Natural History: greater siren

            By the time of our last field trip for the semester, our class had managed to catch representatives from most of the amphibian families found in the SC Lowcountry, including mole salamanders, lungless salamanders, amphiumas, toads, tree frogs, narrow-mouth frogs, and true frogs.  One family we had yet to see was Sirenidae, the sirens.  Thankfully, the Donnelley Wildlife Management Area turned out to be the perfect place to find them!  We had set almost thirty minnow traps the day before, and the first one we pulled out of the shallow swamp contained a Siren lacertina, the greater siren.  Our catch was about ten inches long—small for a greater siren—so it was most likely a juvenile or subadult.  It was dark olive in color with small, greenish-yellow spots, which is how we identified it as S. lacertina rather than S. intermedia; the lesser siren usually has black or brown spots.

           The Sirenidae are a family of obligately paedomorphic salamanders.  They spend their entire life cycle in the water, and they retain many adaptations for this lifestyle that are usually only found in larval salamanders.  Sirens have large, feathery external gills, no eyelids, and a broad tail fin for swimming. While salamanders of the Amphiumidae have reduced all four of their limbs, the Sirenidae have retained their forelimbs but lost their hind limbs and pelvic girdle completely. Because the sirens have no terrestrial stage to their life cycle, they have retained the basal amphibian trait of external fertilization in an aquatic environment.  Their aquatic habitat makes droughts dangerous, but they have the ability to aestivate in mud burrows when their body of water starts to dry up.  After the storms we had this weekend, though, our Donnelley siren seemed perfectly healthy!

Reference:

Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America