Plant love makes for a good defense

Why do some plants defend themselves from insect attacks better than others? New evidence shows that the difference might be due to whether they\'re getting any plant love.

A spot of sex can work wonders for defending against insect attack

In research published in Proceedings of the National Academy of Sciences, scientists from the US discovered that sexually produced evening primrose plants withstand attacks from plant-eaters like caterpillars better than plant relatives that reproduce by themselves.

The findings are important steps to learning more about how plants have evolved defences against insect herbivores, says Dr Marc Johnson, assistant professor of plant biology at NC State and the lead author of the research paper.

“Sex shuffles up genes and allows individual plants to get rid of bad genes and keep good ones,” he said. “That helps them evolve defenses against generalist herbivores. Though there are short-term benefits to asexual reproduction – populations can grow more rapidly and propagate even when pollination is not possible – losing sex puts plants at a long-term disadvantage. In the end, asexual reproduction appears to be an evolutionary dead-end,” he said.

In the study, the researchers performed both lab and field experiments on evening primrose (Onagraceae) plants, a plant family that has 259 different species – 85% of which reproduce sexually with the remainder reproducing asexually – to gauge the effects of plant sex on defence mechanisms. The researchers found that so-called generalist herbivores – those that eat a variety of plants – preferred to feed on the asexual species and lived longer while doing so.

The results were a bit different for so-called "specialist" plant-eaters, however. Those insects that prefer just one kind of food were more apt to munch on sexually reproduced species of plant. This most likely occurs, Johnson says, because specialised plant-eaters evolve alongside their hosts and have found ways to co-opt plant defences. Instead of being deterred by certain chemical compounds produced as defences by the plant, the specialised plant-eaters are attracted to them.