Cottonmouth Moccasins: Adapting to the Beach and Beyond

Could some pit vipers evolve the capacity to invade the world’s oceans?


Last Thursday, while doing some fieldwork in Levy County, I came across this Florida cottonmouth as it was sunning itself after an early morning swim:

The warning behavior being demonstrated in the last photo is how the ‘cottonmouth’ earned its common name; trespassers and would be predators can be caught off-guard and intimidated when the snake curtly flashes the white interior of its mouth. The warning was certainly well received by me – I’ll take being startled over enduring a venomous bite any day of the week!

The Florida cottonmouth Agkistrodon piscivorus conanti is one of three subspecies of water moccasin native to the United States; the other two varieties include the Eastern cottonmouth (Agkistrodon piscivorus piscivorus) and the Western cottonmouth (Agkistrodon piscivorus leucostoma). These three subspecies of semi-aquatic pit vipers are renowned for their exceptional swimming ability and their associated preference for habitats in and around the freshwater lakes, streams and swamps of the Southeast U.S. They have adapted to be masters of wetlands; well, masters of freshwater wetlands anyway…

Even though their preferred range places them in proximity to the Atlantic Ocean and the Gulf of Mexico, the conquest of marine ecosystems by the cottonmouths has been - as it has with most aquatically inclined reptiles - blockaded. The physiological demands of maintaining adequate hydration in a high-saline environment has constrained the Agkistrodon genus to a landward life. But things could change.

Could cottonmouths evolve to live in the sea, like kraits or sea snakes?

As mentioned previously, the above images show a cottonmouth from Levy County, Florida. Levy County is located in West Central Florida and boasts an impressive coastline along the Gulf of Mexico. The coastline even has barrier islands. In fact, one such barrier island, called Seahorse Key, has its very own population of cottonmouths - cottonmouths that have found a niche in the intertidal zone.

Generally considered opportunistic carnivores, the bulk of the average cottonmouth’s diet is derived through consumption of its wetland neighbors - frogs and fish - however, they have been known to occasionally snack on insects, lizards, birds, rats, or even other moccasins. The cottonmouths of Seahorse Key have taken their tastes for fish from the freshwater to the saltwater; there they eat marine fish scavenged from the intertidal zone or haphazardly dropped from the Key’s bird rookeries. In addition to marine fish, the cottonmouths of Seahorse Key will even eat SEAWEED if it has the odor of fish on its leaves.

So, the cottonmouths of Seahorse Key have a proven ability to eat, digest and process marine food resources. They posses elongate lungs to provide buoyancy and streamlined bodies capable of eel-like swimming locomotion. As with other pit vipers they have venom to aid in capture of fast moving fish. And, in regards to reproduction, cottonmouths give birth to live young, so there’s no need to go to shore to lay eggs…

It seems that the only other major factor restricting the cottonmouths’ sea-ward invasion is a limited tolerance for high-salinity…

If only there was a selective pressure for improved salt water tolerance; for instance, a selective pressure something like being stuck on an island that is subject to rising sea levels. What are the chances of that happening?

The behavioral and physiological adaptations required in order for a land animal to successfully undertake a conquest of the sea are undoubtedly both varied and numerous; but, with sufficient selection pressure, ample time, and an incremental, step-wise process it can and has happened.

For example, consider all of the behavioral and physiological changes that must have occurred in order for a few Devonian lobe-finned fish to find their way to shore as fully terrestrial tetrapods! Or, viewing the scenario in reverse, imagine the adaptations that permitted Eocene land mammals to re-enter the sea as a line of cetaceans!

Subtle cumulative changes over time can alter a lineage’s dietary preferences, reproductive rituals and even bodily mechanics.

Lillywhite, H., Sheehy, C., & Zaidan, F. (2008). Pitviper Scavenging at the Intertidal Zone: An Evolutionary Scenario for Invasion of the Sea BioScience, 58 (10) DOI: 10.1641/B581008

An Imminent Creationist Feeding Frenzy, Courtesy of Nature

An article just published to Nature has turned the world of evolutionary biology topsy-turvy!

Or, so they’d like us to believe…

The paper’s authors Chris Venditti, Andrew Meade and Mark Pagel have devised a new model that shows that evolution is not driven by natural selection or through the accumulative effects of random genetic drift. Rather than incremental and gradual change, their study suggests that the vast bulk of speciation results from rare stochastic events. They call this new theory “punctuated equilibrium” – NO WAIT! They don't...

Actually, they don’t call it punctuated equilibrium, which is strange because that’s what it looks like to me… What’s even stranger is that neither Niles Eldredge nor Stephen Jay Gould’s names appear anywhere in the paper – including the references.

Through phylogenetic analysis of 101 different plant, animal and fungi groups the researchers established that - what I’m going to call - the punctuated equilibrium model is the most parsimonious fit for explaining the branch lengths of the studied taxa.

Although, this ‘rediscovery’ of what’s been known for about the last 30-years may not seem too earthshaking, I’m confident that (with Nature’s help of course) creationists around the world will be harvesting quotes from the article and its associated news release.


Check out these lines:

Quotes from Nature’s accompanying news release-

“New species might arise as a result of single rare events, rather than through the gradual accumulation of many small changes over time, according to a study of thousands of species and their evolutionary family trees.”

“This contradicts a widely accepted theory of how speciation occurs: that species are continually changing to keep pace with their environment, and that new species emerge as these changes accrue.”

“The team's findings might stir things up in the world of evolutionary biology.”It really goes against the grain because most of us have this Darwinian view of speciation," says Pagel. "What we're saying is that to think about natural selection as the cause of speciation is perhaps wrong."



Quotes from around the web-

"A new study published in Nature contradicts the commonly-held belief that most species evolve gradually through sexual selection in response to subtle changes in their environment." (SOURCE)

"This new theory is likely to be quite controversial, as it goes against the Darwinian view of evolution that most people are familiar with. "It really goes against the grain because most of us have this Darwinian view of speciation," says Pagel. "What we're saying is that to think about natural selection as the cause of speciation is perhaps wrong." (SOURCE)

'The surprise is that this model is not compatible with the idea that lots of small events combine to bring about speciation,' he adds. (SOURCE)

"Our research indicates that the idea that new species occur by gradually becoming more and more adapted to their particular niches, is not true. In fact, we have found that new species appear due to rare random events that seem to simply just happen." Pagel (SOURCE)



Quotes from the study -

“The Red Queen describes a view of nature in which species continually evolve but do not become better adapted. It is one of the more distinctive metaphors of evolutionary biology, but no test of its claim that speciation occurs at a constant rate has ever been made against competing models that can predict virtually identical outcomes, nor has any mechanism been proposed that could cause the constant-rate phenomenon.”

“This model predicts a constant rate of speciation, and provides a new interpretation of the Red Queen: the metaphor of species losing a race against a deteriorating environment is replaced by a view linking speciation to rare stochastic events…”

“Speciation is freed from the gradual tug of natural selection, there need not be an ‘arms race’ between the species and its environment, nor even any biotic effects.”

“If the original Red Queen model had a ‘whiff’ of a species running out of breath from the accumulation of many detrimental biotic effects, and then being ‘knocked off’ by the next event, the interpretation we propose is different. Species do not so much ‘run in place’ as simply wait for the next sufficient cause of speciation to occur.”

“This means that researchers seeking to develop explanatory theories of speciation should focus their attention on the size of the catalogue of sufficient causes (speciation factors)
shared by a group of organisms, rather than on special driving forces or how these forces might combine.”





Venditti, C., Meade, A., & Pagel, M. (2009). Phylogenies reveal new interpretation of speciation and the Red Queen Nature DOI: 10.1038/nature08630