We recently learned that rats in Africa can use plant poison to kill lions, and their North American counterparts also have a few tricks up their sleeves. Woodrats eat so many different toxic plants, it's impossible to poison them.
Many plants evolve toxins that will poison any animal that tries to eat it. Because woodrats just straight up don't give a crap, they go right ahead and eat all the toxic plants they want. To do that, they simply eat small amounts of lots of different toxic plants, and eat smaller meals at longer time intervals. This unusual eating style allows these rats to build up a general resistance to most plant toxins.
University of Utah biologist Denise Dearing explains:
"For decades, we have been trying to understand how herbivores deal with toxic diets. This study compares woodrats that eat only a single plant — juniper — with another species that eats several kinds of plants, including a small amount of juniper. We were trying to understand how they regulate the dose of toxic chemicals they eat by observing how often and how much they ate. We found that the woodrat that eats many types of plants was better at limiting toxin intake than the woodrat that eats only juniper."
While those rats that exclusively ate juniper built up a strong resistance to those particular toxins, this meant that that was the only plant they could really eat. The "generalists", on the other hand, got to eat lots of different plants thanks to their unusual smorgasbord approach. While a lot of work has been done on so-called "specialists" - those animals that only eat one particular toxic plant - there's a lot we still don't know about generalists.
That's why the biologists examined the white-throated woodrat of the American southwest, as Dearing explains:
"We are interested in knowing how the rats adjust their toxin intake so they don't poison themselves and die. They live in deserts where plants evolved toxins to protect themselves, and the woodrats don't have much choice in what to eat. A lot people in this field focus on trying to understand how the specialist deals with high concentrations of toxins. But generalists in some ways have it harder than specialists because they eat so many different poisons that they have to know when to stop for each poison. We were interested in whether they do that in the course of a night or in the course of a meal."
As it turns out, the rats seem to know instinctively when to stop eating during a meal. While it's possible that they simply eat until they feel sick, Dearing doubts that they would rely on a system as unreliable as that. Instead, she suspects the generalist rats have developed some pretty nifty ways to know when they've taken on too much poison:
"We think there are receptors in the gut that have a way of monitoring the intake of poisons. They may be bitter-taste receptors like those on the tongue. Other researchers have found them in the gut of other rodents."
Via the University of Utah. Photo by Denise Dearing.