Researchers analyze the DNA and hormonal profile of the green turtles to understand their physiology, development and reproduction and ensure their survival
The green sea turtle population in the Mediterranean is endangered and protected by law. This is mainly because in the 30s, during the days of the British Mandate, about 2,000 of the turtles were hunted every year off the coast of Israel for the purpose of trading in their meat and armor. Today the population numbers about 450 laying females in the entire Mediterranean. On the shores of Israel, which used to be a spawning site for thousands of females, today only about ten females lay eggs every year.
Green sea turtles play a key role in maintaining ecological balance in the marine and coastal habitat. They are vegetarians and feed mainly on algae and sea grass and promote their health through grazing. Also, their eggs are used as nutrients for the coastal habitat and its vegetation.
The National Center for the Rescue of Sea Turtles of the Nature and Parks Authority deals with the rehabilitation of damaged turtles and protects their nests on the beach by moving them to fenced and protected breeding farms located in coastal reserves. In addition, he conducts research for their preservation and maintains their breeding nucleus (which includes two huge pools of water and a beach on which the females can lay eggs); In this nucleus, the first of its kind in the world, in 2002, green turtles that hatched from their eggs began to be collected in XNUMX. These turtles contribute a lot to the restoration of the population of the species: when they reach adulthood, they breed among themselves and lay eggs. The eggs are transported to hatcheries, and when the offspring hatch, they are released into the sea. Turtles are released
Turtles that reach the sea safely face many dangers, including the risk of predation and the lack of beaches that are suitable for nesting, laying and the proper development of the eggs (due to extensive human activity such as construction). In addition, they are accidentally caught as by-products and become entangled in plastic waste that resembles their food, as well as fishing hooks and nets. In addition, they are threatened by a direct hit by a vessel (since they must come up to the surface and breathe). Sonic explosions in the sea due to gas and oil exploration, infrastructure development and military activity can also cause damage to the internal organs.
Prof. Yaron Tikochinsky (geneticist) and Dr. Yossi Eisen (biologist and marine endocrinologist) from the Faculty of Marine Sciences at the Rupin Academic Center are researching the genetics and reproduction of the green sea turtle in order to increase its population, contribute to its development and conservation, and support the breeding nucleus of the National Center for the Rescue sea turtles Says Prof. Tikochinski: "I research the genetics of marine populations, especially those that are in danger of extinction. When I started the research on the green sea turtle, about 15 years ago, it was estimated that there were only ten females laying eggs on the shores of Israel. A population cannot exist without genetic variation, and this is where my role comes into play."
In the past, Prof. Tikochinski and researchers from Germany sequenced the entire genome of the green turtle. As part of his ongoing work, Prof. Tykochinski examines his DNA, which is extracted from blood samples taken from the females that come up to lay eggs on the beach, from dead embryos in the nests and live offspring in the reproductive nucleus. According to him: "The DNA tells us about the type of turtles found in the Mediterranean Sea, about the identity of the parents of each turtle (the females give birth to offspring with more than one male, which improves the genetic diversity), and about the degree of closeness between the individuals (of course we are not interested in brothers and sons cousins will mate). We use this information in the breeding kernel. This nucleus started from two families and today it has additional details, quite different from each other genetically. And that is the goal, to create a wide genetic diversity in it." Turtles are released
Dr. Eisen is responsible for the field of nuclear reproduction. As part of his work, he developed bioinformatic tools for measuring the level of hormones related to reproduction in blood samples taken from the turtles regularly, such as LH (which stimulates the ovaries to produce the female hormone progesterone and the testes to produce the male sex hormone testosterone, and also participates in the maturation of eggs and sperm cells); FSH (whose main role is to cause the development of follicles and eggs in the ovaries), progesterone and testosterone. According to him: "We created an annual hormonal profile for the turtles in the core and this way we can identify hormonal patterns in preparation for laying. That means today, according to the level of hormones, we can predict when the females in the nucleus are going to lay".
One of the goals of the researchers' latest study, which won a grant from the National Science Foundation, was to decipher which of the turtles is going to be male and which is female, since until they reach sexual maturity it is not possible to tell by looking. Thanks to the tools developed by Dr. Eisen, the researchers discovered that the ratio between the hormones LH and FSH may indicate whether the turtles are male or female already at the beginning of their lives, based on blood samples taken from 24 turtles from the reproductive nucleus. Now, using additional bioinformatic tools that he is developing, he is trying to identify the structure of hormones.
The researchers took 1,000 blood samples from 1,000 turtles, some from the reproductive nucleus and some from nests scattered on the coasts of Israel (for example Bezikim, Palmachim, Givat Olga and Batza). Analyzing the approximately 2.6 billion letters and bases that make up the DNA in the samples, using statistical and bioinformatic tools developed by Prof. Tikochinsky, comparing the samples and refining the information, will be able to contribute to the identification of the genetic code required to receive male or female and to characterize the genetic variation between them.
"In order to increase the number of turtles and enrich their genetic diversity in the breeding nucleus, one must first determine their sex, understand which females will be able to lay eggs and which are the males. Therefore, at this stage of the research, we regularly sample their blood, decipher differences in DNA that can contribute to understanding physiology, development and reproduction, monitor hormonal changes, and analyze the genetic background and hormones related to reproduction. In the future, we hope that we will be able to contribute in this way to adding individuals to the breeding nucleus (for example, to inject a genetic and hormonal composition that will contribute to their reproduction)", Prof. Tykochinski concludes.
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