2.1 Plant species and study site
Aquilegia buergeriana var. buergeriana f. flavescens is a perennial, protandrous herb endemic to Japan. The spur and sepals of its flowers are pale yellow (yellow-flowered individual) or reddish brown (red-flowered individuals) (Figure 1a, b). Flowers of both colors face downward. In the study area, in the central Japanese Alps, yellow-flowered individuals are more common. Japanese Aquilegiaspecies are mainly visited by bumblebees (Tamura & Shimizu, 1999; Itagaki & Sakai, 2006; Hattori et al., 2014), even though, in general, yellow-flowered Aquilegia are pollinated by hawkmoths (Hodges et al., 2004). Unlike most Aquilegia with yellow flowers, however, the yellow flowers of Japanese Aquilegia buergeriana do not have protruding anthers and pistils and are not visited by hawkmoths (Toji personal observation by camera trap).
We studied Aquilegia populations in four mountain regions (Utsukushigahara, Norikura, Ontake, and Iizuna) of the central Japanese Alps (Figure 1d; supplementary material, Table S1). Field surveys were conducted during the flowering season, from July to September, in 2018 and 2019: Populations in the Utsukushigahara, Norikura, and Ontake mountain regions were surveyed in 2018, and populations in the Iizuna mountain region were surveyed in 2019.