The shrub that knows how to take stock of the situation

IT’S never fazed by seeds of doubt. A shrub with small, edible berries is a cool customer when parasites attack, responding in line with the severity of the infestation. Each fruit of the barberry, Berberis vulgaris, has either one or two seeds, which may be targeted by larvae of the tephritid fruit fly. Katrin Meyer, now at the University of Göttingen, Germany, and her colleagues collected around 2000 berries to study the attacks. If the berries were pierced – a sign the fly had laid eggs inside – the team also dissected them. It was already known that the plant can cut off nutrients to an infested seed, killing the parasite in the process. But the team found that if the berry had two seeds and one was attacked the plant killed off the infested seed 75 per cent of the time, compared with just 5 per cent in single-seeded berries that were attacked. This response makes reproductive sense. Aborting an infested seed in two-seeded fruits might save the other one and keep the fruit fertile. But if there is only one seed, killing it would render the fruit sterile, and it might be better instead to rely on the small chance that the parasite would die naturally (The American Naturalist, doi.org/rtv). Such a sophisticated response in plants is impressive, says Susan Dudley of McMaster University  in Hamilton, Ontario, Canada.  “I think it is a cool result.” Some plants were known to try to ward off infections by varying their defences with the time of day,  but the new finding trumps that in terms of behavioural complexity, she says.