How cities change the evolutionary path of urban wildlife

The northwest corner of Newark Bay This is the kind of place that comedians have in mind when they make fun of New Jersey as a cesspool. The sinister industrial coastline that the bay shares with the Passaic River is lined with the carcasses of old chemical plants that treated their environment like a toilet. The most infamous of these facilities produced nearly a million gallons of Agent Orange, the toxic defoliant whose extensive use during the Vietnam War caused generations of suffering. The Agent Orange plant has rejected ruthless amounts of carcinogenic dioxin, to such an extent that the governor of New Jersey declared the state of emergency in June 1983. While there was no need for a carcinogenic dioxin, the Agent of New Jersey declared a state of emergency. Environmental Protection Agency announced a $ 1.4 billion clean-up effort, the waters closest to Newark's Ironbound neighborhood remain heavily contaminated; In America, there are few places to go swimming.

And yet, Newark Bay is not devoid of life. Under its dull green surface, a population of Atlantic killifish, a silvery water lily spilled along the east coast, is ubiquitous. It is virtually impossible to distinguish these fish from most other members of their species, with the exception of their particular ability to thrive in life-threatening conditions for their parents. When killifish harvested in less polluted environments are exposed to dioxin levels similar to those in the bay, they do not reproduce or their offspring die before hatching. their Newark cousins ​​swim and breed happily in the harmful soup.

Eight years ago, while he was an associate professor at Louisiana State University, Andrew Whitehead, an environmental toxicologist, decided to discover what makes Newark's killifish so difficult. With his research group, he took fish samples from an entrance near the city's airport and began deconstructing their genomes, sifting through millions of lines of genetic code in search of quirks likely to explain the immunity of creatures to the ravages of dioxin.

In late 2014, two years after moving to UC Davis, Whitehead focused on genes related to the aryl hydrocarbon receptor, a protein that regulates a set of cellular functions. When most adult fish-fish encounter dioxin, the signaling pathway of this receptor comes back to life in hopes of metabolizing the chemical invader. But try as it can, the protein can not break down the insidious substance. Instead of acting as a defense mechanism, the frustrated signaling pathway causes chaos during development – causing severe birth defects or death of embryos. "If you inappropriately activate this path when developing your organs, you're really tired," says Whitehead. But this ugly destiny never arrives at the Newark Bay massacres because their bodies are aware of the ruse of the dioxin; genes that control their aryl hydrocarbon receptors, whose DNA sequences are slightly different from those found in other killifish, are dormant when they are confronted with the toxin.

The story that the pioneers of urban evolution associate is darkened by the darkness.

As he explains in a landmark Science In 2016, Whitehead and his colleagues also discovered that Newark Bay killifish did not use this intelligent genetic tactic to survive in contaminated waters. He identified similar killings in three other cities on the east coast whose estuaries are soiled by industry: New Bedford, Massachusetts; Bridgeport, Connecticut; and Portsmouth, Virginia. Since killifish never move far from their place of birth, these resistant populations must have developed identical modifications to their genomes without mixing with each other – or, more simply, distant fish have all evolved remarkably similarly to one another. response to the same environmental pressures. This is convincing evidence for the idea that The evolution, the most sublime of the engines of nature, is not a chaotic phenomenon, but an orderly phenomenon from which we could predict the results.