Those of you who love Neuroscience and Neuroscience only, I must warn you: This is not a Neuroscience-related article! This article is about turtles. And as much as I would like to get an insight into these creatures’ minds, knowing how invasive the current techniques are and that there is not yet a vast literature on this subject, the today’s article will not consider the brain.
Why turtles then? Are they interesting enough for us to mind them? The answer is YES! I am an animal lover, and I believe that all beings of any sort are fascinating and that they deserve to live a happy life. That is not how I became so amazed by the turtles, though.
This summer I volunteered in Kefalonia (one of the Ionian Sea’s Greek islands) for two weeks to work in the only sea turtle conservation there. I spent a wonderful time and I came back with lots of memories and things to share. But the most important thing I gained through my experience there was what I have learnt about sea turtles. The organization that runs the conservation volunteering projects is called Wildlife Sense. You can have a look and if you are turtle lovers and enjoy adventures, you should definitely sign up for volunteering work, which I can assure you, is very rewarding.
As volunteers in the egg-laying season, our task was to take many types of measurements, observe and analyse turtle tracks, the sand, the temperature on the beach, the amount of light and estimate light pollution, find turtle nests, relocate (if necessary) these eggs, tag and microchip the adult turtles etc. It might not sound so exciting, but I felt like both a researcher and an animal protector and I acquired a lot of skills needed for future experiences of this sort and much more.
Know your sea turtle
It is important to know the difference between a turtle and a turtoise. The latter are the ones who walk on the ground and can retract all four limbs and head. Turtles have fins (or flippers) and these are not completely retractable. There are 7 species of sea turtles: leatherbacks (the biggest), loggerheads, greens, kemp’s ridley, olive ridley, howkbill and flatback. On Kefalonia one can only find loggerheads (Caretta caretta) and some say, greens (but we’ve never seen those).
A few anatomy things
Loggerheads are big turtles, with 80 to 110 cm in carapace length and contrary to what some of you might think, they are very strong and can be very aggressive: they can bite and scratch with their claws (one of the volunteers in my team got her trousers ripped off by a turtle). Marine turtles, just like tortoises, terrapins and other reptiles, are covered in scutes and scales. The scales are on the carapace, while the scutes cover the skin and the ones on the head profile are like human fingerprints – they are unique to each turtle. There are some differences between male and female turtles, including size (females tend to be a bit bigger), but to be sure about the gender, look at their tails: males have a tail coming out from underneath the carapace. Nevertheless, some males hide their tails from time to time, giving researchers a hard time about gender identification.
When a turtle needs to lay her eggs, some very interesting things happen: she usually returns to the same beach she was born on, even though they travel long distances and get in the ocean throughout their lifetime. For that, she uses something called geomagnetism which involves Jacobson’s organ for olfaction and the geomagnetic orientation trigeminal system. When she comes out of the sea, a turtle pays a lot of attention to the environment: she wants to make sure there are no predators and that the sand is good enough, so she is very focused on anything that is moving, as well as noises and lights.
Loggerheads alternate their tracks when they move on sand and the tracks are a good indicator for the directions to and from the sea. When they start digging the nest, marine turtles use their front flippers to remove the sand around them, while their bodies form a distinctive (and very relevant for researchers) shape in the sand – a body pit (or an extended body pit). They lay around 100-120 eggs, but due to external factors only few of them (1 in 1000) can reach maturity and lay eggs. Temperature determines the embryo’s sex – eggs kept warmer become females – but it can also affect the embryo’s survival. Therefore, the depth of the whole is very important (16-34 cm from the top five eggs), because it significantly influences the temperature of the egg chamber.
It is said that turtles cry after they lay their eggs. There is a grain of truth here, the turtle does indeed drop a few tears, but this is not because she is sad to leave her babies out in the nowhere (even though, that does not mean she has no feelings of this sort, we do not yet know). It all comes down to maintaining the salt balance and those tears actually help the turtles excrete the excess of salt in their eyes.
After she lays her eggs, the turtle returns to the sea and she might never see her babies again. The hatchlings come out of the eggs after one month and a half-two months and orient themselves towards the sea using light (the sea is the brightest thing on the beach if there’s moon light to reflect in it). They show a tropotactic behaviour (they compare intensities in both eyes and move accordingly). Light pollution from artificial lights on the beach is fatal for many hatchlings (amongst other factors like predators), because the poor babies often get confused and don’t know where to go. Sea turtles do not perceive red light, so volunteers were advised to use red lights when looking for turtles at night, in order not to disturb the egg-laying process. The wavelength of light perceived by marine turtles usually ranges between 360 and 600 nm; green turtles see yellow light and do not mind it, while loggerheads are xanthophobic (averse to yellow-orange light). Once in the sea, baby turtles can encounter many other dangers, but if they survive, they swim to other seas and oceans and they can live up to 60 years.
As for genetics…
It was discovered that male turtles do not have an SRY gene on their Y chromosome, although the presence of another gene, the SOX9 gene, influences the formation of testies. Steroidogenic genes are also thought to be involved in sex determination, along with the DAX1 nuclear receptor protein (encoded by an ‘antitestis’ gene) and the anti-müllerian hormone (for testis differentiation).
Marine turtles, and turtles in general, are still a mystery for biologists, but what has been discovered so far about them did nothing but prove how marvellous these animals are. If what you have read in this article aroused your curiosity, I can only hope you will allow the turtles to amaze you in the future as well.
Below, I have inserted a link to a very interesting paper that raises awareness about relocating eggs and explains it from a different point of view.
For further information:
Lutz et al., 2003. The biology of Sea Turtle, Vol. 2. CRC Press