Natural History

I should note now that I really hate the way science journalism tends to overplay certain discoveries, and this week I saw a great example of “clickbait” science journalism run amok on what really is an interesting finding.

As long time readers know, I have been a bit obsessed with the successful colonization of Burmese pythons in South Florida. As someone who has lived his life in the true temperate zone of Eastern North America, which is usually called “humid continental” by some climate classification schemes, I have lived where most of the reptilian fauna are quite diminutive. The species that I will call a “black rat snake,” because of bizarre taxonomy boondoggle in which it is next to impossible to find a consensus on what one should properly call it, is the largest species of snake. The biggest specimens of that species can approach six feet in length. It’s an impressive snake for something in this cooler temperate zone, but it’s not a monster among squamates.

Florida, though, by a geographical accident, is a place where the lower parts of the peninsula have a climate much like Southeast Asia, and this area is connected to the 48 contiguous states.  This accident of geography means that Florida’s middle class had access to all the wonderful exotic pets that were popular throughout the country in the decades following the Second World War. The problem is that green iguanas and spectacled caimans cannot survive the winter in New Jersey or Michigan, but they can survive in Florida.

Burmese pythons became established in large swathes of South Florida around the year 2000. Lots of studies have gone into figuring out what the establishment of this large non-native constrictor could mean for biodiversity in Florida. A 2012 study concluded that massive declines in mammal diversity coincided with the establishment of the python in Everglades National Park. And a long-going debate still exists about how far north Burmese pythons will spread, a debate that started when the US geological survey released its analysis of how much of the southern US was actually quite good python habitat.

An experiment in which some Burmese pythons were kept outside year-round in South Carolina found the snakes just didn’t do well. The ten snakes died during a January cold snap, but the possibility exists that a more free range population could have found shelter in an armadillo burrow.

So maybe they won’t make it up through the South, but there has always been a catch in those studies. We assume that the Burmese pythons will remain pure, but various species of python do hybridize.  Burmese and African rock pythons do hybridize, and there are reasons to be concerned that a population of African rock pythons has also become established in parts of South Florida.  Many articles have been posted about the potential issues that could result if those two species hybridize, but thus far, no one has documented a hybrid of the two species in the wild.

But a study released a few days ago revealed that there was evidence that some of the feral Burmese pythons have mitochondrial DNA that can be traced to another species of python, the Indian rock python. It was the first study to do any kind of DNA analysis of the feral Burmese python population, and what it found was 13 Florida Burmese pythons out of the 426 sampled had Indian rock python mitochondrial DNA. The study did look at some nuclear DNA characters, and pretty much found that these odd ones still were overwhelming Burmese python in ancestry.

That is a quite small number, and the researchers were careful to point out that the hybridization event probably happened long before the pythons became established as invasive species.

I should note now that for most of my life, we regarded the Burmese python as a subspecies of the Indian rock python. Currently, there is a move to have the Burmese python raised to a full species status, but in the classical definition, the Burmese python was the subspecies of Indian rock python that evolved to live in humid and wetter places in Southeast Asia, while the Indian rock python proper lived in the more arid regions of South Asia.

The authors of the study that found the 13 pythons with Indian rock python mitochondrial DNA are using the paradigm of the Burmese python as a distinct species, so it does look like you have full species hybrid, even if it is just a mitochondrial DNA introgression.

This introgression could have happened in Asia, because it is not exactly clear how much hybridization happens in the wild where the ranges of the two species overlap. To make things even more interesting, the US Fish and Wildlife Service listed the Indian rock python as an endangered species through the ESA, and it was common for keepers of Indian rock pythons to cross them with captive Burmese pythons to avoid regulations on keeping and selling that species.

But the popular press’s understanding of what was discovered has been, well, not that nuanced.

Headlines, like The Guardian‘s “Super-snake: hybrid pythons could pose new threat to Florida Everglades” and Hello SWFL’s “Burmese and Indian Pythons Breeding, Creating New Species,” lead one to think that this discovery is a sign that something really unusual has been discovered.

But the truth is that there is still a debate as to whether Burmese pythons represent a distinct species or not, and the authors have not found anything but some limited introgression of mitochondrial DNA from the Indian rock python in the feral Burmese population.

I should note that I do think that the Indian rock python and the Burmese python are distinct species, because the amount of genetic divergence between the two is pretty significant. However, they can hybridize and probably do so in the wild on a very limited basis. .

And it shouldn’t be a surprise that people would cross related species of exotic pets. Campbell’s and winter white dwarf hamsters have been crossed quite extensively, and hybrids with captive-reared felids are also quite well-known to the public.

Further, there are issues that we don’t know about the evolution of Burmese and Indian Rock pythons. We don’t know which genes each species has that allow them to be adapted to arid or wetter conditions. If we knew about these genetic differences, then we could test those hybrid snakes to see if they had inherited any other genes from the Indian rock python that would make it more easy for the snakes to colonize other areas.

We also don’t know how much Indian and Burmese pythons have been interbred in captivity or in the wild.  It very well could be that having some captive Burmese with this Indian rock python mitochondrial DNA is actually pretty representative of the pet population.

But we don’t have that information yet.  What we do have is the discovery of this mitochondrial DNA in the Burmese population, and that’s a pretty amazing discovery.

But it is not sign of a new hybrid species of super python. I will gladly eat my hat if more evidence is discovered, but I think we have a good case of the press blowing a really interesting discovery totally out of proportion.

Which does happen, especially during the silly season of late August and early September.