Floral Color Diversity: How Are Signals Shaped by Elevational Gradient on the Tropical–Subtropical Mountainous Island of Taiwan?

Abstract

Pollinators with different vision are a key driver of flower coloration. Islands provide important insights into evolutionary processes, and previous work suggests islands may have restricted flower colors. Due to both species richness with high endemism in tropical–subtropical environments, and potentially changing pollinator distributions with altitude, we evaluated flower color diversity across the mountainous island of Taiwan in a comparative framework to understand the cause of color diversity. We sampled flower color signaling on the tropical–subtropical island of Taiwan considering altitudes from sea level to 3300 m to inform how over-dispersion, random processes or clustering may influence flower signaling. We employed a model of bee color space to plot loci from 727 species to enable direct comparisons to data sets from continental studies representing Northern and Southern Hemispheres, and also a continental mountain region. We observed that flower color diversity was similar to flowers that exist in mainland continental studies, and also showed evidence that flowers predominantly had evolved color signals that closely matched bee color preferences. At high altitudes floras tend to be phylogenetically clustered rather than over-dispersed, and their floral colors exhibited weak phylogenetic signal which is consistent with character displacement that facilitated the co-existence of related species. Overall flower color signaling on a tropical–subtropical island is mainly influenced by color preferences of key bee pollinators, a pattern consistent with continental studies.

Flower Color as Predictor for Nectar Reward Quantity in an Alpine Flower Community

“…The number of flowers found in each of the major bee-color categories (sensu Chittka et al, 1994) differed significantly from a uniform distribution, with the majority falling into the "blue-green" sector. This pattern, as well as that obtained when analyzed at a finer resolution (Figure 1C), showed remarkable similarity with data from other habitats and locations, e.g., Germany (Giurfa et al, 1995), Australia (Dyer et al, 2012), Nepal (Shrestha et al, 2014), New Zealand (Bischoff et al, 2013), and Taiwan (Tai et al, 2020). Interpretation and comparison of the distribution is problematic as it may depend on sampling strategy, habitat type, pollinator species and the choice of visual system selected for the color modeling (for a discussion, see Shrestha et al, 2019).…”

Fragmentary Blue: Resolving the Rarity Paradox in Flower Colors

“…Flower color plays an important role in the taxonomy of plants by helping differentiate between single species ( Linnaeus, 1735 , 1755 , 1785 ) as well as in the ecology of plants by attracting pollinators ( Chittka and Menzel, 1992 ; Shrestha et al, 2013 ; Ohashi et al, 2015 ; LeCroy et al, 2021 ). In addition, other factors can also be at play, as recent evidence suggests that increased pollinator competition may also promote convergence toward the most preferred colors ( Shrestha et al, 2019a ; Tai et al, 2020 ), which is discussed in depth below. Accordingly, in harsher conditions, with less competition, higher divergence of flower colors is observed ( Dalrymple et al, 2020 ).…”

A test of Sensory Drive in plant–pollinator interactions: heterogeneity in the signalling environment shapes pollinator preference for a floral visual signal

“…For instance, community composition of flower colour often varies across space (e.g. Shrestha et al ., 2014; Bergamo et al ., 2018; Tai et al ., 2020; LeCroy et al ., 2021), and the signalling environment could be an underappreciated driver of such variation. Finally, plant expansions into novel habitats that differ in signalling conditions from natal habitats may set the stage for novel selection on floral visual signals.…”