Abstract
AbstractChanges in the pollinator assemblage visiting a plant can have consequences for reproductive success and floral evolution. We studied a recent plant trans‐continental range expansion to test whether the acquisition of new pollinator functional groups can lead to rapid adaptive evolution of flowers.InDigitalis purpurea,we compared flower visitors, floral traits and natural selection between native European populations and those in two Neotropical regions, naturalised after independent introductions. Bumblebees are the main pollinators in native populations while both bumblebees and hummingbirds are important visitors in the new range. We confirmed that the birds are effective pollinators and deposit more pollen grains on stigmas than bumblebees.We found convergent changes in the two new regions towards larger proximal corolla tubes, a floral trait that restricts access to nectar to visitors with long mouthparts. There was a strong positive linear selection for this trait in the introduced populations, particularly on the length of the proximal corolla tube, consistent with the addition of hummingbirds as pollinators.Synthesis. The addition of new pollinators is likely to happen often as humans influence the ranges of plants and pollinators but it is also a common feature in the long‐term evolution of the angiosperms. We show how novel selection followed by very rapid evolutionary change can be an important force behind the extraordinary diversity of flowers.
Highlights
| INTRODUCTIONChanges in pollinator communities and plant range shifts are currently affecting pollination interactions across many ecosystems (González-Varo et al, 2013; Goulson et al, 2015; Grass et al, 2014)
Changes in pollinator communities and plant range shifts are currently affecting pollination interactions across many ecosystems (González-Varo et al, 2013; Goulson et al, 2015; Grass et al, 2014)and, in consequence, many plants are experiencing new pollinator environments
We are less certain about the implications for floral evolution in situations where the pollinator community changes to include new functional groups of floral visitors, which could select for new floral traits without necessarily changing the breeding system
Summary
Changes in pollinator communities and plant range shifts are currently affecting pollination interactions across many ecosystems (González-Varo et al, 2013; Goulson et al, 2015; Grass et al, 2014). Over long time-scales, pollinators are important agents of selection of floral morphological traits that increase the mechanical fit between flower and pollinator, regulate access to rewards and optimise the attractiveness of the floral display Evidence for this comes both from macroevolutionary patterns of adaptation to different pollinator functional groups (e.g. pollination syndromes, reviewed by Fenster et al, 2004) and adaptive intraspecific geographical variation resulting from historical local dissimilarity between pollinators, producing floral ecotypes To our knowledge, no studies have investigated the short-term evolutionary consequences for plants of the addition of entirely new functional pollinator groups, as opposed to a reduction in pollinator diversity This is relevant in the context of global pollinator changes and because rapid adaptation to new pollinator environments could be a key driver of angiosperm floral diversity. Convergent variation in floral traits associated to new pollinators in independently evolving naturalised populations can provide evidence for rapid adaptation to novel pollination environments
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