Posts Tagged ‘chemical defense’

The Plot “Thickens”

Tuesday, May 17th, 2011

If you have ever had the misfortune of turning over a log or rock in eastern Oklahoma and grabbing a black salamander with white spots, you know that washing off the thick, sticky liquid that they secrete from their skin in defense is no easy matter. Imagine being a small predator like a snake, biting the salamander, getting a mouthful of that sticky stuff, and then trying to rub it off in the leaf litter ending up with a mouthful of leaves stuck to your mouth! These salamanders, which look pretty much the same from mountain ridge to mountain ridge, and even resemble a lowland salamander, form a complex of species whose identities and relationships are just beginning to be understood. To the layman, these are known as the “slimy” salamanders.

The salamander Plethodon ouachitae, occurs along several ridges in the Ouachita Mountains and is commonly known as the Rich Mountain Salamander.

The Rich Mountain Salamander (P. ouachitae) occurs along several ridges in the Ouachita Mountains.

Dr. Don Shepard, a former graduate student from the University of Oklahoma, has combined field studies with DNA sequence data to unravel relationships among these species. Until recently, these salamanders have been considered as four species. One, Plethodon albagula, appears to be widespread in lowlands and the Ozark foothills of eastern Oklahoma, extending up into Missouri. Three other species, P. caddoensis, P. fourchensis, and P. ouachitae, each occur on their own mountain ridges in the Ouachita Mountains of southeastern Oklahoma and southwestern Arkansas. If only it were that simple!

By combining DNA sequence data with known rates of evolutionary change for specific genes, Don has discovered that not only have some of these “species” experienced divergence into genetically different populations, the causes of divergence differ among species. For P. ouachitae and P. fourchensis, genetically different populations are associated with mountain ridges, indicating that populations were isolated on mountain tops as the climate slowly changed over geologic time. Why would they become isolated? The answer is that these salamanders require a specific set of environmental conditions to survive. These include relatively cool temperatures and high humidity, usually associated with mountain tops. The salamanders appear unable to adapt to warmer and drier conditions so they simply live in the same kind of microhabitats that they lived in historically. This inability to adapt is referred to by scientists as “niche conservatism.”

For P. caddoensis, diversification is associated with stream drainages. Four distinct lineages within P. caddoensis have been identified from each of the following four streams; lower Caddo River, Upper Caddo River, Brushy Creek, and Cossatot and Little Missouri Rivers. Diversification in this “species” appears tied to more recent climatic change and specialized niche characteristics of the salamanders, primarily related to thermal and humidity variables associated with stream drainages.

The Western Slimy Salamander, Plethodon albagula, occurs from Missouri south to extreme southeastern Oklahoma and into Texas.

The Western Slimy Salamander (P. albagula) occurs from Missouri south to extreme southeastern Oklahoma and into Texas.

Dr. Shepard is now beginning to examine the lowland and widespread “species” P. albagula. No doubt this species has undergone some interesting divergences in the past, but what the pattern is and how it occurred remains a mystery to be unraveled. So, the next time you pick up one of these so-called “slimy salamanders,” reflect on their evolutionary history and what they tell us about past events underscoring the remarkable diversity that we see today in eastern Oklahoma. Oh, and if you have been slimed, try WD-40 followed by soap and water. WD-40 seems to be a universal solvent and will clean many things!

“Spreading Adders”

Thursday, April 29th, 2010

The hiss of an Eastern hog-nosed snake as it spreads its neck and acts like a cobra can be quite startling, but it is all bluff. Eastern hog -nosed snakes are completely harmless, and it is nearly impossible to get one to bite. It is no accident that they seem to show up when toads are active. Hog-nosed snakes specialize on toads, eating almost nothing else. Colors and patterns of hog-nosed snakes vary from nearly all black to reddish with various shaped markings, and younger hog-nosed snakes seem to be brighter in color than older and larger ones.

An adul;t (top) and juvenile (bottom) Eastern hog-nosed snake

An adult (top) and juvenile (bottom) Eastern hog-nosed snake

When first disturbed, hog-nosed snakes go through their hissing and spreading display, hence the nickname “spreading adder.” However, if they are bothered a bit more, they switch their behavior to a ridiculous series of movements in which they appear to act as though they have died, going so far as to roll over on their back, open their mouth, drag their tongue in the dirt and lay there motionless. If you wait a few minutes, they will roll their head over and look at you. If you roll them over so that they are upright, they quickly roll back over upside down. And, if you wait long enough, they roll over and crawl away. What could possibly be the advantage of doing this? One would think that simply lying there would make it easier for a predator to eat them.

Starting in the bottom left, follow clockwise, the deith-feigning sequence of a hog-nosed snake

Starting at the bottom left, follow clockwise, the death-feigning sequence of an Eastern hog-nosed snake

If you watch carefully when hog-nosed snakes first start rolling over, you will notice that they cover themselves with bodily wastes released from their cloaca as they twist and coil during their death feigning act. Recall that they eat toads, almost exclusively. Toads eat ants and beetles that produce chemicals (alkaloids) for defense, and toads in turn produce strong chemicals that are released from the large glands (paratoids) just in back of their head that make them very bad tasting and sometimes toxic (don’t lick a toad!). So, when Hog-nosed snakes eat toads, they are also eating a bunch of very bad-tasting chemicals. By covering themselves with excrement, Hog-nosed snakes make themselves very bad to eat. The “playing dead” likely keeps them from being injured while a predator determines that they are not as tasty as they first appeared to be when they were crawling along.

Threat display of an adult Eastern hog-nosed snake. Note the raised tail and the flattened neck, hence, "spreading adder."

Threat display of an adult Eastern hog-nosed snake. Note the raised tail and the flattened neck, hence, "spreading adder."