My first scientific paper: sea snakes may have a unique underwater sense

I'm excited to announce my first lead-author paper has been published in Open Biology. The article has enjoyed great reception from the media, with write ups by Australian GeographicIFL Science, Cosmos and Seeker being my favourites. It is a huge relief to see published as it is the culmination of my Honours research completed at the University of Adelaide in 2014. I will be presenting this research at the 8th World Congress of Herpetology in China thanks to funding from a Gans grant.

Inspiration for the project

My honours thesis, a document of 15,000 words, has been re-read, reshaped, re-analysed, reworked, rewritten, re-submitted and, finally, peer-reviewed and accepted as a scientific article of a scant 4300 words. The research focused on microscopic organs found on the head scales of many squamates (lizards and snakes), we hypothesised that these 'scale sensilla' allow sea snakes to feel vibrations underwater. The project was inspired several years ago when I was on a wildlife survey to Ashmore Reef in the Timor Sea, a place once renowned for its diversity of sea snakes but has since experienced a complete local extinction of its species, leaving scientists entirely baffled as to why. Climate change? Overfishing? Disease? Or perhaps sound pollution? Human-induced sound pollution, such as the air-gunning used in seismic surveys, are so loud that they can mask other, biological pertinent, sound out completely, disorientate sea turtles, whales and squid and can even burst the swim bladders of fish at close ranges. However, this led to another question, can sea snakes even sense sound?  

 An olive sea snake ( Aipysurus laevis ) dives after taking a breath at the water's surface. Sea snakes live their whole lives at sea but very little is known about how they sense their aquatic environment.  Photo credit: Chris Malam

An olive sea snake (Aipysurus laevis) dives after taking a breath at the water's surface. Sea snakes live their whole lives at sea but very little is known about how they sense their aquatic environment. Photo credit: Chris Malam

Sea snakes may be able to sense vibrations underwater

Aquatic snakes evolved from Australian land snakes 9 to 20 million years ago. Vision, hearing and chemoreception (tongue flicking) are important senses for land snakes, but these stimuli become distorted underwater. We predicted that scale sensilla might compensate for the relative lack of sensory cues for fully aquatic sea snakes. We found that shape of sensilla were more protruding in aquatic snakes than land snakes and that some species had a very high proportion of their scales covered in sensilla. These differences suggest a unique sensory function to scale sensilla that may help sea snakes feel vibrations, or sound, underwater.

 Close up photograph of a beaked sea snake ( Hydrophis schistosus ) showing the sensilla protruding from the surface of a scale. Scale bar, 3 mm.  Photo credit: Jenna Crowe-Riddell

Close up photograph of a beaked sea snake (Hydrophis schistosus) showing the sensilla protruding from the surface of a scale. Scale bar, 3 mm. Photo credit: Jenna Crowe-Riddell

To measure these tiny organs in an acurate and repeatable way, we created a silicone replica of each snake head (from preserved specimens from the South Australian Museum), photographed these casts, then devised a software script to automatically measure the surface area and number of scale sensilla. I loved this aspect of the project because it took a creative approach to solving the problem of how to acurately quantify these organs. It took a lot of trial and error to refine the casting and, as far as I know, this technique has only been used on fossils and not actual animal specimens. These measurements were combined with DNA sequences to reconstruct how these organs have changed in the evolutionary transition from land to sea in snakes.

 When science meets art: peeling a silicone cast off a sea snake head specimen

When science meets art: peeling a silicone cast off a sea snake head specimen

Besides the main findings of the shape and coverage of sensilla, we also discovered that the size of sensilla is closely linked to how many sensilla are present on the scale. Perhaps indicating a developmental trade-off between how large a sensilla can grow before becoming overcrowded by other sensilla. For a visually orientated land mammal like ourselves its difficult to fully understand how this trade-off might influence the sensitivity of sensilla over the whole head, and it turn, the entire sensory perception of a sea snake. For me, this is one of the most fascinating aspects of studying sensory biology: can we ever full appreciate the sensory experiences of other species? 

Is there hope for sea snakes?

The recent declines of sea snakes from Ashmore reef are mysterious and alarming. Neighbouring reefs in the Timor Sea, such as Scott reef, also appear to be experiencing similar declines in and rarer species haven't been seen at all in the last decade, despite increases in survey efforts. Sea snakes are top predators that specialise on an array of fish, eels, eggs, cephalopods and crustaceans, they also serve as prey for various sharks and sea birds. The disappearance of 13 ecologically distinct species from a single reef could have downstream effects on that ecosystems food web that are yet to be fully realised. Interestingly, genetic work has indicated that the olive sea snake and dusky sea snake (Aipysurus fuscus) are hybridising (making them ‘olisky sea snakes, I guess) that could result in species 'introgression' (one species being absorbed into another), which effectively reduces overall species diversity. Why these species are suddenly finding each other attractive after millions of years is a mystery, although it certainty could be the result of shifting selection pressure on sea snakes and thus a sign of wider stress in that ecosystem.

There is reason to hope for Ashmore and future conservation efforts. Just earlier this year, an olive sea snake was spotted by an AIMS survey vessel, the first to be spotted in 6 years. Whether that snake is a remnant of the old Ashmore population or a new colonist from neighboring reefs remains to be tested. Meanwhile, populations of two endangered species have recently been discovered off the coast of Broome and Shark Bay in Western Australia. Fundamental research on sea snake biology (e.g. ecology, sensory abilities, genetics) is needed to better understand what exactly has caused these recent declines and whether we can prevent it from happening again.

Further research on the sensory biology of sea snakes

I am collaborating with scientists at the University of Western Australia to test the auditory brain response to underwater sound in sea snakes, and my PhD project is looking at a remarkable sensory adaptation in olive sea snakes.