Abiotic factors may explain the geographical distribution of flower colour morphs and the maintenance of colour polymorphism in the scarlet pimpernel

Abstract

Summary1. Flower colour polymorphism is traditionally attributed to pollinator selection although other factors, such as indirect selection on correlated traits, can play an important role. 2. Lysimachia arvensis is a widespread annual species with two colour morphs differing in anthocyanin composition. We explored the hypothesis that colour polymorphism is maintained by selection related to environmental heterogeneity. Morph frequencies and environmental traits were recorded in 51 populations along a wide geographical range. To explore the existence of morph-by-environment interactions, we conducted an experimental study comparing the two morphs under treatments differing in water and light availability. 3. A geographical pattern was found with a negative association between blue frequencies and latitude. The proportion of the blue morph increased with temperature and sunshine hours, but decreased with precipitation. Flowering onset and flower size differed between morphs and scarcely varied across treatments. In contrast, several fitness components such as germination, seedling survival, seedling mass and flower production showed important morph-by-environment interactions. The blue morph showed higher overall male and female fitness in all the treatment combinations excepting in sun-wet conditions where the red morph had higher fitness. 4. Synthesis. Our results indicate that the mechanism of selection on flower colour seems to be related to differences in fitness of both morphs due to abiotic factors. These differences could explain the geographical distribution of flower colour morphs and the maintenance of the colour polymorphism. The marked difference in flowering time between morphs leaves open the potential for assortative mating and speciation in Lysimachia arvensis.

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

“…Similar mechanisms might also shape flower color polymorphisms. For example, Arista et al (2013) found that pleiotrophic effects explain the maintenance of the flower color polymorphism in scarlet pimpernel (Lysimachia arvensis), with red-flowered individuals performing better as seeds and seedlings in wetter, cooler environments.…”

“…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.…”

“…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. These and several other recent studies across large spatial scales (Amico et al, 2011;Arista et al, 2013;Stournaras et al, 2013) provide a fresh perspective on plant color polymorphisms by offering an alternative explanation for plant color polymorphisms-that some colors of flowers and fruits represent adaptations to abiotic, rather than biotic, factors.…”

Extrapolating from local ecological processes to genus-wide patterns in colour polymorphism in South AfricanProtea

“…The fitness relationships reversed when plants were well watered. Arista et al [27] found a similar pattern in Lysimachia arvensis, and the classic, long-term studies of Linanthus parryae suggest that environmentally variable natural selection contributes to maintenance of that blue-white polymorphism [9,68].…”

“…The rarity of high elevation white monomorphs suggests that pigment production could be among a suite of traits that promotes population persistence and expansion in high elevation sites. When other polymorphic species are subject to harsh experimental conditions, anthocyanin-rich plants often outperform anthocyanin-deficient ones, as mentioned previously [15,27]. A powerful test of this hypothesis would require data from a wider range of polymorphic species in addition to experimental manipulations that test the relationship between pigmentation and survival.…”