Sequential conflicting selection due to multispecific interactions triggers evolutionary trade-offs in a monocarpic herb

Trade-offs are crucial in understanding phenotypic evolution of organisms. A main source of trade-offs is conflicting selection, a phenomenon very likely in complex multispecific scenarios in which many potential selective agents coexist. The main goal of this study is to investigate the selective trade-offs arising due to conflicting selection on female-fitness components in Erysimum mediohispanicum. I quantified the selection exerted on 10 plant traits by a mutualistic (pollinators) and antagonistic (gall-makers, predispersal and postdispersal seed predators, mammalian herbivores) multispecific assemblage acting sequentially throughout eight selective episodes of the plant, from floral bud to juvenile production. Variation in lifetime female fitness (quantified as number of juveniles) was related mostly to variation in number of flowers, fruit initiation, and seedling establishment. The direction of selection changed among different selective episode for many traits. Most importantly, conflicting selection was frequent in the study system, with half of the phenotypic traits experiencing opposing selection in different selective episodes. Selection at individual life-cycle stages diverged remarkably from selection based on total fitness. Consequently, the evolution of many traits is determined by the relative importance of each episode of selection, with conflicting selection inevitably yielding evolutionary compromises.     

Differences in the diversity and composition of the pollinator assemblage of two co-flowering congeneric alpine wallflowers, Erysimum nevadense and E. baeticum

Many alpine plants display a generalist pollination system where almost any available flower visitor could act as a legitimate pollinator. Co-flowering related plant species displaying a generalized pollination system can decrease their fitness due to interspecific mating. In this study, we determine the difference in diversity and composition of the pollination systems of two co-occurring species endemic to the alpine region of the Sierra Nevada (SE Spain), Erysimum nevadense Reut. and Erysimum baeticum baeticum (Heywood) Polatschek (Brassicaceae), and check for the potential role of floral and plant traits in explaining the observed differences. For this, we labeled 30 plants in two populations of each plant species located in the same area. We determined flower visitor assemblage by sampling all insects approaching the flowers and contacting the sexual organs during 60-min surveys. We found that the diversity of the pollinator assemblage was similar between the two studied wallflower species, both species showing a much generalized pollination system. However, the composition of the pollinator assemblage was different, since the flowers of E. nevadense were visited mostly by beetles and in a lesser extent by hover-flies, whereas the flowers of E. baeticum baeticum were visited mostly by ants and bees. Interestingly, flower traits varied between species, with E. nevadense displaying yellow, smaller and shallower flowers and E. baeticum baeticum displaying purple, large and deeper flowers. These findings suggest that differences in floral traits can explain the observed differences in the composition of the pollinator assemblage between both wallflower species.     

Long-term effects of ungulates on phytophagous insects

Abstract.  1. Most plants interact with a diverse suite of herbivores, allowing the opportunity for the existence of positive and negative interactions between highly dissimilar organisms. However, most studies on herbivorous interactions have been performed under the assumption that they occur mainly between similar species. Consequently, ecologists are still far from a full understanding of the ecological factors that determine insect population dynamics.
2. In this study, a 7-year field experiment was conducted that manipulated the presence of ungulates to evaluate their effects on the abundance, attack rate, and survival of four guilds of co-occurring herbivorous insects living on the same host plant: seed predators, stem borers, gall makers and sap suckers. These four guilds differed in habits and behaviour, the first three being sessile and endophytic and the last being free-living.
3. This study shows that the abundance of all four guilds was negatively affected by ungulates. However, the effect on attack rate differed among guilds, as mammals do not affect the seed predator attack rate. Ungulates also differentially affected insect survival, ingesting only seed predators and gall makers.
4. In summary, this study suggests that diverse mechanisms may affect different insect guilds in different ways. Therefore, competition between disparate herbivores appears to be complex and can be provoked by multiple mechanisms.     

HERITABILITY AND GENETIC CORRELATION OF COROLLA SHAPE AND SIZE IN ERYSIMUM MEDIOHISPANICUM

Flower shape has evolved in most plants as a consequence of pollinator-mediated selection. Unfortunately, no study has explored the genetic variation of flower shape, despite that this information is crucial to understand its adaptive evolution. Our main goal here is to determine heritability of corolla shape in Erysimum mediohispanicum (Brassicaceae). Also, we explore heritability of other pollinator-selected traits in this plant species, such as plant size, flower display, and corolla size. In addition, we investigate genetic correlations between all these traits. We found significant heritability for one plant-size trait (stalk height), for number of flowers, for all corolla-size traits (corolla diameter, corolla tube length and corolla tube width), and for corolla shape. Consequently, this species retains a high ability to respond to the selection exerted by its pollinators. Genetic correlation was strong between all functionally related traits and between flower number and plant size, weak between corolla size and plant size and no correlation between corolla shape and any other trait. Thus, selection affecting some E. mediohispanicum traits would also indirectly affect other functionally related and unrelated traits. More importantly, the observed genetic correlation seems to be at least partially adaptive because positive correlational selection currently acts on the covariance between some of these traits ( Gómez 2003 ; Gómez et al. 2006 ).     

Erysimum cephalonicum (Brassicaceae), ein neuer Endemit der Insel Kefallinia (Griechenland)

Erysimum cephalonicum Polatschek is a new taxon, endemic to the isle of Kefallinia. Its closest allies areErysimum pusillum Bory etChaub. andE. trichophyllum Heldr. ex sched.

     

Association between inbreeding depression and floral traits in a generalist‐pollinated plant

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.     

Ploidy effects on the relationship between floral phenotype,reproductive investment,and fitness in an autogamous species complex

Premise

The relationships between reproductive investment, phenotype, and fitness have been broadly studied in cross-pollinated plants in contrast to selfing species, which are considered less interesting in this area because they are supposed to be a dead end in any evolutionary pathway. Still, selfing plants are unique systems to study these questions since the position of reproductive structures and traits related to flower size play an important role in female and male pollination success.

Methods

Erysimum incanum s.l. is a selfing species complex that has three levels of ploidy (diploids, tetraploids, and hexaploids) and traits that are typically associated with the selfing syndrome. Here, we used 1609 plants belonging to these three ploidies to characterize the floral phenotype and spatial configuration of reproductive structures, reproductive investment (pollen and ovule production), and plant fitness. Then, we used structural equation modelling to analyze the relationship between all these variables across ploidy levels.

Results

An increase in ploidy level leads to bigger flowers with anthers exserted farther and more pollen and ovules. In addition, hexaploid plants had higher absolute values for herkogamy, which is positively correlated with fitness. Ovule production significantly mediated the natural selection acting on different phenotypic traits and pollen production, a pattern that is maintained across ploidies.

Conclusions

The changes in floral phenotypes, reproductive investment, and fitness with ploidy level suggest that genome duplication can be a driver for transitions in reproductive strategy by modifying the investment in pollen and ovules and linking them with plant phenotype and fitness.     

Non-additive effects of herbivores and pollinators on Erysimum mediohispanicum (Cruciferae) fitness

In this study, the non-additivity of effects of herbivores and pollinator on fitness of the plant Erysimum mediohispanicum (Cruciferae) has been experimentally tested. The abundance and diversity of the pollinator assemblage of plants excluded from and exposed to mammalian herbivores, and the combined effect of pollinators and herbivores on plant reproduction were determined over a period of 2 years. Pollinator abundance was higher and diversity was lower on plants excluded from herbivores. Furthermore, the experimental exclusions demonstrated that both pollinators and herbivores affected plant fitness, but their effects were not independent. Herbivores only had a detrimental effect on plant fitness when pollinators were present. Similarly, pollinators enhanced fitness only when herbivores were excluded. This outcome demonstrates that the importance of pollinators for plant fitness depends on the occurrence of herbivores, and suggests that herbivores may hamper pollinator-mediated adaptation in plants.     

Evolution of pollination niches and floral divergence in the generalist plant Erysimum mediohispanicum

Background and Aims

How generalist plants diverge in response to pollinator selection without becoming specialized is still unknown. This study explores this question, focusing on the evolution of the pollination system in the pollination generalist Erysimum mediohispanicum (Brassicaceae).

Methods

Pollinator assemblages were surveyed from 2001 to 2010 in 48 geo-referenced populations covering the entire geographic distribution of E. mediohispanicum. Bipartite modularity, a complex network tool, was used to find the pollination niche of each population. Evolution of the pollination niches and the correlated evolution of floral traits and pollination niches were explored using within-species comparative analyses.

Key Results

Despite being generalists, the E. mediohispanicum populations studied can be classified into five pollination niches. The boundaries between niches were not sharp, the niches differing among them in the relative frequencies of the floral visitor functional groups. The absence of spatial autocorrelation and phylogenetic signal indicates that the niches were distributed in a phylogeographic mosaic. The ancestral E. mediohispanicum populations presumably belonged to the niche defined by a high number of beetle and ant visits. A correlated evolution was found between pollination niches and some floral traits, suggesting the existence of generalist pollination ecotypes.

Conclusions

It is conjectured that the geographic variation in pollination niches has contributed to the observed floral divergence in E. mediohispanicum. The process mediating this floral divergence presumably has been adaptive wandering, but the adaptation to the local pollinator faunas has been not universal. The outcome is a landscape where a few populations locally adapted to their pollination environment (generalist pollination ecotypes) coexist with many populations where this local adaptation has failed and where the plant phenotype is not primarily shaped by pollinators.     

小花糖芥花蜜腺的解剖学研究

小花糖芥（Erysimum cheiranthoides L.)花蜜腺位于雄蕊部花托上,仅有2枚侧蜜腺,属十字花科侧蜜腺类型中的侧半环亚型,其2枚密腺均由分泌表皮,产蜜组织和维管束组成。分泌表皮上有变态气孔器,产蜜组织中有维管束分布,属较进化的十字花科花蜜腺亚型类型。蜜腺原基是在花的各部分原基基本分化完成后,由花托表面及雄蕊基部区域的1－2层细胞,经反分化形成,在蜜腺发育过程中,蜜腺组织中的液泡和多糖物质都发生了有规律的变化,其原蜜汁在产蜜组织中加工合成,最后由表皮细胞和变态气孔泌出。