Archive for April, 2010

“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."

Mole salamanders

Wednesday, April 21st, 2010

In an earlier blog, we mentioned that Spotted salamanders (Ambystoma maculatum) were making their way into ponds to breed. We thought that we might tell you about not only Spotted salamanders but also about the family of salamanders that they belong to, the Ambystomatidae. These amphibians are collectively known as “mole” salamanders because they spend much of the year underground. This family is distributed throughout most of North America and contains 37 species. Oklahoma has six species.

Four of the six species of mole salamanders in Oklahoma

Four of the six species of mole salamanders in Oklahoma

Among the Oklahoma species of mole salamanders, some breed in late winter, like the Spotted salamander and the Small-mouthed salamander (A. texanum), some breed in fall, like the Marbled and Ringed salamanders (A. opacum and A. annulatum, respectively), and some breed in spring, like the Tiger and Mole salamanders (A. tigrinum and A. talpoideum, respectively). When they are breeding, many hundreds seem to appear from nowhere. Considering how many arrive at the breeding ponds, it seems that they could be found any time during the remainder of the year—not so! After adults breed in ponds, they leave the ponds and go underground, not to be seen until the next breeding event. Obviously, they must feed while underground in order to grow and save energy to reproduce next time, but very little is known about their underground activity. Some, like Tiger salamanders, are known to live in gopher burrows, often in large numbers, but for the rest, we know very little.

After the breeding events, eggs hatch in ponds, and thousands of tiny salamander larvae emerge. Larvae of all species of mole salamanders look superficially alike, and a bit of skill is required to identify the different species in larval form. They have external gills, a laterally compressed tail that aids in swimming, and when not slowly walking on the pond bottom, they swim with an undulating motion, similar to that of alligators. Temporary ponds are filled with tiny invertebrates, collectively called microinvertebrates, such as ostracods, copepods, and Daphnia (a genus of cladocerans). Larvae of mole salamanders vacuum up these tiny invertebrates by opening the mouth and expanding the throat at the same time. They close the mouth and expel the water out through the gill slits, but retain the prey items. Their diet includes nearly every kind of pond organism small enough to fit into their mouths.

Larvae of Mole salamanders grow rapidly, but should rain be scarce, their pond might dry up before they are large enough to transform into adults. Ponds are also filled with predators that eat salamander larvae, including watersnakes, bullfrogs, giant waterbugs, and larvae of dragonflies and predaceous diving beetles. Some species of birds also visit ponds and capture salamander larvae. As salamander larvae grow, it is less likely that they will be captured and eaten by an insect. Large larvae are particularly attractive to birds and snakes. Life in the pond is risky for salamander larvae, and the best thing to do is grow fast and leave the pond as quickly as possible.  Of the thousands of eggs that are deposited each year, some will survive to become adults and breed, and most won’t. Variation among individual offspring sets the stage for natural selection.

Larva of a Tiger salamander

Larva of a Tiger salamander

The First Spring Rains Bring Out Frogs and Salamanders

Wednesday, April 21st, 2010

Rains that occurred several weeks ago in southeastern Oklahoma brought out all of the early spring frogs, including Spring peepers (Pseudacris crucifer), Cajun chorus frogs (Pseudacris fouquettei), Pickerel frogs (Lithobates palustris), and Southern crawfish frogs (Lithobates areolata). Even Southern leopard frogs (Lithobates sphenocephala) and American toads (Anaxyrus americanus) were active. In addition to running our traps at our primary research site in Le Flore County, we spent time driving roads at night in both Le Flore and McCurtain Counties. Nearly every roadside pond contained some mix of the above frog species. The only two that did not occur together were Pickerel and Crawfish frogs.

An adult Cajon chorus frog

An adult Cajun chorus frog

A number of amphibian species in Oklahoma breed during late winter and early spring, and their nearly deafening choruses can be easily experienced by driving around in rural areas at night. Males congregate in ponds when rains first begin, and their calls attract females that have spent the fall and winter converting energy that they stored from spring, summer, and fall activity into eggs. Examination of ponds during the daytime usually reveals many egg masses attached to vegetation or floating on the pond surfaces.

In addition to frogs that reveal their presence by calling, salamanders are moving into ponds to breed. We found large numbers of Spotted salamanders (Ambystoma maculatum) moving across roads heading for ponds during rains, and we captured some in our traps. Unlike frogs, salamanders do not vocalize. Whereas female frogs are attracted to individual males by the quality of the call, female salamanders are attracted to individual males by the quality of their courtship behavior.

An adult Spotted salamander

An adult Spotted salamander

So, for those of you are interested in amphibians, drive around in rural areas when it begins to rain and listen for frog choruses.  With the windows cracked, you can hear choruses in breeding ponds along the roads.  If you find a chorus on public property, put on your boots, turn on your good flashlight or headlight (preferred), and see if you can locate individual frogs that are calling. Chorus frogs are tiny and usually call inside grass clumps at the surface of the water. A Chorus frog calling right at your feet can be difficult to locate and requires persistence. If you are lucky enough to hear the low snoring calls of Pickerel or Crawfish frogs, you will need to move slowly without sloshing the water.  Even slight movement of the water caused these wary frogs to stop calling and dive below the surface. If you stand quietly for ten minutes or so, males will reappear and begin calling.

Sirens galore!

Tuesday, April 20th, 2010

Several weeks ago, a group from the museum visited the ODWC’s Red Slough in search of some salamanders that only occur in swamps of the southeastern part of Oklahoma. We were able to trap more than 20 sirens, which are elongate, eel-shaped salamanders that live their lives in water. They are in their own family, the Sirenidae, and the species that occurs in Oklahoma is the Western lesser siren, Siren intermedia.

Adult Lesser siren

Adult Western lesser siren

Unlike eels, sirens have external gills and a pair of tiny front legs, that on first glance, appear useless. Believe it or not, they use these legs on rainy nights when they move short distances across land. These sirens can reach eight inches in length, but most are slightly smaller. In most salamanders that have aquatic larvae, external gills used for respiration in water are lost when the salamanders metamorphose into terrestrial adults. In sirens, no obvious metamorphosis takes place, with the adults looking exactly like the “larvae,” just larger in size. However, close examination of the internal morphology reveals that reproductive organs develop as the “larvae” increase in size and age. Consequently, they do “metamorphose” but retain some larval characteristics (external gills).

Sirens reach sexual maturity in about two years. They deposit from 100–200 eggs in cavities in mud at the bottom of swamps. One of the most interesting aspects of the biology of sirens is their ability to form a cocoon around their body when swamps dry up. They burrow into the mud and secrete mucous that forms the cocoon, the function of which is to prevent them from drying up. Sirens can remain inactive for as much as eight months in their cocoon until rains fill the swamps that they live in.

Although sirens are difficult to observe because they are under water, they can be easily trapped with minnow traps, and no bait is needed. If you should trap one to observe, be sure to keep it in water that contains oxygen and is not chlorinated. It might also be useful to drop a few dried pine needles or oak leaves into the aquarium as tannins released from needles and leaves can keep mold from attacking the skin of sirens and other aquatic amphibians and reptiles.

Head of Lesser siren showing external gills

Head of Western lesser siren showing external gills

Blog Readers, we are back!

Tuesday, April 20th, 2010

Just after our last blog, rains brought frogs and salamanders out all over the place, which sent us racing around different parts of southeastern Oklahoma. We also ran our drift fence traps at our field site in Le Flore County, trying to keep up with movements of amphibians. A brief trip to Florida to present a talk to one of the Florida herpetological societies in Gainesville interrupted our amphibian and reptile excursions in Oklahoma, but only for about a week. As a result, we have been so busy that we have not been able to keep up with our blog. However, as the title says, we are back, and we will try to catch you up on what we have been doing in the following series of blogs. We hope you will all stick with us, and many thanks for all of your kind comments.