Resistance to toxins produced by certain plants and toads has evolved independently through a similar molecular mechanism across an unprecedented range of animals, from insects to snakes to hedgehogs. The work, published in Proceedings of the National Academy of Sciences this week, suggests that there is some predictability to evolution.
Examples of convergent evolution are everywhere: bat, bird, and pterosaur wings, for example, or the body shape of dolphins and fish. But at the molecular level, documented examples of convergence are rare and limited to specific groups. In this new study,Nicholas Casewell from the Liverpool School of Tropical Medicine and colleagues present evidence of convergent molecular evolution spanning the breadth of the animal kingdom.
Cardiac glycoside toxins are produced by true toads and milkweed, foxglove, and oleander plants as a defense. These toxins act as molecular corks that plug sodium-potassium pumps on nerve cell membranes, New Scientist explained, causing heart failure. Reptiles that feed on these toads have developed toxin resistance, which is conferred by mutations that have evolved on four separate occasions: in three snake lineages and one lizard family. The sodium-potassium pumps of these animals can’t be blocked by the toxin.
Resistance to cardiac glycosides appears to have evolved independently via a similar molecular mechanism in insects, frogs, toad-eating toads, rodents, and European hedgehogs as well. The team found similar changes to the pump in each of the animals they looked at. “There are very few options for a gene to modify itself to develop resistance without impairing function,” Casewell told New Scientist. “It suggests that in this system, evolution can be highly predictable.” When the range of possible solutions is sufficiently limited, they found, evolution can follow expected pathways.
Another paper, published last week in BMC Evolutionary Biology, also examined the predictability of evolution. When the changing climate surrounded isolated ant colonies with desert, the queens in different populations all lost their wings, Science explains. Flight was too risky because they could be blown out into the desert.