From “Road Runoff Spurring Spotted Salamander Evolution” (ScienceDaily, Feb. 1, 2012), we learn,
Spotted salamanders exposed to contaminated roadside ponds are adapting to their toxic environments, according to a Yale paper in Scientific Reports. This study provides the first documented evidence that a vertebrate has adapted to the negative effects of roads apparently by evolving rapidly.
How are they evolving? As a result of contact with road salt, they
have higher mortality, grow at a slower rate and are more than likely to develop L-shaped spines and other disfigurements. In roadside ponds, only 56 percent of salamander eggs survive the first 10 weeks of development, whereas 87 percent survive in the woodland ponds. As roadside ponds become more toxic, the surviving salamanders may develop a genetic advantage over their counterparts living in woodland ponds.
It’s not clear what advantages deformity and mortality due to excess salt provide, or why we should regard them as evidence for evolution. In any event, what is predicted to happen if the county decides to use more sand and less salt, for road traction? Will the salamanders de-evolve rapidly to more normal development and mortality rates?
We’re told that, when raised together with salamanders from cleaner ponds, the salt-tolerant salamanders “actually do better – substantially better.” Perhaps because they are the tough 56% to begin with, though details are not provided.
“While the evolutionary consequences of roads are largely unknown, we know they are strong agents of natural selection and set the stage for fast evolution,” said Steven Brady, the study’s author and a doctoral student at the Yale School of Forestry & Environmental Studies.
How do we know that roads are strong agents of natural selection if their evolutionary consequences are unknown? In any event, how long have roads actually been around? And how long have life forms been around? Is there nearly enough evidence to be sure of roads’ role in evolution?
Has any life form developed and passed on a complex new mechanism as a result of run-ins with roads? Formed a new species in consequence?
Salt aside, one obvious problem with any “fast evolution due to roads” thesis is summed up in two words: Road kill. The survivors of the species who mate may not be the ones with so much experience of roads …