It is easy to forget that other organisms also affect the “environment” of a given species. No one is evolving in a vacuum. The existence of other species can not only affect an organism, but also its evolution.
Leigh Maiorana Van Valen, a preeminent American evolutionary biologist, suggested that a constantly changing environment will force organisms to adapt, as others around them adapt to survival. He termed this idea the Red Queen Hypothesis, a name derived from something Alice hears the Red Queen say in Lewis Carroll’s Through the Looking-Glass:
” Now, here, you see, it takes all the running you can do,to keep in the same place.”
An adaptation of one species to a change in the environment could alter the selection pressure on another species, causing it to adapt as well—and these adaptations need not always be mutually beneficial. Indeed, they can be quite sinister.
Some times, coevolution can provide a happy outcome to all participants. For instance, some humming birds have coevolved with flower species—the birds have developed long slender beaks and the flowers have specially shaped corollas. The bird has to probe the flower in a particular manner, with a particular beak, in order to access its nectar. This in turn allows the flower to deposit pollen from its stamen (the male reproductive organ) on a specific part of the bird’s body, ideal for transfer to the stigma, or the female reproductive organ of the same (in self-pollination) or a different (in cross-pollination) flowering plant.
Coevolution can also be manipulated to appear like a mutualism, but secretly favour one player over another. The caterpillars of the Lycaenid butterflies have this down to an art. They produce a sweet secretion that attracts a colony of ants, which literally herd the caterpillars to safety at night (up a tree!) and milk them for nectar during the day. Although the ants receive some nutrition, caterpillar benefits much more by being protected from other predators.
Voila! A personal army!
Some predator-prey relationships have been drawn into extended ‘arms-races’ during their evolution. The rough-skinned newt (Taricha granulosa) produces a potent neurotoxin (called tetrodotoxin) that is concentrated in its skin, as a defense from predators. Garter snakes (Thamnophis sirtalis) have evolved a resistance to this toxin. In response, the newts have upped their toxin production and now possess extremely high toxicity to avoid being eaten by garter snakes. And so it goes.
A recent study by Hannah Moir and colleagues from the University of Strathclyde published in Biology Letters has addressed another such arms race—this time, between the greater wax moth (Galleria mellonella) and their chief predators, bats.
Many bats use echolocation to navigate through space, specially while hunting; echolocation allows them to detect the presence of prey. But the hunters themselves are not silent, since echolocation by definition uses sound to bounce off substrates. These sounds are not audible to humans—we max out at ~20 KHz, while bats typically echolocate at 14-100 KHz. Thus, if a prey species could only hear the bats echolocating, they could potentially avoid becoming their dinner!
Alas, some bats can echolocate using extremely high frequency calls—as high as 212 KHz—which, until recently, were thought to be well beyond the auditory capacity of any insect prey.
Enter the Greater Wax Moth
Moir and her team discovered that the moths could detect sounds at frequencies up to a whopping 300 KHz! In fact, sound does not propagate very well at > 200 KHz, which is why not that many bats attempt to echolocate at such high frequencies. Most remarkably, this level of sound detection implies that this moth might just be the only creature ever known to be able to hear frequencies this high!
We also now know that moths not only hear the bats coming, but also use these high frequencies to engage in vocal courtship displays that absolutely no one else on the planet can hear!