By Cindy Spence
As a child in the Rift Valley of Kenya, surrounded by creatures that are bedtime stories or stuffed animals for most children, Gavin Naylor had questions.
Much like the Elephant’s Child in Rudyard Kipling’s “Just So Stories,” Naylor had an insatiable curiosity about the lions and wildebeests, zebras and giraffes around him.
For the Elephant’s Child, curiosity leads to a question too many when he asks a crocodile where he gets his dinner. The crocodile bites the baby elephant on the nose, and in the ensuing tug of war, voilà, the elephant gets his trunk. For Naylor, curiosity has led to three decades of research in evolutionary biology. The Elephant’s Child is spanked for his curiosity, and Naylor says he has run across a professor or two annoyed by his curiosity and need for answers to questions about life’s diversity.
In Rudyard Kipling's "Just So Stories," a crocodile bites the Elephant's Child on the nose to pull him into the water, but a Bi-Coloured-Python-Rock-Snake rushes to his aid. In the tug of war, the baby elephant's nose stretches into a trunk. Illustration courtesy of the University of Florida's Baldwin Library of Historical Children's Literature.
“We know mutations are correlated with variation, but we don’t know the nuts and bolts,” says Naylor, the director of the University of Florida Program for Shark Research. “This has bothered me since I was a teenager. I would ask ‘How,’ and teachers would tell me ‘There are millions of mutations, Gavin, evolution just happens.’
“We need more than Just So Stories and the notion that somehow you pull a rabbit out of a hat and something happens – the elephant gets its trunk,” Naylor says. “That is not very satisfying.
“I want the theory that makes evolution inevitable,” he says, “not unlikely.”
Primed by biodiversity for a life in science, Naylor got a Ph.D. in zoology and began his own research in molecular genetics and phylogenetics.
But as a scientist, it wasn’t the animals of the East African bush that caught his attention. For the fossil record he needed to tell an evolutionary story, he had to turn to a watery world: How did the hammerhead shark get its hammer? The sawfish its serrated snout? The ray its water wings?
Naylor arrived at UF’s Florida Museum of Natural History in 2017 to direct the Florida Program for Shark Research and the International Shark Attack File, built up and made famous by Director Emeritus George Burgess.
A year after his arrival he still has a kid-in-the-candy-store demeanor about the resources available to him at UF. He has connected with computer scientists, statisticians, biochemists and others whose specialties he can tap into to develop his own work. In his previous positions, he found collaborators off campus to help with facets of his research. Those collaborations were fruitful, but time-consuming.
Gavin Naylor directs the Florida Program for Shark Research and the International Shark Attack File, both housed in UF's Florida Museum of Natural History. Photo by Kristen Grace.
“Here, I can just go knock on somebody’s door and say ‘Hey, I’ve got this problem.’ Usually, they’re like, ‘Yeah, that’s easy.’ So, coming to a big research university, I can find people with unimaginable skills, and I can find them just down the corridor.”
By their nature, evolutionary questions are multidisciplinary, and he says that means he constantly bumps up against areas where, without collaborators, he would lack the expertise to forge ahead. He says he is fortunate that his colleagues at UF seem to be interested in the same evolutionary and biodiversity questions that drive him.
“I’m cursed by being interested in problems that I don’t have the skills to solve,” Naylor says. “But in this environment, there are people who will help.”
He understands the public’s fascination with the charismatic animals he studies but would like to see that thirst for knowledge last long after Discovery Channel’s hugely popular Shark Week, which runs every summer and sprinkles science in with sensational footage. He admits, almost reluctantly, that he has never seen an episode of Shark Week – “maybe I shouldn’t say that” – but a week of sharks would not satisfy his curiosity anyway.
Since his arrival, he has become acquainted with the huge popularity of UF’s shark attack file and is now the go-to source for help in identifying the shark in a shark-human interaction. In 2018, as of Oct. 1, there were 40 attacks listed in the shark attack file database, and Naylor says documenting the attacks involves about 200 variables, from the temperature of the water to the spacing of the teeth in a wound.
One encounter yielded an opportunity for more than an educated guess. After an attack this summer off Fire Island, New York, Naylor was asked to help identify the species. The shark left behind a rare clue – a tooth fragment – so he was glad to help. Postdocs in his lab sequenced the mitochondrial genome and identified the attacker as a sand tiger shark, likely following a school of fish, and not the great white shark the community had feared. The ID yielded a short item in the journal Nature.
“I don’t know why it is better to be eaten by one species than another,” Naylor says. “But it seemed to calm them down.”
Naylor says the shark attack files are an important avenue for outreach, extending even to his work in evolutionary biology.
“If I can lure people in with a shark attack files carrot and they leave out the exit door being interested in evolutionary biology,” Naylor says, “that’s great.”
Naylor stumbled into the world of chondrichthyans – sharks, skates and rays in graduate school. To examine the evolutionary questions he had in mind, he knew he needed a living creature with a long fossil record. Mammals are well studied, Kipling’s explanations for how the leopard got its spots or the elephant its trunk or the camel its hump notwithstanding. Naylor’s adviser suggested snails, but snails were taken; someone already deep into snail evolution.
“So he said, ‘What about sharks? They have a huge fossil record and we don’t know how the hell to interpret it. See if anyone is doing sharks,’” Naylor recalls.
“Nobody was doing sharks,” Naylor says, “so that’s what I did.”
About 425 million years ago, sharks, skates and rays took a detour on the tree of life, branching off on their own. The branch they left behind gave rise to bony fishes, amphibians, snakes, birds and mammals, 64,000 or more species. The chondrichthyan branch, however, evolved independently and gave rise to just 1,200 species.
But the chondrichthyan branch has been resilient.
About 250 million years ago, more than half the planet’s living creatures died out along with 90 to 96 percent of the planet’s marine species in the Permian extinction. About 60 million years ago, the Cretaceous extinction wiped out non-avian dinosaurs. Sharks, skates and rays survived both, and that makes Naylor think they have a few tricks up their sleeve.
One of those tricks may be epigenetic regulation, turning genes on or off quickly, so they can adapt without a need for evolution.
“When they go to cold temperatures, a suite of genes switches on. They don’t have to wait until the genome responds,” Naylor says. “If they can put on an overcoat when it gets cold, and their bikini when it gets warm, then they’re equipped to deal with a changing environment.”
Diversity is a strong suit, too.
While most people know the great white shark, the star of “Jaws,” no one has made a movie about the lantern shark, which can glow in the dark and use camouflage. By controlling how much light it emits, it creates a cloaking device that makes it invisible to anything swimming above it or below it.
“The only time you can really see them is from the side, and if you see them from the side, it’s probably too late,” Naylor says.
Others, like the Greenland shark, are estimated to live 400 years.
“There are probably Greenland sharks swimming around that were alive at the time of George Washington,” Naylor says.
Sharks’ reproductive methods are as diverse as the rest of vertebrates combined, Naylor says. Some lay eggs that hatch outside the body, others lay eggs that hatch inside the body. Some have a placental connection to the mother. The sand tiger shark nourishes its developing young by letting the siblings fight it out in utero. As eggs hatch and develop, the tiny sharks swim around the uterus attacking each other. It’s a winner-take-all strategy, with each of the sand tiger’s uteri producing one offspring.