act causes a hormonal change in the females, inducing receptory behaviour that causes the female to lift her anal scales, a process dubbed cloacal gaping.
“The rostral spine may be used to stimulate the female, such types of tactile foreplay are thought to be important for mating in snakes because they can cause beneficial hormonal changes and receptive behaviours in females,” said Crowe-Riddell. Reptiles are not typically appreciated for their intimate interactions, but our research is revealing that sea snakes have fascinating tactile adaptations for intra-species communication.”
The evolutionary transition from terrestrial to aquatic life has influenced the signalling systems of many secondarily aquatic animals. It seems that an aquatic lifestyle has made male sea snakes evolve adaptations that eases the stress of underwater intercourse in snakes and helps the tough courting and mating process.
“As we build a more complete picture of underwater perception, sea snakes are becoming a fantastic example of how evolution creates opportunity from constraints,” said Crowe-Riddell.
With a better understanding of these touch receptors, we can further understand how sea snakes choose a partner, mate and use touch to communicate. Most reptiles are often seen as creatures of instinct with no real social structure and interactions. The study of sea snakes could help shed light on the complex lives these creatures live underwater.