Changes in pollinator fauna affect altitudinal variation of floral size in a bumblebee‐pollinated herb

Abstract

Geographic trait variations are often caused by locally different selection regimes. As a steep environmental cline along altitude strongly influences adaptive traits, mountain ecosystems are ideal for exploring adaptive differentiation over short distances. We investigated altitudinal floral size variation of Campanula punctata var. hondoensis in 12 populations in three mountain regions of central Japan to test whether the altitudinal floral size variation was correlated with the size of the local bumblebee pollinator and to assess whether floral size was selected for by pollinator size. We found apparent geographic variations in pollinator assemblages along altitude, which consequently produced a geographic change in pollinator size. Similarly, we found altitudinal changes in floral size, which proved to be correlated with the local pollinator size, but not with altitude itself. Furthermore, pollen removal from flower styles onto bees (plant's male fitness) was strongly influenced by the size match between flower style length and pollinator mouthpart length. These results strongly suggest that C. punctata floral size is under pollinator-mediated selection and that a geographic mosaic of locally adapted C. punctata exists at 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.…”

“…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).…”

“…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).…”

“…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.…”

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)

“…Because the species composition of bumblebee populations varies among regions [17]- [19] [21], the floral traits of bumblebee-pollinated plants are expected to vary among regions. In fact, a number of studies have presented evidence from several plant species supporting this expectation [14] [22]- [24]. These studies focus on the interaction between summer-flowering plants and bumblebee workers in summer [25]; the influence of bumblebee queens, which are active in spring, on floral trait variation in spring-flowering plants has less been studied (but see [26]).…”