Natural History of Lithobates spenocephalus
Common Name: Southern Leopard Frog Taxonomic Classification: Amphibia; Lissamphibia; Anura; Ranidae; Genus-Species; Lithobates spehnocephalus.
Physical characteristics: Typically 2-3 inches as adults, They have a large tympanum with a light spot in the center behind the eyes and have a triangular-shaped head, distinct dorsolateral folds that extend to the hind legs and of course the most obvious being that unmistakable leopard spot pattern!
Collection Site/Conditions: It has been unusually warm in Memphis this winter and on 02/09/13, the conditions were no exception. At the Meeman Biological Field Station in Millington, TN, weather was mild at 50-55 degrees farenheit with overcast skies and winds at about 10-15mph. While setting up for my first field season, I came across this beautiful Southern Leopard frog while scouting using dip nets in a small pool just outside our lab's mesocosm array. This was no surprise to our lab members and I'd like to discuss some of the natural history and interesting facts about this species, L. sphenocephalus.
Habitat and distribution in Tennessee: L. sphenocephalus is a common Ranid frog species throughout Tennesse except in high elevations in Eastern TN (Tennessee Wildlife Resources Agency) and are typically found in or near ponds and other stagnant waters with dense vegetation. In this case, I found it interesting that despite the pool having a small diameter of about 3 feet or so and the water being very cold, there were a few individuals in the murky bottom within the leaf litter. Its pretty much a sure bet that you can find L. sphenocephalus in any pond or pool of water that does not contain large fish but you will need to be fast as these frogs are avid swimmers and leapers.
Life History: So one of the selling points for herpetologists who would like to study and/or collect L. sphenocephalus is the easily identifiable egg clutches. Clutches are large with thousands, yes thousands of eggs (3,000-5,000) contained within one gelatinous mass in which they are usually found attached to various substrate and vegetation in ponds. This species lay so many eggs because only a very small percentage of tadpoles will survive to adulthood, some estimate as little as less than 10 percent! Eggs are typically laid in late February- early March here in Tennesee and this was the primary goal of my trip to Meeman but unfortunately, I only found a few adults like those pictured above. L. sphenocephalus tadpoles will hatch in about seven to ten days and are small at about 20 to 25 mm long (Texas Parks and Wildlife). The tadpoles will double and even triple before metamorphosing into frogs, which can occur in about two-three months. L. sphenocephalus will typically live 3 years in the wild.
Behavior and other unique characteristics: So one of the things that I really enjoy is listening to frog calls during the breeding season and L. sphenocephalus males have vocal sacs that inflate like balloons when calling for a female. The call is very hard to describe other than saing it is a very fast, intense trill so I've attached this link for those of you who would like to hear it and yes it's worth it! (http://www.youtube.com/watch?v=-B_yrYDLb9Y). L. sphenocephalus are also nocturnal by nature and hide in dense vegetation and water during the day and they eat a large variety of insects and small invertebrates. Like many amphibian species, sexual dimorphism is present in L. sphenocephalus. Sexual dimorphism is apparent when the physical appearance of males and females are significantly different. Males are smaller than females, have paired vocal sacs and when breeding season approaches, males will develop enlarged forearms and thumbs. The latter is an adaptation that allows for the male to more readily attach to the female during inguinal amplexus in which the male wraps his forelimbs around the dorsal side of the female just behind her forelimbs. So if you find a beefy male, chances are he's looking for a mate!
References:
Texas Parks and Wildlife. http://www.tpwd.state.tx.us/huntwild/wild/species/southernleopardfrog/.
Conant, Roger, & Joseph T. Collins. A Field Guide to Reptiles and Amphibians Eastern and Central North America.Third Edition, Houghton Mifflin Company, 1998.
Tennessee Wildlife Resources Agency. http://www.tn.gov/twra/tamp/frogid.shtml
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