Some animals convince predators to look for a meal elsewhere by making themselves taste unpleasant, either by manufacturing foul-tasting substances or by eating other plants or animals that contain poisons. Now new research has shown that chemical defences can also be sexually transmitted between partners.
To ward off predatory spiders, arctiid moths Utethesia ornatrix use chemicals called pyrrolizidine alkaloids (PA), which they leak out as a froth when they are under attack. Though these chemicals are extracted by moth larvae from certain food plants, Andrés Gonzáles and colleagues at Cornell University, New York, have discovered that adult females have an additional source.
Males transmit PA to females with the sperm package delivered during mating. The female bestows part of this gift on her eggs to protect them against predation. By raising vulnerable female moths, fed only on PA-free food, and then allowing them to mate with males who had access to PA, the researchers have now shown that the females also benefit from the males’ nuptial gift - females who mated with PA-laden males immediately had enough chemical defences to protect them from spiders for the rest of their lives. Such are the advantages of acquiring PA defences that females judge potential partners by smelling them. Males produce a perfume derived from their PA reserves. The more PA a male has to offer, the stronger his smell, and the more likely he is to be chosen by a female as a mate.
(Proceedings of the National Academy of Sciences, vol. 96, p5570-4).