Main Axis Of Variation Research Articles

Gymnosperms demonstrate patterns of fine‐root trait coordination consistent with the global root economics space

Abstract Gymnosperms encompass a diverse group of mostly woody plants with high ecological and economic value, yet little is known about the scope and organization of fine‐root trait diversity among gymnosperms due to the undersampling of most gymnosperm families and the dominance of angiosperm groups in recent syntheses. New and existing data were compiled for morphological traits (root diameter, length, tissue density, specific root length [SRL] and specific root area [SRA]), the architectural trait branching ratio, root nitrogen content [N] and mycorrhizal colonization. We used phylogenetic least squares regression and principal component analysis to determine trait–trait relationships and coordination across 66 species, representing 11 of the 12 extant gymnosperm families from boreal, temperate, subtropical and tropical biomes. Finally, we compared the relationship between family divergence time and mean trait values to determine whether evolutionary history structured variation in fine‐root traits within the gymnosperm phylogeny. Wide variation in gymnosperm root traits could be largely captured by two primary axes of variation defined by SRL and diameter, and root tissue density and root nitrogen, respectively. However, individual root length and SRA each had significant correlations with traits defining both main axes of variation. Neither mycorrhizal colonization nor root branching ratio were closely related to other traits. We did not observe a directional evolution of mean trait values from older to more recently diverged gymnosperm families. Synthesis. Despite their unique evolutionary history, gymnosperms display a root economic space similar to that identified in angiosperms, likely reflecting common constraints on plants adapting to diverse environments in both groups. These findings provide greater confidence that patterns observed in broad syntheses justly capture patterns of trait diversity among multiple, distinct lineages. Additionally, independence between root architecture and other traits may support greater diversity in below‐ground resource acquisition strategies. Unlike angiosperms, there were no clear trends towards increasingly thin roots over evolutionary time, possibly because of lower diversification rates or unique biogeographic history among gymnosperms, though additional observations are needed to more richly test evolutionary trends among gymnosperms.

Quantifying climatic and socioeconomic drivers of urban malaria in Surat, India: a statistical spatiotemporal modelling study

Cities are becoming increasingly important habitats for mosquito vectors of disease. The pronounced heterogeneity of urban landscapes challenges our understanding of the effects of climate and socioeconomic factors on mosquito-borne disease dynamics at different spatiotemporal scales. Here, we quantify the impact of climatic and socioeconomic factors on urban malaria risk, using an extensive dataset in both space and time for reported Plasmodium falciparum cases in the city of Surat, northwest India. We analysed 10 years of monthly P falciparum cases resolved at three nested spatial resolutions (seven zones, 32 units, and 478 worker units) with a Bayesian hierarchical mixed model that incorporates the effects of population density, poverty, relative humidity, and temperature, in addition to random effects (structured and unstructured). To reduce dimensionality and avoid correlation of covariates, socioeconomic variables from survey data were summarised into main axes of variation using principal component analysis. With model selection, we identified the main drivers of spatiotemporal variation in malaria incidence rates at each of the three spatial resolutions. We also compared observations to model-fitted cases by quantifying the percentage of predictions within five discrete levels of malaria risk. The spatial variation of urban malaria cases was stationary over time, whereby locations with high and low yearly cases remained largely consistent across years. Local socioeconomic variation could be summarised with three principal components accounting for approximately 80% of the variance. The model that incorporated local temperature and relative humidity together with two of these principal components, largely representing population density and poverty, best explained monthly malaria patterns in models formulated at the three different spatial scales. As model resolution increased, the effect size of humidity decreased, whereas those of temperature and the principal component associated with population density increased. Model predictions accurately captured aggregated total monthly cases for the city; in space-time, they more closely matched observations at the intermediate scale, with around 57% of units estimated to fall in the observed category on average across years. The mean absolute error was lower at the intermediate level, showing that this is the best aggregation level to predict the space-time dynamics of malaria incidence rates across the city with the selected model. This statistical modelling framework provides a basis for development of a climate-driven early warning system for urban malaria for the units of Surat, including spatially explicit prediction of malaria risk several weeks to months in advance. Results indicate environmental and socioeconomic covariates for which further measurement at high resolution should lead to model improvement. Advanced warning combined with local surveillance and knowledge of disease hotspots within the city could inform targeted intervention as part of urban malaria elimination efforts. US National Institutes of Health.

Plant trait relationships are maintained within a major crop species: lack of artificial selection signal and potential for improved agronomic performance.

The exploration of phenotypic spaces of large sets of plant species has considerably increased our understanding of diversification processes in the plant kingdom. Nevertheless, such advances have predominantly relied on interspecific comparisons that hold several limitations. Here, we grew in the field a unique set of 179 inbred lines of durum wheat, Triticum turgidum spp. durum, characterized by variable degrees of artificial selection. We measured aboveground and belowground traits as well as agronomic traits to explore the functional and agronomic trait spaces and to investigate trait-to-agronomic performance relationships. We showed that the wheat functional trait space shared commonalities with global cross-species spaces previously described, with two main axes of variation: a root foraging axis and a slow-fast trade-off axis. Moreover, we detected a clear signature of artificial selection on the variation of agronomic traits, unlike functional traits. Interestingly, we identified alternative phenotypic combinations that can optimize crop performance. Our work brings insightful knowledge about the structure of phenotypic spaces of domesticated plants and the maintenance of phenotypic trade-offs in response to artificial selection, with implications for trade-off-free and multi-criteria selection in plant breeding.

A comparison of free-living and sponge-associated bacterial communities from a remote oceanic island with a focus on calcareous sponges.

Calcareous sponges are an often overlooked element of sponge communities. In contrast to most other sponges, calcareous sponges produce calcium carbonate spicules, as opposed to the siliceous spicules of most sponges. Here, we investigated the bacterial communities of 17 sponge species, including type and paratype specimens of recently described calcareous species, sampled off the remote island of Rodrigues, in the Indian Ocean. The main axis of variation in a PCO analysis of all samples separated noncalcareous sponge species, including Axinyssa aplysinoides, Cinachyrella aff. australiensis, Petrosia seychellensis, Ircinia aff. variabilis, Spongia ceylonensis, Plakinastrella aff. clipptertonensis, Agelas aff. ceylonica, Agelas aff. mauritiana, and Hyrtios erectus from calcareous sponges, the noncalcareous Biemna tubulata, sediment, and seawater. Overall, the bacterial communities of calcareous sponges revealed unique prokaryotic profiles with low abundances of several bacterial phyla, and relatively high abundances of other taxa, for example, the phyla Fibrobacterota, Proteobacteria, and the SAR324 clade, the class Alphaproteobacteria, and orders Cytophagales and Cyanobacteriales, although there was considerable variation among species. Calcareous sponges also had a high dominance of unknown bacterial operational taxonomic units (OTUs). Considering the unique nature of these communities, further studies are needed to better understand the environmental and ecological drivers of calcareous sponge-associated bacterial communities and their relevance as potential sources of novel microbes of biotechnological interest.

How large-scale geographic factors affect the different dimensions of functional diversity: evidence from the beech forest herb layer (Apennines, Italy)

Background and aims – The research aim was to investigate the relation between large-scale geographic factors and the functional structure of the herbaceous layer of calcareous beech forests in the Apennines, managed as high forest.Material and methods – We selected 163 plots (20 × 20 m), ranging from Central to South Italy, using a random stratified sampling design. We correlated the effect sizes of traits’ community-weighted means, functional richness, evenness, divergence, dispersion, and Rao’s quadratic entropy, with the main axes of variation in species composition.Key results – The geographical range played a weak role in shaping the species composition of the herbaceous layer. However, we found evidence of functional convergence towards the northern sectors of the study area, where traits linked to resource retention strategies and vegetative spread are filtered. We did not find any evidence of convergence northwards for leaf phenology and pollination types.Conclusion – The increase of the intensity in the environmental stress was associated with a decrease of diversity for traits related to resource conservation strategies and vegetative propagation. On the contrary, the lower cold stress intensity southwards fostered a better niche partitioning, ensuring the coexistence of species with different modalities of resource acquisition and conservation.

Mandible shape variation and feeding biomechanics in minks

European and American minks are very similar in ecology, behavior and morphology. Both species hunt terrestrial vertebrates and aquatic prey, but the American mink is a more generalist predator which, among other factors, allows it to outcompete the European mink in areas where it has been introduced. We used 3D geometric morphometrics and estimates of muscle mechanical advantage to assess the degree of variation in mandibular morphology, and to determine whether such variation reflects dietary differences between the two species. The three main axes of variation represented interspecific differences, a common allometric trajectory between species and sexes, and the interspecific effect of sexual size dimorphism, with males having overall stronger bites than females. Differences in mandible shape and biomechanical parameters suggest that American minks are better equipped for preying on terrestrial vertebrates, while the features seen in European mink could be related to tougher prey, fish capture, or both. Additionally, within each species, the larger specimens of each sex present indicators of a higher percentage of terrestrial prey in their diet. These results indicate a low potential dietary overlap between both species, suggesting that factors other than prey competition may have a role in the decline of the European mink.

Ecomorphology of the tarsometatarsus of waterfowl (Anseriformes) based on geometric morphometrics and its application to fossils.

Anseriformes is a diverse group of birds that comprises screamers, the Magpie Goose, and swans ducks and geese, with a relatively rich fossil record. Waterfowl live in close relation to water bodies, but show a diversity of locomotory habits, being typically categorized as walkers, dabblers, and divers. Owing to its functional significance and high preservation potential, the tarsometatarsus has been considered to be a "key" element upon which to base ecomorphological inferences in fossil waterfowl. For instance, based on features of the tarsometatarsus the Miocene flightless duck Cayaoa bruneti and the Oligocene-Miocene large waterfowl Paranyroca have been inferred as divers. Herein, we use a geometric morphometric approach and comparative methods to assess the phylogenetic and ecomorphological signals in the shape and size of waterfowl tarsometatarsi in relation to their locomotory habits. We also apply phylogenetic flexible discriminant analysis (pFDA) to test the inferred diving habits in the extinct waterfowl Cayaoa and Paranyroca. Extant waterfowl species are largely distributed according to their locomotory habit along the main axis of variation in the shape space, a pattern mirrored by the phylogenetic generalized least squares model, which shows that a third of the shape variation is significantly explained by the habit. The pFDA reclassifies correctly almost all extant species and classified with high posterior probabilities the fossil Cayaoa and Paranyroca as a diver and as a dabbler, respectively. Our quantitative multivariate approach confirms the tarsometatarsus as a useful source of data upon which reliably assesses locomotory habits of fossil waterfowl.

Climatic and soil factors explain the two-dimensional spectrum of global plant trait variation

Plant functional traits can predict community assembly and ecosystem functioning and are thus widely used in global models of vegetation dynamics and land–climate feedbacks. Still, we lack a global understanding of how land and climate affect plant traits. A previous global analysis of six traits observed two main axes of variation: (1) size variation at the organ and plant level and (2) leaf economics balancing leaf persistence against plant growth potential. The orthogonality of these two axes suggests they are differently influenced by environmental drivers. We find that these axes persist in a global dataset of 17 traits across more than 20,000 species. We find a dominant joint effect of climate and soil on trait variation. Additional independent climate effects are also observed across most traits, whereas independent soil effects are almost exclusively observed for economics traits. Variation in size traits correlates well with a latitudinal gradient related to water or energy limitation. In contrast, variation in economics traits is better explained by interactions of climate with soil fertility. These findings have the potential to improve our understanding of biodiversity patterns and our predictions of climate change impacts on biogeochemical cycles.

Dietary affinities, resource overlap and core structure in Atlantic Forest phyllostomid bat communities

Abstract The Phyllostomidae is arguably the most diverse family‐level clade of mammals. Associated with this high diversity is considerable heterogeneity in resource utilisation among species and across locales of the Neotropics. Despite heterogeneity, few attempts have been made to synthesise dietary patterns even for smaller regions within the Neotropics. Atlantic Forest is a large dynamic ecoregion in the southern Neotropics that is distinct from other Tropical forests because of its extensive latitudinal extent, elevated climatic heterogeneity, biodiversity and long history of anthropogenic modification. I obtained data on dietary affinities of 34 species of bats from 35 different sites spanning the entire Atlantic Forest. In Atlantic Forest, as in other places in the Neotropics, phyllostomids consumed arthropods, vertebrates, fruits, nectar and blood. Frugivores consumed and dispersed the fruits of 99 different species of plants and nectarivores pollinated an additional nine others. Dietary overlap was modest, yet significantly greater than expected based on a null model. The main axis of variation in diet separated species that primarily consumed animal material from those that primarily consumed plant material and this axis was significantly related to phylogenetic affinities of species. Unlike in other places in the Neotropics, frugivorous bats did not exhibit a core structure related to genus‐to‐genus matching of bat genera with plant genera. Generality of diets of frugivorous bats, further indicated by non‐randomly high dietary overlap, is likely to degrade core structure in these primarily Subtropical communities. Co‐occurrence of a large number of generalist bat species, seasonal climates and ubiquitous anthropogenic modification may serve to promote generality of resource utilisation of bats in Atlantic Forest. The Neotropics is vast and the bats that live within it are diverse. Future studies should explore spatial dynamics of dietary affinities and resource overlap to increase understanding of the context of strong and weak core structure of phyllostomid bat communities.

Changes in plant species abundance alter the multifunctionality and functional space of heathland ecosystems.

Though it is well established that species composition affects ecosystem function, the way in which species combine to control overall ecosystem functioning is still debated. In experimental mesocosms, we planted three functionally distinct dry-heath species in varying proportions and measured multiple ecosystem properties related to nutrient cycling and carbon storage (hereafter functions). Overall ecosystem functioning was described as the main axes of variation in ecosystem functioning (functional space) and the proportion of ecosystem functions at high levels; for example, fast carbon and nutrient cycling (cluster-based multifunctionality). The first functional space axis, related to nitrogen availability, was driven by plant species abundance, particularly that of legumes, which strongly affected many individual functions. The second, related to total plant biomass and woodiness, was mostly driven by the abundance of dwarf shrubs. Similarly, cluster-based multifunctionality was related to the initial abundance of all species, but particularly the legume. Interactions between species also affected ecosystem multifunctionality, but these effects were smaller in magnitude. These results indicate that species interactions could play a secondary role to species abundance and identity in driving the overall ecosystem functioning of heathlands, but also that axes of variation in functional space are clearly linked to plant functional composition.

What it means to be a lexicographer

"In this paper I will present some reflections and analyses, and draw some conclusions, based on my own activity as a linguist and lexicographer. I will speak neither about bilingual or multilingual lexicography, nor about specialised, terminological dictionaries (that is lexicons concerning different domains: juridical, scientific, medical, IT, etc.), because I have no work experience in this respect. I will speak about general, purely linguistic (non-terminological) dictionaries. There will be two main directions: i) Linguistic dictionaries which deal with contemporary language, intended for the general public. Mono-volume dictionaries like the well-known DEX represent this type. The main characteristics of this type of dictionaries are related to their synchronic, explanatory, and normative approach(es); ii) Linguistic dictionaries, which treat the language in variation from different points of view: diachronic, dialectal, stylistic, etc. This type is intended mainly for the specialists, and it is represented by multi-volume dictionaries like DA/DLR, DELR and others. Their main characteristics are linked to their variational (diachronic or historic, dialectal, etc.), explanatory and etymological approach(es). The main axis of variation considered is diachronic or historic, and that is why this type of lexicography is usually labelled as diachronic or historic lexicography. But personally I prefer to label it as variational lexicography. “Variational” includes “diachronic”, as well as the variation in respect with other axes. I will focus my attention mostly on the theoretical and methodological principles defining the approaches that differentiate the two main types of linguistic dictionaries mentioned above."

Geographical location and habitat predict variation in prokaryotic community composition of Suberites diversicolor

PurposeMarine lakes are unique habitats that house diverse assemblages of benthic and planktonic organisms including endemic species. In this study, we aimed to assess to what extent geographical location (Berau versus Papua) and the degree of marine lake connectivity (relatively open versus closed) to the surrounding marine environment structures the prokaryotic community composition of the sponge species Suberites diversicolor.MethodsSponge specimens were sampled in five marine lakes in Borneo and Papua and one open sea habitat in Taiwan.ResultProkaryotic communities of S. diversicolor were dominated by members assigned to the Proteobacteria (particularly Alphaproteobacteria and Gammaproteobacteria) and Cyanobacteria, which together made up from 78 to 87% of sequences in all samples. The dominant operational taxonomic units (OTUs) in most samples, OTUs 1 and 3, were both assigned to the alphaproteobacterial order Rhodospirillales with OTU-1 dominant in the marine lakes of Berau and Papua and OTU-3 in Taiwan. OTU-3 was also largely absent from Papuan samples but present in all Berau samples. Compositionally, S. diversicolor samples clustered according to geographical location with the main axis of variation separating marine lake samples collected in Berau from those collected in Papua and the second axis of variation separating open sea samples collected in Taiwan from all marine lake samples. In addition, our results suggest that the degree of lake connectivity to the open sea also influences prokaryotic composition.ConclusionAlthough previous studies have shown that sponge-associated microbial communities tend to be stable across different geographical and environmental gradients, in the present study, both geography and local environmental conditions were significant predictors of variation in prokaryotic community composition of S. diversicolor.

The relation between petrophysical and transport properties of the Boom Clay and Eigenbilzen Sands

Within the framework of safe disposal of high and intermediate level radioactive waste, it is well known that for both the Boom Clay and overlying Eigenbilzen Sands (early Oligocene; Rupelian), the composition varies with depth. Though, a detailed understanding of how these intrinsic variations may affect the basic transport properties is still missing. Therefore, a small but comprehensive and unique data set, containing transport parameters (hydraulic conductivity and diffusivity) and related properties (mineral composition and texture, grain size distribution, specific surface area and pore size distribution) of different samples of the Boom Clay and Eigenbilzen Sands has been gathered during recent years. First, the variability in transport parameters and petrophysical properties is discussed and mutual relationships are investigated. Second, the performance of predictive modelling is explored. The multivariate analysis clearly illustrates that the data are mainly explained by two main axes of variation. One corresponds to the logarithmic hydraulic conductivity (logK) and all petrophysical properties that are very strongly correlated to it. The second axis is independent of logK, and relates to the size of the diffusing molecules. Finally, predictive modelling seems promising at this point, but the limited quality of the currently available test cases prohibits being conclusive on the model performance and its generalisability.

Towards a comparative approach to the structure of animal personality variation.

Latent personality traits underpinning observed behavioral variation have been studied in a great many species. However, a lack of standardized behavioral assays, coupled to a common reliance on inferring personality from a single, observed, behavioral trait makes it difficult to determine if, when, and how conclusions can be directly compared across taxa. Here, we estimate the among-individual (co)variance structure (ID) for a set of four behaviors expressed in an open field trial, putatively indicative of boldness, in seven species of small freshwater fish. We show that the ID matrices differ in terms of the total amount of variation present, and crucially the orientation, and as a consequence, biological interpretation of the first eigenvector. Specifically, loading of observed traits on the main axis of variation in ID matched a priori expectations for a shy-bold continuum in only three of the seven cases. Nonetheless, when the “shape” of the matrices was compared in higher dimensions, there was a high level of similarity among species, and weak evidence of phylogenetic signal. Our study highlights the present difficulty of trying to compare empirical inferences about specific personality traits across studies. However, it also shows how multivariate data collection and analysis allows the structure of behavioral variation to be quantitatively compared across populations or species without reliance on ambiguous verbal labels. This suggests that the field may have much to gain from greater uptake of phylogenetically informed comparative approaches when seeking to test evolutionary hypotheses about the origin and maintenance of personality variation.

What can observational data reveal about metacommunity processes?

A key challenge for community ecology is to understand to what extent observational data can be used to infer the underlying community assembly processes. As different processes can lead to similar or even identical patterns, statistical analyses of non‐manipulative observational data never yield undisputable causal inference on the underlying processes. Still, most empirical studies in community ecology are based on observational data, and hence understanding under which circumstances such data can shed light on assembly processes is a central concern for community ecologists. We simulated a spatial agent‐based model that generates variation in metacommunity dynamics across multiple axes, including the four classic metacommunity paradigms as special cases. We further simulated a virtual ecologist who analysed snapshot data sampled from the simulations using eighteen output metrics derived from beta‐diversity and habitat variation indices, variation partitioning and joint species distribution modelling. Our results indicated two main axes of variation in the output metrics. The first axis of variation described whether the landscape has patchy or continuous variation, and thus was essentially independent of the properties of the species community. The second axis of variation related to the level of predictability of the metacommunity. The most predictable communities were niche‐based metacommunities inhabiting static landscapes with marked environmental heterogeneity, such as metacommunities following the species sorting paradigm or the mass effects paradigm. The most unpredictable communities were neutral‐based metacommunities inhabiting dynamics landscapes with little spatial heterogeneity, such as metacommunities following the neutral or patch sorting paradigms. The output metrics from joint species distribution modelling yielded generally the highest resolution to disentangle among the simulated scenarios. Yet, the different types of statistical approaches utilized in this study carried complementary information, and thus our results suggest that the most comprehensive evaluation of metacommunity structure can be obtained by combining them.

Vertical gradient in bryophyte diversity and species composition in tropical and subtropical forests in Yunnan, SW China

AbstractQuestionsWe sampled epiphytic bryophytes along the entire vertical gradient, from tree base to upper canopy, in tropical and subtropical forests in order to answer the following questions: (a) how do diversity, composition and life forms differ between forests; (b) how do communities change along the vertical gradient in each forest; (c) what are the likely environmental drivers of this; and (d) what is the conservation significance of the results?LocationCanopy crane sites in tropical lowland seasonal rain forest (TRF) and subtropical montane moist forest (STF) in Yunnan, southwest China.MethodsBryophytes were sampled from 1,600–2,400 cm2 of bark surface in 14 vertical segments in three canopy layers on 142 trees, using canopy cranes. Microclimate was measured at five levels on the crane towers. Diversity was compared within and between forests using ANOVA. NMDS was used to compare species composition and assess potential drivers.ResultsIn total, 184 species were recorded in 106 genera and 39 families. STF had a richer bryoflora than TRF. More species occurred in the canopy than the sub‐canopy and understorey in both sites. The fan life form was dominant in the lower two layers of both forests, while mats were more common in the canopy of TRF and tall turfs in STF. The main axis of variation in species composition was associated with the vertical gradient of declining humidity and vapour pressure, and increasing temperature, light and wind speed.ConclusionsThis study demonstrates the value of canopy cranes for complete sampling of the epiphytic bryoflora in complex forests. Both forest types had very high species richness, reflecting the diversity of microhabitats along the vertical gradient. Observed and projected climate change may threaten this bryoflora as a result of rising temperatures and, in some areas, declining rainfall and fog frequency.

High dispersal ability is related to fast life‐history strategies

Abstract Seed dispersal is an essential, yet often overlooked process in plant ecology and evolution, affecting adaptation capacity, population persistence and invasiveness. A species’ ability to disperse is expected to covary with other life‐history traits to form dispersal syndromes. Dispersal might be linked to the rate of life history, fecundity or generation time, depending on the relative selection pressures of bet‐hedging, kin competition or maintaining gene flow. However, the linkage between dispersal and plant life‐history strategies remains unknown because it is difficult to observe, quantify and manipulate the influence of dispersal over large spatiotemporal scales. We integrate datasets describing plant vital rates, dispersal and functional traits to incorporate dispersal explicitly into the rich spectra of plant life‐history strategies. For 141 plant species, we estimated dispersal ability by predicting maximum dispersal distances using allometric relationships based on growth form, dispersal mode, terminal velocity and seed mass. We derived life‐history traits from matrix population models parameterized with field data from the COMPADRE Plant Matrix Database. We analysed the covariation in dispersal ability and life‐history traits using multivariate techniques. We found that three main axes of variation described plant dispersal syndromes: the fast‐slow life‐history continuum, the dispersal strategy axis and the reproductive strategy axis. On the dispersal strategy axis, species’ dispersal abilities were positively correlated with aspects of fast life histories. Species with a high net reproductive rate, a long window of reproduction, low likelihood of escaping senescence and low shrinkage tendencies disperse their seeds further. The overall phylogenetic signal in our multidimensional analyses was low (Pagel's λ < 0.24), implying a high degree of taxonomic generality in our findings. Synthesis. Dispersal has been largely neglected in comparative demographic studies, despite its pivotal importance for populations. Our explicit incorporation of dispersal in a comparative life‐history framework provides key insights to bridge the gap between dispersal ecology and life‐history traits. Species with fast life‐history strategies disperse their seeds further than slow‐living plants, suggesting that longer dispersal distances may allow these species to take advantage of habitats varying unpredictably in space and time as a bet‐hedging strategy.

Seeking stable traits to characterize the root system architecture. Study on 60 species located at two sites in natura.

In several disciplines, identifying relevant root traits to characterize the root system architecture of species or genotypes is a crucial step. To address this question, we analysed the inter-specific variations of root architectural traits in two contrasting environments. We sampled 60 species in natura, at two sites, each presenting homogeneous soil conditions. We estimated for each species and site a set of five traits used for the modelling of the root system architecture: extreme tip diameters (Dmin and Dmax), relative diameter range (Drange), mean inter-branch distance (IBD) and dominance slope between the diameters of parent and lateral roots (DlDm). The five traits presented a highly significant species effect, explaining between 77 and 98 % of the total variation. Dmin, Dmax and Drange were particularly determined by the species, while DlDm and IBD exhibited a higher percentage of environmental variations. These traits make it possible to confirm two main axes of variation: 'fineness-density' (defined by Dmin and IBD) and 'dominance-heterorhizy' (DlDm and Drange), that together accounted for 84 % of the variations observed. We confirmed the interest of these traits in the characterization of the root system architecture in ecology and genetics, and suggest using them to enrich the 'root economic spectrum'.

Father absence and gendered traits in sons and daughters.

Research has previously found a number of apparently contradictory patterns in the relationship between ‘father absence’ (having a non-resident father during childhood) and the expression of gender roles, as well as other sexually dimorphic traits such as aggression. In the current study we measured a battery of sexually differentiated traits in relation to family background. 133 men and 558 women from the United States and Australia completed the Bem Sex Role Inventory, the Barrett Impulsivity Scale, the Fear Survey Schedule and the Buss & Perry Aggression Questionnaire. Principal components analysis found two main axes of variation in these traits. Firstly, a general ‘reactivity’ factor, on which aggression, impulsivity, and fear all loaded positively, was weakly associated with father absence in women. Secondly, ‘masculinity’ (consisting of high scores on masculine traits, low fear, and physical and verbal aggression) was not associated with father absence. Participants (except American males) reporting a poor childhood relationship with their parents also had high ‘reactivity’ but not higher ‘masculinity’. We found some evidence of a link between father absence and earlier age of first coitus in American females (although not in Australia), but there was no link with age of menarche in either country. Overall, the current results suggest that previous findings linking gender development with father absence in girls may have arisen from a tendency towards greater externalising and reactive behaviour rather than a change in gender development per se.

Cohort variation in individual body mass dissipates with age in large herbivores

AbstractEnvironmental conditions experienced during early growth and development markedly shape phenotypic traits. Consequently, individuals of the same cohort may show similar life‐history tactics throughout life. Conditions experienced later in life, however, could fine‐tune these initial differences, either increasing (cumulative effect) or decreasing (compensatory effect) the magnitude of cohort variation with increasing age. Our novel comparative analysis that quantifies cohort variation in individual body size trajectories shows that initial cohort variation dissipates throughout life, and that lifetime patterns change both across species with different paces of life and between sexes. We used longitudinal data on body size (mostly assessed using mass) from 11 populations of large herbivores spread along the “slow‐fast” continuum of life histories. We first quantified cohort variation using mixture models to identify clusters of cohorts with similar initial size. We identified clear cohort clusters in all species except the one with the slowest pace of life, revealing that variation in early size is structured among cohorts and highlighting typological differences among cohorts. Growth trajectories differed among cohort clusters, highlighting how early size is a fundamental determinant of lifetime growth patterns. In all species, among‐cohort variation in size peaked at the start of life, then quickly decreased with age and stabilized around mid‐life. Cohort variation was lower in species with a slower than a faster pace of life, and vanished at prime age in species with the slowest pace of life. After accounting for viability selection, compensatory/catch‐up growth in early life explained much of the decrease in cohort variation. Females showed less phenotypic variability and stronger compensatory/catch‐up growth than males early in life, whereas males showed more progressive changes throughout life. These results confirm that stronger selective pressures for rapid growth make males more vulnerable to poor environmental conditions early in life and less able to recover after a poor start. Our comparative analysis illustrates how variability in growth changes over time in closely related species that span a wide range on the slow‐fast continuum, the main axis of variation in life‐history strategies of vertebrates.