Functional and historical drivers of leaf shape evolution in palms (Arecaceae)

Aim

Leaves display a remarkable variety of shapes, each with potential ecological advantages in specific climates. While the relations between leaf shape and either climate or height have been relatively well studied in eudicots, the macroecological drivers of shape remain poorly known in monocots. Here, we investigated the associations between climate and plant height with the evolution of leaf shape in a clade with high species and morphological diversity.

Location

Global.

Time period

Cretaceous to contemporary.

Major taxa studied

Palms (Arecaceae).

Methods

We apply a Bayesian phylogenetic mixed model to test for associations between climate and leaf shape (all – entire-leaved, pinnate-dissected, palmate-dissected and costapalmate). We further reconstruct the ancestral leaf shape using multistate speciation and extinction models and compare the frequency of shapes with global temperatures through time.

Results

We find that plant height associates with dissected leaves and that annual precipitation associates with pinnate shapes. The ancestral leaf shape is unclear, but early diversification was dominated by pinnate-dissected palms, which has remained the most species-rich form of leaves throughout palm history.

Main Conclusions

Palms that are tall and live in humid regions are more likely to have pinnate leaves. Through geological time scales, temperature did not play an obvious role in determining leaf shapes. This study contributes to our understanding of how the diversity of leaf shapes is linked to biological and climatic factors.     

Size of the leaf as a marker of birch productivity at a distance from the climatic optimum

Morphometric parameters of mature leaves (area, venation density, and shape coefficient) and trunks (size and biomass) of two edificatory birch species, Betula pendula Roth and B. pubescens Ehrh., were characterized. These species inhabit a 1600-km transect of the Urals, from forest-tundra to forest-steppe. In both species, the highest trunk biomass was observed in the subzone of south taiga. Trunk parameters and leaf sizes of B. pendula varied in a narrower range than in B. pubescens. As distinct from leaf shape, leaf size was correlated with the average multiyear climate characteristics but not with the weather during a given growth season. In B. pubescens, which range extends wide from its climatic optimum, leaf area was positively correlated with trunk biomass. In B. pendula, growing mainly within the area of its climatic optimum, such correlation was not observed. We concluded that such parameter as mature leaf size could be used for prediction of tree productivity growing outside of the zone of their climatic optimum.     

酸枣叶表皮微形态对不同生态环境的适应特征

以生长于烟台—石家庄—宁夏—新疆不同生境形成的自然梯度干旱环境中的酸枣(Ziziphus jujuba var.spinosas)为材料,应用扫描电镜和能谱分析研究酸枣叶表皮微形态对不同自然梯度干旱环境的适应特征。结果表明:酸枣叶片的上、下表皮都有表皮毛着生且在叶脉处分布浓密;叶片表层覆盖有较厚的角质层和蜡质并形成突起,其主要成分为C、O、Ca三种元素;叶片表面气孔数量平均40个/视野且按一定规律分布。不同生境中酸枣叶片表面都分布有大量的晶体,且晶体的形态和组成成分表现出一定的生态适应特征。晶体的形状多样,有正六棱体、长六棱体、不规则片状、正方体、棒状晶体或针状,晶体的分布方式有单晶和簇晶。从烟台到新疆随干旱梯度的加剧,酸枣叶片表皮毛逐渐增多,气孔数量减少,气孔腔下陷明显,有助于植株减少蒸腾保水抗旱;晶体的体积逐渐变小,数量增多,密度增大,提升了叶片硬度及抗旱性;酸枣叶片晶体的主要成分为C、O、Ca三种元素,且随生境干旱加剧,C元素的含量逐渐增加,O和Ca元素含量依次减少,此外宁夏的晶体中还含有Si元素,进一步提升了叶片的机械性能。酸枣叶表皮微形态中表皮毛、角质层与蜡质、气孔、晶体等在形态结构、生物功能和组成成分上特异性的变化是其长期生存于不同梯度干旱生境的生态适应特征。     

Climatic drivers of leaf traits and genetic divergence in the tree Annona crassiflora: a broad spatial survey in the Brazilian savannas

The Cerrado is the largest South American savanna and encompasses substantial species diversity and environmental variation. Nevertheless, little is known regarding the influence of the environment on population divergence of Cerrado species. Here, we searched for climatic drivers of genetic (nuclear microsatellites) and leaf trait divergence in Annona crassiflora, a widespread tree in the Cerrado. The sampling encompassed all phytogeographic provinces of the continuous area of the Cerrado and included 397 individuals belonging to 21 populations. Populations showed substantial genetic and leaf trait divergence across the species' range. Our data revealed three spatially defined genetic groups (eastern, western and southern) and two morphologically distinct groups (eastern and western only). The east‐west split in both the morphological and genetic data closely mirrors previously described phylogeographic patterns of Cerrado species. Generalized linear mixed effects models and multiple regression analyses revealed several climatic factors associated with both genetic and leaf trait divergence among populations of A. crassiflora. Isolation by environment (IBE) was mainly due to temperature seasonality and precipitation of the warmest quarter. Populations that experienced lower precipitation summers and hotter winters had heavier leaves and lower specific leaf area. The southwestern area of the Cerrado had the highest genetic diversity of A. crassiflora, suggesting that this region may have been climatically stable. Overall, we demonstrate that a combination of current climate and past climatic changes have shaped the population divergence and spatial structure of A. crassiflora. However, the genetic structure of A. crassiflora reflects the biogeographic history of the species more strongly than leaf traits, which are more related to current climate.     

Phenotypic plasticity and gene diversity in Pistacia lentiscus L. along environmental gradients in Israel

The Mediterranean common shrub Pistacia lentiscus is distributed in a wide range of habitats along the climatic gradient in Israel. We studied the factors that may shape its morphological, physiological, and genetic differentiation. We examined the phenotypic and molecular genetic variability among and within the six Israeli populations as correlated with the local environmental conditions. The genetic structure of the shrub on the island of Cyprus was also examined. Plant morphological parameters correlated significantly with the local environmental conditions, especially with the annual precipitation and temperature. Gene diversity did not differ significantly among locations, and, hence, no differentiation among Israeli populations or between populations in Israel and Cyprus was found. The major part of the molecular variance (69%) was found within the populations, 22% of the variance was found between Israel and Cyprus and 9% among the populations within the region. Gene flow estimates among all the tested populations were high with no indication for the isolation by distance. We did not find any pattern of ecologically related genetic differentiation; hence, the morphological and physiological differences are probably due to phenotypic plasticity. It seems that the ability of P. lentiscus to express the different phenotypes in response to the varying conditions in the Mediterranean region is an adaptive trait in a species that is characterized by intensive gene flow.     

Responses of foliage‐living spider assemblage composition and traits to a climatic gradient in Themeda grasslands

For speciose, but poorly known groups, such as terrestrial arthropods, functional traits present a potential avenue to assist in predicting responses to environmental change. Species turnover is common along environmental gradients, but it is unclear how this is reflected in species traits. Community‐level change in arthropod traits, other than body size, has rarely been explored across spatial scales comparable to those examined here. We hypothesized that the composition and morphological traits of spider assemblages would differ across a gradient of climate and habitat structure. We examined foliage‐living spider assemblages associated with Themeda triandra grasslands along a 900 km climatic gradient in south‐eastern Australia. We used sweep‐netting to collect T. triandra‐associated spiders and counted juveniles and identified adults. We also measured morphological traits of adult spiders and noted their hunting mode. Associations with measures of habitat structure were less consistent than relationships with climate. Both juvenile and adult spiders were more abundant in warmer sites, although species richness was not affected by temperature. We found distinct turnover in species composition along the climatic gradient, with hunting spiders, particularly crab spiders (Thomisidae), making up a greater proportion of assemblages in warmer climates. A range of traits of spiders correlated with the climatic gradient. For example, larger spider species and species that were active hunters were more common in warmer climates. Changes in morphological traits across species, rather than within species drove the morphology‐climate relationship. Strong climate‐trait correlations suggest that it may be possible to predict changes in functional traits of assemblages in response to anthropogenic disturbances such as climate change.     

Genetic diversity is related to climatic variation and vulnerability in threatened bull trout

Understanding how climatic variation influences ecological and evolutionary processes is crucial for informed conservation decision‐making. Nevertheless, few studies have measured how climatic variation influences genetic diversity within populations or how genetic diversity is distributed across space relative to future climatic stress. Here, we tested whether patterns of genetic diversity (allelic richness) were related to climatic variation and habitat features in 130 bull trout (Salvelinus confluentus) populations from 24 watersheds (i.e., ~4–7th order river subbasins) across the Columbia River Basin, USA. We then determined whether bull trout genetic diversity was related to climate vulnerability at the watershed scale, which we quantified on the basis of exposure to future climatic conditions (projected scenarios for the 2040s) and existing habitat complexity. We found a strong gradient in genetic diversity in bull trout populations across the Columbia River Basin, where populations located in the most upstream headwater areas had the greatest genetic diversity. After accounting for spatial patterns with linear mixed models, allelic richness in bull trout populations was positively related to habitat patch size and complexity, and negatively related to maximum summer temperature and the frequency of winter flooding. These relationships strongly suggest that climatic variation influences evolutionary processes in this threatened species and that genetic diversity will likely decrease due to future climate change. Vulnerability at a watershed scale was negatively correlated with average genetic diversity (r = ?0.77; P < 0.001); watersheds containing populations with lower average genetic diversity generally had the lowest habitat complexity, warmest stream temperatures, and greatest frequency of winter flooding. Together, these findings have important conservation implications for bull trout and other imperiled species. Genetic diversity is already depressed where climatic vulnerability is highest; it will likely erode further in the very places where diversity may be most needed for future persistence.     

Leaf miner and plant galler species richness on Acacia: relative importance of plant traits and climate

Diversity patterns of herbivores have been related to climate, host plant traits, host plant distribution and evolutionary relationships individually. However, few studies have assessed the relative contributions of a range of variables to explain these diversity patterns across large geographical and host plant species gradients. Here we assess the relative influence that climate and host plant traits have on endophagous species (leaf miners and plant gallers) diversity across a suite of host species from a genus that is widely distributed and morphologically variable. Forty-six species of Acacia were sampled to encapsulate the diversity of species across four taxonomic sections and a range of habitats along a 950 km climatic gradient: from subtropical forest habitats to semi-arid habitats. Plant traits, climatic variables, leaf miner and plant galler diversity were all quantified on each plant species. In total, 97 leaf mining species and 84 plant galling species were recorded from all host plants. Factors that best explained leaf miner richness across the climatic gradient (using AIC model selection) included specific leaf area (SLA), foliage thickness and mean annual rainfall. The factor that best explained plant galler richness across the climatic gradient was C:N ratio. In terms of the influence of plant and climatic traits on species composition, leaf miner assemblages were best explained by SLA, foliage thickness, mean minimum temperature and mean annual rainfall, whilst plant gall assemblages were explained by C:N ratio, %P, foliage thickness, mean minimum temperature and mean annual rainfall. This work is the first to assess diversity and structure across a broad environmental gradient and a wide range of potential key climatic and plant trait determinants simultaneously. Such methods provide key insights into endophage diversity and provide a solid basis for assessing their responses to a changing climate.     

New costapalmate palm leaves from the Oligocene Ningming Formation of Guangxi,China, and their biogeographic and palaeoclimatic implications

New palm leaves from the Oligocene Ningming Formation are placed into the morphogenus Sabalites because of their costapalmate leaf shape. Four taxa are described on the basis of leaf compressions with cuticular structure. S. guanxiensis sp. nov. is characterised by hypostomatic leaf blades with a stout costa and a symmetrical base. Sabalites cf. asymmetricus has amphistomatic leaf blades with a long, delicate costa and an asymmetrical base. Sabalites sp. 1 has amphistomatic leaf blades with a long, massive costa and wide segments. Sabalites sp. 2 is characterized by hypostomatic leaf blades with a prominent costa and an asymmetrical base. The four new palm taxa expand our understanding of the floristic elements and features of the Oligocene Ningming flora. Together with the other three palm taxa that were previously reported from the Ningming Formation, our material indicates that the Oligocene Ningming flora had a rich diversity of costapalmate palms. The relatively high species diversity of palms and other plants corroborate that the Oligocene Ningming flora represents a warm and humid climate.     

Strategies of leaf expansion in Ficus carica under semiarid conditions

Leaf area expansion, thickness and inclination, gas exchange parameters and relative chlorophyll content were analysed in field‐grown fig (Ficus carica L.) leaves over time, from emergence until after full leaf expansion (FLE). Ficus carica leaves showed a subtle change in shape during the early stages of development, and FLE was reached within ca. 30 days after emergence. Changes in leaf thickness and inclination after FLE demonstrated good adaptation to environmental conditions during summer in areas with a Mediterranean climate. Changes in gas exchange parameters and relative chlorophyll content showed that F. carica is a delayed‐greening species, reaching maximum values 20 days after FLE. Correlation analysis of datasets collected during leaf expansion, confirmed dependence among structural and functional traits in F. carica. Pn was directly correlated with stomatal conductance (Gs), transpiration (E), leaf area (LA) and relative chlorophyll content up to FLE. The effect of pruning on leaf expansion, a cultural technique commonly applied in this fruit tree, was also evaluated. Although leaf development in pruned branches gave a significantly higher relative leaf area growth rate (RGR_l) and higher LA than non‐pruned branches, no significant differences were found in other morphological and physiological traits, indicating no pruning effect on leaf development. All studied morphological and physiological characteristics indicate that F. carica is well adapted to semiarid conditions. The delayed greening strategy of this species is discussed.     

Leaf and stem economics spectra drive diversity of functional plant traits in a dynamic global vegetation model

Functional diversity is critical for ecosystem dynamics, stability and productivity. However, dynamic global vegetation models (DGVMs) which are increasingly used to simulate ecosystem functions under global change, condense functional diversity to plant functional types (PFTs) with constant parameters. Here, we develop an individual‐ and trait‐based version of the DGVM LPJmL (Lund‐Potsdam‐Jena managed Land) called LPJmL‐ flexible individual traits (LPJmL‐FIT) with flexible individual traits) which we apply to generate plant trait maps for the Amazon basin. LPJmL‐FIT incorporates empirical ranges of five traits of tropical trees extracted from the TRY global plant trait database, namely specific leaf area (SLA), leaf longevity (LL), leaf nitrogen content (N_area), the maximum carboxylation rate of Rubisco per leaf area (), and wood density (WD). To scale the individual growth performance of trees, the leaf traits are linked by trade‐offs based on the leaf economics spectrum, whereas wood density is linked to tree mortality. No preselection of growth strategies is taking place, because individuals with unique trait combinations are uniformly distributed at tree establishment. We validate the modeled trait distributions by empirical trait data and the modeled biomass by a remote sensing product along a climatic gradient. Including trait variability and trade‐offs successfully predicts natural trait distributions and achieves a more realistic representation of functional diversity at the local to regional scale. As sites of high climatic variability, the fringes of the Amazon promote trait divergence and the coexistence of multiple tree growth strategies, while lower plant trait diversity is found in the species‐rich center of the region with relatively low climatic variability. LPJmL‐FIT enables to test hypotheses on the effects of functional biodiversity on ecosystem functioning and to apply the DGVM to current challenges in ecosystem management from local to global scales, that is, deforestation and climate change effects.     

Divergence of functional traits at early stages of development in Stipa tenacissima populations distributed along an environmental gradient of the Mediterranean

Assessing differences in plant functional traits (PFTs) along climatic gradients is potentially useful for understanding variation within and across populations, and for predicting their responses to climate change. This study investigates the intraspecific variability of several PFTs in Stipa tenacissima (Alpha grass) seedlings from different populations distributed across a climatic gradient. Seven populations from Tunisia to Spain within a 100–600 mm/year rainfall range were selected. Seedlings from each population were grown in a common garden. We expected the functional characteristics to differ among seedling populations according to their climatic gradient. The response patterns were helpful to predict acclimation and fitness under future climatic conditions in these populations. The seedling development analysis showed differences in PFTs among S. tenacissima populations. The biomass traits analysis revealed that higher above-ground biomass was related to higher below-ground development. The leaf traits proved that seedlings with longer leaf length would have less sclerophyllous leaves, a trade-off between productivity and drought resistance. The root traits analysis reflects seedling strategies to maximize resource uptake efficiency. PFTs showed several significant relationships with climatic conditions. The less rainfall, the higher plant allocation to root systems exploring soil. Higher mean temperatures were related to reduced root/plant development. The PFT analysis proves that species followed the ‘optimal partitioning theory’, in that plants preferentially allocate biomass to acquire the resource that most limits their development. However, both the environmental conditions and genetic diversity in S. tenacissima populations influenced seedling growth and behaviour to face ongoing climate change.

     

Plasticity of functional traits varies clinally along a rainfall gradient in Eucalyptus tricarpa

Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in south‐eastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ¹³C and δ¹⁸O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.     

Leaf morphological responses to variation in water availability for plants in the <Emphasis Type="Italic">Piriqueta caroliniana</Emphasis> complex

Distribution of plants and the expression of traits associated with environmental variation can be affected by both average conditions and the variance in conditions including extreme climatic events. We expect that these same factors should affect the distribution of plants in hybrid zones between ecologically distinct species where the hybrids should occupy ecotones or intermediate habitats. We evaluated water availability and leaf morphological differences among parental and hybrid populations of herbaceous perennial plants in the Piriqueta caroliniana complex along environmental gradients in Southeastern North America. We focus on two taxa in this group; the viridis morphotype, which occurs in southern Florida, and the caroliniana morphotype, which is distributed from northern Florida to southern Georgia. Advanced-generation hybrid derivatives of these morphotypes occupy a broad geographic region that extends across much of central Florida. Overall, we found that hybrid populations occurred in significantly drier locations, indicating that their habitat requirements are transgressive (i.e., exceeding parental values) rather than intermediate to the parental morphotypes. Water availability differed between the two sampling years, and plants displayed morphological changes in response to these changes in moisture. During the drier year, leaves were narrower and more hirsute, corroborating experimental results that these leaf traits are plastic, and confirming that plasticity occurs in natural habitats. Hybrids exhibited intermediate leaf traits (shape and size) across both years, and displayed transgressive (hair density) leaf traits during the drier year. The apparent canalization of the hybrids’ leaf morphological traits may contribute to their tolerance of variable environmental conditions and may partially explain why they have displaced the caroliniana morphotype in central Florida.     

Climate‐driven vital rates do not always mean climate‐driven population

Current climatic changes have increased the need to forecast population responses to climate variability. A common approach to address this question is through models that project current population state using the functional relationship between demographic rates and climatic variables. We argue that this approach can lead to erroneous conclusions when interpopulation dispersal is not considered. We found that immigration can release the population from climate‐driven trajectories even when local vital rates are climate dependent. We illustrated this using individual‐based data on a trans‐equatorial migratory seabird, the Scopoli's shearwater Calonectris diomedea, in which the variation of vital rates has been associated with large‐scale climatic indices. We compared the population annual growth rate λ_i, estimated using local climate‐driven parameters with ρ_i, a population growth rate directly estimated from individual information and that accounts for immigration. While λ_i varied as a function of climatic variables, reflecting the climate‐dependent parameters, ρ_i did not, indicating that dispersal decouples the relationship between population growth and climate variables from that between climatic variables and vital rates. Our results suggest caution when assessing demographic effects of climatic variability especially in open populations for very mobile organisms such as fish, marine mammals, bats, or birds. When a population model cannot be validated or it is not detailed enough, ignoring immigration might lead to misleading climate‐driven projections.     

Climatic niche and neutral genetic diversity of the six Iberian pine species: a retrospective and prospective view

Quaternary climatic fluctuations have left contrasting historical footprints on the neutral genetic diversity patterns of existing populations of different tree species. We should expect the demography, and consequently the neutral genetic structure, of taxa less tolerant to particular climatic extremes to be more sensitive to long‐term climate fluctuations. We explore this hypothesis here by sampling all six pine species found in the Iberian Peninsula (2464 individuals, 105 populations), using a common set of chloroplast microsatellite markers, and by looking at the association between neutral genetic diversity and species‐specific climatic requirements. We found large variation in neutral genetic diversity and structure among Iberian pines, with cold‐enduring mountain species (Pinus uncinata, P. sylvestris and P. nigra) showing substantially greater diversity than thermophilous taxa (P. pinea and P. halepensis). Within species, we observed a significant positive correlation between population genetic diversity and summer precipitation for some of the mountain pines. The observed pattern is consistent with the hypotheses that: (i) more thermophilous species have been subjected to stronger demographic fluctuations in the past, as a consequence of their maladaptation to recurrent glacial cold stages; and (ii) altitudinal migrations have allowed the maintenance of large effective population sizes and genetic variation in cold‐tolerant species, especially in more humid regions. In the light of these results and hypotheses, we discuss some potential genetic consequences of impending climate change.     

Microevolutionary relationships between phylogeographical history,climate change and morphological variability in the common vole (Microtus arvalis) across France

Aim In this study, we analyse microevolutionary processes in common voles (Microtus arvalis) through the investigation of tooth morphological structure, in order to assess the relative impact of climate and phylogeographical history. Microevolutionary studies have shown that climate change may play a role in both population phylogeography and phenotypic differentiation. However, relatively little is known about the precise relationship between phylogeography and phenotypic variability and about how organisms respond to climate change. Location France, from sea level to the Alps (5 to > 2300 m a.s.l.). Methods This morphological analysis is based on first lower molar measurements from 16 geographically distinct common vole populations. Size and shape components are assessed separately. Population structure patterns are characterized using canonical variate analysis. We use phylogenetic analyses of two regions of mitochondrial DNA (the control region and the cytochrome b gene) to infer genetic structure. We calculate climate parameters from temperature and precipitation data. We investigate the influence of climate, geography and phylogeographical history on the phenotype using (1) multiple regression tests, (2) pairwise comparison of observation‐by‐variable matrices, and (3) a correlation method designed to compare three matrices. Results All populations were clearly structured, whatever the dataset. Neither size nor shape variation was correlated with climate parameters, but tooth shape was strongly correlated with both genetic structure and geographical distance. Main conclusions In French Microtus arvalis populations, molar shape differentiation is clearly associated with both phylogeographical history and geographical distance. Population phylogeographical history has a greater relevance than climate in accounting for variation in tooth morphology.     

Lizard scales in an adaptive radiation: variation in scale number follows climatic and structural habitat diversity in Anolis lizards

Lizard scales vary in size, shape and texture among and within species. The overall function of scales in squamates is attributed to protection against abrasion, solar radiation and water loss. We quantified scale number of Anolis lizards across a large sample of species (142 species) and examined whether this variation was related either to structural or to climatic habitat diversity. We found that species in dry environments have fewer, larger scales than species in humid environments. This is consistent with the hypothesis that scales reduce evaporative water loss through the skin. In addition, scale number varied among groups of ecomorphs and was correlated with aspects of the structural microhabitat (i.e. perch height and perch diameter). This was unexpected because ecomorph groups are based on morphological features related to locomotion in different structural microhabitats. Body scales are not likely to play an important role in locomotion in Anolis lizards. The observed variation may relate to other features of the ecomorph niche and more work is needed to understand the putative adaptive basis of these patterns. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 570–579.