Predators can kill by presence alone

Abstract

Plants called cycads, which resemble ferns and palms, emerged more than 260 million years ago and are thought to have changed little since. However, today's cycads have more recent roots. Nathalie Nagalingum at the Royal Botanic Garden Sydney in Australia, Sarah Mathews at Harvard University in Cambridge, Massachusetts, and their team created an evolutionary tree charting the relationships between two-thirds of the world's 300 extant cycad species (one, Cycas thouarsii, pictured). The tree, based on genetic data and fossil records, points to a boom in cycad diversity less than 12 million years ago, during the late Miocene. A shift to more seasonal climates across the globe during this period may have driven cycad diversification by allowing the plants to expand their range, the authors say.