Newswise – “With their genomes decoded at high resolution, we have a much better window into the evolutionary history of this endangered species,” Mahmoud ShivjiAnd the Ph.D.professor at Nova Southeastern University (NSU) Halmos College of Arts and Sciences and manager Save Our Seas Foundation Shark Research Center And the Guy Harvey Research Institute at NSU.
It’s a stunning photo describing a milestone in shark conservation. shivji, Michael Stanhope, Ph.D., From Cornell University College of Veterinary Medicine Their collaborators got a glimpse into the history by sequencing to the chromosome level of the genome (the complete blueprint) of great hammerhead sharks and shortfin sharks. Their DNA timeline shows that their population has declined dramatically over the past 250,000 years. What the scientists also found is troubling: Great hammerhead sharks have low genetic diversity, which makes them less resilient in adapting to our rapidly changing world. The species also shows signs of inbreeding, a problem that can reduce the viability of its population.
However, the shortfin mako shark showed higher diversity and limited inbreeding, a glimmer of hope in the bleak conservation climate. Understanding change on such a large time scale can contextualize the current conservation status of these endangered animals. The findings can help point us towards more precise management strategies for sharks.
research paper, Genomes of the critically endangered Great Hammerhead and shortfin mako sharks reveal historical population declines and high levels of inbreeding in the Great Hammerhead.was published in iScience:
This research was led by Stanhope and Shivji, with collaborators from Cornell University, University of New South Wales, Temple University, Governors State University and the San Diego Wildlife Alliance.
The scientists compiled and compiled whole genome sequences of hammerhead and shortfin mako sharks and compared their genomes with available genome information for the whale shark, white shark, brown bamboo shark, and cloudy cat shark. Their methods read like the construction of intricate puzzles by scientific investigators: the sequential assembly of tiny fragments of different DNA sequences like a wonderful patchwork detailing the blueprint of life. Reaching the chromosome level represents the latest in high-quality whole-genome sequencing research—and a difficult feat to achieve for species like sharks that have massive genomes.
They found that great hammerhead sharks have a high probability of inheriting two copies of the same DNA sequence (homozygosity), including different genes, from their parents.
“To understand why this is undesirable, you can think about it in terms of disease,” Shivji said. You need two copies of a gene to express some recessive diseases: one from your mother and one from your father. If you are homozygous for a trait, you have inherited the same genetic sequence from both your mother and father, and the trait will be expressed.”
In the case of the great hammerhead sharks, showing what scientists call “high strings of homozygosity” in their genome meant that large sections of their genome were homozygous, increasing the chances of them expressing undesirable traits. By contrast, if one inherits two different sequential forms (alleles) of a gene from the mother and father (i.e., heterozygosity), the effects of the recessive allele can be masked by the dominant allele. If the undesirable trait is recessive in this heterozygous case, it will not be expressed. The shortfin mako sharks had lower groups of homozygosity relative to the great hammerheads, a genetic gain that may put them in a better position to adapt to change.
The application of advanced techniques comes amid grim reports of sharks and rays.
“Technical advances in the study of genomes mean that DNA sequencing approaches are now more robust and efficient,” said Stanhope. “We can apply these new techniques to gain insights about the organism, information that we hope can be leveraged to protect sharks and rays.”
While we don’t know the exact effects of inbreeding in sharks, the findings in wolves and leopards show that problematic traits can creep in over time. The result is often reduced survival of the species.
The image of large hammerhead sharks — overfished and traded for their fins — is alarming. But without these important genetic insights, we wouldn’t be able to adjust how we manage their currently vulnerable populations.
The researchers caution against exaggerating the results.
“Genetics has advanced such that chromosomal level genomes are a predictor of genomes of species reference quality, however, conservation research presents its own challenges to achieve this consistently and in accordance with the resolution expected in other fields,” said Shivji. Obtaining tissue samples from endangered marine vertebrates is a major hurdle. You can assemble the genome with a single tissue sample from a single shark, but the ideal circumstance would be to sequence genomes from multiple individuals from different parts of their surroundings, which is an ethically difficult and expensive endeavor.”
In fact, the researchers state that this is a limitation of their current study. Ethical constraints on working with endangered species mean that conservation geneticists must balance the latest developments in relation to the vulnerable populations they study. In addition to revealing the genetic diversity and fragile status of two endangered shark species, the researchers hope their findings will provide what they call reference-quality genomes, upon which foundational science can build in the future to improve what we know about sharks. Certainly, as new possibilities emerge, our insights into the blueprint for sharks will help strengthen the way we understand these ecologically important species and preserve their vulnerable populations.
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About the Save Our Seas Foundation: Founded in Geneva, Switzerland, in 2003, Save Our Seas (SOSF) is a charitable organization whose ultimate goal is to create a legacy to secure the health and sustainability of our oceans, and the communities that depend on them, for generations to come. Its support for research, conservation, and education projects around the world focuses on endangered sharks, rays, and skates. SOSF’s three permanent research and teaching centers advance its work in the Seychelles, South Africa, and the USA. Please visit https://saveourseas.com/sosf-shark-research-center for more information.
About Cornell University College of Veterinary Medicine: The College of Veterinary Medicine (CVM) at Cornell University is internationally recognized as a leader in animal medicine, public health, biomedical research, and veterinary medical education. Ranked as one of the top veterinary colleges in the country by US News & World Report consistently since 2000, the college will continue to excel in providing education through its cutting-edge case-based curriculum and advanced training that prepares veterinarians and scientists to serve the community in critical roles in Clinical and diagnostic veterinary medicine, public health, scientific research, and public policy. Please visit www.vet.cornell.edu for more information.