Sharks are often thought of in terms of superlatives, and perhaps no species has racked up as many “mosts” as the Great White Shark, Carcharodon carcharias. This is the star of “Jaws” after all, and probably the species most people who aren’t devoted to being familiar with fish visualize when they hear the word “shark.” Thanks to new research by Marra and friends (2019), we’re becoming familiar with the White Shark on the most basic level of all: the genetic level.
Not every species has had its entire genome decoded, and the White Shark is one of only a handful shark species to get this level of attention. The Whale Shark and the Elephant Shark (actually a species of chimera) have also had their genetic codes mapped, providing a couple of fairly closely-related species for comparison. By comparing the full genome of the White Shark with these other shark species and other vertebrates, the authors were able to identify specific mutations that have stood the tests of time and natural selection. Many of these genes are associated with the very traits that have made sharks such incredible survivors for going on 450 million years.
Photo credit: study author Pascal Geraghty, New South Wales Department of Primary Industry
Last week, a team of 10 Australian scientists announced that they had found the world’s first “shark hybrids”, offspring of individuals from two different shark species which had interbred. During a routine survey of Australian marine life, 57 sharks were found that physically resembled one species of shark, but had genetic markers inconsistent with that species. Subsequent genetic investigation revealed that these 57 animals were hybrids between common blacktip sharks (Carcharhinus limbatus) and Australian blacktip sharks (C. tilstoni).
Some of these hybrids were “F1″, meaning that one parents was a common blacktip and one was an Australian blacktip. Others were “B+”(backcrossed), which means that one parent was a common blacktip/Australian blacktip hybrid, and the other was a “purebreed” of one of those two species. According to the study’s lead author, Dr. Jess Morgan of the University of Queensland, “our genetic marker tells us that these hybrids are ‘at least’ F1, and that these animals are reproductively viable and can produce an F2…the hybrids may be generations past F2 but the existing genetic markers can’t distinguish how many generations past the second cross have occurred.”