By LESLIE BISHOP, guest columnist
Spring is finally here. The first spring beauties are blooming in the forest, and the vociferous chorus of spring peepers fills the evening air with sound.
Yet there are many silent signs of spring, including the emergence of the secretive amphibians, the salamanders.
Beginning in early spring, terrestrial salamanders crawl from their winter hideouts and begin to move toward their mating and reproducing sites, and in some cases this can be quite a dramatic announcement of spring.
For example, on the first warm, rainy night of spring, spotted salamanders migrate in great numbers from their forest burrows to woodland ponds to reproduce. The numbers can be so great that the police in a New Jersey town close a road to protect the moving salamanders from being hit by cars.
The breeding sites are vernal ponds that will be dry by summer. These temporary ponds are free of fish predators who would otherwise eat the eggs and the larval salamanders. Generations of salamanders will return to the same pond for mating year after year.
The first to arrive at these ponds are the males who gather in wiggling clusters called congresses. As the females arrive, an individual male will leave the congress to follow an individual female. This begins an elaborate courtship involving circling with heads under tails, climbing on backs and rubbing of chins.
After establishing themselves as a couple, the male will lead the female with his wagging tail to a place where he has left a sperm packet, or spermatophore, attached to submerged plants. The female then wiggles over the spermatophore to insert it into her cloaca. She may repeat this courtship with several males before leaving the pond. She then lays her fertilized eggs in large, gelatinous masses on submerged vegetation.
The jelly coating on the eggs prevents desiccation, but it also inhibits oxygen from diffusing into the egg. Spotted salamander eggs thus have a fascinating symbiosis with green algae.
Recent research found that the algae isn’t just in the gelatinous layer but actually is in the tissue of the developing embryo. Photosynthesis by the algae provides oxygen to the developing larvae, and the larvae in turn provides a rich nitrogenous environment for the algae. Scientists have many questions about this intimate symbiosis and research is ongoing.
Larvae with gills hatch in about a month and remain in the water until they develop into adults. During metamorphosis, they lose their gills and develop lungs. They then leave the vernal pools and return to live in the forest where it takes two to four years to become reproductive adults.
The spotted salamander is a member of the mole salamander family, the Ambystomatidae. Like moles, they spend most of their lives underground in burrows or in the shelter of the forest leaf litter. During the summer, the only time to see them is at night when they emerge from their burrows to hunt for food. They eat a variety of insects, spiders, earthworms, slugs and millipedes.
Indiana is host to 23 species of salamanders. Among these species, there are representatives of diverse lifestyles. Some are aquatic their whole lives and others are terrestrial. Some have gills, some have lungs, and some have neither and simply use moist skin for the diffusion of gases. But all salamanders require moist environments and their skin is extremely absorbent.
Of these Indiana species, eight are on the state endangered or special concern list. Five of these eight species live in our hardwood forests.
The aquatic species are sensitive to water polluted with industrial contaminants, agricultural pesticides and excess fertilizer, as well as increased sediment from soil erosion after timber harvest.
The forest species are sensitive to microhabitat change through development or logging. The removal of trees also removes the protective canopy that shades the forest floor. The increased sunlight from these openings results in higher temperatures and loss of moisture on forest floor. Vernal pools, the crucial reproduction sites for salamanders, rapidly dry up after logging.
In addition to habitat degradation and pollution, salamanders face an additional deadly threat. Since 2014, an Asian fungal pathogen (a chytrid fungus named Bsal) has spread from the Netherlands to Germany and Belgium through the pet trade. The fungus affects salamanders’ sensitive skin, and the infected animals die within days. If Bsal crosses the Atlantic, scientists predict catastrophic effects on North American salamander species.
So far, our salamanders are not affected, and scientists are now working on developing a protective skin barrier using beneficial bacteria. In January 2016, the U.S. Fish and Wildlife Service ordered a ban on interstate travel and importation of many salamander species as a protective measure. But scientists feel that the arrival of Bsal in the United States is inevitable.
Another threat to healthy populations of salamanders is the pet trade. Salamanders are often captured from the wild to be sold through the internet or in pet stores. By capturing salamanders from their natural habitats, the pet trade severely depletes already at-risk wild populations. In the U.S, more than 20 million amphibians are taken from the wild and sold every year.
For all these reasons, we need to protect our native wetlands and forests. These gentle and silent salamanders with their fascinating spring rituals deserve our attention, as well as our delight.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She is a volunteer interpretive naturalist at Brown County State Park. She can be reached through the newspaper at firstname.lastname@example.org.