Melissa León: Red flowers from the Mediterranean Basin, color strategists.

In the present blogpost Melissa León, PhD student at University Pablo Olavide in Spain, presents her research ‘Unravelling the mystery of red flowers in the Mediterranean Basin: How to be conspicuous in a place dominated by hymenopteran pollinators’. She shows the different methods plants use to attract pollinators, potential evolutionary implications of these methods, and her passion for ecological sciences.

A Spanish version of this blogpost is available to read here.

About the paper

Plants display a variety of traits to attract pollinators—among these, flower colour influences detectability and plant fitness. Red flowers in some regions of the world, such as America or Australia, are often associated with bird pollination according to the ‘bee-avoidance’ hypothesis which suggests that red flowers are less detectable by bees. Thus, bird-pollinated red flowers can avoid bee visitation and originate a private communication channel with birds. Colour perception in bees and birds are substantially different since birds are tetrachromatic—perceiving light wavelengths extending from ultraviolet (UV) to red regions—and bees are commonly trichromatic perceiving light between UV and green wavelengths. This makes them virtually blind to red colours! Given that bird pollination is nearly absent in the Eurasia, and the main pollinator in this region are bees, we asked the question: How are Mediterranean red-flowered species conspicuous to bees?

Left: Torcal de Antequera (Málaga) one of the sampling sites where we found Pardoglossum cheirifolium. Right: one of the UV-reflective species.

In our study, we modelled the reflectance spectra of Mediterranean red-flowered species in the visual system of hymenopterans, dipterans, coleopterans, and lepidopterans, and consequently performed a literature review of potential pollinators of the studied species. We found that most red-flowered species of the Mediterranean Basin are potentially pollinated by hymenopterans, invalidating the bee avoidance hypothesis. Interestingly, red flowers from the Mediterranean Basin presented two colour signal strategies: to show UV reflection, and/or to display patterned flowers (i.e. flowers with more than one colour). Both strategies might help the detection of red flowers not only by hymenopterans but also other red-sensitive insects such as coleopterans. Taking all of this information together, our results suggest that these colour signal strategies can be interpreted as signs of adaptation to these pollinators without restricting visitation from other insect groups.

About the research

This research improves our knowledge of the adaptative mechanisms present in the species from the Mediterranean Basin hot spot. Modelling the visual system of studied pollinators was the most time-consuming step—you not only must know the sensitivity data, but also you have to understand the neurological processing of light through each pollinator visual system.

Papaver rhoeas field in Huelva, one of the studied populations.

At first, I expected almost all studied species to be UV-reflective; therefore, the results showing a ‘low’ number of these species puzzled me. I wondered how that result coupled with other field observations of bees foraging red flowers, I.E., how do non-UV-reflective red flowers manage to attract bees? Following this, we then identified the second strategy—colour patterns! The fact that there was more than one strategy for detection really impressed me!

Syrphid (non red-sensitive) visiting a flower of Scrophularia canina showing the second strategy depicted in the paper, to display two flower colours—red & white.

Regarding red flowers, there are many questions still to answer—we are currently performing a comparison between Mediterranean red flowers in California and Spain. Considering the fact that pollinator faunas are substantially different due to the absence of hummingbirds in the latter, we hypothesise that flowers may show different strategies to target their own pollinators. We are also studying the pigments that produce this flower colour to try to identify a relationship with biotic and or/abiotic pressures.

About the author

The authors Melissa León-Osper (left) and Eduardo Narbona (right).

Since I was a little girl, the ‘green’ subjects have always caught my eye but there were so many to pick from that it made it difficult to choose just one! I ended up studying Environmental Science at Huelva’s University, Spain, where I attended my first ecology lesson which taught me that everything in nature is linked. Therefore, if you are curious about the whole ecosystem that we live in and depend on, ecology is your discipline!

Later, I completed my Master’s degree at Pablo de Olavide University, Spain, where I focused on my interests in conservation biology and plant reproductive biology. At the same time, I became interested in visual ecology and joined the project: “Reconciling patterns and processes in flower colour evolution”. Today, I see myself as a ‘rookie researcher’ as I’ve just started my PhD thesis at Pablo de Olavide University which aims to study macro- and micro-ecological patterns of flower colour evolution. Macroecological patterns will be studied by comparing the independently assembled floras of two Mediterranean regions with different pollinator faunas. Microecological patterns will then be approached by focusing on some species of Papaver genus that show similar red colours and blossom in sympatry. Thus, we expect some strategies to avoid interspecific pollen deposition.

Some young researchers—like me—might think that there are only a few questions left to be answered; however, as you get to know more your field, you will find many questions yet to solve and I’m sure all of them will have exciting answers!

Enjoyed the blogpost? Read the research here!

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