Plants that use animals to disperse their seeds can find themselves in a pickle. They need to make fruit tasty enough to entice the local fauna. But they also need to make sure that their animal assistants don’t digest the very seeds they’re meant to spread.
In Israel’s Negev Desert, a plant called sweet mignonette came up with a distasteful strategy. Critters called spiny mice feed on mignonette. They love the fruit. But they hate the seeds. And so they spit them out all over the place. Just as the plant planned. That’s according to a study in the journal Current Biology. [Michal Samuni-Blank et al.,"Intraspecific Directed Deterrence by the Mustard Oil Bomb in a Desert Plant"]
Sweet mignonette produces little black berries that house about 20 seeds apiece. Inside those seeds is an enzyme. When a berry-chomping mouse crushes a seed, the enzyme is freed up to produce compounds that taste like hot mustard. Hence, ptooey, better leaving through chemistry.
Researchers armed with video cameras observed the mice spitting the pits like kids eating watermelon on a summer day. Nearly three-quarters of the spit-soaked seeds landed intact—and they actually germinated twice as fast as seeds taken directly from the fruit itself. It’s like a Dickens book: Great Expectorations.
[The above text is an exact transcript of this podcast.]