No one would guess Hyalella azteca’s importance just by looking at it. Toxicologists use this unassuming, shrimp-like animal to test water quality. A body of water can be proclaimed healthy or toxic based on whether Hyalellas raised in a sample live or die.
Yet the story behind this important little amphipod is far more complicated than scientists have understood according to a study just published in PNAS Early Edition. Researchers testing three lab and seven wild populations found a huge spread in pyrethroid insecticide sensitivity–550-fold.
“This is fascinating or scary, depending on your viewpoint,” says lead author Don Weston, an environmental toxicologist at the University of California, Berkeley.
Toxicologists have noticed for sometime, he says, that water from some areas which will kill lab-raised H. azteca are known to support thriving wild populations. Now we know that wild populations can acquire resistance, he says. In fact they’ve acquired it multiple times.
Among seven sampled wild populations, the authors believe resistance has arisen at least three separate times. Resistance appeared in two separate species among the populations; one species achieved resistance in two different ways. (The crustaceans referred to as H. azteca are actually a group of species. Since they all look the same, it takes genetic analysis to separate one from the others.)
The full extent of resistance, Weston estimates, is vast. If true, the implications are alarming. Remember, Weston says, pyrethroids are applied on land.
We’re seeing resistance emerge in an aquatic invertebrate that, if everything was working properly, wouldn’t even see pyrethroids. Ideally they shouldn’t be leaving where they are sprayed, but people are deluding themselves if they think they aren’t. We’re seeing the biota respond.
Broadly, Weston sees two implications of this study. On a practical side, toxicologists who keep Hyalella in culture should never supplement their culture from the wild (a practice that used to be more common). This could contaminate lab cultures with resistant mutants and totally wipe out consistency in results between labs.
On a more philosophical level, he says, the implications are hard to grapple with. Some could argue that the emergence of resistance is a good thing. The animals were in a stressful environment and they’ve mutated their way out of the problem. Others might ask, should the animal have to mutate to survive pollution? Is that the world we want to live in?
“That’s entering a philosophical realm that goes beyond the science,” Weston says.