CHS Blog

A Summer Spent Salamander-ing

November 03, 2020
Meghan Ward

For as long as I can remember, I spent childhood summers at the cottage catching frogs and searching for salamanders under logs. My most trusted tools were a little plastic frog-shaped net and a big red bucket. If eight-year-old Meghan had been told she would be doing the same thing 15 years later, she would have been as ecstatic as I was while preparing to embark on a salamander study last summer. I swapped the cottage for Pelee Island and the frog-shaped net for knee-high rain boots and waders. I will admit, the bugs were much worse on Pelee and the food not nearly as good as cottage fare, but I loved every minute of it. Mixed in with measuring soil moisture, estimating canopy cover, and recording leaf litter was Dr. Thomas Hossie’s historical re-telling of the complicated Ambystoma salamander story on Pelee. As a result, I quickly came to appreciate the fascinating ecology of these creatures.

Salamanders of the genus Ambystoma on Pelee Island present a unique and interesting history. Surrounded by Lake Erie, and closer to the U.S. than the Leamington shore in Ontario, Pelee Island is Canada’s most southerly point. The salamanders that live there were separated from mainland populations some 4,000 years ago, and their subsequent murky history has captivated many ecologists. As it stands today, two species, the Small-mouthed Salamander (Ambystoma texanum) and the Blue-spotted Salamander (Ambystoma laterale), live alongside a third biotype that isn’t quite its own species — a swarm of unisexual Ambystoma, each of which contains a varying number of genomes from both Small-mouthed and Blue-spotted Salamanders. Together, these salamanders form what’s known as a “unisexual complex.”

The unisexuals, which are all female, produce unreduced eggs, meaning their offspring get a full complement of the mother’s DNA (not just half, like in humans). To reproduce, the unisexuals “steal” sperm from male Blue-spotted or Small-mouthed Salamanders, a process known as kleptogenesis. The sperm is needed to kickstart development of the unisexuals’ eggs, but the sperm nucleus — and therefore the male’s DNA — typically isn’t incorporated into the developing embryo. Thus, many unisexual individuals on Pelee Island are female clones of each other. Very occasionally, however, the male’s DNA is incorporated, adding a genome to those offspring with the result that unisexuals can have anywhere from 2-5 sets of chromosomes! (Most animals, including humans, only have 2 sets: one from mom + one from dad.)

Unfortunately, the Pelee Island salamanders are suffering from habitat loss. In the 1880s, much of the island was drained and transformed into agricultural fields, destroying many pond and wetland breeding habitats. Since then, even more breeding habitat has been lost. Within the last decade, many new ponds were constructed across the island in an attempt to mediate the historical loss of wetlands. My role as an undergraduate thesis student was to assess whether these constructed ponds appropriately replicated the habitat required to support breeding populations of Ambystoma.

We found that both natural and constructed ponds used by breeding Ambystoma had lots of trees shading the water (high canopy cover) and there tended to be crayfish burrows present around the pond margins. Interestingly, when searching for adult Ambystoma salamanders we often found them hiding in crayfish burrows. Higher numbers of larvae were associated with ponds that had more leaf litter in the substrate, and ponds with submergent vegetation present. Importantly, we found that different environmental variables predicted larval presence versus larval abundance. Presence was related to terrestrial variables, including canopy cover and crayfish burrows, whereas abundance was impacted by pond-related variables that included submergent vegetation and leaf litter. From these results we can tentatively conclude that different parts of the environment influence salamanders differently depending on their life stages, as larvae and adults are impacted by both aquatic and terrestrial features.

Compared to natural ponds, we found that constructed ponds generally had less canopy cover and therefore less leaf litter, and fewer contained submergent vegetation. During our fieldwork, larvae were caught in only 33% of constructed ponds, versus 88% of natural ponds. As well, the abundance of larvae in constructed ponds ranged from ~4 – 10x lower than in natural ponds. Thus, it appears that constructed ponds on Pelee Island will require additional restoration support and/or time to naturalize before they can provide suitable habitat for salamander larvae.

My summer spent salamander-ing on Pelee showed me how imperative it is to preserve wetlands. While the construction of new ponds may benefit amphibians over time, we cannot presume that these will immediately offset the loss of natural ponds. As wetland loss continues, conservation of amphibian breeding habitat should be at the forefront of our conservation work. Many aspects of amphibian ecology, including the inability to travel far distances and the innate need to return to the same breeding pond annually, increase the challenges associated with constructed wetlands.

Looking into the future, I know that whatever-age-Meghan will still spend her summer looking for salamanders in ponds and under logs. I hope the conservation work we do now will support this never-ending search.

References:

Ward, M. and Hossie, T.J. (2020). Do existing constructed ponds on Pelee Island, Ontario match the habitat requirements of endangered Ambystoma larvae? Wetlands. https://doi.org/10.1007/s13157-020-01364-8