Trapped in a hot microcosm: how flower microclimate contributes to pollination syndrome in a thermogenic system

Microclimates within microcosms are often stated to shelter occupants from adverse conditions, yet our limited knowledge narrows our ability to estimate the vulnerability to warming of species exploiting them. We characterized the microclimate temperature of the floral chamber of a thermogenic plant that produces heat in the context of pollination syndrome. Pollinators (Psychoda moth flies) of Arum italicum are trapped within the floral chamber for 24 h, thereby potentially exposing insects to dangerous temperatures. We report a strong temperature gradient across the floral chamber. We propose two hypotheses for the role of this temperature gradient in the pollination syndrome depending on environmental context. Under moderate conditions, the system relies on the exact position of the thermogenic organ to discourage insects from escaping the chamber, while temperature at the bottom of the chamber corresponds to the moth fly's preferred temperature, motivating the insect to remain there long enough to get covered by pollen. Under extreme conditions, the floral chamber may provide a thermal reward to avoid the Psychoda fly from reaching its thermal limits. Our comprehensive mechanistic analysis of the microclimate in a thermogenic flower highlights the importance of coevolutionary trajectories between temperature regulation by plants and their pollinators' thermal biology. This article is part of the theme issue 'Life in natural microcosms'.