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

Climate Change and the Velocity of the Shifting Niche

A little more than a month ago, I posted a three-part series on the topic of ecological niches with specific reference to their ability to track the ever shifting variables of climate. In large part drawn from research out of UC Berkeley and the ongoing Grinnell Project, those posts focused on the weather patterns associated with the mountainous terrain of Yosemite National Park. Today, Nature published a letter in which other California based scientists have extrapolated the shifting niche model in order to estimate the anticipated ‘velocity’ of temperature change across different biomes.

The ability of an organism to confront ever-shifting environmental attributes with resilience and flexibility is critical to maintaining lineages with the capacity to undergo the morphological and behavioral modifications required for continued survival. Regardless if such elastic traits are realized through major swings in ontogenic development, or through the advent of novel life-history strategies, the ability of an organism to accommodate ecological variability is essential. This biological tenet is certainly true today as anthropogenically incited climate change is forcing accelerated rates of ecological alteration.

Just how fast are these alterations occurring? How fast are the biomes moving?

In tropical and subtropical coniferous forests at a rate of 0.08 km/yr

In flooded grasslands at about 1.26 km/yr

In tropical and subtropical dry broadleaf forests at 0.42 km/yr

Mangroves forests 0.95 km/yr

Within Mediterranean forests, woodlands and scrub at around 0.26 km/yr

In tropical and subtropical moist broadleaf forests 0.33 km/yr

In temperate broadleaf and mixed forests at 0.35 km/yr

In temperate grasslands, savannas and shrublands at 0.59 km/yr

Etc… The paper offers more biome classifications.

In looking at the rates of spatially shifting biomes, the researchers found that only about “8% of global protected areas have residence times exceeding 100 years.” Niche’s are definitely on the move.


ALSO SEE: Adapting to Climate Change, the Uphill Pursuit of the Shifting Niche


Loarie, S., Duffy, P., Hamilton, H., Asner, G., Field, C., & Ackerly, D. (2009). The velocity of climate change Nature, 462 (7276), 1052-1055 DOI: 10.1038/nature08649

Thinking Outside the Niche

Ecologist and evolutionary biologist Dr. Mark McPeek (Professor at Dartmouth College, and Editor-in-Chief of The American Naturalist) spoke at Florida State Thursday and Friday of last week. Unfortunately, fieldwork prevented my attendance at the first lecture, but luckily I did manage to make Friday’s session.

McPeek’s recent work has centered on community assembly in freshwater ponds, with a specific focus on the evolution and ecology of damselflies. His work as a whole (See his publications HERE) demonstrates an exceptional cross-discipline framework with representation from both the applied and theoretical aspects of population ecology, genetics, molecular systematics, comparative biology, geology and paleontology.

During Friday’s talk, McPeek discussed the biogeography, reproduction, speciation and coexistence/co-occurrence of several Enallagma species. After first describing the spatial and temporal similarities that exist between periods of past glaciation and the range expansion/speciation events recorded in the DNA of damselflies, he moved on to the neutral theory of community ecology.

The neutral theory of ecology basically maintains that a portion of the biodiversity displayed within an ecosystem is attributable to species that occupy identical, or nearly identical, niches (i. e. these species occupy comparable positions in the foodweb and utilize the same biotic and non-biotic resources). In addition, the neutral perspective states that although some phenotypic disparities may occur between different species, these disparities have no affect on the critters’ fitness or demography.

Using Enallagma as a case study, McPeek described a recent experiment in which the neutral theory was put to the test. Through directly manipulating the relative abundance (the number of one species) and absolute abundance (the total number of both species) of two like-species, McPeek placed two varieties of Enallagma in identical cages with tightly controlled environmental parameters; included as part of the tightly controlled parameters was the presence of a fish – a predator of Enallagma.

What McPeek discovered was that manipulation of one species’ relative abundance affected fitness little, whereas manipulation of the total abundance of both species showed direct effects for both.

His conclusion…

Although the two varieties of damselflies are sexually isolated, for the purposes of ecological functionality the two species are essentially one in the same.


For more on McPeek’s ideas regarding the neutral theory and niche differentiation, check out his publications list (linked above), specifically the article:

Leibold, M., & McPeek, M. (2006). COEXISTENCE OF THE NICHE AND NEUTRAL PERSPECTIVES IN COMMUNITY ECOLOGY Ecology, 87 (6), 1399-1410 DOI: 10.1890/0012-9658(2006)87[1399:COTNAN]2.0.CO;2