Below is an excerpt from a piece I wrote pulling together some of the research on contemporary evolution in vertebrates for an interesting new magazine, AEON, focusing on ideas, culture and sciences, hope you enjoy it!
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.
Curious about how populations could survive such harsh conditions, Brady devised an elegant reciprocal transplant study: a sort ofSwitched at Birth for salamanders. The set-up was simple: several dozen shoebox-sized salamander egg incubators, some glue and some duct tape. Brady collected freshly laid eggs from both woodland and roadside ponds. He then put subsamples of eggs from each environment into woodland water and others in roadside run-off. He watched how the creatures fared through hatching and their early stages of development. In the end, the roadside salamanders out-survived woodland salamanders in a pattern that suggested the roadside populations had become locally adapted to their harsh conditions.
Years ago, my own research investigated a similar phenomenon. I focused on a common biological marker of exposure to dioxins and similar chemicals. Dioxins, like other organochlorines, including polychlorinated biphenyls (PCBs), are the product of a marriage between carbons and chlorine. Rare but not absent from nature, they occur most often as a by-product of industrial processes (paper bleaching, for example, or the combustion of plastics). Their persistence and broad spectrum toxicity, not to mention the poisoning of the former Ukrainian president Viktor Yushchenko, have solidified their reputation as one of the most notorious industrial-age pollutants.
I knew that if either dioxin or dioxin-like chemicals were present in the environment, any organisms exposed to them would show increased levels of a particular enzyme, along with toxic symptoms of the chemicals themselves. But a few studies had suggested that this enzyme and associated toxicity were suppressed in populations of killifish (a minnow-like species) inhabiting highly contaminated sites. Intrigued about this resistance, a couple of colleagues and I designed studies a little like Brady’s to find out whether it was heritable.
Unfortunately, our studies took place in the wilds of urban New Jersey rather than the country roads of Connecticut. After months of planning, building cages, and collecting and placing fish, our test subjects disappeared, cage and all, over less than a week. Either the contaminants were capable of inducing more evolutionary changes than even we had imagined, or else someone thought the risk of wading into ooze brimming with PCBs and dioxins was worth a few sickly minnows….for more see Unnatural Selection