Unnatural Selection

Salamanders, fish and perhaps even humans are evolving fast in response to toxic chemicals. Is that bad?

In the hemlock and oak forests of northeastern Connecticut, Steve Brady stood thigh deep in black muck and scooped up a handful of spotted salamander eggs. A Yale PhD student, he had once fancied himself zipping across tropical waters in a Zodiac boat or scanning rainforest canopies in search of exotic birds. Instead, he had just planted his budding career as an evolutionary biologist in a muddy ditch. The eggs, nestled in a protective jelly stained golden by tannins that glistened in the light, might have looked like any other clutch of salamander eggs from a woodland pond. But they weren’t, and this was no pristine sylvan pool. It was a roadside puddle, and those eggs promised to contain something unsettling. If Brady was right, the toxic brew associated with road run-off had forced the spotted salamanders to evolve in the space of decades. In the time since Neil Armstrong first set foot on the moon in 1969, these animals had been reinvented by nature to cope with life on the road. Adult salamanders, slick black with their brilliant yellow spots, thick tails and deliberate walk, already look like creatures from a B-movie. And while the chemicals that might be responsible for their evolution are a far cry from atomic radiation and other horror film toxicants, Brady’s research suggests that this basic scifi premise — rapid evolution as a means of surviving exposure to toxic chemicals — is rooted in reality.

The roadside salamanders out-survived woodland salamanders in a pattern that suggested they had become locally adapted to their harsh conditions

Roadside ponds are a harsh place to rear a family. ‘The chance of survival in roadside pools is much lower than that in a woodland pool,’ Brady told me. ‘Even in adapted populations, a little over half the eggs survived the first 10 weeks of development.’ That’s a major hurdle, especially for wetland amphibians that already face intense natural challenges. As Brady observed: ‘These pools frequently dry up before the animals have reached metamorphosis, leading to the loss of an entire generation.’ And as the pools dry up, the contaminants in them — metals and salts, for the most part — become concentrated and increasingly toxic. More at aeon magazine