Green (Chelonia mydas) and leatherback (Dermochelys coriacea) sea turtles thrive the in the ocean. Although they have striking similarities in their genome, there's also a key difference in their genetics that may help both species survive.
Green And Leatherback Sea Turtles' Genomes Examined
Around 100 million years ago, a group of land-dwelling turtles took the ocean. They evolved and gave rise to sea turtles.
A team of 48 researchers ed by the University of Massachusetts Amherst, in collaboration with the Leibniz Institute for Zoo and Wildlife Research and the Vertebrate Genome Project, studied and created a detailed genetic map of two sea turtle species - green and leatherback.
The genome of a single species contains the set of genetic instructions used to construct that species, and sequencing the genome of any species is an arduous task. It is analogous to translating an entire library into a language that scientists can understand, and it has only become possible in the last few decades. Since 2013, a "draft" genome containing approximately 100,000 pieces of genetic information has been available for green sea turtles, Phys.org reported.
However, according to Blair Bentley, a postdoctoral researcher in environmental conservation at the University of Massachusetts Amherst and the study's lead author, the genetic information was not mapped out and she likened it to entering a library with all the 100,000 pages scattered on the floor a library and discovered 100,000 pages on the floor."
To catalogue the turtles' genomes accurately, the international team resorted to new technologies - the Nature's Method of the Year for 2022. This has made it possible to sequence the genomes of virtually every living species with greater precision than ever before.
They sequenced the genomes, organized them and annotated the genetic data. They were surprised when they discovered that after 60 million years, the leatherback and green turtles' genomes are remarkably similar.
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Green And Leatherback Sea Turtles Could Help Each Other Survive
According to the researchers, the genomes showed that green and leatherback sea turtles have similar, but not identical, genetics. And the difference is what makes each species unique, said Lisa Komoroske, professor of environmental conservation at the University of Massachusetts and one of the two senior authors of the paper.
In addition, the differences may hold the key to each species' long-term survival, given that populations of both green and leatherback turtles have experienced steep declines due to human activity.
It turns out that green turtles have evolved more genes dedicated to immunity, indicating that their immune system is better equipped to deal with new pathogens, as well as more olfactory receptors, suggesting that they have enhanced senses of smell. In addition, the leatherback genome demonstrates that their genetic diversity is low and that their population levels have historically been low.
Komoroske said it's a blessing and a curse because while leatherbacks are resilient, they lack the genetic diversity to adapt to their rapidly changing environment. These insights will assist conservation biologists in making more informed decisions regarding how to best protect these animals as they face the challenges of adapting to a rapidly changing planet.
In addition, the more time Bentley and Komoroske spent examining the turtles' genomes, the clearer it became that the majority of the genetic difference between the two species lies not in the macrochromosomes, but in what was once thought to be "genetic junk": microchromosomes, or small genetic bits that do not appear to exist in mammalian genomes but are typical of avian and reptilian genomes.
Camila Mazzoni, a researcher at the Leibniz Institute for Zoo and Wildlife Research and the study's other senior author, said the study helped them see the divergence between the green and leatherback sea turtles. She added that their work contributes to the expanding body of knowledge regarding the significance of microchromosomes in vertebrate evolution.
The study is published in Proceedings of the National Academy of Sciences.
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