THE POLLINATION ECOLOGY OF PEDICULARIS (SCROPHULARIACEAE) IN THE YUKON TERRITORY

Abstract

The pollination ecology of six native species of Pedicularis (Scrophulariaceae) was investigated in the Kluane Range of the St. Elias Mountains in the Yukon Territory (Canada). Seed production in all species depended upon pollination by bumblebees (Bombus Latr. spp.). Asexual propagation by root and crown branching was present in P. capitata and P. langsdorfii. Cinematographic and stereophotographic records indicated that bumblebee queens foraged in an upright (nototribic) position for nectar and pollen. Bombus workers foraged upright on P. verticillata, inverted (sternotribic) on P. labradorica, and in both positions on P. capitata, P. kanei, P. langsdorfii, and P. sudetica. The potential for hybridization between Pedicularis species by reason of overlapping blooming periods, sharing of the same or adjacent habitats, and recovery of individually marked pollinators was noted. Analysis of 1402 corbicular pollen loads from 1769 pollinating bumblebees of 14 species of Bombus on Pedicularis revealed that equal numbers of pure and mixed loads were collected. This suggested a low level of forager fidelity to a single plant species. Investigation of colors of corollas in visible light by reflectance spectrophotometry and in long‐wave (360 nm) ultraviolet light by photography revealed distinct reflectance spectra for visible light but no ultraviolet reflectance. A wide range of concentrations of sugar in nectars from the six species of Pedicularis was detected by refractometry. Chromatographic analysis of nectars indicated fructose and sucrose in nectars of four species with P. kanei and P. langsdorfii having additional glucose and raffinose or glucose and rhamnose, respectively. Nectar was abundant in all species except P. labradorica. A comparison of lengths of nectariferous tubes of corollas, lengths of tongues (prementum plus glossa) of pollinators, behavior of pollinators, and diversity of species of pollinators on each species of Pedicularis indicated that adaptive behavior of pollinators was related to the length of tongues of pollinators. It is suggested that interactions between floral mechanisms and pollinating insects probably contributed substantially to the present diversity of floral form in species of Pedicularis in North America.