Invasive pythons surviving cold in Florida of all places are an unlikely source of hope for surviving climate change.
Burmese pythons are indigenous to southeast Asia. Though the swamps of Florida are ecologically distinct from southeast Asia, whether because of irresponsible ophidiophiles or because of their penchant for escaping, Burmese pythons now throng the swamps of Florida too.
What caught the attention of biologists at the University of Texas is how at least some of these alien reptiles survived uncharacteristically icy weather in Florida in 2010, they report in Molecular Ecology.
Genetic analysis elucidated that they had undergone rapid evolution as a result of unique climatic and ecological conditions present in Florida.
What happened is that the environmental stressor of extreme cold did cause a large percentage of the pythons in Florida to die. However, a small proportion of individuals that possessed versions of genes, called alleles, that allowed for better tolerance of cold temperatures survived the freeze.
There was, in the jargon, a high non-random chance of survival for snakes with the relevant alleles under the acute selection pressure of sudden cold, UoT Prof. Todd Castoe explains.
Following this freeze event, the python population was much smaller, but now largely comprised of the individuals possessing alle les allowing for better cold tolerance. As these individuals reproduced and the population size grew, these alleles were passed on to subsequent generations, resulting in massive and rapid changes in the genetic makeup of the python population in a relatively short period of time. This is a stunning example of rapid evolution.
And what was the crucial adaptation? That they never shut their faces and spent their waking time eating. The surviving snakes were, as they say in Yiddish, fressers.
“Our data suggests the snakes that survived the freeze events tended to be snakes that possess genetic variants that keep their physiology constantly unregulated,” says the professor, adding that the survivors included adult snakes, not just babies.
Longer-term selection for a very different physiology in Florida, together with the acute selection pressure of the cold snap, imposed strong selection on this existing variation among the snakes, Castoe explains.
When oranges freeze
In January 2010, Florida experienced a severe cold snap, freezing oranges on the trees, fish in their ponds, and so on. With crop losses of around 4 percent, the chill wasn’t a patch on the 1985 blast that decimated 90 percent of the Florida citrus crop. But this was not weather that cold-blooded pythons were expected to survive. Indeed, somewhere between half and most died. So how did any survive?
The UoT researchers analyzed genetic data of dozens of pythons caught in Florida before and after the freeze event and identified parts of the genome that may have permitted some individuals to survive the freeze.
The researchers assumed that the surviving snakes possessed specific genetic variants allowing more resistance to cold. What they found was something very different.
“We kept seeing evidence of adaptation in genes related to cell division, organ growth and tissue development, which admittedly puzzled us at first,” explains Daren Card, who did his PhD on these snakes.
In the python, tissue development corresponds with its feeding cycles. And yes, observation showed that, like tourists at a buffet, the Burmese pythons in Florida are constantly feeding.
"Florida pythons appear to have adapted to regulating their digestive physiology to more efficiently eat prey constantly," the team wrote, and the constant upregulation of digestive physiology and metabolism may have allowed some snakes to survive the otherwise deadly freeze.
The Floridan python and you
Leaving aside the charming aspect of giant snakes eating their way to kingdom come, there is another upside to this story.
There is concern that species, plant and animal alike, will fail to adapt fast enough to cope with the pace of anthropogenic climate change. Put otherwise, the climate is changing faster than most life-forms can adapt to cope with it – and not only because of habitat loss. But maybe there’s hope yet.
“This particular example suggests that perhaps in some cases [like the python], some populations might be able to adapt quite quickly to at least some challenges posed by a new or changing environment,” Castoe agrees.
Which begs the question of whether snakes are known for adapting faster than other animals of comparable size or lifespan.
“Snakes don’t appear to have overly extreme mutation rates. However, we do see numerous examples of extremely rapid adaptation at the genetic level,” Castoe tells Haaretz. “This means that while the rate of mutation does not seem different, the relative strength of selection on snakes (for whatever reason) has been extremely strong in several cases over evolutionary time, and they have responded with extreme bouts of adaptation. While this is a general phenomenon that is possible in any organism, it does seem that snakes have a large number of examples where they have responded to strong selection with extreme adaptation.”
Asked for examples of extreme adaptation in the snake set, Castoe offers the re-evolution of bright-light vision early in snake history, and the evolution of extremely toxic venom systems in multiple lineages.
The downside of this story is concern for other animal life in the area.
“These snakes have already been shown to have major negative impacts on endemic mammalian and bird populations in South Florida, including Everglades National Park,” says Card. “Our data was suggesting that, through rapid adaptation, they are only ‘getting better’ at being an effective invasive predator.”