Lizards as a plant's 'hired help': letting pollinators in and seeds out

Abstract

It is well-known that plants utilize many different kinds of animals for pollination and dispersal of their seeds, but an alternative kind of evolutionary relationship has attracted less attention: animals can facilitate pollen and seed transport without acting as a vector. We studied interactions between an epacridaceous plant (the honey bush, Richea scoparia) and a lizard (the snow skink, Niveoscincus microlepidotus) near the summit of Mount Wellington, Tasmania. The lizards gain access to the plant's nectar by tearing the fused petals (the calyptra) from the flower, thus exposing the plant's reproductive organs. Snow skinks forage selectively on flowers with higher-than-average nectar content, suggesting that this behaviour has evolved in response to plant characteristics. Lizard foraging may benefit R. scoparia, because calyptra remain attached unless a lizard tears the flower open. Our experiments demonstrated that the lizard's calyptra removal dramatically increased the plant's seed release. In 60 fruits from flowers with their calyptra intact, no seeds at all were released. However, 57 out of 60 (87%) fruits from flowers with their calyptra removed by the lizards successfully released their seeds. This system appears to involve reciprocal evolutionary changes in the interacting species (behaviour in the lizards and reproductive morphology in the plant). Thus the system seems to provide an unusual case of coevolution.