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 27 Lonchocarpus toxicity DHJanzen100549.jpg high resolution
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The question became just what is the compound in a Lonchocarpus seed that is so repugnant or toxic to Liomys salvini? A large number of seeds were sent to Linda Fellows at Kew Gardens in England, Linda being a specialist on toxic alkaloids and other nitrogenous compounds in seeds. She immediately noted that the seeds contained a high content of several alkaloids, and we all thought that this is what must be stopping the mice. She extracted and purified many grams of these compounds and sent them back. I mixed them up into lab chow, and fed them to the mice. The mice were delighted. Either the alkaloids were directly non-noxious to the mice, or the lab chow offered such good nutrients that they compensated for whatever effects the alkaloids were having (sugar and milk in your cup of coffee? can you survive on a diet of brownies?). But Linda noticed that when she sliced open and ground up the seeds, there were pockets of what seemed to be oils in them (see section through a fruit) and noted that these were rich in flavonoids. So, I sent yet more Lonchocarpus seeds to Peter Waterman in Scotland, a flavonoid specialists. Peter allowed as how there were 7 kinds of flavonoids in the seeds, many of which were new to science. He isolated and described them to me, and sent back 8 vials of nicely separated pure compounds. Being a dutiful scientist, I mixed them one by one into lab chow diets and presented them hopefully to my mouse taste panel. They gobbled them all down, and grew fat and sassy on their flavonoid-laced diets. At this point my frustration moved me away from the rigrous chemist-oriented tester to being an ecologist. Of course. The mice do not encounter one or the other flavonoid, but all 8 in a bite. I had a bit of material remaining in each of the vials (because I had so carefully measured out the dosages), which I slopped all together and put into lab chow. It stopped every member of the taste panel. They would not touch it. So, do we now know the defenses of the Lonchocarpus seed? Not yet, not by a long shot. All we know is that one complex of flavonoids stops the mice. Indeed, there could well be yet other compounds in that seed that also stop the mice. We do know there are also protease inhibitors in the seed, but these compounds in general do not deter Liomys mice (these mice love lab chow laced up to 25% dry weight protease inhibitors). |
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