Subtle ecophysiological divergences in a deceptive strategy to attract the same pollinators in two sympatric Arum

Integrative approaches are mandatory to comprehend the evolution of deceptive pollination strategies, by combining the co-variations in different floral traits and the behaviour of the insects. We applied an ecophysiological approach to compare floral traits (scent and thermogenesis) in two deceptive sympatric Arum that are pollinated mainly by Psychoda moth flies. We hypothesized that floral traits diverged between the two arums to minimize their interference in attraction of pollinators.

We measured several floral traits, including the timing of anthesis, thermogenesis patterns and floral volatile organic compounds, in Arum italicum and Arum maculatum. Additionally, we conducted laboratory experiments to determine the diel activity rhythm of the moth fly Psychoda sigma. We compared the activity window of the fly with the timing of anthesis, and we compared the two arums in the ability of their volatiles to increase pollinator activity.

The main thermogenesis peak involved in pollinator attraction was cooler and occurred slightly earlier during the day in A. maculatum compared with A. italicum. The fly P. sigma appeared to be nocturnal, hence inflorescences emitting their floral scent before sunset are less likely to be visited by pollinators owing to the relatively short attractive (few hours) female phase. Regarding scents, we confirmed a strong differentiation between the two Arum species. Behavioural assays with P. sigma revealed a slightly stronger stimulation to the odour of A. maculatum compared with A. italicum.

Our integrative approach highlights that the two Arum species exhibit slightly shifted daily timing of anthesis, indicating a fine-tuned variation in their attractive volatiles and thermogenesis sequences in relationship to pollinator behaviour. A trade-off might exist between odour specificity and the ability to maximize volatile emission. These findings illustrate how evolutionarily close and sympatric species have shifted their attraction systems, potentially reducing competition within sympatric populations.