Intraspecific independent evolution of floral spur length in response to
local flower visitor size in Japanese Aquilegia in different
mountain regions
Abstract
Geographic differences in floral traits may reflect geographic
differences in effective pollinator assemblages. Independent local
adaptation to pollinator assemblages in multiple regions would be
expected to cause parallel floral trait evolution, although sufficient
evidence for this is still lacking. In this study, we investigated the
relationship between flower spur length and pollinator size in 16
populations of Aquilegia buergeriana var. buergeriana
distributed in four mountain regions in the Japanese Alps. We also
examined the genetic relationship between yellow- and red-flowered
individuals, to see if color differences caused genetic differentiation
by pollinator isolation. Genetic relationships among 16 populations were
analyzed based on genome-wide single-nucleotide polymorphisms. Even
among populations within the same mountain region, pollinator size
varied widely, and the average spur length of A. buergeriana var.
buergeriana in each population was strongly related to the
average visitor size of that population. Genetic relatedness between
populations was not related to the similarity of spur length between
populations; rather, it was related to the geographic proximity of
populations in each mountain region. Our results indicate that spur
length in each population evolved independently of the population
genetic structure but in parallel in different mountain regions.
Further, yellow- and red-flowered individuals of A. buergeriana
var. buergeriana were not genetically differentiated. Unlike
other Aquilegia species in Europe and America visited by hummingbirds
and hawkmoths, this species is consistently visited by bumblebees in
Japan. As a result, genetic isolation by flower color has not occurred.