Floral pigmentation patterns provide an example of Gloger's rule in plants

Abstract

Ecogeographic rules explain spatial trends in biodiversity, species interactions and phenotypes(1). Gloger's rule and its corollaries state that pigmentation of endothermic animals will increase from more polar to equatorial regions due to changing selective pressures including heat, humidity, predation and UV irradiance(2-4). In plants, floral pigmentation varies within and among taxa, yet causes of wide-scale geographic variation are lacking. We show that Gloger's rule explains patterns of variation in UV-absorbing floral pigmentation in a widespread plant, Argentina anserina (Rosaceae). Specifically, the floral pigmentation pattern unique to the UV spectrum (UV 'bullseye') increases with proximity to the Equator in both hemispheres, and larger bullseyes are associated with higher UVB incidence. Experiments confirm UV as an agent of selection and bullseye size as a target. Results extend the generality of an ecogeographic rule-formulated for animals-to plants, implicating UV as a selective agent on a floral trait generally assumed to enhance plant-pollinator interactions. Global change is expected to alter UV irradiance in terrestrial systems(5), potentially intensifying the importance of UV-mediated selection to floral evolution. Because floral UV reflectance and pattern enhance pollinator attraction(6,7), altered selective regimes could disrupt coevolved plant-pollinator interactions, weakening an important ecosystem service(8).

The color of plant reproduction: macroecological trade-offs between biotic signaling and abiotic tolerance

“…A key, unifying feature of recent work on the color of plant reproduction is their geographic scope (e.g., Amico et al, 2011;Arista et al, 2013;Stournaras et al, 2013;Koski and Ashman, 2015). A growing body of literature across macroecological spatial scales illustrates that variation fruit and flower colors often matches geographic variation in both biotic and abiotic factors.…”

“…Koski and Ashman (2015) recently documented that UV-absorbing pigments in the flowers of Argentina anserina increases toward the tropics. Although these floral pigments could be signals to insect pollinators, they might also help to protect gametes against the harmful effects of UV light, which increases at lower latitudes.…”

Functional optics of glossy buttercup flowers

“…Abiotic factors, including sunlight, have been previously documented to impose selective pressures on flower anatomy and coloration [53,55,56]. For example, Koski & Ashman [56] recently reported that exhaustive amounts of internal UV reflections can be deleterious for plant reproduction.…”

Gloger’s Rule in Plants: The Species and Ecosystem Levels

“…10 However, there are many cases that show opposite patterns because of specific local or regional selective agents. Since very little attention has been given to Gloger's rule in plants, we still do not know the extent of its significance in plant biology.…”

“…Lev-Yadun 7 also proposed that since many desert animals tend to be paler than other members of the same taxa that inhabit wetter environments, according to Gloger's rule, 4 the abovementioned light-colored plant species are a good indication that Gloger's rule applies to plants. Recently it was elegantly demonstrated that Gloger's rule applies at the intraspecific level concerning UVB absorption via dark areas in flowers to defend their anthers and pollen from exposure to UV light reflected from petals, 10 this being the second system where Gloger's rule operates in plants. In both cases, flowers 10 and coastal/sand dune/desert plants, 7 the characters involved in the operation of Gloger's rule in plants belong to complex functions, the probable outcome of several simultaneous selective agents that together resulted in the Gloger's rule phenomenon.…”