Amphibians: Rising in Fall

by Jeff Beane

To everything there is a season. The lives of most amphibians are particularly seasonally oriented. Amphibian literally means “double life” or “both lives,” referencing the dependence of these animals on both land and water. It’s not precisely true. Some amphibian species are entirely aquatic and some are exclusively terrestrial, defying the very definition of amphibian. But except for the fully terrestrial plethodontid salamanders in the genera Aneides and Plethodon, all amphibians in the Carolinas depend on either wetlands or permanent water for breeding.

Every amphibian species has a different life cycle and survival strategy. Some possess extreme seasonal adaptability, potentially breeding whenever weather conditions are favorable. Others breed at very specific times of year—some only in winter, others only in spring, and still others only in summer. This seasonal partitioning is one of many strategies serving to reduce competition, allowing multiple species to coexist. Fall is often thought of as a slow time or “down time” for many species, and this does include some amphibian species. But for others, fall is the most important time of year.

Marbled salamander (Ambystoma opacum) - North Carolina's state salamander - breeds only in the Fall. (Photo by Alvin Braswell)

One obligate fall breeder is North Carolina’s official state salamander—the marbled salamander, Ambystoma opacum. Salamanders in the family Ambystomatidae are collectively called “mole salamanders” because the adults are fossorial, spending most of their lives in burrows on land. Most mole salamanders have life cycles like those of our frogs and toads—they lay their eggs in water, the eggs develop into aquatic larvae, and the larvae develop into terrestrial juveniles. All six mole salamander species in the Carolinas (marbled, spotted, mole, tiger, Mabee’s, and frosted flatwoods) are heavily dependent on fish-free, ephemeral wetlands for breeding. While most deposit their eggs in these wetlands, usually in winter or early spring, marbled salamanders switch things up a little, moving into their breeding sites on rainy nights in late summer or early fall. They utilize a variety of ephemeral wetlands, including floodplain pools, borrow pits, and even ditches and logging ruts, but high-quality upland vernal pools provide the best breeding habitat. Males move into the breeding sites first, sometimes as early as late August. The females follow, usually in September or October. Typically, the pools are bone-dry when they arrive. Not only does this fail to disappoint the salamanders—it’s just what they’re hoping for. They will mate beneath surface litter in the dry pools, the male depositing a sperm packet called a spermatophore and the female retrieving it with her cloaca and retaining it internally to fertilize her eggs as they are deposited. She selects a log or other sheltering object in the dry pool basin and deposits her eggs in a cluster underneath. Then comes a waiting game. She remains with the eggs, attending them until fall or winter rains flood the pool, whereupon she abandons them and returns to her terrestrial burrow. The eggs hatch quickly once inundated, and the aquatic larvae begin developing with a head-start over the other species using the pool later that winter or spring.

Empheral pond at Raberdo Bog (Uwharrie National Forest, west-central Montgomery Co., NC) provides habitat for the mole salamander (Ambystoma talpoideum) (Photo by Alvin Braswell)

Marbled salamanders are not the only fall breeders. The rare frosted flatwoods salamander (Ambystoma cingulatum), still persisting in scattered localities in the South Carolina Lowcountry, typically breeds from October to December. This species also deposits its eggs terrestrially—although usually unattended—amid vegetation in the dry basins of ephemeral wetlands. Tiger and Mabee’s salamanders also may breed as early as October or November, or as late as March, depending on weather. They deposit their eggs (gelatinous masses for tigers, single eggs attached individually to leaves for Mabee’s) in water, so the ponds they use (often Carolina bays) must be flooded before they can breed. During droughts, they may miss breeding for a year, or even several consecutive years.

Spotted salamander (Ambystoma maculatum) (Photo by Alvin Braswell)

Several other amphibians that usually breed in winter or spring, can breed opportunistically in fall if conditions are favorable, especially following hurricane rains. These include the southern leopard frog, Carolina gopher frog, pine woods treefrog, eastern spadefoot, eastern newt, and little grass frog. In some (leopard frog, gopher frog, newt), the larvae will live in the pond all winter. But spadefoot tadpoles develop so rapidly that they will transform and leave before freezing weather, even if breeding occurs as late as October. Some plethodontid salamanders, including mud, red, two-lined, dwarf, and Chamberlain’s dwarf, may mate in fall, although their eggs are laid later in the winter. They are therefore often active on rainy autumn nights.

Fall may be a winding-down time for some creatures, but for certain amphibians it is a new beginning. On every day of the year, there is something important happening in our wetlands!

About the Author

Jeff Beane is the Herpetology Collections Manager at the North Carolina Museum of Natural Sciences in Raleigh, NC.  His research focuses on gathering basic information on the natural history, geographic distribution, and conservation status of all reptile and amphibian species in North Carolina.   More Info.