Associations between leaf developmental stability,variability, canalization,and phenotypic plasticity in Abutilon theophrasti

Developmental stability, canalization, and phenotypic plasticity are the most common sources of phenotypic variation, yet comparative studies investigating the relationships between these sources, specifically in plants, are lacking. To investigate the relationships among developmental stability or instability, developmental variability, canalization, and plasticity in plants, we conducted a field experiment with Abutilon theophrasti, by subjecting plants to three densities under infertile vs. fertile soil conditions. We measured the leaf width (leaf size) and calculated fluctuating asymmetry (FA), coefficient of variation within and among individuals (CV_intra and CV_inter), and plasticity (PI_rel) in leaf size at days 30, 50, and 70 of plant growth, to analyze the correlations among these variables in response to density and soil conditions, at each of or across all growth stages. Results showed increased density led to lower leaf FA, CV_intra, and PI_rel and higher CV_inter in fertile soil. A positive correlation between FA and PI_rel occurred in infertile soil, while correlations between CV_inter and PI_rel and between CV_inter and CV_intra were negative at high density and/or in fertile soil, with nonsignificant correlations among them in other cases. Results suggested the complexity of responses of developmental instability, variability, and canalization in leaf size, as well as their relationships, which depend on the strength of stresses. Intense aboveground competition that accelerates the decrease in leaf size (leading to lower plasticity) will be more likely to reduce developmental instability, variability, and canalization in leaf size. Increased developmental instability and intra‐ and interindividual variability should be advantageous and facilitate adaptive plasticity in less stressful conditions; thus, they are more likely to positively correlate with plasticity, whereas developmental stability and canalization with lower developmental variability should be beneficial for stabilizing plant performance in more stressful conditions, where they tend to have more negative correlations with plasticity.     

Phenotypic integration may constrain phenotypic plasticity in plants

Phenotypic plasticity is essential for plant adaptation to changing environments but some factors limit its expression, causing plants to fail in producing the best phenotype for a given environment. Phenotypic integration refers to the pattern and magnitude of character correlations and it might play a role as an internal constraint to phenotypic plasticity. We tested the hypothesis that phenotypic integration – estimated as the number of significant phenotypic correlations between traits – constrains phenotypic plasticity of plants. The rationale is that, for any phenotypic trait, the more linked with other traits it is, the more limited is its range of variation. In the perennial species Convolvulus chilensis (Convolvulaceae) and Lippia alba (Verbenaceae) we determined the relationship between phenotypic plasticity to relevant environmental factors – shading for C. chilensis and drought for L. alba– and the magnitude of phenotypic integration of morphological and biomass allocation traits. In C. chilensis plants, plasticity to shading of a given trait decreased with the number of significant correlations that it had with the other traits. Likewise, the characters that showed greater plasticity to experimental drought in L. alba plants had fewer significant phenotypic correlations with other characters. We report a novel limit to phenotypic plasticity of plants by showing that the phenotypic trait architecture may constrain their plastic, functional responses to the environment.     

Phenotypic integration plasticity in Daphnia magna: an integral facet of G × E interactions

Phenotypic integration can be defined as the network of multivariate relationships among behavioural, physiological and morphological traits that describe the organism. Phenotypic integration plasticity refers to the change in patterns of phenotypic integration across environments or ontogeny. Because studies of phenotypic plasticity have predominantly focussed on single traits, a G × E interaction is typically perceived as differences in the magnitude of trait expression across two or more environments. However, many plastic responses involve coordinated responses in multiple traits, raising the possibility that relative differences in trait expression in different environments are an important, but often overlooked, source of G × E interaction. Here, we use phenotypic change vectors to statistically compare the multivariate life‐history plasticity of six Daphnia magna clones collected from four disparate European populations. Differences in the magnitude of plastic responses were statistically distinguishable for two of the six clones studied. However, differences in phenotypic integration plasticity were statistically distinguishable for all six of the clones studied, suggesting that phenotypic integration plasticity is an important component of G × E interactions that may be missed unless appropriate multivariate analyses are used.     

Environmental Heterogeneity and Population Differentiation in Plasticity to Drought in <Emphasis Type="Italic">Convolvulus Chilensis</Emphasis> (Convolvulaceae)

Plant populations may show differentiation in phenotypic plasticity, and theory predicts that greater levels of environmental heterogeneity should select for higher magnitudes of phenotypic plasticity. We evaluated phenotypic responses to reduced soil moisture in plants of Convolvulus chilensis grown in a greenhouse from seeds collected in three natural populations that differ in environmental heterogeneity (precipitation regime). Among several morphological and ecophysiological traits evaluated, only four traits showed differentiation among populations in plasticity to soil moisture: leaf area, leaf shape, leaf area ratio (LAR), and foliar trichome density. In all of these traits plasticity to drought was greatest in plants from the population with the highest interannual variation in precipitation. We further tested the adaptive nature of these plastic responses by evaluating the relationship between phenotypic traits and total biomass, as a proxy for plant fitness, in the low water environment. Foliar trichome density appears to be the only trait that shows adaptive patterns of plasticity to drought. Plants from populations showing plasticity had higher trichome density when growing in soils with reduced moisture, and foliar trichome density was positively associated with total biomass. Co-ordinating editor: F. Stuefer     

Life history responses to irradiance at the early seedling stage of Picea omorika (Pančić) Purkyňe: adaptiveness and evolutionary limits

A multivariate selection analysis has been implemented for testing the adaptiveness of life history plasticity to irradiance during the seedling establishment in Picea omorika plants raised in a growth-room. Siblings of a synthetic population comprising 21 families from six natural populations were exposed to contrasting light levels to explore variation in phenotypic expression of three seedling traits: days from germination to cotyledon opening (DGTOC), days from cotyledon opening to epicotyl appearance (DCTOE), and epicotyl length at 6 weeks (EPL6). Ambient light conditions significantly affected DCTOE and EPL6, but not DGTOC. Phenotypic selection analysis revealed that DGTOC was under negative directional selection in both radiation environments, suggesting that canalization of DGTOC was promoted across different light conditions, as well as that the observed pattern of canalization might be regarded as adaptive. DCTOE was also found to be under negative directional selection in both light treatments, but the plastic responses of this trait were opposite to the values favoured by selection within environments. Since there was evidence for selection against plasticity in DCTOE, the pattern of plastic responses in DCTOE to variation in light conditions could be diagnosed as maladaptive. Multiple regression analysis revealed a cost of canalization in DGTOC regardless of light environment, as well as a cost of plasticity in DCTOE under high light intensity. All genetic correlations across light environments were significantly different from unity, indicating the existence of heritable variation for plasticity in these traits. However, since DGTOC and DCTOE were involved in a genetic trade-off with respect to both trait mean and plasticity, these early life histories would never reach their optimal values across radiation environments.     

Phenotypic plasticity and integration in response to flooded conditions in natural accessions of Arabidopsis thaliana (L.) Heynh (Brassicaceae)

Flood response is a crucial component of the life strategy of many plants, but it is seldom studied in non-flooded tolerant species, even though they may be subjected to stressful environmental conditions. Phenotypic plasticity in reaction to environmental stress affects the whole plant phenotype and can alter the character correlations that constitute the phenotypic architecture of the individual, yet few studies have investigated the lability of phenotypic integration to water regime. Moreover, little has been done to date to quantify the sort of selective pressures that different components of a plant's phenotype may be experiencing under contrasting water regimes. Genetic differentiation and phenotypic plasticity at the single-trait and multivariate levels were investigated in 47 accessions of the weedy plant Arabidopsis thaliana, and the relationship of plastic characters to reproductive fitness was quantified. Results indicate that these plants tend to be highly genetically differentiated for all traits, in agreement with predictions made on the basis of environmental variation and mating system. Varied patterns of apparent selection under flooded and non-flooded conditions were also uncovered, suggesting trade-offs in allocation between roots and above-ground biomass, as well as between leaves and reproductive structures. While the major components of the plants' multivariate phenotypic architecture were not significantly affected by environmental changes, many of the details were different under flooded and non-flooded conditions.     

Phenotypic plasticity closely linked to climate at origin and resulting in increased mortality under warming and frost stress in a common grass

Phenotypic plasticity is important for species responses to global change and species coexistence. Phenotypic plasticity differs among species and traits and changes across environments. Here, we investigated phenotypic plasticity of the widespread grass Arrhenatherum elatius in response to winter warming and frost stress by comparing phenotypic plasticity of 11 geographically and environmentally distinct populations of this species to phenotypic plasticity of populations of different species originating from a single environment. The variation in phenotypic plasticity was similar for populations of a single species from different locations compared to populations of functionally and taxonomically diverse species from one environment for the studied traits (leaf biomass production and root integrity after frost) across three indices of phenotypic plasticity (RDPI, PIN, slope of reaction norm). Phenotypic plasticity was not associated with neutral genetic diversity but closely linked to the climate of the populations’ origin. Populations originating from warmer and more variable climates showed higher phenotypic plasticity. This indicates that phenotypic plasticity can itself be considered as a trait subject to local adaptation to climate. Finally, our data emphasize that high phenotypic plasticity is not per se positive for adaptation to climate change, as differences in stress responses are resulting in high phenotypic plasticity as expressed by common plasticity indices, which is likely to be related to increased mortality under stress in more plastic populations.     

Geographic variation and plasticity to water and nutrients in Pelargonium australe

Here, patterns of phenotypic plasticity and trait integration of leaf characteristics in six geographically discrete populations of the perennial herb Pelargonium australe were compared. It was hypothesized that populations would show local adaptation in trait means, but similar patterns of plasticity and trait integration. Further, it was questioned whether phenotypic plasticity was positively correlated with environmental heterogeneity and whether plasticity for water-use traits in particular was adaptive. Seedlings were grown in a glasshouse at six combinations of water and nutrient availability. Leaf anatomical, morphological and gas exchange traits were measured. High amounts of plasticity in leaf traits were found in response to changes in growth conditions and there was evidence of local adaptation among the populations. While there were significant correlations between plasticity and environmental heterogeneity, not all were positive. Notably, patterns of plasticity and trait integration varied significantly among populations. Despite that variation, some of the observed plasticity was adaptive: fitness was correlated with conservative water use when water was limiting. Pelargonium arrived in Australia approximately 5 million yr ago. It is concluded here that high amounts of plasticity, in some cases adaptive, and weak integration among traits may be key to the spread and success of this species.     

Phenotypic plasticity of Capsella bursa-pastoris (Brassicaceae) and its effect on fitness in response to temperature and soil moisture

Capsella bursa-pastoris is one of the most common plants on earth. Although phenotypic plasticity of ecologically important traits possibly contributes to its wide geographic range, little is known about the plasticity of C. bursa-pastoris and its effects on its fitness. In a laboratory, we assessed the phenotypic plasticity in response to two representative climatic conditions: temperature and soil moisture. In addition, we quantitatively evaluated the relationship between phenotypic plasticity and fruit production. Most measured morphological and physiological traits exhibited plastic responses to temperature and fitness based on fruit production was maintained across temperatures. In contrast, no plasticity to soil moisture was detected, and plants produced fewer fruits in dry soil. Selection analysis revealed that the plasticity of the flowering time and the water-use efficiency had positive effects on fruit production over the tested temperature regime. These experimental results suggest that phenotypic plasticity probably enables C. bursa-pastoris to cope with heterogeneous temperature environments and thereby probably contributes to its wide geographic range.     

Plasticity of physiology in Lobelia: testing for adaptation and constraint

Phenotypic plasticity is thought to be a major mechanism allowing sessile organisms such as plants to adapt to environmental heterogeneity. However, the adaptive value of many common plastic responses has not been tested by linking these responses to fitness. Even when plasticity is adaptive, costs of plasticity, such as the energy necessary to maintain regulatory pathways for plastic responses, may constrain its evolution. We used a greenhouse experiment to test whether plastic physiological responses to soil water availability (wet vs. dry conditions) were adaptive and/or costly in the congeneric wildflowers Lobelia cardinalis and L. siphilitica. Eight physiological traits related to carbon and water uptake were measured. Specific leaf area (SLA), photosynthetic rate (A), stomatal conductance (gs), and photosynthetic capacity (Amax) responded plastically to soil water availability in L. cardinalis. Plasticity in Amax was maladaptive, plasticity in A and g(s) was adaptive, and plasticity in SLA was adaptively neutral. The nature of adaptive plasticity in L. cardinalis, however, differed from previous studies. Lobelia cardinalis plants with more conservative water use, characterized by lower g(s), did not have higher fitness under drought conditions. Instead, well-watered L. cardinalis that had higher g(s) had higher fitness. Only Amax responded plastically to drought in L. siphilitica, and this response was adaptively neutral. We detected no costs of plasticity for any physiological trait in either L. cardinalis or L. siphilitica, suggesting that the evolution of plasticity in these traits would not be constrained by costs. Physiological responses to drought in plants are presumed to be adaptive, but our data suggest that much of this plasticity can be adaptively neutral or maladaptive.     

Phenotypic plasticity: Eco-Devo and evolution

Phenotypic plasticity refers to the ability of an organism to alter its physiology/morphology/behavior in response to changes in environmental conditions. Although encompassing various phenomena spanning multi-ple levels of organization, most plastic responses seem to take place by altering gene expression and eventually altering ontogenetic trajectory in response to environmental variation. Epigenetic modifications provide a plausi-ble link between the environment and alterations in gene expression, and the alterations in phenotype based on environmentally induced epigenetic modifications can be inherited transgenerationally. Even closely related species and populations with different genotypes may exhibit differences in the patterns and the extents of plastic responses, indicating the wide existence of plasticity genes which are independent of trait means and directly respond to environmental stimuli by triggering phenotypic changes. The ability of plasticity is not only able to affect the adaptive evolution of species significantly, but is also an outcome of evolutionary processes. Therefore, phenotypic plasticity is a potentially important molder of adaptation and evolution.     

Characterization,costs, cues and future perspectives of phenotypic plasticity

BackgroundPlastic responses of plants to the environment are ubiquitous. Phenotypic plasticity occurs in many forms and at many biological scales, and its adaptive value depends on the specific environment and interactions with other plant traits and organisms. Even though plasticity is the norm rather than the exception, its complex nature has been a challenge in characterizing the expression of plasticity, its adaptive value for fitness and the environmental cues that regulate its expression.ScopeThis review discusses the characterization and costs of plasticity and approaches, considerations, and promising research directions in studying plasticity. Phenotypic plasticity is genetically controlled and heritable; however, little is known about how organisms perceive, interpret and respond to environmental cues, and the genes and pathways associated with plasticity. Not every genotype is plastic for every trait, and plasticity is not infinite, suggesting trade-offs, costs and limits to expression of plasticity. The timing, specificity and duration of plasticity are critical to their adaptive value for plant fitness.ConclusionsThere are many research opportunities to advance our understanding of plant phenotypic plasticity. New methodology and technological breakthroughs enable the study of phenotypic responses across biological scales and in multiple environments. Understanding the mechanisms of plasticity and how the expression of specific phenotypes influences fitness in many environmental ranges would benefit many areas of plant science ranging from basic research to applied breeding for crop improvement.     

Quantitative trait loci affecting delta13C and response to differential water availibility in Arabidopsis thaliana

Phenotypic plasticity is an important response mechanism of plants to environmental heterogeneity. Here, we explored the genetic basis of plastic responses of Arabidopsis thaliana to water deficit by experimentally mapping quantitative trait loci (QTL) in two recombinant inbred populations (Cvi x Ler and Ler x Col). We detected genetic variation and significant genotype-by-environment interactions for many traits related to water use. We also mapped 26 QTL, including six for carbon isotope composition (delta13C). Negative genetic correlations between fruit length and fruit production as well as between flowering time and branch production were corroborated by QTL colocalization, suggesting these correlations are due to pleiotropy or physical linkage. Water-limited plants were more apically dominant with greater root:shoot ratios and higher delta13C (higher water-use efficiency) when compared to well-watered plants. Many of the QTL effects for these traits interacted significantly with the irrigation treatment, suggesting that the observed phenotypic plasticity is genetically based. We specifically searched for epistatic (QTL-QTL) interactions using a two-dimensional genome scan, which allowed us to detect epistasis regardless of additive genetic effects. We found several significant QTL-QTL interactions including three that exhibited environmental dependence. These results provide preliminary evidence for proposed genetic mechanisms underlying phenotypic plasticity.     

Root morphological responses to population density vary with soil conditions and growth stages: The complexity of density effects

AimHow plants cope with increases in population density via root plasticity is not well documented, although abiotic environments and plant ontogeny may have important roles in determining root response to density. To investigate how plant root plasticity in response to density varies with soil conditions and growth stages, we conducted a field experiment with an annual herbaceous species (Abutilon theophrasti).MethodsPlants were grown at low, medium, and high densities (13.4, 36.0, and 121.0 plants m⁻², respectively), under fertile and infertile soil conditions, and a series of root traits were measured after 30, 50, and 70 days.ResultsRoot allocation increased, decreased, or canalized in response to density, depending on soil conditions and stages of plant growth, indicating the complex effects of population density, including both competitive and facilitative effects.Main conclusionsRoot allocation was promoted by neighbor roots at early stages and in abundant resource availability, due to low‐to‐moderate belowground interactions among smaller plants, leading to facilitation. As plants grew, competition intensified and infertile soil aggravated belowground competition, leading to decreased root allocation in response to density. Root growth may be more likely restricted horizontally rather than vertically by the presence of neighbor, suggesting a spatial orientation effect in their responses to density. We emphasized the importance of considering effects of abiotic conditions and plant growth stages in elucidating the complexity of density effects on root traits.     

A modular concept of phenotypic plasticity in plants

Based on empirical evidence from the literature we propose that, in nature, phenotypic plasticity in plants is usually expressed at a subindividual level. While reaction norms (i.e. the type and the degree of plant responses to environmental variation) are a property of genotypes, they are expressed at the level of modular subunits in most plants. We thus contend that phenotypic plasticity is not a whole-plant response, but a property of individual meristems, leaves, branches and roots, triggered by local environmental conditions. Communication and behavioural integration of interconnected modules can change the local responses in different ways: it may enhance or diminish local plastic effects, thereby increasing or decreasing the differences between integrated modules exposed to different conditions. Modular integration can also induce qualitatively different responses, which are not expressed if all modules experience the same conditions. We propose that the response of a plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to integration. The local response rules to environmental variation, and the modular interaction rules may be seen as evolving traits targeted by natural selection. Following this notion, whole-plant reaction norms are an integrative by-product of modular plasticity, which has far-reaching methodological, ecological and evolutionary implications.     

Plasticity and environment-specific covariances: an investigation of floral-vegetative and within flower correlations

Floral traits are commonly thought to be more canalized than vegetative ones. In addition, floral and vegetative traits are hypothesized to be genetically decoupled, enabling vegetative structures to respond plastically to environmental heterogeneity, and to evolve in response to selection without disrupting the reproductive function of flowers. To test these hypotheses, we evaluate the genetic architecture of floral and vegetative traits in natural populations of Arabidopsis thaliana raised under variable light-quality environments. Plants were grown either under high or low ratios of red to far-red (R:FR) light, an aspect of light quality that varies with neighbor proximity and regulates competitive shade-avoidance responses. Across environments, we detected significant genetic variation for the average expression of all measured floral traits (petal length and width, stamen length, pistil length, stigma-anther separation, and exsertion of both the stamen and pistil beyond the corolla). Light quality significantly influenced the absolute size of several floral traits as well as the allometry (i.e., relative scaling) of all floral traits, and genotypes differed in the plasticity of floral traits to the light treatments. Exposure to low relative to high R:FR resulted in significantly greater elongation in the vegetative trait, petiole length, and genotypes again differed in the plasticity of this trait to R:FR. Consistent with prior studies, most floral traits were less plastic than the vegetative trait; herkogamy (i.e., stigma-anther separation) was the exception and expressed more variable trait values across environments than petiole length, apparently as a consequence of the independent responses of stamens and pistils. Flowers also showed strong phenotypic integration; genotypic correlations were significantly positive among floral traits within each light treatment. Although floral-vegetative correlations were not significant in the high R:FR light treatment, significant correlations were detected between petal traits, pistil length, and petiole length under low R:FR, in contrast to the widely held hypothesis that floral and vegetative traits are genetically independent. Finally, we detected selection for reduced herkogamy in the low R:FR light treatment. The observed correlation between functional trait groups suggest that vegetative plasticity may affect the expression of floral traits in some environments, and that environment-specific constraints may exist on the evolution of floral and vegetative traits.     

Adaptive phenotypic plasticity and genetics of larval life histories in two Rana temporaria populations

Phenotypic plasticity provides means for adapting to environmental unpredictability. In terms of accelerated development in the face of pond-drying risk, phenotypic plasticity has been demonstrated in many amphibian species, but two issues of evolutionary interest remain unexplored. First, the heritable basis of plastic responses is poorly established. Second, it is not known whether interpopulational differences in capacity to respond to pond-drying risk exist, although such differences, when matched with differences in desiccation risk would provide strong evidence for local adaptation. We investigated sources of within- and among-population variation in plastic responses to simulated pond-drying risk (three desiccation treatments) in two Rana temporaria populations originating from contrasting environments: (1) high desiccation risk with weak seasonal time constraint (southern population); and (2) low desiccation risk with severe seasonal time constraint (northern population). The larvae originating from the environment with high desiccation risk responded adaptively to the fast decreasing water treatment by accelerating their development and metamorphosing earlier, but this was not the case in the larvae originating from the environment with low desiccation risk. In both populations, metamorphic size was smaller in the high-desiccation-risk treatment, but the effect was larger in the southern population. Significant additive genetic variation in development rate was found in the northern and was nearly significant in the southern population, but there was no evidence for genetic variation in plasticity for development rates in either of the populations. No genetic variation for plasticity was found either in size at metamorphosis or growth rate. All metamorphic traits were heritable, and additive genetic variances were generally somewhat higher in the southern population, although significantly so in only one trait. Dominance variances were also significant in three of four traits, but the populations did not differ. Maternal effects in metamorphic traits were generally weak in both populations. Within-environment phenotypic correlations between larval period and metamorphic size were positive and genetic correlations negative in both populations. These results suggest that adaptive phenotypic plasticity is not a species-specific fixed trait, but evolution of interpopulational differences in plastic responses are possible, although heritability of plasticity appears to be low. The lack of adaptive response to desiccation risk in northern larvae is consistent with the interpretation that selection imposed by shorter growing season has favored rapid development in north (approximately 8% faster development in north as compared to south) or a minimum metamorphic size at the expense of phenotypic plasticity.     

Effects of population,family, and diet on craniofacial morphology of Icelandic Arctic charr (Salvelinus alpinus)

We evaluated hypotheses of intralacustrine diversification and plastic responses to two diet environments in Icelandic Arctic charr (Salvelinus alpinus). Full‐sib families of progeny of wild polymorphic charr from two lakes where morphs vary in their degree of phenotypic and ecological divergence were split, with half of the offspring reared on a benthic and half on a limnetic type of diet to estimate family norms of reaction. We focused on variation in craniofacial traits because they are probably functionally related to diet and complement a previous study of body shape in these charr. A hierarchical analysis of phenotypic variation between lakes, pairs of morphs within each lake, and two families within each morph found that phenotypic variation partitioned between families relative to morphs was reduced in the more ecologically diversified population, which is consistent with adaptive diversification. The effect size of plastic responses between lake populations was similar, suggesting little difference in the degree of canalization in contrast to a previous analysis of body form plasticity. Thus, the role that plastic morphological responses play in the adaptive diversification of morphs and different lake populations of Arctic charr may depend on the trait. © 2013 The Linnean Society of London     

Patterns of genotypic variation and phenotypic plasticity of light response in two tropical Piper (Piperaceae) species

Patterns of phenotypic plasticity and genotypic variation in light response of growth and photosynthesis were examined in two species of rain forest shrub that differ in ecological distribution within the forest. We further examined correlations among photosynthetic and growth traits. We hypothesized that the pioneer species, Piper sancti-felicis, would display greater phenotypic plasticity than the shade-tolerant species, Piper arieianum. We further proposed that, in both species, genotypic effects would be more apparent in growth-related traits than photosynthetic traits due to more concentrated selection pressure on gas-exchange traits. P. sancti-felicis did not demonstrate greater phenotypic plasticity of light response. Although many of the traits measured had significant genotype effects, neither species showed any significant effects of genotype on light response of photosynthesis, suggesting little genetic variation for this trait within populations. A principal components analysis clearly illustrated both species and light effects, with the treatments dividing neatly along the axis of the first principal component and the species separating along the second principal component axis. Results indicated general similarities between the species in their trait correlation structure and level of integration among traits, but characteristic differences were observed in the patterns of change between low and high light. Both species had more correlations than expected within groups of growth-related or photosynthetic traits; strong correlations of traits between these two groups were underrepresented. The similar pattern of genetic variation and phenotypic integration observed in these two congeners may be due more to their close phylogenetic relation than to their ecological distributions.