Confirmed mixed bird-insect pollination system of Scrophularia trifoliata L., a Tyrrhenian species with corolla spots.

Abstract

Both bird and mixed vertebrate-insect (MVI) pollination systems are very rare in Europe and the Mediterranean region. Because MVI can ensure reproduction over a wider range of environmental conditions than when insects are the sole pollinators, under certain circumstances such systems are highly advantageous to plants. Here, we investigated the pollination and some reproductive traits of the Tyrrhenian Scrophularia trifoliata, the only species of the genus possessing two showy dark spots inside the corolla, for which MVI pollination system had been inferred on the basis of limited censuses. We conducted field experiments to study MVI pollination and some reproductive traits and elucidate the role of corolla spots, analysing their ultraviolet pattern, histology and pigments versus the rest of the corolla. The primary pollinators were wasps and passerine birds. Corolla spots absorb UV light, present abundant anthocyanins and are histologically identical to the rest of the corolla. Control flowers had higher visitation frequency than flowers without spots. S.trifoliata is self-compatible, with efficient intrafloral protogyny and herkogamy that prevent self-pollination but not geitonogamy. We confirmed the existence of a mixed bird-insect pollination system in S.trifoliata. This system is found in three other Scrophularia species with large, showy flowers - two Mediterranean (S.grandiflora and S.sambucifolia) and one Macaronesian (S.calliantha). Unlike those species, S.trifoliata has two large spots inside the corolla. These likely operate as nectar guides and their dark colouration is related to abundant anthocyanin content.