Rapid Communication, Geoinfor Geostat An Overview Vol: 5 Issue: 1
The Unique Patterns of Green Turtle Mitochondrial DNA Short Tandem Repeats as a Tool for Geographic Patterns Exposure
| Tikochinski Y* | |
| Marine Sciences School, Ruppin Academic Center, Michmoret, 40297, Israel | |
| Corresponding author : Yaron Tikochinski Senior Lecturer, Marine Sciences School, Ruppin Academic Center, Michmoret, 40297, Israel Tel: 972-50-755-4582 E-mail: yaront@ruppin.ac.il |
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| Received: May 18, 2016 Accepted: December 27, 2016 Published: January 04, 2017 | |
| Citation: Tikochinski Y (2017) The Unique Patterns of Green Turtle Mitochondrial DNA Short Tandem Repeats as a Tool for Geographic Patterns Exposure. Geoinfor Geostat: An Overview 5:1. doi: 10.4172/2327-4581.1000155 |
Abstract
Sea turtles have become the flagship of marine ecosystem conservation in the past three decades. Five out of the seven existing sea turtle species (green, hawksbill, loggerhead, leatherback and olive ridley) were declared endangered or even critically endangered by the International Union for Conservation of Nature (IUCN). In addition to being an animal that people tend to like and identify with, their cultural significance and tourism value, sea turtles are important components of the coastal and pelagic ecosystems in tropical and subtropical regions of the world. Sea turtles, when in high population levels, have substantial effect on the marine systems they inhabit as consumers, prey and competitors. They are hosts for parasites and pathogens, substrates for epibionts, nutrient transporters and modifiers of the landscape, especially by maintaining sea grass beds and coral reefs.
Keywords: Sea turtles; Endangered species; Satellite tracking; Mitochondrial DNA; Short tandem repeats; Stranded
Keywords |
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| Sea turtles; Endangered species; Satellite tracking; Mitochondrial DNA; Short tandem repeats; Stranded | |
Introduction |
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| Sea turtles have become the flagship of marine ecosystem conservation in the past three decades. Five out of the seven existing sea turtle species (green, hawksbill, loggerhead, leatherback and olive ridley) were declared endangered or even critically endangered by the International Union for Conservation of Nature (IUCN). In addition to being an animal that people tend to like and identify with, their cultural significance and tourism value, sea turtles are important components of the coastal and pelagic ecosystems in tropical and subtropical regions of the world. Sea turtles, when in high population levels, have substantial effect on the marine systems they inhabit as consumers, prey and competitors. They are hosts for parasites and pathogens, substrates for epibionts, nutrient transporters and modifiers of the landscape, especially by maintaining sea grass beds and coral reefs [1]. | |
| Sea turtles are philopatric animal, which travel hundreds to thousands of miles for feeding, mating and nesting. Satellite tracking became a popular and effective way to discover their migratory patterns. Natal homing has been shown in populations of green as well as other sea turtles in females that come ashore to nest, males and even juvenile turtles [2,3]. Since mating occurs just offshore from the nesting beach, nesting colonies can be separate reproductive units that do not blend demographically between each other. Lohmann et al. [4] suggested geomagnetic imprinting and magnetic navigation as a unifying hypothesis of long-distance natal homing in sea turtles. Monitoring population changes and new colonization events as a result of changes in Earth’s magnetic field will help solidifying this hypothesis. | |
| Like other philopatric species, sea turtles are in danger of decreased genetic variability. They compensate by traveling long distances, polyandric reproduction and sperm conservation [5]. The ability of sea turtles to sustain for more than a hundred million years is even more remarkable since they have temperature-dependent sex determination (TSD). How sea turtles have maintained a normal female to male ratio in temperature-changing nesting environments is beyond our understanding. | |
| The development of molecular biology techniques enabled the genetic analysis and better understanding of populations’ composition and dynamics. The importance of the nesting females in sea turtle global populations’ formation and structure has led to genetic typing using the maternally inherited mitochondrial DNA. Due to its recorded low mutation rates, the typing revealed only limited variation. In green turtles, less than 200 haplotypes have been found, about half of them in the Atlantic and practically a single Mediterranean haplotype shared by 95% of the population. Recently, Tikochinski et al. [6] have started using a new haplotyping method that was based on the 3’ region of the mtDNA control region. In green turtles, this region contains several AT short tandem repeat (STR) regions. All Atlantic and Mediterranean turtles have 4 STRs, each one with variable numbers of the tandem repeats. Therefore, turtles can be typed by a unique 4-number barcode. Forty different haplotypes were found in the Mediterranean population alone. The pacific green turtles exhibit even more variability as the number of STRs also varies and their barcode may contain four to seven different repeat numbers. | |
Discussion |
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| There is an increasing need of human assistance and intervention in sustaining and rescue of sea turtle populations around the world. Sea turtle awareness and education programs, rescue centers, breeding stocks and basic biological and ecological research have increased worldwide in recent years. One of the most intriguing research questions is the migratory patterns of sea turtle, probably the key factor of their ability to survive more than 100 million years of extreme environmental changes around the globe. Resolving population boundaries and migratory connectivity have been highlighted as critical research priorities for marine turtles globally [7]. Satellite tracking have been the most popular tool, allowing us to follow individual turtles in their quest for food and reproduction. Researchers got insights into the spatial ecology of sea turtles in several areas, demonstrating not only the high accuracy of natal homing, but also high levels of fidelity to foraging areas across multiple years, trans- Pacific migration and even juvenile hibernation [8]. Though satellite tracking is the most efficient way to follow individual turtles, it is a very limited research tool. It is fairly expensive and only a very small number of individuals are tracked and usually the tracking devices fall off the turtle after a few months. Genetic analysis of populations in many species has helped assessing not only the current situation of those populations, but also gave an insight into their history. The main condition for such an analysis would be polymorphic markers. The new green turtle mtDNA STR haplotyping method clearly shows enough polymorphism to define populations, and track their migration patterns as well as their roots. | |
| Shamblin et al. [9] have used the new haplotyping method to study the 3 major rookeries the Southwest Atlantic, on three Brazilian oceanic islands. Using the previous mtDNA haplotyping method, most of the females shared the CM-A8 haplotype, while the new haplotyping method revealed 21 different haplotypes. The three populations were significantly different despite their geographic proximity (150 km between two of the islands) and represent discrete populations with respect to female natal homing. The Mediterranean green turtle population was considered non-polymorphic using the previous haplotyping method since the most frequent haplotype, CM-13, was found in more than 95% of the turtles. Tikochinski et al. [10] have found 37 different haplotypes in 471 turtles sampled in 4 locations in the eastern basin of the Mediterranean. Despite having the same arrangement of 4 STRs, none of these haplotypes were shared with the Atlantic population. The 4 different Mediterranean locations (Turkey, North Cyprus, South Cyprus and Israel) had a significantly diverse composition of haplotypes. An important aspect of the Mediterranean research was the sample of Israeli shore stranded turtles. According to its haplotypes, this sample had a high resemblance to the Turkish population. The researchers have concluded that this high haplotype occurrence represent a major migration pattern of these turtles. Satellite tracking support the findings, showing that Turkish green turtles migrate along the shores of Syria and Israel on their way to the feeding grounds of North Africa, while most of the Cyprians make the shortcut way south, skipping the Israeli shores on their way to the same destinations. | |
| Another contribution to our understanding of population dynamics processes comes from mtDNA heteroplasmy. Unlike genomic DNA, where only one allele is inherited through the gametes to the zygote and to all the offspring’s cells, many mtDNA molecules are inherited by the mother’s egg and may contain more than one haplotype in different ratios. By looking at individual turtles (mothers in particular) related haplotypes can be detected and population changes can be tracked. | |
| Haplotyping of stranded green turtles is of extreme importance. Many of the sea turtles that reach the shores for reasons other than nesting are casualties of their encounter with human activities like fishing, boating and ecological accidents, and not because of their genetic weakness. Therefore, they can serve as a genetic sample of populations’ patterns without the need for constant satellite tracking. | |
Conclusion |
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| Green sea turtles are of major conservation concern as the result of a variety of past and ongoing processes; most of them are influenced by man. There is a great need for us to take profound and immediate actions to assist in the conservation of green turtle populations around the world. Stable populations are measured not only by their size but especially by their genetic variability. The new mtDNA STR haplotyping method is a good genetic marker for population identification. The ongoing effort of to recover declining populations, including the formation of breeding stocks, must be planned and supported by genetic analysis. We expect mtDNA STR haplotyping to expand to all green turtle habitats and reveal more populations’ characteristics and boundaries as well as understanding of the global picture of green turtle dynamics. | |
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