" / > " / > Wild Thing: Energy Efficient Salamander|December 2019| TPW magazine
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WILD THING

Energy Efficiency

Spotted dusky salamanders don’t waste body heat.

By Paul Crump


It’s a common perspective that because reptiles and amphibians are ectotherms (they rely on the environment to obtain their body heat by basking), they are less “evolved” or somehow physiologically inferior to mammals and birds, which generate body heat internally (endotherms).

Maybe on a cold spring day it’s easier for a bird to move around its territory than a lizard, but this ectotherm vs. endotherm difference is more complicated than you might think.

For example, mammals and birds use 90 percent of the energy from what they eat to keep their bodies warm, with very little left over for growth and reproduction. But reptiles and amphibians efficiently convert about 90 percent of what they consume into growth and reproduction, wasting very little.

With this metabolic efficiency, they can achieve remarkably high population densities. One study from the northeastern United States showed that all the salamanders in the forest weighed twice as much as all the birds during the peak breeding season and about the same as all the small mammals. With such high densities, they are critical for food webs and the movement of energy from the forest floor to the other parts of the ecosystem.

Texas is home to 27 species of salamander, and about half of them belong to a group known as lungless salamanders. While other salamanders breathe using lungs, lungless salamanders exchange gases across their moist skin.

One such species that we’re particularly concerned about in Texas is the spotted dusky salamander (Desmognathus conanti). This species has disappeared from its spring and wetland habitats in East Texas; in fact, it’s gone from most of its historical range and is currently known to be in only six locations.

The spotted dusky salamander is a small animal that hides in and under vegetation along the edges of water features. It lays eggs on land, and when they hatch, the young wiggle their way into the water where they complete development and metamorphose into the adult, terrestrial form. Like all salamanders, they eat small insects and are, in turn, eaten by all manner of larger animals.

Dusky salamanders are a fascinating group because they have re-evolved an aquatic larval stage. Their nearest relatives have no larval stage; they complete metamorphosis inside the egg. They are thought to have re-evolved this larval stage in response to competition in the terrestrial environment.



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