Evolution of nectar spur length in a clade of Linaria reflects changes in cell division rather than in cell expansion.

BACKGROUND AND AIMS: Nectar spurs (tubular outgrowths of a floral organ which contain, or give the appearance of containing, nectar) are hypothesized to be a 'key innovation' which can lead to rapid speciation within a lineage, because they are involved in pollinator specificity. Despite the ecological importance of nectar spurs, relatively little is known about their development. We used a comparative approach to investigate variation in nectar spur length in a clade of eight Iberian toadflaxes. METHODS: Spur growth was measured at the macroscopic level over time in all eight species, and growth rate and growth duration compared. Evolution of growth rate was reconstructed across the phylogeny. Within the clade we then focused on Linaria becerrae and Linaria clementei, a pair of sister species which have extremely long and short spurs, respectively. Characterization at a micromorphological level was performed across a range of key developmental stages to determine whether the difference in spur length is due to differential cell expansion or cell division. KEY RESULTS: We detected a significant difference in the evolved growth rates, while developmental timing of both the initiation and the end of spur growth remained similar. Cell number is three times higher in the long spurred L. becerrae compared with L. clementei, whereas cell length is only 1.3 times greater. In addition, overall anisotropy of mature cells is not significantly different between the two species. CONCLUSIONS: We found that changes in cell number and therefore in cell division largely explain evolution of spur length. This contrasts with previous studies in Aquilegia which have found that variation in nectar spur length is due to directed cell expansion (anisotropy) over variable time frames. Our study adds to knowledge about nectar spur development in a comparative context and indicates that different systems may have evolved nectar spurs using disparate mechanisms

The evo-devo of plant speciation

Speciation research bridges the realms of macro- and microevolution. Evolutionary developmental biology (evo-devo) has classically dealt with macroevolutionary questions through a comparative approach to distantly related organisms, but the field later broadened in focus to address recent speciation and microevolution. Here we review available evidence of the power of evo-devo approaches to understand speciation in plants at multiple scales. At a macroevolutionary scale, evidence is accumulating for evolutionary developmental mechanisms giving rise to key innovations promoting speciation. At the macro microevolution transition, we review instances of evo-devo change underlying both the origin of reproductive barriers and phenotypic changes distinguishing closely related species. At the microevolutionary scale, the study of developmental variation within species provides insight into the processes that generate the raw material for evolution and speciation. We conclude by advocating a strong interaction between developmental biology and evolutionary biology at multiple scales to gain a deeper understanding of plant speciation.M.F.-M. has been supported by the Marie Curie Intra-European Fellowship LINARIA-SPECIATION (FP7-PEOPLE-2013-IEF, project reference 624396 to M.F.-M and B.J.G) and an Isaac Newton Trust Research Grant (Trinity College, Cambridge)

A synopsis of the Iberian clade of Linaria subsect. Versicolores (Antirrhineae, Plantaginaceae) based on integrative taxonomy

Integrative taxonomy, based on the combination of multiple lines of evidence, provides the foundations for a robust species delimitation. Here we provide a taxonomic synopsis of the Iberian clade of Linaria subsect. Versicolores based on recently published morphometric and phylogenomic data. This clade radiated in the Iberian Peninsula (western Mediterranean)during the Quaternary, and is being intensively studied from phylogenetic, evolutionary, biogeographic, ecological and developmental standpoints. Eight morphologically and genetically distinct species are recognized in the clade: L. algarviana, L. becerrae, L. clementei, L. incarnata, L. onubensis, L. salzmannii, L. spartea and L. viscosa. For each accepted species, the type material and notes on diagnostic characters, distribution, habitat and intraspecific variability are provided. Five names are typified (four neotypes and one lectotype are designated), and references to previous typifications are also presented. A distribution map and an identification key are presented. This synopsis will provide the basis for future research on speciation and evolution of the clade

The effect of the ‘Bee Gym™’ grooming device on Varroa destructor mite fall from honey bee (Apis mellifera) colonies

Grooming is a honey bee behavior that has the potential to minimize and manage the detrimental effects of $\textit{Varroa destructor}$. Here we tested the efficacy of the Bee Gym™, a device hypothesized to increase honey bee auto-grooming and increase mite removal from colonies. Natural mite fall from 20 colonies was counted for 14 days, after which half the colonies were fitted with a Bee Gym and half with a control object. Mite fall and the proportion of damaged mites were then recorded for another 14 days. Total mite fall was generally higher over the second 14 days, but this increase was not significantly higher for the Bee Gym colonies than for the control colonies. There was also no difference in the proportion of damaged mites between the two treatments. Mite fall and damage to mites may be influenced by other factors, and this is discussed; however, given that we found no effect of the Bee Gym, we conclude that there is no evidence from this study of its efficacy as a management strategy for $\textit{V. destructor}$. El aseo es un comportamiento de la abeja de la miel que tiene el potencial de minimizar y de manejar los efectos perjudiciales de $\textit{Varroa destructor}$. Aquí hemos probado la eficacia del Bee Gym ™, un dispositivo que hipotéticamente aumenta el auto-aseo en la abeja de la miel y aumentar la eliminación de ácaros de las colonias. La caída natural de ácaros de 20 colonias se contó durante 14 días, tras lo cual la mitad de las colonias fueron equipadas con un Bee Gym y la otra mitad con un objeto de control. La caída de ácaros y la proporción de ácaros dañados se registraron durante otros 14 días. La caída total de ácaros fue generalmente mayor durante los segundos 14 días, pero este aumento no fue significativamente mayor para las colonias con Bee Gym que para las colonias de control. Tampoco hubo diferencias en la proporción de ácaros dañados entre los dos tratamientos. La caída de ácaros y el daño a los ácaros pueden estar influidos por otros factores, lo cual se discute; sin embargo, dado que no encontramos ningún efecto del Bee Gym, concluimos que no hay evidencia en este estudio de su eficacia como estrategia de manejo para $\textit{V. destructor}$.Stuart Roweth supplied the Bee Gyms and control frames and provided funding for equipment and travel costs. JGP was funded by a Biotechnology and Biological Sciences Research Council Doctoral Training Partnership studentship under Grant [BB/J014540/1]

Spur length evolution in Linaria reflects changes in cell division

Background and aims Nectar spurs (tubular outgrowths of a floral organ which contain or give the appearance of containing nectar) are hypothesized to be a ‘key innovation’ which can lead to rapid speciation within a lineage, because they are involved in pollinator specificity. Despite the ecological importance of nectar spurs, relatively little is known about their development. We used a comparative approach to investigate variation in nectar spur length in a clade of eight Iberian toadflaxes. Methods Spur growth was measured at the macroscopic level over time in all eight species, and growth rate and growth duration compared. Evolution of growth rate was reconstructed across the phylogeny. Within the clade we then focused on Linaria becerrae and Linaria clementei, a pair of sister species which have extremely long and short spurs, respectively. Characterisation at a micromorphological level was performed across a range of key developmental stages to determine whether the difference in spur length is due to differential cell expansion or cell division. Key results We detected a significant difference in the evolved growth rates, while developmental timing of both the initiation and the end of spur growth remained similar. Cell number is 3 times higher in the long spurred Linaria becerrae compared to Linaria clementei, whereas cell length is only 1.3 times greater. In addition, overall anisotropy of mature cells is not significantly different between the two species. Conclusions We found that changes in cell number and therefore in cell division largely explain evolution of spur length. This contrasts with previous studies in Aquilegia which have found that variation in nectar spur length is due to directed cell expansion (anisotropy) over variable timeframes. Our study adds to knowledge about nectar spur development in a comparative context and indicates that different systems may have evolved nectar spurs using disparate mechanisms

Structural colour from helicoidal cell-wall architecture in fruits of Margaritaria nobilis

The bright and intense blue-green coloration of the fruits of Margaritaria nobilis (Phyllanthaceae) was investigated using polarization-resolved spectroscopy and transmission electron microscopy. Optical measurements of freshly collected fruits revealed a strong circularly polarized reflection of the fruit that originates from a cellulose helicoidal cell wall structure in the pericarp cells. Hyperspectral microscopy was used to capture the iridescent effect at the single-cell level.This work was supported by the Leverhulme Trust (F/09- 741/G) and a BBSRC David Phillips fellowship (BB/K014617/1). P.V. acknowledges support from the US Air Force Office of Scientific Research under award number FA9550-10-1-0020. U.S. acknowledges support from the Adolphe Merkle foundation and the Swiss National Science Foundation through the National Centre of Competence in Research Bio-Inspired Materials

Determining the Contribution of Epidermal Cell Shape to Petal Wettability Using Isogenic Antirrhinum Lines

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Differential regulation of a MYB transcription factor is correlated with transgenerational epigenetic inheritance of trichome density in Mimulus guttatus

This is the peer reviewed version of the following article: Scoville, A. G., Barnett, L. L., Bodbyl-Roels, S., Kelly, J. K. and Hileman, L. C. (2011), Differential regulation of a MYB transcription factor is correlated with transgenerational epigenetic inheritance of trichome density in Mimulus guttatus. New Phytologist, 191: 251–263. doi:10.1111/j.1469-8137.2011.03656.x, which has been published in final form at http://doi.org/10.1111/j.1469-8137.2011.03656.x. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Epigenetic inheritance, transgenerational transmission of traits not proximally determined by DNA sequence, has been linked to transmission of chromatin modifications and gene regulation, which are known to be sensitive to environmental factors. Mimulus guttatus increases trichome (plant hair) density in response to simulated herbivore damage. Increased density is expressed in progeny even if progeny do not experience damage. To better understand epigenetic inheritance of trichome production, we tested the hypothesis that candidate gene expression states are inherited in response to parental damage. Using M. guttatus recombinant inbred lines, offspring of leaf-damaged and control plants were raised without damage. Relative expression of candidate trichome development genes was measured in offspring. Line and parental damage effects on trichome density were measured. Associations between gene expression, trichome density, and response to parental damage were determined. We identified M. guttatus MYB MIXTA-like 8 as a possible negative regulator of trichome development. We found that parental leaf damage induces down-regulation of MYB MIXTA-like 8 in progeny, which is associated with epigenetically inherited increased trichome density. Our results link epigenetic transmission of an ecologically important trait with differential gene expression states – providing insight into a mechanism underlying environmentally induced ‘soft inheritance’

Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency

Enhanced light harvesting is an area of interest for optimizing both natural photosynthesis and artificial solar energy capture1,2. Iridescence has been shown to exist widely and in diverse forms in plants and other photosynthetic organisms and symbioses3,4, but there has yet to be any direct link demonstrated between iridescence and photosynthesis. Here we show that epidermal chloroplasts, also known as iridoplasts, in shade-dwelling species of Begonia5, notable for their brilliant blue iridescence, have a photonic crystal structure formed from a periodic arrangement of the light-absorbing thylakoid tissue itself. This structure enhances photosynthesis in two ways: by increasing light capture at the predominantly green wavelengths available in shade conditions, and by directly enhancing quantum yield by 5-10% under low-light conditions. These findings together imply that the iridoplast is a highly modified chloroplast structure adapted to make best use of the extremely low-light conditions in the tropical forest understorey in which it is found5,6. A phylogenetically diverse range of shade-dwelling plant species has been found to produce similarly structured chloroplasts7-9, suggesting that the ability to produce chloroplasts whose membranes are organized as a multilayer with photonic properties may be widespread. In fact, given the well-established diversity and plasticity of chloroplasts10,11, our results imply that photonic effects may be important even in plants that do not show any obvious signs of iridescence to the naked eye but where a highly ordered chloroplast structure may present a clear blue reflectance at the microscale. Chloroplasts are generally thought of as purely photochemical; we suggest that one should also think of them as a photonic structure with a complex interplay between control of light propagation, light capture and photochemistry