you're reading...

Book Review

Skin that Sees: Evolution and Mechanism of Phototaxis in Sea Snake Tails

Researchers have discovered light sensing abilities in the tails of sea snakes. This unique adaptation in one genus of snakes may allow them to sense and respond to impending danger.

Crowe-Riddell, J. M., Simões, B. F., Partridge, J. C., Hunt, D. M., Delean, S., Schwerdt, J. G., … Sanders, K. L. (2019). Phototactic tails: Evolution and molecular basis of a novel sensory trait in sea snakes. Molecular Ecology. doi:10.1111/mec.15022


Imagine having eyes on your feet. This is essentially the body plan of some sea snakes. With a paddle-shaped tail for locomotion, the olive sea snake (Figure 1) goes to extremes to protect it. The skin in this snake’s tail region is embedded with unique light sensors, allowing it to respond to impending danger. Crowe-Riddel et al. have discovered other sea snakes that have also evolved this phototaxis, or response to light, and begin to understand the evolution of and underlying mechanisms of the trait.

Figure 1. Olive sea snake, Source: Wikimedia Commons

In a marine environment, we find many invertebrates (organisms without a backbone) that use non-visual light sensors. Octopuses, for example, use chromatophores to sense light and respond by changing color, or camouflaging. There are not many marine vertebrates (animals with a backbone), however, that have the ability to sense light in this way. In 1990, Zimmerman and Heatwole reported that the olive sea snake senses light with its skin. It is believed that this ability protects the vulnerable tail from predators during the snake’s resting period. Crowe-Riddel’s team wanted to know whether there were other sea snakes that shared this light sensing ability.


Where did Phototactic Tails Originate?

If other sea snakes could sense light with their tails, scientists would be able to figure out where the trait arose, evolutionarily. Crowe-Riddel et al. therefore began testing various sea snakes for this phototactic tail. The team collected 17 live snakes from 8 species and began testing for phototaxis. Equipped with colored flashlights, the scientists shined light on the paddle-like tails of the specimens, recording the responses.

The sea snakes’ reactions to the light varied by species. Some snakes responded to certain colors of light by retracting their tails, as if escaping a predator. Others exhibited no response to the light stimulation. Because Crowe-Riddel et al. noticed that only sea snakes of the Aipysurus genus had phototactic tails, they suggested that the trait evolved from a common ancestor of Aipysurus. Since only 10% of known sea snakes are from genus Aipysurus, this photosensitive tail may not be a very common trait among the serpents (Figure 2).


Figure 2. Aipysurus sea snake taxonomy, Source: Constance Sartor


Skin that “Sees”

Although we know that the tails of sea snakes respond to light, we do not understand how this occurs. Since snakes do not have eyes or visible photoreceptors, their light-sensing ability most likely lies within their dermis, or skin.

To take a closer look at the skin of sea snakes, Crowe-Riddel et al. collected skin tissue samples from the tails of the specimens that responded to light. Using a genetic method called transcriptomics, the team was able to take a “snapshot” of the genes that were expressed in the snakes’ tails during a response to light.

After genetic analysis, the team found two genes that were likely associated with the sea snakes’ phototactic tails. The first was xenopus-like melanopsin. The other was neuropsin, a gene found in tadpoles.


Injured Tails

Most organisms cannot sense light without eyes. So, what is the advantage of a light-sensing tail? Perhaps the trait protects them from predators that could injure their tails. Crowe-Riddel decided to take a look at 111 museum specimens to see if the species of snakes with tail injuries was correlated with the species of snakes who could not sense light. Essentially, they wanted to see if the phototaxis served as a defense mechanism from predators who injured their tails.

After comparing light sensing to tail injuries of the specimens, Crowe-Riddel et al. found no correlation between the two. Perhaps the light sensing tails had not evolved to keep the snakes free from harm.

With only 10% of sea snakes known to possess phototactic tails, there is still much to learn about this unique sense. Crowe-Riddel’s team unraveled some of the evolution and genetic basis of the trait, but we still do not understand what the Aipysurus sea snakes use their light sensing tails for. With this new information on the genes involved in phototaxis, we can begin to test other individuals to see if they too can sense light with their skin. Perhaps there are more marine vertebrates with “skin that sees”.



No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com