RESUMEN
Individual variation in the magnitude of inbreeding depression (ID) in plants and its association with phenotypic traits may have important consequences for mating system evolution. This association has been investigated only scarcely, and always considering traits functionally related to autogamy. Here, we explore the association between individual variation in ID and plant traits associated with pollinator attractiveness (related to plant size, corolla size and corolla shape) in two populations of Erysimum mediohispanicum (Brassicaceae). ID was calculated along the entire life cycle of the plants. In addition, we also explored the relationship between phenotypic traits and the individual levels of heterozygosity. We found significant associations between ID and corolla diameter and stalk height, being taller plants with larger corollas those undergoing a lower intensity of ID. Furthermore, we found a negative relationship between corolla diameter and heterozygosity, suggesting that plants with large flowers have purged their genetic load. Finally, we found a significant effect of corolla diameter on the intrapopulation genetic structure. All these findings suggest that plants with large flowers have secularly suffered frequent inbreeding in the study populations. Because corolla diameter is a trait frequently selected by pollinators in E. mediohispanicum, we believe that the observed relationship between this trait and ID could be mediated by pollinators, probably throughout an increasing in biparental inbreeding, geitonogamy or autogamy.
Asunto(s)
Erysimum/genética , Evolución Biológica , Erysimum/anatomía & histología , Erysimum/fisiología , Flores/anatomía & histología , Flores/genética , Aptitud Genética , Heterocigoto , Endogamia , Fenotipo , Polinización/genética , Reproducción/genética , Selección Genética , Autofecundación/genéticaRESUMEN
Flowers of animal-pollinated plants are integrated structures shaped by the action of pollinator-mediated selection. It is widely assumed that pollination specialization increases the magnitude of floral integration. However, empirical evidence is still inconclusive. In this study, we explored the role of pollinator diversity in shaping the evolution of corolla-shape integration in Erysimum, a plant genus with generalized pollination systems. We quantified floral integration in Erysimum using geometric morphometrics and explored its evolution using phylogenetic comparative methods. Corolla-shape integration was low but significantly different from zero in all study species. Spatial autocorrelation and phylogenetic signal in corolla-shape integration were not detected. In addition, integration in Erysimum seems to have evolved in a way that is consistent with Brownian motion, but with frequent convergent evolution. Corolla-shape integration was negatively associated with the number of pollinators visiting the flowers of each Erysimum species. That is, it was lower in those species having a more generalized pollination system. This negative association may occur because the co-occurrence of many pollinators imposes conflicting selection and cancels out any consistent selection on specific floral traits, preventing the evolution of highly integrated flowers.
Asunto(s)
Adaptación Biológica/fisiología , Biodiversidad , Evolución Biológica , Erysimum/anatomía & histología , Flores/anatomía & histología , Insectos/anatomía & histología , Polinización/fisiología , África del Norte , Animales , Secuencia de Bases , Teorema de Bayes , ADN Ribosómico/genética , Europa (Continente) , Insectos/fisiología , Modelos Biológicos , Modelos Genéticos , Datos de Secuencia Molecular , Filogenia , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
Symmetry is an important feature of floral structure, and floral symmetries are diverse and often complex. We use a new morphometric approach for analysing shapes with complex types of symmetry, which partitions shape variation into a component of symmetric variation and different components of asymmetry. This approach, based on the mathematical theory of symmetry groups, can be used for landmark configurations with any type of symmetry and is therefore promising as a general framework for morphometric analyses of floral symmetry and asymmetry. We demonstrate this approach by quantifying floral shape variation in a wild population of Erysimum mediohispanicum (Brassicaceae). Flowers of this species are disymmetric, so that the symmetry in the left-right and adaxial-abaxial directions can be considered separately and in combination. Both principal component analysis and Procrustes ANOVA indicate that symmetric variation accounts for most of the total variance and that adaxial-abaxial asymmetry is the dominant component of fluctuating asymmetry. Each component is associated with specific patterns of shape variation. These results illustrate the potential of the new method and suggest new areas for future research. The new morphometric approach is promising for further analyses of floral symmetry and asymmetry in evolutionary and developmental contexts.
Asunto(s)
Biología Computacional/métodos , Erysimum/anatomía & histología , Flores/anatomía & histología , Desarrollo de la Planta , Análisis de Varianza , Evolución Biológica , Erysimum/crecimiento & desarrollo , Flores/crecimiento & desarrollo , Análisis de Componente Principal , Especificidad de la EspecieRESUMEN
The Geographic Mosaic Theory of Coevolution predicts the occurrence of mosaics of interaction-mediated local adaptations and maladaptations. Empirical support to this prediction has come mostly from specialist interactions. In contrast, local adaptation is considered highly unlikely in generalist interactions. In this study, we experimentally test local adaptation in a generalist plant-pollinator geographic mosaic, by means of a transplant experiment in which plants coming from two evolutionary hotspots and two coldspots were offered to pollinators at the same four localities. Plants produced in the hotspots attracted more pollinators in all populations, whereas coldspot plants attracted fewer pollinators in all populations. Differences in adaptation were not related to genetic similarity between populations, suggesting that it was mainly due to spatial variation in previous selective regimes. Our experiment provides the first strong support for a spatially structured pattern of adaptation and maladaptation generated by a generalist free-living mutualism.
Asunto(s)
Adaptación Fisiológica , Erysimum/fisiología , Geografía , Polinización , Animales , Abejas/fisiología , Evolución Biológica , Mariposas Diurnas/fisiología , Escarabajos/fisiología , Dípteros/fisiología , Erysimum/anatomía & histología , Conducta Alimentaria , Modelos LinealesRESUMEN
Petals and leaves share common evolutionary origins but perform very different functions. However, few studies have compared leaf and petal senescence within the same species. Wallflower (Erysimum linifolium), an ornamental species closely related to Arabidopsis (Arabidopsis thaliana), provide a good species in which to study these processes. Physiological parameters were used to define stages of development and senescence in leaves and petals and to align these stages in the two organs. Treatment with silver thiosulfate confirmed that petal senescence in wallflower is ethylene dependent, and treatment with exogenous cytokinin and 6-methyl purine, an inhibitor of cytokinin oxidase, suggests a role for cytokinins in this process. Subtractive libraries were created, enriched for wallflower genes whose expression is up-regulated during leaf or petal senescence, and used to create a microarray, together with 91 senescence-related Arabidopsis probes. Several microarray hybridization classes were observed demonstrating similarities and differences in gene expression profiles of these two organs. Putative functions were ascribed to 170 sequenced DNA fragments from the libraries. Notable similarities between leaf and petal senescence include a large proportion of remobilization-related genes, such as the cysteine protease gene SENESCENCE-ASSOCIATED GENE12 that was up-regulated in both tissues with age. Interesting differences included the up-regulation of chitinase and glutathione S-transferase genes in senescing petals while their expression remained constant or fell with age in leaves. Semiquantitative reverse transcription-polymerase chain reaction of selected genes from the suppression subtractive hybridization libraries revealed more complex patterns of expression compared with the array data.
Asunto(s)
Erysimum/genética , Expresión Génica , Genes de Plantas , Arabidopsis/genética , Northern Blotting , Erysimum/anatomía & histología , Erysimum/crecimiento & desarrollo , Flores/anatomía & histología , Flores/genética , Flores/crecimiento & desarrollo , Perfilación de la Expresión Génica , Biblioteca de Genes , Análisis de Secuencia por Matrices de Oligonucleótidos , Filogenia , Hojas de la Planta/anatomía & histología , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Especificidad de la EspecieRESUMEN
An adaptive role of corolla shape has been often asserted without an empirical demonstration of how natural selection acts on this trait. In generalist plants, in which flowers are visited by diverse pollinator fauna that commonly vary spatially, detecting pollinator-mediated selection on corolla shape is even more difficult. In this study, we explore the mechanisms promoting selection on corolla shape in the generalist crucifer Erysimum mediohispanicum Polatschek (Brassicaceae). We found that the main pollinators of E. mediohispanicum (large bees, small bees and bee flies) discriminate between different corolla shapes when offered artificial flowers without reward. Importantly, different pollinators prefer different shapes: bees prefer flowers with narrow petals, whereas bee flies prefer flowers with rounded overlapping petals. We also found that flowers with narrow petals (those preferred by bees) produce both more pollen and nectar than those with rounded petals. Finally, different plant populations were visited by different faunas. As a result, we found spatial variation in the selection acting on corolla shape. Selection favoured flowers with narrow petals in the populations where large or small bees are the most abundant pollinator groups. Our study suggests that pollinators, by preferring flowers with high reward, exert strong selection on the E. mediohispanicum corolla shape. The geographical variation in the pollinator-mediated selection on E. mediohispanicum corolla shape suggests that phenotypic evolution and diversification can occur in this complex floral trait even without specialization.
Asunto(s)
Erysimum/fisiología , Insectos/crecimiento & desarrollo , Polinización/fisiología , Adaptación Fisiológica , Animales , Erysimum/anatomía & histología , Erysimum/genética , Flores/anatomía & histología , Flores/genética , Fenotipo , Selección GenéticaRESUMEN
Paleontological and phylogenetic studies have shown that floral zygomorphy (bilateral symmetry) has evolved independently in several plant groups from actinomorphic (radially symmetric) ancestors as a consequence of strong selection exerted by specialized pollinators. Most studies focused on unraveling the developmental genetics of flower symmetry, but little is known about the adaptive significance of intraspecific flower shape variation under natural conditions. We provide the first evidence for natural selection favoring zygomorphy in a wild population of Erysimum mediohispanicum (Brassicaceae), a plant showing extensive continuous variation in flower shape, ranging from actinomorphic to zygomorphic flowers. By using geometric morphometric tools to describe flower shape, we demonstrate that plants bearing zygomorphic flowers received more pollinator visits and had the highest fitness, measured not only by the number of seeds produced per plant but also by the number of seeds surviving to the juvenile stage. This study provides strong evidence for the existence of significant fitness differences associated with floral shape variation in E. mediohispanicum, thus illuminating a pathway for the evolution of zygomorphy in natural populations.