Shark genome secrets revealed
The great white is beautifully bad all the way to its DNA. Samantha Page reports.
The secret to the success of the great white shark (Carcharodon carcharias) may be in its DNA.
Researchers have revealed that the genome of the great white, the ancestors of which evolved 45 million years ago, is one-and-a-half times bigger than that of humans. It contains adaptive genetic changes that could be responsible for the species’ long history, its lifespan, and even its remarkable sense of smell.
With its length and high amount of repetition, the shark’s genome is particularly well adapted to staying healthy, the researchers say.
"Not only were there a surprisingly high number of genome stability genes that contained these adaptive changes, but there was also an enrichment of several of these genes, highlighting the importance of this genetic fine-tuning in the white shark," says study co-author Mahmood Shivji, of Nova Southeastern University (NSU) in Florida, US.
The details appear in the journal PNAS.
Shivji and colleagues found that the white shark genome has one of the highest proportions of long interspersed nuclear elements (LINEs) discovered so far in any vertebrate. LINEs are a type of transposons, also known as “jumping genes”, which are able to change where they are located and could help efficiently repair DNA, thus maintaining stability.
"Genome instability is a very important issue in many serious human diseases,” explains Shivji. “Now we find that nature has developed clever strategies to maintain the stability of genomes in these large-bodied, long-lived sharks."
The researchers suggest that it is “the molecular adaptive emphasis on genome stability” in the great white’s DNA that allows the apex predator to succeed.
"There’s still tons to be learned from these evolutionary marvels, including information that will potentially be useful to fight cancer and age-related diseases, and improve wound healing treatments in humans, as we uncover how these animals do it," Shivji adds.
Eating shark cartilage, such as found in their fins, has been touted as an alternative treatment for cancer, because it was once thought that sharks don’t get cancer. (As one researcher told the website LiveScience, "Even if they didn't get cancer, eating shark products won't cure cancer any more than me eating Michael Jordan would make me better at basketball".) Shark fin soup is still touted in some regions as having particular health benefits.
Consequently, shark hunting has significantly contributed to the decline of many species – including the great white, which is currently listed as vulnerable on the IUCN Red List.
“Decoding the white shark genome will also assist with the conservation of this and related sharks, many of which have rapidly declining populations due to overfishing," says co-author author Steven O'Brien, also at NSU.
“The genome data will be a great asset for understanding white shark population dynamics to better conserve this amazing species that has captured the imagination of so many.”
Other highlights from the genome sequencing include evidence that great white shark genes provide superior wound-healing abilities, and what could be the key to understanding their incredible sense of smell.
The researchers find a high number of vomeronasal type 2 (V2R) genes that may explain why – even with “very few olfactory receptor genes” – sharks are able to smell blood in the water.
“Molecular adaptation for wound healing was also evident, with positive selection in key genes involved in the wound-healing process,” write the researchers.
Co-author Michael Stanhope adds: "We found positive selection and gene content enrichments involving several genes tied to some of the most fundamental pathways in wound healing, including in a key blood clotting gene.
“These adaptations involving wound healing genes may underlie the vaunted ability of sharks to heal efficiently from even large wounds.”