Unravelling the mystery of red flowers in the Mediterranean Basin: How to be conspicuous in a place dominated by hymenopteran pollinators

Abstract

Red‐flowered species have traditionally been related to ornithophily, and the ‘bee avoidance’ hypothesis, that is, red flower colouration is a way to reduce visits from hymenopterans, has been proposed to explain this association. In the Mediterranean Basin, ornithophily is almost absent, and hymenopterans are the most common group of pollinators. The fact that hymenopterans are virtually red‐blind raises the question of how red‐flowered species are pollinated in this region. Are these flowers pollinated by other groups of red‐sensitive insects such as lepidopterans and coleopterans, or do they have visual cues that make them attractive to hymenopterans? We examined the reflectance spectra of 51 red‐flowered species from the Mediterranean Basin and modelled these spectra in the visual system of hymenopterans, dipterans, coleopterans and lepidopterans to obtain colour and conspicuousness. According to their reflectance curves, species were classified as pure red and UV‐red flowers, and the presence of more than one flower colour (patterned flowers) was studied. We evaluated the match between flower reflectance spectra and the maximum discrimination abilities of hymenopteran and lepidopteran visual system. All these metrics were analysed in a phylogenetically explicit framework, and a literature review of potential pollinators was performed. The vast majority of red‐flowered species in the Mediterranean Basin are potentially pollinated by hymenopterans, and only three species are exclusively visited by coleopterans. We found that 90% of these species showed at least one colour signal strategy that helps to enhance conspicuousness to hymenopterans: to produce UV‐red flower type spectra and/or patterned flowers. The UV‐red colour showed a significant phylogenetic signal, but the presence of patterned flowers did not. Even though the red‐flowered species of the Mediterranean Basin did not optimally match the colour vision of hymenopterans or lepidopterans, the presence of patterned and UV‐red colours suggests an improvement in detection and discrimination by hymenopterans. The bee‐avoidance hypothesis seems to be ruled out for the red‐flowered species of the Mediterranean Basin. Our results suggest that red‐flowered species are mostly pollinated by hymenopterans and show different flower colour signal strategies that can be interpreted as signs of adaptation to these pollinators. Read the free Plain Language Summary for this article on the Journal blog.

Covariation among reproductive traits in flowering plants shapes their interactions with pollinators

“…We suggest that while plant reproductive traits do influence which pollinators they interact with, at a macroecological scale, pollination syndromes possibly take the form of a multifaceted, context‐dependent continuum (e.g. ornithophilous versus entomophilous pollination of red flowers; León‐Osper & Narbona, 2022).…”

“…We did not include the quantitative variables of flower length and inflorescence width because they were TA B L E 1 Quantitative and categorical traits used in this study. and then z-transformed (X = 0, SD = 1) these variables so that they were within the same numerical range, as recommended for principal component analysis (Legendre & Legendre, 2012). Although qualitative traits were not included in the dimensionality reduction analysis, we also investigated their position in the trait space and the statistical association of the different qualitative traits with the main axes of trait variation using an ANOVA and Tukey test.…”

Flower visits of cockroaches (Insecta: Blattodea) in the Iberian Peninsula: Are they neglected pollinators?

“…Iberian cockroaches were found mostly visiting white or yellow (scented or not) flowers with easily‐accessible reproductive parts from the plant families Apiaceae, Asteraceae and Cistaceae which in addition are usually visited by a great number of different insects. Most plants have developed several strategies to attract pollinators such as floral scent and odours (Hossaert‐McKey et al, 2010; Raguso, 2008), energy resources such as nectar (Pyke, 2016) or the development of important floral visual signs to be easily detected (Dyer et al, 2012; García et al, 2021; León‐Osper & Narbona, 2022).…”

“…We used floral reflectance data already measured by the authors for other projects, matching with some of the visited plant species ( N = 6; Cistus albidus L., Cistus salviifolius L., Crepis vesicaria L., Daucus carota L., Erica australis L. and Halimium halimifolium (L.) Willk.). We measured UV–visible flower spectral reflectance using a FLAME spectro‐photometer (Ocean Insight Inc., Orlando, USA), and processed them before performing further analysis using PAVO R‐package (Maia et al, 2019) following methodology applied in León‐Osper and Narbona (2022). While measuring floral reflectance, we recorded data for apex and base of the flower or inflorescence.…”

Clinical Animal Behaviour: Paradigms, Problems and Practice

“…For example, in the case of vision, it is well established that humans perceive only a small part of the electromagnetic spectrum (between about 380 and 750 nm), whereas bees and many birds perceive a different range (extending into ultraviolet), which is utilized by many flowers to provide important information that aids pollination. Only when researchers step away from studying the behaviour of other animals within the context of human sensory and cognitive abilities, do certain mysteries become potentially explainable [ 27 ].…”