Within-individual phenotypic plasticity in flowers fosters pollination niche shift

Phenotypic plasticity, the ability of a genotype of producing different phenotypes when exposed to different environments, may impact ecological interactions. We study here how within-individual plasticity in Moricandia arvensis flowers modifies its pollination niche. During spring, this plant produces large, cross-shaped, UV-reflecting lilac flowers attracting mostly long-tongued large bees. However, unlike most co-occurring species, M. arvensis keeps flowering during the hot, dry summer due to its plasticity in key vegetative traits. Changes in temperature and photoperiod in summer trigger changes in gene expression and the production of small, rounded, UV-absorbing white flowers that attract a different assemblage of generalist pollinators. This shift in pollination niche potentially allows successful reproduction in harsh conditions, facilitating M. arvensis to face anthropogenic perturbations and climate change.


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Here we demonstrate the occurrence of discrete, reversible within-individual floral plasticity that modulates the interaction with pollinators. Individuals of Moricandia arvensis produce two types of flowers, large, cross-shaped, and UV-reflecting lilac in spring; small, rounded, and UV-absorbing white in summer. Transcriptional responses to changes in temperature and photoperiod mediated this plasticity. Plastic change in photosynthesis metabolism, from C2 in spring to values closer to C4 in summer, probably facilitates plants to bloom during summer and allow the expression of the floral plastic phenotype. By displaying two different but functionally and phenotypically integrated flowers, the same individuals interacted with different pollinator networks. The discrete floral plasticity described in this study allows M. arvensis to jump to a different region of the floral phenotypic space and exploit alternative pollination niches. We presume that phenotypic plasticity is an important but neglected factor facilitating shifts in biotic niches.
We worked with Moricandia arvensis (Brassicaceae) a weedy herb from the Mediterranean area that inhabits the dry lands of Iberian Peninsula and North Africa. We chose this plant species because it flowers from February to July and displays two different types of flowers, the main focus of our study. We worked in a extense area of the SE Iberian Peninsula, a place where this plant species lives both associated to humans and also in natural ecosystems.
Sample size, both between and within plant, was determined by running GLMMs with individual as random factors. Number of plants per population (4 populations) was fixed to 50 to ensure enough statistical power. Plant ecological and physiological traits were replicated for each single plant. Insect surverys were performed every day of 2019 to ensure that any seasonal change in insect availability was captured. We did a field experiment in summer 2019 and a second one early spring 2020.
Data were collected by all authors and by four technicians, always under our supervision, directly from the experimental plants We started compiling data in January 2018 and ended in March 2020 We excluded from our analyses those plants failing to flower during each season.
All methods are exhaustively described in the Method section to ensure any researcher understands and can reproduce our study.
In all experiments, plants were randomly allocated to each treatment. In field study, plants of similar size were chosen from large populations.

Dry lands of the Southeastern Iberian Peninsula, mostly badlands and semideserts
Four populations in Andalusia region in Spain, belonging to Granada, Jaen, Almería provinces ranfing between 300 and 1200 m a.s.l. Geographical coordinate are provided in Supplementary Material. Climate is Mediterranean, with average daily temperature ranging from 15ºC in spring to 28ºC in summer.
We have been extremely careful with not interfering with the natural dynamics of the ecosystems. Our study plant is a nonprotected weed, so, no specific permit was required to study it. Because all the study was performed outside any protected area, no permit was either required. NA