Altitudinal flower size variation correlates with local pollinator size in a bumblebee‐pollinated herb,Prunella vulgarisL. (Lamiaceae)

Abstract

The influence of locally different species interactions on trait evolution is a focus of recent evolutionary studies. However, few studies have demonstrated that geographically different pollinator-mediated selection influences geographic variation in floral traits, especially across a narrow geographic range. Here, we hypothesized that floral size variation in the Japanese herb Prunella vulgaris L. (Lamiaceae) is affected by geographically different pollinator sizes reflecting different pollinator assemblages. To evaluate this hypothesis, we posed two questions. (1) Is there a positive correlation between floral length and the proboscis length of pollinators (bumblebees) across altitude in a mountain range? (2) Does the flower-pollinator size match influence female and male plant fitness? We found geographic variation in the assemblage of pollinators of P. vulgaris along an altitudinal gradient, and, as a consequence, the mean pollinator proboscis length also changed altitudinally. The floral corolla length of P. vulgaris also varied along an altitudinal gradient, and this variation strongly correlated with the local pollinator size but did not correlate with altitude itself. Furthermore, we found that the size match between the floral corolla length and bee proboscis length affected female and male plant fitness and the optimal size match (associated with peak fitness) was similar for the female and male fitness. Collectively, these results suggest that pollinator-mediated selection influences spatial variation in the size of P. vulgaris flowers at a fine spatial scale.

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.…”

“…The primary flower visitor to I. noli-tangere was also B. diversus, as Tokuda et al (2015) also reported ( Table 1). The flower-pollinator size match often influences plant fitness more than other factors Kuriya et al 2015). Therefore, these results suggest that flower dimensions were affected not by a clinal change in any abiotic environmental factor along altitude but by the size-match between the flowers and the B. diversus body size.…”

“…air temperature), or by an altitude-related pollen limitation (Cosacov et al 2008), than by size-matching between flower and pollinator, because the pollinator species composition in central Japan seems to be similar, regardless of time or place. Various environmental factors such as air temperature and pollinator abundance change along an altitudinal gradient (Körner 1999;Nagano et al 2014;Kuriya et al 2015). These environmental factors can affect flower size variation along the gradient (Galen 2000;Knight et al 2005;Parachnowitsch & Kessler 2010).…”

“…meteorological changes) cause variations in plant vegetative size (Fabbro & Körner 2004;Anderson & Johnson 2009;Hautier et al 2009). Moreover, in some bumblebee-pollinated species, altitudinal changes in biotic interactions have been shown to influence flower size indirectly (Dohzono & Suzuki 2010;Nagano et al 2014;Kuriya et al 2015). In this study, we investigated altitudinal variations in flower dimensions and flower visitors in two native Japanese Impatiens species that have broad altitudinal distributions.…”

“…pollinator distribution, plant community composition) influencing the diversification and evolution of floral traits such as shape, color, and scent ( Van der Niet et al 2014). In many animal-pollinated plants, evidence has accumulated that floral diversification and adaptation occur in response to selection by pollinators (Schemske & Bradshaw 1999;Whittall & Hodges 2007;Pauw et al 2009;Gómez et al 2014;Nagano et al 2014;Kuriya et al 2015). Although many floral adaptations have undoubtedly arisen under selection pressure by pollinators, other selection agents also drive floral adaptation (reviewed by Strauss & Whittall 2006).…”