The nectar spur is not only a simple specialization for long‐proboscid pollinators

Abstract

Since the time of Darwin, biologists have considered the floral nectar spur to be an adaptation representing a high degree of plant specialization. Nevertheless, some researchers suggest that nature is more complex and that even morphologically specialized plants attract a wide spectrum of visitors. We observed visitors on Impatiens burtonii (Balsaminaceae) and measured the depth of the proboscis insertion into the spur, the distance of the nectar surface from the spur entrance and the visitor's effectiveness. The hoverfly Melanostoma sp., with the shortest proboscis, was most active early in the morning and fed on pollen and nectar near the spur entrance. The honeybee Apis mellifera and the hoverfly Rhingia mecyana were the most frequent visitors before and after noon, respectively. Although R. mecyana, the only visitor able to reach the end of the spur, was the most frequent, it did not deposit the largest number of pollen grains per visit. Nectar spurs may function as complex structures allowing pollination by both short- and long-proboscid visitors and separating their spatial and temporal niches. Spurred plants should be considered as more generalized and exposed to more diverse selection pressures than previously believed.

Phylogenetic relationships of the bacchine flower flies (Diptera: Syrphidae) based on molecular characters, with a description of a new species of Melanostoma (Schiner, 1860)

“…This new species to science is refereed as Melanostoma sp. in Vlašánková et al (2017). In the present study, the division between Bacchini sensu stricto and Melanostomini stated by Thompson & Skevington (2014) will be followed to discuss the results.…”

“…The new species of Melanostoma was collected during the field work done by Vlašánková et al (2017) in the Mendong Buo area (6.592699°N, 10.189999°E; 2100-2200 m above sea level), ca. 5 km south-east of Big Babanki, in the Bamenda Highlands, North-West Province, Cameroon.…”

A study of floral shape variation in Delphinieae (Ranunculaceae) using geometric morphometrics on herbarium specimens

“…Geometric morphometric analyses can enrich studies on the phenotypic evolution of flowers and of their pollinators. In the case of the spurred flowers of Delphinieae, for which the pollinators are expected to be specialists (but see Hollens et al 2017;Vlašánková et al 2017), comparing the form of the dorsal floral module with the front of the pollinator's body would allow testing the mutual fit of both structures. The collections (herbarium, entomological and ornithological) kept at natural history museums would be very useful in this respect.…”

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“…Several studies reported that selectivity of some hoverfly species depends on certain plant traits. Overall, hoverflies seem to visit mostly open bowl-shaped flowers (Branquart and Hemptinne, 2000), where they feed on both nectar and pollen (Gilbert, 1981), but some of them have relatively long proboscises which allow them to reach nectar even in flowers with relatively long spurs (Gilbert, 1981;Vlašánková et al, 2017). In addition, inflorescence height also affects flower visitation by some species (Gervasi and Schiestl, 2017;Klecka et al, 2017).…”