Local adaptation: Mechanical fit between floral ecotypes ofNerine humilis(Amaryllidaceae) and pollinator communities

Abstract

Geographic variation in floral morphology is often assumed to reflect geographic variation in pollinator communities and associated divergence in selective pressures. We studied populations of Nerine humilis (Amaryllidaceae) to assess whether geographic variation in floral form is the result of local adaptation to different pollinator communities. We first tested for associations between floral traits and visitor communities, and found that populations with similar floral morphologies were visited by similar insect communities. Mean style length in each population was also closely associated with the mean body length of the local visitor community. A reciprocal translocation experiment demonstrated that native phenotypes set more seed than translocated phenotypes. Single visitation experiments showed that native flowers received more pollen, and set more seed per visit, than introduced phenotypes in both populations. This suggests that the effectiveness of pollinator visits is determined by the degree of mechanical fit between flowers and visitors. We provide strong evidence that the observed among-population variation in floral traits is an adaptive response to geographic variation in the pollinator community.

Real-time divergent evolution in plants driven by pollinators

“…Following the work of pioneering pollination biologists such as Charles Darwin2, a modern hypothesis of how pollinators cause floral diversification across a geographic range is the Grant–Stebbins model of pollinator-driven plant divergence345. In this model, geographical differences in pollinator abundance, the so-called pollinator mosaic, drive adaptive divergence in floral traits across plant populations leading to pollination ecotypes678910. A further consequence can be speciation through establishment of reproductive isolation mediated by a lack of pollinator sharing (that is, floral isolation) between incipient plant lineages11.…”

“…This is so because not only pollinators, but also herbivores, pathogens and abiotic factors impose selection on flowers121617. In addition, only a few studies have targeted pollinator-mediated selection in different populations to analyse divergent selection10181920. Studies that document established floral trait differences among plant populations (ecotypes) or species face similar problems in identifying the primary cause for the evolution of such variation, because floral diversification is often linked to shifts in more than one ecological factor, for example in both habitat-type and pollinators212223.…”

Geographic variation of reproductive traits and competition for pollinators in a bird‐pollinated plant

“…Much of the striking floral variation within and among angiosperms has been attributed to evolutionary responses to variation in the pollinator environment (Johnson, 2010;Kay & Sargent, 2009). Geographic variation in the pollinator landscape can potentially drive mosaics in selection regimes and floral phenotype (Herrera, Castellanos, & Medrano, 2006;Newman, Manning, & Anderson, 2015;Paudel et al, 2016). For example, differences in the relative abundance of pollinators (Anderson, Alexandersson, & Johnson, 2010;Boberg et al, 2014;van der Niet, Pirie, Shuttleworth, Johnson, & Midgley, 2014), as well as morphology (Anderson & Johnson, 2008) and preference differences in a single pollinator species (Newman, Anderson, & Johnson, 2012) may select for distinct floral ecotypes adapted to different pollinators across the geographical range of a species.…”

“…For example, differences in the relative abundance of pollinators (Anderson, Alexandersson, & Johnson, 2010;Boberg et al, 2014;van der Niet, Pirie, Shuttleworth, Johnson, & Midgley, 2014), as well as morphology (Anderson & Johnson, 2008) and preference differences in a single pollinator species (Newman, Anderson, & Johnson, 2012) may select for distinct floral ecotypes adapted to different pollinators across the geographical range of a species. Plant responses to mosaics in the quantity and quality of pollinators may include morphological adaptations to the composition of different pollinator communities (e.g., Anderson, Ros, Wiese, & Ellis, 2014;Newman et al, 2015). In addition, evolutionary responses may include changes in mating system associated with variation in the abundance of pollinators (i.e., degree of pollinator limitation; Barrett & Husband, 1990;Eckert, Samis, & Dart, 2006;Lloyd, 1979), although other adaptive responses can also occur (Harder & Aizen, 2010).…”

Gene flow and metacommunity arrangement affects coevolutionary dynamics at the mutualism–antagonism interface

“…coevolution [9]. Coevolution and selection mosaics result in patterns of local adaptation between species [10]. These patterns, however, can be homogenized by the effects of gene flow between communities [11].…”