The effect of trap colour and trap‐flower distance on prey and pollinator capture in carnivorous Drosera species

Abstract

Summary1. The functional features of carnivorous plants' traps have been mostly interpreted as adaptations to capture prey. Carnivorous plants that feed on insects, however, run the risk that increasing trapping effectiveness might in turn reduce reproductive success through capture of pollinators. Such a pollinator-prey conflict might play an important role in the evolution of trap features. In carnivorous plants with sticky leaves (e.g. Drosera, Pinguicula), both spatial distance between traps and flowers and their visual signals (e.g. colour, display size) likely play a role in attracting prey but it has also been suggested that they affect the risk of potential pollinators landing on a trap. It has been reported, for example, that red pigmentation in carnivorous plants may lure insect prey to traps. This idea remains controversial, however, because colour vision of most insects does not extend very far into the red part of the spectrum. 2. We tested an alternative hypothesis, namely that red pigmentation of the trapping leaves may reduce the risk of a pollinator-prey conflict. Experiments were conducted in a natural habitat of Drosera arcturi and D. spatulata in the Southern Alps of New Zealand. Using sticky model traps similar in shape to Drosera leaf traps and flowers, we investigated the effect of colour (green vs. red vs. white) and flower-trap distance (flower stalk length and leaf arrangement, that is upright as in D. arcturi vs. flat ground rosette as in D. spatulata) on composition and abundance of insects landing and being trapped. 3. Flower-trap distance had no significant effect on the risk of pollinators being trapped but model flowers higher above the ground received more pollinator landings. Across all model traps, the number of trapped potential pollinators was significantly lower in traps with red leaves compared to green ones. 4. The results suggest that the typical red pigmentation of the trapping leaves in Drosera may be a way to protect pollinators from being attracted and captured. However, our data also suggest that pollinator protection via red traps may come with a trade-off since total prey capture was also significantly reduced.

Venus Flytrap Rarely Traps Its Pollinators

“…In Drosera species, some of which also bear flowers on tall scapes, absolute height aboveground (and thus visibility to pollinators)-rather than flower-trap separation-appears to be the trait under selection, even though separation may sometimes reduce pollinator bycatch (Anderson and Midgley 2001;Anderson 2010;El-Sayed et al 2016). Red Drosera trap color, on the other hand, deters pollinators but does not attract prey; Jürgens et al (2015) suggest that selection against pollinator-prey overlap may favor this trait. The results we present for D. muscipula build a foundation for its inclusion in evolutionary ecological studies of the carnivore's dilemma.…”

“…They may therefore face trade-offs between pollination services and nutrient intake, known as pollinator-prey conflict (Juniper et al 1989;Zamora 1999;Jürgens et al 2012). For example, recent experiments suggest that the red color of sundew (Drosera) traps reduces pollinator bycatch but at the expense of total prey capture (Jürgens et al 2015). With few exceptions, however, the extent and strength of pollinator-prey conflict is poorly quantified (but see Zamora 1999;Murza et al 2006;El-Sayed et al 2016).…”

Keeping an eye on coloration: ecological correlates of the evolution of pitcher traits in the genus Nepenthes (Caryophyllales)

“…Despite being a conspicuous feature of Nepenthes, pitcher coloration is poorly understood. A few studies have examined the role of red pigmentation as a visual signal in carnivorous plants (Schaefer & Ruxton, 2008;Bennett & Ellison, 2009;Foot, Rice, & Millet, 2014;Jürgens et al, 2015;El-Sayed, Byers, & Suckling, 2016), and a number have hypothesized that the contrast of red against a green background of foliage could be attractive, although many insects lack red perception (Briscoe and Chittka, 2001). Red was not found to be a prey attractant in studies with sundews (Foot, Rice, & Millet, 2014;Jürgens et al, 2015;El-Sayed, Byers, & Suckling, 2016), but results have been conflicting in pitcher plants (Schaefer & Ruxton, 2008;Bennett & Ellison, 2009).…”

The Role of Red Leaf Coloration in Prey Capture forPinguicula planifolia

“…Anthocyanins are prominent in the vegetative tissues of several evolutionarily distinct carnivorous plant families, and an emerging argument suggests that these pigments serve a role in prey capture (Joel 1988, Jürgens et al 2015, Moran et al 1999. Schaefer and Ruxton (2008) demonstrated that the markedly red coloration on the pitchers of Nepenthes (tropical pitcher plants) species may enhance prey capture compared to pitchers without red coloration.…”

“…(Spoon-leaved Sundew) are produced when the plants become nitrogen deficient, and that this pigment production subsequently increases prey attraction in both species, providing a means to regain nutrients lacking in the substrate. Jürgens et al (2015) proposed that anthocyanins reduce the risk of pollinator-prey conflict in sundew species because the pigments tended to deter pollinating insects while still attracting insect prey, but the red-pigmented leaves also lowered total prey-capture. The debate associated with the involvement of red pigmentation in prey capture is due partly to the widely accepted argument that insects' color vision is poor in the red spectrum of light (Bennett andEllison 2009, Chittka et al 2001).…”