POLLINATION ADAPTATION IN PEDICULARIS GROENLANDICA

Cinematographic and stereophotographic records indicate that Pedicularis groenlandica is pollinated in the Colorado Front Range by seven species of pollen-foraging bumblebees (Bombus sp.) to which the nectarless flower is intricately adapted functionally and structurally. Removing pollen by wing vibrations of an oscilloscopically identified frequency significantly distinct from flight vibration frequency, foragers carried pollen loads with up to three foreign pollen types in addition to Pedicularis pollen, which was found in all loads. No direct correlation was evident between flight vibration frequency and combined body-pollen load weight, ambient air temperature, or forager species. The flower is phenologically and morphologically adapted to the worker caste of apparently any Bombuts species available to it throughout the plant's montane-alpine zone vertical-distribution range. The evolutionary position of the pollination mechanism is considered in relation to the floral morphology of other species in the genus Pedicularis. THE EVOLUTION of the Pedicularis flower has been attributed to relationships with its animal pollen vectors. Although systematic accounts of the genus by Prain (1891), Pennell (1935, 1943), Li (1948, 1949), Wendelbo (1965) and others have described floral morphology, mutual adaptations of flower and forager in the pollination process have been insufficiently studied. Pollinator foraging behavior in Pedicularis has been described by Meehan (1873), Weed (1884), Olberg (1951), Sprague (1962), and Faegri and van der Pijl (1966). Muiller (1873) has summarized earlier accounts. The present study is an attempt to record with substantial precision the operation of the pollination mechanism of Pedicularis groenlandica Retz in Colorado. METHODS AND MATERIALS During the summers of 1966 and 1967 the behavior of insect foragers on the flowers of Pedicularis groenlandica was observed in wet meadows of the subalpine and alpine zones of the Rocky Mountain Front Range in Colorado at altitudes of 9,150 (midJuly), 10,600 (early August), and 12,750 ft above mean sea level (mid-August). Permanent records of this activity were made by high-speed cinematography and close-up (90 mm) stereophotography. Wing-vibration sounds produced by insects during pollen foraging were recorded on magnetic tape and their frequencies determined and compared oscilloscopically with those produced during flight. To test the hypothesis that wing-vibration frequency may be related to ambient air temper' Received for publication 17 January 1968. This study was supported by National Science Foundation Grant GB-5184. 2Permanent address: Department of Biology, University of Akron, Akron, Ohio 44304. ature and forager species, pairs and trios of foragers with combined body-pollen load weights differing by less than 1 mg were compared. A possible correlation of frequency with the combined weight was also investigated. Three air temperatures, viz., 59, 63, and 71 F, were available during several field studies conducted between 8:15AM and 3:45 PM Mountain Daylight Time at an elevation of 9,150 ft. Only Bombus bifarius and B. melanopygus yielded sufficient numbers of individuals for comparison of flight vibration frequencies. The latter were preferred to foraging-vibration frequencies, which may have been complicated by interaction with flower resonance. Pollen from corbicular loads was mounted in glycerin jelly tinted with methyl green for identification (to genus only) by comparison with samples in a reference collection prepared from flowers in the research area. OBSERVATIONs-Pedicularis groenlandica (Fig. 1) is a low-growing arctic-alpine herb. Its zygomorphic, sympetalous, hypogynous flower (Fig. 16A-C), resembling an elephant's head with ears formed of two lateral petals flanking a medium lower petal and two upper median petals fused dorsally but not ventrally to form a galea with a rostral extension resembling a proboscis, is attached perpendicularly to an 8-17-cm spike (Fig. 2). During the course of its development the originally straight rostrum tip extends in a clockwise or counterclockwise circular pattern in a plane perpendicular to its original horizontal direction of growth. At full anthesis the rostrum tip points approximately in its original direction (Fig. 12, upper flower). The deep-pink corolla is marked with two vertical magenta blotches above the base of the rostrum and flanking a median ridge (Fig. 16A).