Bumblebee Pollinators and Pollination Ecotypes of Isodon umbrosus and I. shikokianus (Lamiaceae)

Abstract

Abstract Morphological and geographical correspondence of floral variants of Isodon to their pollinating bumblebees shows that the selection pressure exerted through the glossa lengths has resulted in differentiation of three pollination ecotypes of Isodon umbrosus and I. shikokianus. The first was pollinated by long‐tongued Bombus diversus. It includes I. umbrosus var. excisinflexus and I. shikokianus var. occidentalis with long corolla tubes (>8 mm). The second type was pollinated by B. honshuensis, which has a medium‐sized proboscis, and includes I. umbrosus var. umbrosus, a part of I. umbrosus var. leucanthus, var. komaensis, and var. hakusanensis, and I. shikokianus var. shikokianus with medium length corolla tubes (6–8 mm). However, B. honshuensis was not found on I. shikokianus var. intermedius of this second type, but Bombus diversus thieved nectar from this variety. The third type was pollinated by B. beaticola, which has a short glossa, and includes I. umbrosus var. latifolius and a part of I. umbrosus var. leucanthus with short corolla tubes (<6 mm). The floral variants that belong to the same pollination ecotype were not distributed sympatrically, while different types (the first type and the second or the third type) are distributed sympatrically.