Geographic Variation in Flower Size and Flower-Visitor Composition of Two Bumblebee-Pollinated, Spring-Flowering Herbs, <i>Lamium album</i> L. var. <i>barbatum</i> (Lamiaceae) and <i>Meehania urticifolia</i> (Lamiaceae)

Abstract

Geographic variation of flower size is potentially affected by various biotic and abiotic factors such as pollinator size, abundance of nectar robbers, and temperature. To elucidate the effect of geographic variation of flower-visitor fauna on flower size, we investigated two spring-flowering, bumblebee-pollinated herbs, Lamium album L. var. barbatum (seven populations) and Meehania urticifolia (five populations), in central Japan. Flower-size variations were not correlated with altitude (an index of abiotic environmental change) in either species, but in both species they were related to the local species composition of flower visitors. In L. album, flowers were bigger in populations visited by long-tongued Bombus consobrinus and B. diversus queens, whereas they were smaller in populations visited by short-tongued bees such as Apis mellifera. Flower size did not vary much among populations of M. urticifolia visited by long-tongued bumblebees, but it was uniquely small in a population whose flowers were predominantly visited by the nectar-robbing bee Megachile japonica. In conclusion, both the size and nectar-robbing behavior of bees affect local flower-size adaptation in these two long-tubed, spring-flowering herbs.

Pattern of flower size variation along an altitudinal gradient differs between Impatiens textori and Impatiens noli-tangere

“…Previous studies that have investigated flower size variations along an altitudinal gradient in mountainous environments have reported corresponding altitudinal variations in, for example, pollinator species composition and nectar robbing frequency (Hattori et al , 2015Nagano et al 2014;Kuriya et al 2015;Zhao & Wang 2015). In this study, we showed that the pattern of flower size variation along an altitudinal gradient differed between two Impatiens species growing in similar habitats.…”

Intraspecific Convergence of Flower Size Correlates With Pollinator Size on Different Mountains: A Case Study of a Bumblebee-Pollinated Lamium (Lamiaceae) Flowers in Japan

“…barbatum (Lamiaceae) is a perennial herb that grows along forest edges throughout East Asia [47]. It produces creamy white, twolipped, entomophilous, and self-incompatible owers [40,41]. The owers are frequently visited by various bumblebee species, and in Japan, the corolla tube length of the owers may correlate with the size (proboscis length and head length) of their bumblebee pollinators.…”

“…In addition to bumblebees, honeybees and wild bees have been observed to visit L. album var. barbatum owers, but in Japan bumblebees are their main pollinators [40].…”

“…First, 18-170 individuals were haphazardly selected from each population. Then, following the method of Hattori et al (2015) [40], we measured the corolla tube length of 1-6 owers per individual plant with a digital caliper (precision, 0.01 mm). The corolla tube length was de ned as the distance from the ower's base at the stem to its tip (Fig.…”

“…In Japan, corolla tube length varies geographically in Lamium album L. var. barbatum Franch (Lamiaceae) [40]. In Europe, L. albumbarbatum is reported to be visited mainly by bumblebees [40], whereas L. album is visited by small wild bees and honeybees [41].…”