Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.     

Local plant density,pollination and trait–fitness relationships in a perennial herb

Both differences in local plant density and phenotypic traits may affect pollination and plant reproduction, but little is known about how density affects trait–fitness relationships via changes in pollinator activity. In this study we examined how plant density and traits interact to determine pollinator behaviour and female reproductive success in the self‐incompatible, perennial herb Phyteuma spicatum. Specifically, we hypothesised that limited pollination service in more isolated plants would lead to increased selection for traits that attract pollinators. We conducted pollinator observations and assessed trait–fitness relationships in a natural population, whose individuals were surrounded by a variable number of inflorescences. Both local plant density and plant phenotypic traits affected pollinator foraging behaviour. At low densities, pollinator visitation rates were low, but increased with increasing inflorescence size, while this relationship disappeared at high densities, where visitation rates were higher. Plant fitness, in terms of seed production per plant and per capsule, was related to both floral display size and flowering time. Seed production increased with increasing inflorescence size and was highest at peak flowering. However, trait–fitness relationships were not density‐dependent, and differences in seed production did not appear to be related to differences in pollination. The reasons for this remain unclear, and additional studies are needed to fully understand and explain the observed patterns.     

Nectar yeasts enhance the interaction between Clematis akebioides and its bumblebee pollinator

• It has been hypothesised that intense metabolism of nectar‐inhabiting yeasts (NIY) may change nectar chemistry, including volatile profile, which may affect pollinator foraging behaviours and consequently plant fitness. However, empirical evidence for the plant–microbe–pollinator interactions remains little known.
• To test this hypothesis, we use a bumblebee‐pollinated vine Clematis akebioides endemic to southwest China as an experimental model plant. To quantify the incidence and density of Metschnikowia reukaufii, a cosmopolitan NIY in floral nectar, a combination of yeast cultivation and microscopic cell‐counting method was used. To examine the effects of NIY on plant–pollinator interactions, we used real flowers filled with artificial nectar with or without yeast cells. Then the volatile metabolites produced in the yeast‐inoculated nectar were analysed with coupled gas chromatography and mass spectrometry (GC‐MS).
• On average 79.3% of the C. akebioides flowers harboured M. reukaufii, and cell density of NIY was high to 7.4 × 10⁴ cells mm^?3. In the field population, the presence of NIY in flowers of C. akebioides increased bumblebee (Bombus friseanus) pollinator visitation rate and consequently seed set per flower. A variety of fatty acid derivatives produced by M. reukaufii may be responsible for the above beneficial interactions.
• The volatiles produced by the metabolism of M. reukaufii may serve as an honest signal to attract bumblebee pollinators and indirectly promote the female reproductive fitness of C. akebioides, forming a potentially tripartite plant–microbe–pollinator mutualism.

     

Density and assemblage influence the nature of the species richness–productivity relationship in Australian dry sclerophyll forest species

The relationship between species richness and productivity is important from both a basic, theoretical perspective and also because it has important ramifications for applied ecology including ecosystem restoration and the design of carbon offset plantings. While a more species‐rich community is often believed to be more productive than a species‐poor community, findings from observational and experimental studies differ and our understanding of the relationship comes largely from grasslands. Consequently, we aimed to determine for the first time the nature of the species richness–productivity relationship in a southern‐hemisphere dry sclerophyll ecosystem. We investigated the impact of species richness on productivity, plant density and mean plant biomass at three sowing densities in three species assemblages. Eucalyptus globulus, Acacia mearnsii and Allocasuarina verticillata were each grown as monocultures and included in every subsequent level of species richness, forming three distinct species assemblages. Communities were grown in a glasshouse pot experiment for four months, then harvested and above‐ground biomass measured. We found no general species richness–productivity relationship in the communities studied. There were no overall increases in productivity as species richness increased and in fact in most cases the productivity of communities with 4 and 8 species was lower than monocultures of the dominants. Importantly, density influenced the way richness affected productivity and this effect was dependent upon assemblage, indicating that species identity is a key determinant of productivity. These results demonstrate important ecological principles in a previously untested system. A key outcome of this experiment is that density alters the relationship between species richness and initial productivity in assemblages of Australian dry sclerophyll species.     

Functional traits associated with plant colonizing and competitive ability influence species abundance during secondary succession: Evidence from subalpine meadows of the Qinghai–Tibetan Plateau

It is widely recognized that colonists and competitors dominate early and late succession, respectively, with selected species having different colonizing and competitive abilities. However, it remains unknown whether colonizing and competitive ability can determine species abundance directly over succession. The data for five key functional traits were collected (photosynthesis rate, leaf turgor loss point, leaf proline content, seed mass, and seed germination rate), which are direct indicators of plant competitive and colonizing abilities including growth, drought and cold stress resistance, dispersal, and seed dormancy. Here, we tested the effects of colonizing and competitive abilities on species abundance, by employing a linear mixed‐effects model to examine the shifts in the relationship between species abundance and these five colonization and competition‐related traits in species‐rich subalpine secondary successional meadows (at 4, 6, 10, 13 years of age, and undisturbed, respectively) of the Qinghai–Tibetan Plateau. The abundant species at the early‐successional meadows tend to have high photosynthetic rate, high leaf proline content, low seed mass, and seed germination rate for having high colonizing ability, but low competitive ability. By contrast, late‐successional communities tend to be dominated by species with high competitive ability, but low colonizing ability, indicated by large seeds, high seed germination rate, low photosynthetic rate, and leaf proline content. The observed directional shifts in the relationships between traits (photosynthetic rate, leaf proline content, seed mass, and seed germination rate) and abundance with successional age, bring two new understandings of community assembly during succession of subalpine meadows in the Qinghai–Tibetan Plateau. First, it discloses that the differences in species abundance over succession can be directly attributed to differences in colonizing and competitive abilities of different species. Second, it expands the effects of multiple life historical differences including growth, resource competitive ability, cold stress resistance, dispersal, and seed germination strategy, represented by functional traits on community assembly along succession, that is, from the species to the community level.     

Pollen S–locus F–box proteins of Petunia involved in S–RNase‐based self‐incompatibility are themselves subject to ubiquitin‐mediated degradation

Many flowering plants show self‐incompatibility, an intra‐specific reproductive barrier by which pistils reject self‐pollen to prevent inbreeding and accept non‐self pollen to promote out‐crossing. In Petunia, the polymorphic S–locus determines self/non‐self recognition. The locus contains a gene encoding an S–RNase, which controls pistil specificity, and multiple S‐locus F‐box (SLF) genes that collectively control pollen specificity. Each SLF is a component of an SCF (Skp1/Cullin/F‐box) complex that is responsible for mediating degradation of non‐self S‐RNase(s), with which the SLF interacts, via the ubiquitin–26S proteasome pathway. A complete set of SLFs is required to detoxify all non‐self S‐RNases to allow cross‐compatible pollination. Here, we show that SLF1 of Petunia inflata is itself subject to degradation via the ubiquitin–26S proteasome pathway, and identify an 18 amino acid sequence in the C‐terminal region of S₂‐SLF1 (SLF1 of S₂ haplotype) that contains a degradation motif. Seven of the 18 amino acids are conserved among all 17 SLF proteins of S₂ haplotype and S₃ haplotype involved in pollen specificity, suggesting that all SLF proteins are probably subject to similar degradation. Deleting the 18 amino acid sequence from S₂‐SLF1 stabilized the protein but abolished its function in self‐incompatibility, suggesting that dynamic cycling of SLF proteins is an integral part of their function in self‐incompatibility.     

Xanthomonas euvesicatoria type III effector XopQ interacts with tomato and pepper 14–3–3 isoforms to suppress effector‐triggered immunity

Effector‐triggered immunity (ETI) to host‐adapted pathogens is associated with rapid cell death at the infection site. The plant‐pathogenic bacterium Xanthomonas euvesicatoria (Xcv) interferes with plant cellular processes by injecting effector proteins into host cells through the type III secretion system. Here, we show that the Xcv effector XopQ suppresses cell death induced by components of the ETI‐associated MAP kinase cascade MAPKKKα MEK2/SIPK and by several R/avr gene pairs. Inactivation of xopQ by insertional mutagenesis revealed that this effector inhibits ETI‐associated cell death induced by avirulent Xcv in resistant pepper (Capsicum annuum), and enhances bacterial growth in resistant pepper and tomato (Solanum lycopersicum). Using protein–protein interaction studies in yeast (Saccharomyces cerevisiae) and in planta, we identified the tomato 14–3–3 isoform SlTFT4 and homologs from other plant species as XopQ interactors. A mutation in the putative 14–3–3 binding site of XopQ impaired interaction of the effector with CaTFT4 in yeast and its virulence function in planta. Consistent with a role in ETI, TFT4 mRNA abundance increased during the incompatible interaction of tomato and pepper with Xcv. Silencing of NbTFT4 in Nicotiana benthamiana significantly reduced cell death induced by MAPKKKα. In addition, silencing of CaTFT4 in pepper delayed the appearance of ETI‐associated cell death and enhanced growth of virulent and avirulent Xcv, demonstrating the requirement of TFT4 for plant immunity to Xcv. Our results suggest that the XopQ virulence function is to suppress ETI and immunity‐associated cell death by interacting with TFT4, which is an important component of ETI and a bona fide target of XopQ.     

Inclusion of ecologically based trait variation in plant functional types reduces the projected land carbon sink in an earth system model

Earth system models demonstrate large uncertainty in projected changes in terrestrial carbon budgets. The lack of inclusion of adaptive responses of vegetation communities to the environment has been suggested to hamper the ability of modeled vegetation to adequately respond to environmental change. In this study, variation in functional responses of vegetation has been added to an earth system model (ESM) based on ecological principles. The restriction of viable mean trait values of vegetation communities by the environment, called ‘habitat filtering’, is an important ecological assembly rule and allows for determination of global scale trait–environment relationships. These relationships were applied to model trait variation for different plant functional types (PFTs). For three leaf traits (specific leaf area, maximum carboxylation rate at 25 °C, and maximum electron transport rate at 25 °C), relationships with multiple environmental drivers, such as precipitation, temperature, radiation, and CO₂, were determined for the PFTs within the Max Planck Institute ESM. With these relationships, spatiotemporal variation in these formerly fixed traits in PFTs was modeled in global change projections (IPCC RCP8.5 scenario). Inclusion of this environment‐driven trait variation resulted in a strong reduction of the global carbon sink by at least 33% (2.1 Pg C yr^?1) from the 2nd quarter of the 21st century onward compared to the default model with fixed traits. In addition, the mid‐ and high latitudes became a stronger carbon sink and the tropics a stronger carbon source, caused by trait‐induced differences in productivity and relative respirational costs. These results point toward a reduction of the global carbon sink when including a more realistic representation of functional vegetation responses, implying more carbon will stay airborne, which could fuel further climate change.     

Space–time clusters for early detection of grizzly bear predation

Accurate detection and classification of predation events is important to determine predation and consumption rates by predators. However, obtaining this information for large predators is constrained by the speed at which carcasses disappear and the cost of field data collection. To accurately detect predation events, researchers have used GPS collar technology combined with targeted site visits. However, kill sites are often investigated well after the predation event due to limited data retrieval options on GPS collars (VHF or UHF downloading) and to ensure crew safety when working with large predators. This can lead to missing information from small‐prey (including young ungulates) kill sites due to scavenging and general site deterioration (e.g., vegetation growth). We used a space–time permutation scan statistic (STPSS) clustering method (SaTScan) to detect predation events of grizzly bears (Ursus arctos) fitted with satellite transmitting GPS collars. We used generalized linear mixed models to verify predation events and the size of carcasses using spatiotemporal characteristics as predictors. STPSS uses a probability model to compare expected cluster size (space and time) with the observed size. We applied this method retrospectively to data from 2006 to 2007 to compare our method to random GPS site selection. In 2013–2014, we applied our detection method to visit sites one week after their occupation. Both datasets were collected in the same study area. Our approach detected 23 of 27 predation sites verified by visiting 464 random grizzly bear locations in 2006–2007, 187 of which were within space–time clusters and 277 outside. Predation site detection increased by 2.75 times (54 predation events of 335 visited clusters) using 2013–2014 data. Our GLMMs showed that cluster size and duration predicted predation events and carcass size with high sensitivity (0.72 and 0.94, respectively). Coupling GPS satellite technology with clusters using a program based on space–time probability models allows for prompt visits to predation sites. This enables accurate identification of the carcass size and increases fieldwork efficiency in predation studies.     

Assessment of identity disequilibrium and its relation to empirical heterozygosity fitness correlations: a meta‐analysis

Heterozygosity fitness correlations (HFCs) have frequently been used to detect inbreeding depression, under the assumption that genome‐wide heterozygosity is a good proxy for inbreeding. However, meta‐analyses of the association between fitness measures and individual heterozygosity have shown that often either no correlations are observed or the effect sizes are small. One of the reasons for this may be the absence of variance in inbreeding, a requisite for generating general‐effect HFCs. Recent work has highlighted identity disequilibrium (ID) as a measure that may capture variance in the level of inbreeding within a population; however, no thorough assessment of ID in natural populations has been conducted. In this meta‐analysis, we assess the magnitude of ID (as measured by the g₂ statistic) from 50 previously published HFC studies and its relationship to the observed effect sizes of those studies. We then assess how much power the studies had to detect general‐effect HFCs, and the number of markers that would have been needed to generate a high expected correlation (r² = 0.9) between observed heterozygosity and inbreeding. Across the majority of studies, g₂ values were not significantly different than zero. Despite this, we found that the magnitude of g₂ was associated with the average effect sizes observed in a population, even when point estimates were nonsignificant. These low values of g₂ translated into low expected correlations between heterozygosity and inbreeding and suggest that many more markers than typically used are needed to robustly detect HFCs.     

Common ancestry or environmental trait filters: cross‐continental comparisons of trait–habitat relationships in tropical anuran amphibian assemblages

Aim To investigate whether trait–habitat relations in biological communities converge across three global regions. The goal is to assess the role of habitat templets in shaping trait assemblages when different assembly mechanisms are operating and to test whether trait–habitat relations reflect a common evolutionary history or environmental trait filters. Location Guiana Shield, South America; Upper Guinea Forest Block, West Africa; Borneo rain forests, Southeast Asia. Methods We compared large anuran amphibian data sets at both the regional and cross‐continental scale. We applied a combination of three‐table ordinations (RLQ) and permutation model‐based multivariate fourth‐corner statistics to test for trait–habitat relationships at both scales and used phylogenetic comparative methods to quantify phylogenetic signal in traits that enter these analyses. Results Despite the existence of significant trait–habitat links and congruent trait patterns, we did not find evidence for the existence of a universal trait–habitat relationship at the assemblage level and no clear sign for cross‐continental convergence of trait–habitat relations. Patterns rather varied between continents. Despite the fact that a number of traits were conserved across phylogenies, the phylogenetic signal varied between regions. Trait–habitat relations therefore not only reflect a common evolutionary history, but also more recently operating environmental trait filters that ultimately determine the trait composition in regional assemblages. Main conclusions Integrating trait–habitat links into analyses of biological assemblages can enhance the predictive power and general application of species assembly rules in community and macroecology, particularly when phylogenetic comparative methods are simultaneously applied. However, in order to predict trait composition based on habitat templets, trait–habitat links cannot be assumed to be universal but rather have to be individually established in different regions prior to model building. Only then can direct trait‐based approaches be useful tools for predicting fundamental community patterns.     

The effects of competition on fitness depend on the sex of both competitors

In intraspecific competition, the sex of competing individuals is likely to be important in determining the outcome of competitive interactions and the way exposure to conspecifics during development influences adult fitness traits. Previous studies have explored differences between males and females in their response to intraspecific competition. However, few have tested how the sex of the competitors, or any interactions between focal and competitor sex, influences the nature and intensity of competition. We set up larval seed beetles Callosobruchus maculatus to develop either alone or in the presence of a male or female competitor and measured a suite of traits: development time, emergence weight; male ejaculate mass, copulation duration, and lifespan; and female lifetime fecundity, offspring egg–adult survival, and lifespan. We found effects of competition and competitor sex on the development time and emergence weight of both males and females, and also of an interaction between focal and competitor sex: Females emerged lighter when competing with another female, while males did not. There was little effect of larval competition on male and female adult fitness traits, with the exception of the effect of a female competitor on a focal female's offspring survival rate. Our results highlight the importance of directly measuring the effects of competition on fitness traits, rather than distant proxies for fitness, and suggest that competition with the sex with the greater resource requirements (here females) might play a role in driving trait evolution. We also found that male–male competition during development resulted in shorter copulation times than male–female competition, a result that remained when controlling for the weight of competitors. Although it is difficult to definitively tease apart the effects of social environment and access to resources, this result suggests that something about the sex of competitors other than their size is driving this pattern.     

A before–after control–impact assessment to understand the potential impacts of highway construction noise and activity on an endangered songbird

Anthropogenic noise associated with highway construction and operation can have individual‐ and population‐level consequences for wildlife (e.g., reduced densities, decreased reproductive success, behavioral changes). We used a before–after control–impact study design to examine the potential impacts of highway construction and traffic noise on endangered golden‐cheeked warblers (Setophaga chrysoparia; hereafter warbler) in urban Texas. We mapped and monitored warbler territories before (2009–2011), during (2012–2013), and after (2014) highway construction at three study sites: a treatment site exposed to highway construction and traffic noise, a control site exposed only to traffic noise, and a second control site exposed to neither highway construction or traffic noise. We measured noise levels at varying distances from the highway at sites exposed to construction and traffic noise. We examined how highway construction and traffic noise influenced warbler territory density, territory placement, productivity, and song characteristics. In addition, we conducted a playback experiment within study sites to evaluate acute behavioral responses to highway construction noises. Noise decreased with increasing distance from the highways. However, noise did not differ between the construction and traffic noise sites or across time. Warbler territory density increased over time at all study sites, and we found no differences in warbler territory placement, productivity, behavior, or song characteristics that we can attribute to highway construction or traffic noise. As such, we found no evidence to suggest that highway construction or traffic noise had a negative effect on warblers during our study. Because human population growth will require recurring improvements to transportation infrastructure, understanding wildlife responses to anthropogenic noise associated with the construction and operation of roads is essential for effective management and recovery of prioritized species.     

Selection on intra‐individual variation in stigma–anther distance in the tropical tree Ipomoea wolcottiana (Convolvulaceae)

• It is well known that animals can exert strong selective pressures on plant traits. However, studies on the evolutionary consequences of plant–animal interactions have mainly focused on understanding how these interactions shape trait means, while overlooking its potential direct effect on the variability among structures within a plant (e.g. flowers and fruits). The degree of within‐plant variability can have strong fitness effects but few studies have evaluated its role as a potential target of selection.
• Here we reanalysed data on Ipomoea wolcottiana stigma–anther distance to test alternate mechanisms driving selection on the mean as well as on intra‐individual variance in 2 years. We found strong negative selection acting on intra‐individual variation but not on mean stigma–anther distance, suggesting independent direct selection on the latter.
• Our result suggests that intra‐individual variance has the potential to be an important target of selection in nature, and that ignoring it could lead to the wrong characterisation of the selection regime.
• We highlight the need for future studies to consider patterns of selection on the mean as well as on intra‐individual variance if we want to understand the full extent of plant–animal interactions as an evolutionary force in nature.

     

The transmembrane domain of N –acetylglucosaminyltransferase I is the key determinant for its Golgi subcompartmentation

Golgi‐resident type–II membrane proteins are asymmetrically distributed across the Golgi stack. The intrinsic features of the protein that determine its subcompartment‐specific concentration are still largely unknown. Here, we used a series of chimeric proteins to investigate the contribution of the cytoplasmic, transmembrane and stem region of Nicotiana benthamiana N–acetylglucosaminyltransferase I (GnTI) for its cis/medial‐Golgi localization and for protein–protein interaction in the Golgi. The individual GnTI protein domains were replaced with those from the well‐known trans‐Golgi enzyme α2,6–sialyltransferase (ST) and transiently expressed in Nicotiana benthamiana. Using co‐localization analysis and N–glycan profiling, we show that the transmembrane domain of GnTI is the major determinant for its cis/medial‐Golgi localization. By contrast, the stem region of GnTI contributes predominately to homomeric and heteromeric protein complex formation. Importantly, in transgenic Arabidopsis thaliana, a chimeric GnTI variant with altered sub‐Golgi localization was not able to complement the GnTI‐dependent glycosylation defect. Our results suggest that sequence‐specific features in the transmembrane domain of GnTI account for its steady‐state distribution in the cis/medial‐Golgi in plants, which is a prerequisite for efficient N–glycan processing in vivo.     

Predators in the plant–soil feedback loop: aboveground plant‐associated predators may alter the outcome of plant–soil interactions

Plant–soil feedback (PSF) can structure plant communities, promoting coexistence (negative PSF) or monodominance (positive PSF). At higher trophic levels, predators can alter plant community structure by re‐allocating resources within habitats. When predator and plant species are spatially associated, predators may alter the outcome of PSF. Here, I explore the influence of plant‐associated predators on PSF using a generalised cellular automaton model that tracks nutrients, plants, herbivores and predators. I explore key contingencies in plant–predator associations such as whether predators associate with live vs. senesced vegetation. Results indicate that plant‐associated predators shift PSF to favour the host plant when predators colonise live vegetation, but the outcome of PSF will depend upon plant dispersal distance when predators colonise dead vegetation. I apply the model to two spider‐associated invasive plants, finding that spider predators should shift PSF dynamics in a way that inhibits invasion by one forest invader, but exacerbates invasion by another.