Floral Color Variation in Drosera cistiflora Is Associated With Switches in Beetle Pollinator Assemblages

Abstract

Floral color shifts are thought to be one of the most common evolutionary transitions in plants, and pollinators are often proposed as important selective agents driving these transitions. However, shifts in flower color can also be related to neutral genetic processes or pleiotropy linked with selection via other biotic agents or abiotic factors. Here we ask whether abiotic factors or pollinators provide the best explanation for divergence in flower color among populations of the sundew Drosera cistiflora s.l. (Droseraceae). This species complex in the Greater Cape Floristic Region contains at least five distinctive floral color forms. Abiotic factors do not appear to play a significant role in color determination, as the forms are not specific to a single soil or vegetation type, sometimes co-occur in the same habitat, and maintain their color traits in common-garden and soil switching experiments. Instead, we found strong associations between flower color and the composition of pollinator assemblages which are dominated by hopliine scarab beetles. Pollinator assemblages show geographical structuring, both within and among color forms. This makes it difficult to dissect the roles of geography versus floral traits in explaining pollinator assemblages, but strong pollinator partitioning among color forms at sites where they are sympatric indicates that pollinators may select strongly on color. These results suggest that beetle pollinators are a significant factor in the evolution of D. cistiflora s.l. flower color.

Floral colour variation ofNicotiana glaucain native and non‐native ranges: Testing the role of pollinators' perception and abiotic factors

“…2015; Smith 2016; Johnson et al . 2020). In fact, pollinator‐mediated selection on other flower traits ( i.e .…”

Geographical Variation in Flower Color in the Grassland Daisy Gerbera aurantiaca: Testing for Associations With Pollinators and Abiotic Factors

“…While the lack of a clear association with abiotic factors points to a biotic explanation for the evolutionary divergence in flower color among populations, the role of pollinators as drivers of the color change in G. aurantiaca is not entirely clear. Pollination studies have shown that a single hopliine scarab beetle species, E. vulpina, is responsible for the majority of all floral visits to G. aurantiaca (Johnson et al, 2004), unlike the color polymorphic Drosera cistiflora in the western Cape region of South Africa, where several different species of hopliine scarab beetles discriminate between different color forms in the same population (Johnson et al, 2020). Our study did not provide clear evidence that E. vulpina beetles prefer any particular capitulum color within a population as they were recorded visiting capitula in both the red and yellow-flowered populations, and they did not appear to discriminate between G. aurantiaca color morphs at the northern color polymorphic RH site.…”

“…Geographical variation in the availability of pollinators with different color preferences would be expected to lead to intraspecific divergence in flower color among plant populations (Stebbins, 1970). For example, the floral color polymorphism in Drosera cistiflora may be accounted for by the spatiotemporal variation in pollinator assemblages which display different color preferences (Johnson et al, 2020). This micro-evolutionary process could account for macro-evolutionary pattern if populations that differ in flower color were to diverge to the point of speciation (Johnson, 2006).…”

“…Capitula of G. aurantiaca are typically bright red with a dark center, but several recently discovered populations are either entirely yellowflowered (Johnson et al, 2005) or color polymorphic (ranging from yellow through orange to red). The combination of a red display and black center is typical of a guild of plants attractive to glaphyrid scarab beetles in the Mediterranean region (Dafni et al, 1990;Streinzer et al, 2019) and is also found in some members of various guilds of South African plants which are pollinated solely or primarily by hopliine scarab beetles (Bernhardt, 2000;Goldblatt and Manning, 2011;Johnson et al, 2020). The primary pollinators in red-flowered population of G. aurantiaca are hopliine scarab beetles, but honeybees are frequent visitors in yellow-flowered populations (Johnson et al, 2004;IM Johnson unpublished data).…”

Editorial: Sensory ecology of plant-pollinator interactions

“…Intriguingly, they found no clear association between morph color and any of the studied parameters. This contrasts with the case of colorpolymorphic South-African Drosera cistiflora that is pollinated by related hopliine beetles (Johnson et al, 2020;von Witt et al, 2020). It seems unlikely that the color polymorphism in G. aurantiaca is purely coincidental, but what other factor(s) (e.g., floral scent) may determine the geographic pattern remains a question that begs to be answered.…”