Developmentally-programmed division of labour in the clonal invader Carpobrotus edulis

Abstract

Invasive species are one of the main causes for the loss of global biodiversity. However, the mechanisms that explain the success of invasive species remain unsolved. Clonal growth has been pointed out as an attribute that could contribute to the invasiveness of plants, however little research has been conducted to determine the importance of clonal traits in successful invaders. One of the most interesting attributes related to clonal growth is the capacity for division of labour. In this experiment we investigated the capacity for division of labour in the aggressive invader Carpobrotus edulis, and how clonal integration can contribute to the expansion of this species. Division of labour was determined by studying the degree of morphological and physiological specialization of individual ramets to a specific activity: acquisition of soil or aboveground resources and aboveground expansion. Our results showed that there is division of labour in the clonal fragments, with older ramets increasing the biomass allocated to roots (specialization in the uptake of belowground resources) and younger ramets increasing the chlorophyll content and aboveground biomass (specialization in the uptake of aboveground resources). Physiological integration allows division of labour, and as consequence the overall performance of the clonal fragment was enhanced, with connected clonal fragments showing a higher total biomass than severed clonal fragments. Division of labour increased the aboveground growth of apical ramets of C. edulis, and therefore could contribute to an effective colonization of the surrounding area by this aggressive invader. Our study is the first exploring the role of division of labour in the expansion of an invader, and supports the idea that clonal traits could increase the invasiveness of plant species.