Florida’s Dragon Problem
Huge monitor lizards have invaded the state, and the rest of the U.S. is one unlucky boatload away.
by
Ed Yong
The speckled body of the Nile monitor lizard
can reach up to 2 meters in length. At one end is a powerful tail that
propels the animal through water and whips attackers with surprising
force. At the other is a sinuous head that will devour rodents, birds,
fish, crocodile eggs, and pretty much anything else within range of its
fearsome, recurved teeth. The monitor isn’t fussy. It’s a formidable
animal, and the largest lizard in Africa.
It’s also the largest lizard in Florida.
No one knows exactly when the monitor arrived in Florida, but it was first spotted in 1990.
It was probably introduced as part of the pet trade. It then either
escaped or was released by people who realized much too late that maybe a
huge, intelligent, active, predatory lizard doesn’t make a great pet.
Once
the monitors were free, events unfolded predictably. These lizards
wander over large areas, grow quickly, breed at an early age, and lay up
to 60 eggs in a single clutch—so their numbers quickly grew. They love
water, and were drawn to the same waterfront properties that attract
Florida home-owners. There are now three permanent breeding populations
in the state, the largest of which includes more than 1,000 individuals.
To predict what the monitor lizard will do in the future,
Stephanie Dowell from Fordham University decided to look at how it behaves in its native home. Together with her supervisor,
self-confessed museum geek Evon Hekkala, Dowell sequenced the DNA of
dozens of Nile monitors from all over Africa—both freshly caught individuals and those preserved in museum collections.
She found several surprises.
A supposedly distinct species called the ornate monitor turned out to
be the Nile monitor under a different name. So two lizards became one.
But the canonical “Nile monitor” actually comprises
three
genetically distinct lineages from the west, north, and south of Africa.
The western one should count as a distinct species: It separated from
the others 7.7 million years ago and its genome differs by up to 9
percent, a far greater gulf than exists between us and chimpanzees. So
one lizard became two again.
West Africa Nile monitor
The West Africa Nile monitor (Varanus stellatus) is a cryptic species of Polydaedalus monitor lizard from West Africa
The newly minted
West African Nile monitor
isn’t just genetically distinct, but also genetically narrow. Based on
the similarities between different individuals, Dowell estimated that
the lizard’s population crashed between 1,000 and 1,800 years ago. That
coincides with the rapid expansion of the ancient Malian city of
Djenné-Djenno—a
major hub for trans-Saharan trade.
Archaeological evidence confirmed
that people were indeed catching and trading monitor lizards, probably
for food. That’s why the lizard’s numbers plummeted.
Such
exploitation continues today. Every year, around 500,000 Nile monitor
skins are shipped around the world to be made into shoes, bags, and
accessories. Another 10,000 live individuals are exported for the pet
trade. And some of them have made their way to Florida.
When Dowell analyzed the DNA of 25 Florida monitors, caught by colleague
Todd Campbell,
she found that all of them belong to the West African species. All are
descendants of lizards that had been captured somewhere between Liberia
and Cameroon and shipped across the Atlantic. This happened on at least
three separate occasions, giving rise to populations now living in Cape
Coral, West Palm Beach, and Homestead.
Knowing where the lizards came from, Dowell could predict where they’ll go.
Their West African home has a remarkably similar climate to southern
Florida, so assuming that the invasive lizards are adapted to such
environments, they’ll likely stay put. “I don’t think that they’re going
to spread that far into the north,” says Dowell. “If we really want to
target the surveying and eradication efforts, we should look further
south.”
But the other species of Nile monitor is another
matter. It can survive through the cold and frosty winters of southern
Africa by hibernating. If it got into the U.S., Dowell’s simulations
predict that it could make itself comfortable across the eastern and
western seaboards, especially if the climate continues to warm.
“If,
for example, we decided to crack down on the trade in West Africa, and
the exploitation shifted to south Africa, that lineage could spread very
quickly,” says Hekkala. “Its invasiveness is much greater. It is so
pre-adapted to the North American climate that it could spread almost to
Chicago, even without climate change.”
This scenario shows how
important it is to stop the lizards from entering the country in the
first place. “Once we figure out that a species is here, and there are
multiple reports, it’s too late. We need to do a better job screening,”
says Steve Johnson from the University of Florida. “We don’t do a good
enough job as a state to regulate what’s coming in.”
He’s not wrong. Florida is the world’s number one hub for invasive reptiles and amphibians.
It has several ports, a large population of potential pet-owners, and a
warm, humid climate. Almost 140 alien species have made their home
there, including cane toads, panther chameleons, Burmese pythons, giant
tegu lizards, green anacondas, and tentacled snakes.
“Every bit of
biological and ecological info we can get about a species in its native
range takes us one step closer to coming up with a management strategy
to control it in its introduced range,” says Johnson. “I don’t think
we’ll ever eradicate Nile monitors from Florida but hopefully we can
contain them.” And in the meantime, if you spot one, the Florida Fish and Wildlife Commission wants you to tell them about it on IveGot1.org (yes, really) or their IveGot1 app. And for pity’s sake, don’t try to capture one.
image:
Source:
http://www.theatlantic.com/science/archive/2016/04/the-past-and-future-of-floridas-dragon-problem/478905/
