Tuesday, April 13, 2010

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

Sunday, April 11, 2010

What Spider is this?

Anyone know which species of spider this is?

It was in west central Florida - near Crystal River, Levy County.

I'm guessing Gea heptagon, but haven't seen one quite like this one - with so many numerous huge spines...

Tuesday, April 6, 2010

Awesome Picture: Florida Panthers in the Picayune

I was just emailed this picture of a mama panther and her cubs:

The email (from a reliable source) advises that the photo was recently taken during a fly-over of the Picayune Strand near Naples in South Florida.

Looks like three wild Florida panthers - cool!

Also pictured are what looks like a recently cleared road and stands of noxious Melaleuca – could be better! (As a matter of fact it is getting better - click here for info).

In addition to dealing with us ecosystem-altering and land-lusting apes, Florida panthers must also cope with other parasites – including highly specialized trematodes that have evolved a fancy for fare of the feline sort...

Trematodes are flukes of nature (sorry, couldn’t resist) in that they've evolved an astonishing, almost incomprehensible level of developmental plasticity. Most have evolved the ability to subtly manipulate their growth rates and sexual maturation to track the resources available in their environment. For parasitic nematodes, their environment is manifested by the internal chemistry of their victims. Id est, the digestive enzymes, hormones and antibodies expressed through the physiology of their hosts help the trematodes gauge the probability of reproductive success and to tune their own developmental process accordingly. This fantastic capacity for flexibility is of survival benefit because should a trematode happen to find itself immersed in the body of an unsuitable host, it can induce a state of arrested development and shift its metabolism to complete dormancy while awaiting transmission to a more favorable chemical climate. As a natural corollary, if the trematode succeeds in locating its target host (aka, its 'definitive host') it can quickly push development into overdrive and achieve reproductive adulthood in short order, thereby maximizing the opportunity to its individual advantage. Being unrestrained by the ticking-clock of reproductive efficacy, trematodes can migrate from host-to-host and even between species with relative ease. As a case study, consider the misadventures undertaken by the trematode species named Alaria marcianae.

Alaria marcianae is a fascinating organism known to target, as definitive hosts, the kittens of the Florida Panther (Puma concolor couguar). The Florida Panther holds a critically endangered status and, as the common name strongly suggests, resides in the state of Florida. The tawny colored Florida Panther is one variety of a widely recognized group of felids that are also known by the names cougar, mountain lion and puma. The panther-intersecting life cycle of Alaria marcianae is complex with several possible vectors of transmission, but in choosing an arbitrary starting point for the purpose of description, we can assume that its convoluted journey begins within the intestines of an adult panther.

Having recently been deposited in the intestinal tract of an adult feline, members of Alaria marcianae start their lifecycle as eggs. The eggs, unembryonated germ cells, intermix with the partially digested remnants of raccoons, armadillos and other common delicacies found in the panther's system, and are then excreted with the animal's feces. On being submerged in the inundated wetlands for which south Florida – and the Picayune Strand - is renowned, water stimulates the eggs to internally develop embryos. Once these embryos have achieved sufficient maturation, sunlight triggers the eggs to hatch free swimming, cilia-driven, paramecium-looking critters called miracidia.

The miracidia are not adult Alaria marcianae, rather they represent a sexually immature stage of development that is specialized for seeking out a very specific (obligate) intermediate host. To ultimately succeed in stalking a panther, the miracidia of Alaria marcianae must first locate and infect a ram's horn snail of the genus Helisoma.

On locating a ram's horn, the miracidium attaches itself to the soft exposed flesh of the snail, and by excreting tissue-degrading enzymes, it parts ways with its cilia-bearing outer layer. It then penetrates into the snail's body cavity. Shedding its ciliated epithelium, the miracidium becomes an immature sporocyst. Although sporocysts still lack the ability to reproduce sexually, by embedding in the snail's nutrient rich organs they acquire the power to produce additional replicates of themselves - clones called 'daughter sporocysts.'

Further advancing on the panther, the new daughters promptly leave their mother's side and venture to the snail's gonads. Mollusk hormones produced by the gonads fuel special cells within the daughters as they morph into tailed, tadpole-looking larval forms called cercariae. The cercariae swim to, and exit from, the snail's shell-producing mantle. From there, they return once again to the open water as free-swimmers.

Leaving the snail behind, the cercariae swim to the water's surface and hunt down the true tadpoles of the leopard frog (Rana pipiens) - their second intermediate host. Hijacking the leopard frog's tadpoles for transport, the cercariae drop their own tail and burrow into the tadpole's skin. There's no need for self-propulsion when riding inside a tadpole. Once inside the developing frog, Alaria marcianae, then at a stage where they're referred to as mesocercaria, cease further development and undergo another round of asexual cloning. As numbers continue to multiply, they patiently rest, waiting for the tadpoles to carry them landward as adult leopard frogs.

In time, the mesocercaria-bearing tadpoles grow into leopard frogs and move their parasitic cargo to land. On terra firma the leopard frogs are hunted by a wide range of predators; occasionally falling prey to yet another preferred host (aka, a 'paratenic host') of Alaria marcianae, the raccoon. After catching an infested frog, the raccoon's digestive enzymes make short work of the frog's flesh - in the process releasing the mesocercaria. As with its previous host, the mesocercaria multiply in the raccoon, but continue to maintain a state of arrested development - they are not yet adults.

Did I mention that raccoons in south Florida happen to be a favorite prey item of the endangered panther?

Utilizing methods similar to those during the frog-to-raccoon transmission, Alaria marcianae find their way into adult panthers by contaminating raccoons - panther prey. During the process of raccoon digestion, mesocercaria are liberated from tissue and enter the bloodstream by penetrating the intestinal wall.

Now, if the panther they find themselves parasitizing, by chance, turns out to be a lactating female, her hormones will stir the mesocercaria into migrating to her mammary glands where they will transmit (trans-mammary) to the digestive system of her kittens'. The term used to describe the situation in which a mother acts as a paratenic host to her own offspring is called 'amphiparatenesis.'

Here, amphiparatenesis results in the imbibing of mesocercaria-laden milk by the kittens. As with the mesocercaria residing within their mother, the parasites in the kittens will penetrate the intestinal wall and enter the blood stream. They'll surf the blood stream until reaching the lungs where they become metacercaria; as metacercaria they harden the surrounding lung tissue forming protective cysts. Having profitably acquired housing in their definitive host, the cysts in the lungs will eventually be coughed-up the trachea and then promptly swallowed into the esophagus. Once back in the intestines, Alaria marcianae accelerates its developmental process, achieves sexually reproductive adulthood (as sequential hermaphrodites), and deposits the next generation of eggs in the intestine.

Thus the cycle comes full circle.

Foster, G., Kinsella, J., Sheppard, B., & Cunningham, M. (2009). Transmammary Infection of Free-Ranging Florida Panther Neonates by Alaria marcianae (Trematoda: Diplostomatidae) Journal of Parasitology, 95 (1), 238-239 DOI: 10.1645/GE-1749.1

Saturday, April 3, 2010

Douglas Adams on Lemurs, Dolphins and other Wildlife

Cool just found this at TED - funny!

It's From back in 2001.

Douglas Adams' close encounters with these rare and unusual animals reveal that evolution, ever ingenious, can be fickle too -- in a University of California talk that sparkles with his trademark satiric wit.