POLLEN TRANSFER EFFICIENCY IS A CHARACTERISTIC OF SPECIES RATHER THAN POPULATIONS IN THE MEDITERRANEAN FOOD-DECEPTIVE ORCHID ORCHIS ANTHROPOPHORA

Pollen transfer efficiency (PTE), i.e. the proportion of exported pollen reaching conspecific stigmas, is a key factor for the evolution of pollination systems in flowering plants. The success of entomophilous pollination systems is largely dependent on the increasing of PTE with respect to anemophilous systems (1). In this context, orchids have pollen packed in peculiar structures called pollinaria that allow an insect to carry all or half of the total amount of the pollen produced by a flower in a single visit thus further increasing PTE. Recent studies (2, 3) showed that in deceptive pollination strategies PTE differs in generalised and specialised systems being higher in the latters and likely representing one of the reasons that lay at the basis of the multiple independent transitions occurred among pollination strategies in this plant group (2). This finding suggests that PTE can be linked to the specific pollination system employed by a species rather than being influenced by local environmental and pollinator community differences as occurs for male (MRS) and female (FRS) reproductive success. However, the levels of variability of this parameter in multiple conspecific populations are still unclear. Here we surveyed seven different populations of the Mediterranean food-deceptive orchid species Orchis anthropophora. We estimated PTE as well as MRS and FRS by observing the amount of pollen exported and deposited. Overall, our results show that although MRS and FRS vary among populations, PTE, that is a combination of both, is less variable (Fig. 1). These results strongly suggest that PTE is mostly characteristic of species rather than populations and likely depends on pollinator behavior being thus less influenced by ecological factors that can alter the pollinator local abundance and composition