A taste for poison in warmer climates?
Q: Why does venom seem to be more favored as a defense by animals in warmer latitudes?
A: “It is not entirely clear that the premise of the question is true,” said Mark E. Siddall, a curator in the division of invertebrate zoology at the American Museum of Natural History. For example, “spiders are no more likely to be venomous in the tropics than they are in temperate regions,” he said. “There are just more spiders in the tropics.”
In fact, he said, there is typically more tropical diversity of any natural trait — “be it poison, venom or long tail feathers for attracting mates” — because “there is just more diversity in the tropics than in temperate zones, period.”
Why there should be so much more diversity of all species, from snakes to spiders, in the tropics is heavily debated by evolutionary ecologists. Siddall said that partial answers were easy, however. For one simple explanation, “energy input from the sun over time predicts that the tropics can sustain more biomass and thus more species,” he said.
Another partial explanation is that the temperate regions have been quite unstable in climate in comparison with the tropics and thus have not had as much time to generate and maintain diversity.
Siddall pointed out that some newts in the genus Taricha in the forests of the Pacific Northwest are just as poisonous as the poison dart frogs of tropical South and Central America. But there are only four species of Taricha left. “As recently as 26,000 years ago, huge swaths of temperate regions were scraped clean and trapped under tons of ice,” Siddall said, including about half of Washington state.
In comparison, there are dozens of poison dart frogs, which diverged from other frogs about 55 million years ago.