Stability of the replicator equation for a single species with a multi-dimensional continuous trait space

The replicator equation model for the evolution of individual behaviors in a single species with a multi-dimensional continuous trait space is developed as a dynamics on the set of probability measures. Stability of monomorphisms in this model using the weak topology is compared to more traditional methods of adaptive dynamics. For quadratic fitness functions and initial normal trait distributions, it is shown that the multi-dimensional continuously stable strategy (CSS) of adaptive dynamics is often relevant for predicting stability of the measure-theoretic model but may be too strong in general. For general fitness functions and trait distributions, the CSS is related to dominance solvability which can be used to characterize local stability for a large class of trait distributions that have no gaps in their supports whereas the stronger neighborhood invader strategy (NIS) concept is needed if the supports are arbitrary.     

Evolutionary Branching in a Finite Population: Deterministic Branching vs. Stochastic Branching

Adaptive dynamics formalism demonstrates that, in a constant environment, a continuous trait may first converge to a singular point followed by spontaneous transition from a unimodal trait distribution into a bimodal one, which is called “evolutionary branching.” Most previous analyses of evolutionary branching have been conducted in an infinitely large population. Here, we study the effect of stochasticity caused by the finiteness of the population size on evolutionary branching. By analyzing the dynamics of trait variance, we obtain the condition for evolutionary branching as the one under which trait variance explodes. Genetic drift reduces the trait variance and causes stochastic fluctuation. In a very small population, evolutionary branching does not occur. In larger populations, evolutionary branching may occur, but it occurs in two different manners: in deterministic branching, branching occurs quickly when the population reaches the singular point, while in stochastic branching, the population stays at singularity for a period before branching out. The conditions for these cases and the mean branching-out times are calculated in terms of population size, mutational effects, and selection intensity and are confirmed by direct computer simulations of the individual-based model.     

ADAPTIVE DIVERGENCE IN DARWIN'S RACE: HOW COEVOLUTION CAN GENERATE TRAIT DIVERSITY IN A POLLINATION SYSTEM

Understanding how reciprocal selection shapes interacting species in Darwin's coevolutionary race is a captivating pursuit in evolutionary ecology. Coevolving traits can potentially display following three patterns: (1) geographical variation in matched traits, (2) bias in trait matching, and (3) bimodal distribution of a trait in certain populations. Based on the framework of adaptive dynamics, we present an evolutionary model for a coevolving pollination system involving the long‐proboscid fly (Moegistorhynchus longirostris) and the long‐tubed iris (Lapeirousia anceps). The model successfully demonstrates that Darwin's hypothesis can lead to all three patterns if costs are involved. Geographical variation in matched traits could be driven by geographical variation in environmental factors that affect the cost rate of trait escalation. Unequal benefits derived from the interaction by the fly and the flower could potentially cause the bias in trait matching of the system. Different cost rates to trait elongation incurred by the two species and weak assortative interactions in the coevolutionary race can drive divergent selection (i.e., an evolutionary branching) that leads to the bimodal distribution of traits. Overall, the model highlights the importance of assortative interactions and the balance of costs incurred by coevolving species as factors determining the eventual phenotypic outcome of coevolutionary interactions.     

Preservation of winter social dominance status in Brent Geese Branta bernicla bernicla within and across winters

Dominant and subordinate individuals in a group may benefit from the stability of the social dominance organisation, avoiding excessive waste of time and energy in aggressive interactions and reducing injury risks. Nevertheless, the likely evolutionary incentive for individuals to become, and furthermore to stay, dominant may destabilise such dominance hierarchies. In this context, the relative importance of fixed (e.g. sex, morphological size) and fluctuating (e.g. body condition, mating status, reproductive success, social unit size) traits influencing the establishment and preservation of dominance relationships could play a key role in group structure. We investigated the relative role of fixed and fluctuating traits on social status in Dark-bellied Brent Geese Branta bernicla bernicla which form large fairly unstable groups both within and across winters. We compared individual dominance scores of ringed Brent Geese during four consecutive winters. Brent Geese conserved their dominance score within a given winter irrespective of their age but were generally unable to conserve it across consecutive winters. As winter dominance scores correlated best with social unit size, dominance status thus appeared to be mostly a by-product of a fluctuating trait: breeding success in the previous summer. When we considered only adults that had the same social unit size during two consecutive winters, we observed a significant preservation of dominance scores. This result suggests that a fixed trait such as sex or morphological size may still play a role in setting dominance status.     

An Evolutionary Perspective for Bimodal Respiration: A Biological Synthesis of Fish Air Breathing

SYNOPSIS: The broad phyletic distribution of bimodal breathingamong the fishes, the diversity of this group's aerial-respiratoryspecializations, and the numerous ways that bimodality has permeatedthe natural history of many species provide a broad perspectiveon the evolution and biological significance of bimodal breathing.The long term evolutionary view of bimodal breathing emphasizesits importance in the evolutionary transition to terrestriality;a key role in this process was played by the fishes which werethe first air-breathing vertebrates. On the other hand, in mostextant fishes bimodality has not led to terrestriality. Rather,auxiliary air breathing enables a species to remain in or toexploit an aquatic habitat from which it would otherwise beexcluded.     

Spatial scaling of species abundance distributions

Species abundance distributions are an essential tool in describing the biodiversity of ecological communities. We now know that their shape changes as a function of the size of area sampled. Here we analyze the scaling properties of species abundance distributions by using the moments of the logarithmically transformed number of individuals. We find that the moments as a function of area size are well fitted by power laws and we use this pattern to estimate the species abundance distribution for areas larger than those sampled. To reconstruct the species abundance distribution from its moments, we use discrete Tchebichef polynomials. We exemplify the method with data on tree and shrub species from a 50 ha plot of tropical rain forest on Barro Colorado Island, Panama. We test the method within the 50 ha plot, and then we extrapolate the species abundance distribution for areas up to 5 km². Our results project that for areas above 50 ha the species abundance distributions have a bimodal shape with a local maximum occurring for the singleton classes and that this maximum increases with sampled area size.     

Predicting the past distribution of species climatic niches

Predicting past distributions of species climatic niches, hindcasting, by using climate envelope models (CEMs) is emerging as an exciting research area. CEMs are used to examine veiled evolutionary questions about extinctions, locations of past refugia and migration pathways, or to propose hypotheses concerning the past population structure of species in phylogeographical studies. CEMs are sensitive to theoretical assumptions, to model classes and to projections in non-analogous climates, among other issues. Studies hindcasting the climatic niches of species often make reference to these limitations. However, to obtain strong scientific inferences, we must not only be aware of these potential limitations but we must also overcome them. Here, I review the literature on hindcasting CEMs. I discuss the theoretical assumptions behind niche modelling, i.e. the stability of climatic niches through time and the equilibrium of species with climate. I also summarize a set of 'recommended practices' to improve hindcasting. The studies reviewed: (1) rarely test the theoretical assumptions behind niche modelling such as the stability of species climatic niches through time and the equilibrium of species with climate; (2) they only use one model class (72% of the studies) and one palaeoclimatic reconstruction (62.5%) to calibrate their models; (3) they do not check for the occurrence of non-analogous climates (97%); and (4) they do not use independent data to validate the models (72%). Ignoring the theoretical assumptions behind niche modelling and using inadequate methods for hindcasting CEMs may well entail a cascade of errors and naïve ecological and evolutionary inferences. We should also push integrative research lines linking macroecology, physiology, population biology, palaeontology, evolutionary biology and CEMs for a better understanding of niche dynamics across space and time.     

An interpretation of morphometric and gravimetric differences shown by adult Steganacarus magnus (Acari: Cryptostigmata)

The weights and lengths of about a thousand individuals of Steganacarus magnus (Nic.) have been analysed and found to have a bimodal distribution. It is suggested that this can be used as an aid to separating the sexes in this species.  

Summary:

An analysis of the weight distributions of adult Steganacarus magnus (Nic.) showed them to be bimodal. Small individuals, without eggs and pre-larvae had a mean weight of 159 μg and large individuals with eggs and pre-larvae had a mean weight of 335 μg. It is suggested that these two weight classes represent male and female individuals.     

Evaluating differences in the shape of native and alien plant trait distributions will bring new insights into invasions of plant communities

Failure to quantify differences in the shape of inter‐specific trait distributions (e.g., skew, kurtosis) when comparing co‐occurring alien and native plants hinders the integration of biological invasions and plant community ecology. Within a plant community, understanding the circumstances that lead to the shape of the inter‐specific distribution of one or more functional plant traits being unimodal, bimodal, multimodal or skewed has the potential to shed new light on community vulnerability to invasion, subsequent ecosystem impacts and the selection pressures (e.g., stabilizing, directional or disruptive) acting upon native and alien species. Ignoring differences in the shape of inter‐specific trait distributions of alien and native species could miss important insights into plant invasions, including: the existence of unsaturated native plant communities, empty niches, shifting trait optima of species as a result of environmental change and incomplete colonization–extinction processes following invasion. Future comparisons of functional trait differences between native and alien species should include assessment of the shapes of inter‐specific trait distributions since these may differ even when the mean values of traits are similar for native and alien species. The infrequent application of such approaches may explain the limited generalizations regarding the drivers and consequences of plant invasions in plant communities.     

Bimodal trait distributions with large variances question the reliability of trait-based aggregate models

Functionally diverse communities can adjust their species composition to altered environmental conditions, which may influence food web dynamics. Trait-based aggregate models cope with this complexity by ignoring details about species identities and focusing on their functional characteristics (traits). They describe the temporal changes of the aggregate properties of entire communities, including their total biomasses, mean trait values, and trait variances. The applicability of aggregate models depends on the validity of their underlying assumptions that trait distributions are normal and exhibit small variances. We investigated to what extent this can be expected to work by comparing an innovative model that accounts for the full trait distributions of predator and prey communities to a corresponding aggregate model. We used a food web structure with well-established trade-offs among traits promoting mutual adjustments between prey edibility and predator selectivity in response to selection. We altered the shape of the trade-offs to compare the outcome of the two models under different selection regimes, leading to trait distributions increasingly deviating from normality. Their biomass and trait dynamics agreed very well for stabilizing selection and reasonably well for directional selection, under which different trait values are favored at different times. However, for disruptive selection, the results of the aggregate model strongly deviated from the full trait distribution model that showed bimodal trait distributions with large variances. Hence, the outcome of aggregate models is reliable under ideal conditions but has to be questioned when confronted with more complex selection regimes and trait distributions, which are commonly observed in nature.     

Pattern of evolutionarily distinct species among four classes of animals and their conservation status: a comparison using evolutionary distinctiveness scores

The percentage of species with high evolutionary distinctiveness (ED) scores in four different classes was related to conservation concern. We considered the number of species belonging to the upper level of the distribution of ED scores, and the overall distribution of ED scores in each category of concern assigned by IUCN. Generalized linear and mixed models were used to explore the relationship between variables, separately for each animal class. Overall values of ED score were higher for Squamates, Rhynchocephalia and amphibians than mammals and birds. However, the frequency distribution of ED scores was similar among classes, with a leptokurtotic distribution. Amphibians, reptiles, birds and mammals showed a markedly right skewed distribution, with a similar proportion of species in each equal category of the distribution. In all classes, the number of species with the highest ED score (positioned in the upper 20% of the frequency distribution of the variable) was very small ranging between 0.01 and 0.05%. ED score was slightly but negatively correlated with IUCN conservation status in amphibians, but unrelated in the other three classes. The bird population trend was unrelated to ED score of bird species in both USA and Europe. Also, the population’s trend for selected mammal species was unrelated to the ED score of those species. Our results provide more evidence that distribution shape of ED of animal forms is uniform among classes, with only very few species characterized by highest ED scores in each group. Surprisingly, ED score and IUCN conservation status were unrelated in the four classes examined. Finally, our study underlines that declining animals are not necessarily the most evolutionarily distinct species.     

Development and evolution of the muscles of the pelvic fin

Locomotor strategies in terrestrial tetrapods have evolved from the utilisation of sinusoidal contractions of axial musculature, evident in ancestral fish species, to the reliance on powerful and complex limb muscles to provide propulsive force. Within tetrapods, a hindlimb-dominant locomotor strategy predominates, and its evolution is considered critical for the evident success of the tetrapod transition onto land. Here, we determine the developmental mechanisms of pelvic fin muscle formation in living fish species at critical points within the vertebrate phylogeny and reveal a stepwise modification from a primitive to a more derived mode of pelvic fin muscle formation. A distinct process generates pelvic fin muscle in bony fishes that incorporates both primitive and derived characteristics of vertebrate appendicular muscle formation. We propose that the adoption of the fully derived mode of hindlimb muscle formation from this bimodal character state is an evolutionary innovation that was critical to the success of the tetrapod transition.     

Bimodality of stable and plastic traits in plants

Key message

We discovered an unexpected mode of bimodal distribution of stable and plastic traits, which was consistent for homologous traits of 32 varieties of seven species both in well-irrigated fields and dry conditions.

Abstract

We challenged archived genetic mapping data for 36 fruit, seed, flower and yield traits in tomato and found an unexpected bimodal distribution in one measure of trait variability, the mean coefficient of variation, with some traits being consistently more variable than others. To determine the degree of conservation of this distribution among higher plants, we compared 18 homologous phenotypes, including yield and seed production, across different crop species grown in a common ‘crop garden’ experiment. The set included 32 varieties of tomato, eggplant, pepper, melon, watermelon, sunflower and maize. Estimates of canalization were obtained using a ‘canalization replication’ experimental design that generated multiple estimates of the coefficient of variation of traits, as well as their reaction norms in optimal and water-stressed field plots. A common pattern of bimodal distribution of stable and plastic traits was observed for all the varieties and for a wild weed (Solanum nigrum). We propose that canalization profiles of traits in a variety of taxa were ancestrally selected to maximize adaptation and reproductive success.

     

Temporally stable abundance–occupancy relationships and occupancy frequency patterns in stream insects

The interspecific relationship between local abundance and regional distribution, as well as the occupancy frequency distribution, are widely studied topics in macroecology. A positive abundance-occupancy relationship has been found in a majority of studies, and satellite species modes are typically dominant in occupancy frequency distributions. However, there are a number of exceptions to these "general" findings, and only a few studies have examined these patterns and their temporal variability in stream organisms. I examined both abundance-occupancy relationships and occupancy frequency distributions in stream insects in a boreal drainage system over six consecutive years. I found that the positive interspecific abundance-occupancy relationship was highly stable temporally, with coefficients of determination ranging from 0.25 to 0.47 over the years. There were no strong differences in the strength and slope of the abundance-occupancy relationship between non-predatory and predatory insect species in each year. Temporally stable abundance-occupancy relationships were paralleled by among-year patterns in both abundance and occupancy, with locally abundant and widely distributed species remaining locally abundant and widely distributed over the years, while locally uncommon and regionally rare species showed the opposite. Occupancy frequency distributions were strongly right-skewed, mirroring the dominance of the left-most satellite mode of regionally rare species. That the abundance-occupancy relationship, species' abundances and distributions, as well as the dominance of satellite species in occupancy frequency distribution were temporally stable suggest that niche-based models are strong candidates for explaining these patterns in stream insects. By contrast, metapopulation-based models that predict clear temporal variability in species' abundance and occupancy, as well as bimodal occupancy frequency distributions, are less plausible candidates for explaining the observed patterns. The present findings are the opposite to those in some terrestrial studies, but they are in agreement with other terrestrial studies and with a few previous studies on stream organisms.     

The role of size and dominance in the feeding behaviour of coexisting hummingbirds

Interspecific competition can strongly influence community structure and limit the distribution and abundance of species. One of the main factors that determine hummingbird community structure is competition for food. The temporal and spatial distribution of nectar has a strong impact on hummingbird assemblages, shaping foraging niches according to hummingbird dominance and foraging strategy. We investigated whether body size and the degree of aggressive dominance influence feeding behaviour of hummingbirds in a temperate forest in northwestern Mexico (El Palmito, Mexico) when winter migrant hummingbirds are present in the community. First, we determined the dominance status of hummingbirds and evaluated the relationship between dominance and body mass, wing disc loading and migratory status. Secondly, we determined how hummingbird species used plant species differently. Thirdly, we examined whether the most dominant hummingbird species defended floral patches with more energy and/or with a larger number of flowers. At each flower patch, hummingbird species, number of hummingbird interactions, feeding time and number of flowers present were recorded. The total number of calories available within each floral patch was also determined. Our results demonstrate that the dominance hierarchy of 13 hummingbird species (migratory and resident) was correlated with body size but not wing disc loading, and that members of the hummingbird community showed a clear separation in resource use (by plant species). Hummingbirds at the top of the dominance hierarchy defended and fed on the best flower patches, defined by the quantity of calories available. Hence, the feeding behaviour of hummingbirds at El Palmito depends on the abundance of plant species used by hummingbirds and on the amount of energy available from each flower patch. Thus, hummingbird body size, aggressive dominance and defence of quality flower patches determines niche partitioning among species.     

Trait syndromes among North American trees are evolutionarily conserved and show adaptive value over broad geographic scales

Adaptive syndromes and their evolutionary constraints represent a powerful construct for understanding plant distributions. However, it is unclear how the species requirements to face multiple stressors promotes syndrome formation and to which abiotic stressors these syndromes show adaptive value over broad geographic scales. We combined local occurrence data from the U.S. Forest Inventory and Analysis (FIA) of 219 angiosperm and 85 gymnosperm species living across the conterminous US with phylogenies and trait data to identify tree syndromes, their evolutionary conservatism, and their adaptive value over broad scales. Factor analyses and evolutionary model selection revealed that trees possess functional trait syndromes that are strongly conserved. Major syndromes at the species level differed between angiosperms and gymnosperms. While the two main syndromes in angiosperms were related to cold and drought‐waterlogging tolerance, in gymnosperms a trade‐off between shade and drought tolerance was the main syndrome followed by a growth‐fire resistance syndrome. Additional RLQ and fourth‐corner approaches revealed that trait syndromes at the community level were broadly similar to those observed at the species level for angiosperms, although this was less clear for gymnosperms. This suggests that syndrome evolution has played an important role on angiosperm distributions, whereas additional ecological factors explain gymnosperm distributions. Importantly, syndromes show adaptive value, as they were geographically associated with several environmental variables showing structure from continental to local scales, being temperature the main abiotic stressor. Our results indicate that across the conterminous US tree species possess clear syndromes that are subjected to strong evolutionary constraints driving tree species and forest community distribution.     

Convergent succession of plant communities is linked to species’ functional traits

Functional traits reflecting the resource economy and growth strategy of plants vary widely both within and among ecosystems. Theory suggests that trait variation within a community may determine the relative abundance of species, though this idea requires more empirical support.We set up a long-term succession experiment in a nutrient-poor wetland, planting seedlings of twelve fenland species in different relative abundances and absolute densities, thereby creating 24 communities. The biomass of these species and the soil water and nutrient status of the system were monitored over ten years. Using these data, we could relate the changing relative abundance of species to five traits – leaf dry matter content (LDMC), leaf nitrogen concentration (LNC), specific leaf area (SLA), relative growth rate (RGR), and seed mass (SM).The initial communities converged after ten years to a common dominance–diversity structure, with two species accounting for 82% of total biomass. Soil water and nutrient conditions remained largely constant. By the end of the experiment, community trait structure had changed so that species functional traits were significantly related to their relative abundance. The most abundant species had high LDMC and SM, but low RGR and SLA, and varied little in LNC, suggesting that investment in leaf structure and retention of nutrients were most important for species dominance under low nutrient conditions. Our results provide experimental evidence that dominance–subdominance structures in plant communities are governed by functional traits.     

Enthalpy distribution functions for protein-DNA complexes: example of the binding of AT-hooks to target DNA

In this article we use the published heat capacity data of Dragan et al. [A.I. Dragan, et al., The energetics of specific binding of AT-hooks from HMGA1 to target DNA, J. Mol. Biol. 327 (2003) 393-411] on the association of proteins with DNA duplexes to construct enthalpy probability distributions for the protein/DNA complexes formed in these systems. We first analyze the multistep equilibrium that determines the species concentrations in this system to determine whether or not the DNA-peptide complex goes cleanly to DNA single-strands and peptide. Using the heat capacity data for this case we employ the maximum-entropy method to construct enthalpy probability distribution functions for the species involved in this equilibrium. We find that the distribution functions for this system clearly show bimodal behavior indicating a two-state transition from complex to non-complex form.     

The effects of the genetic background on herbicide resistance fitness cost and its associated dominance in Arabidopsis thaliana

The advantage of the resistance conferred by a mutation can sometimes be offset by a high fitness-cost penalty. This balance will affect possible fate of the resistance allele. Few studies have explored the impact of the genetic background on the expression of the resistance fitness cost and none has attempted to measure the variation in fitness-cost dominance. However, both the fitness penalty and its dominance may modify evolutionary trajectory and outcome. Here the impact of Arabidopsis thaliana intraspecific genetic diversity on fitness cost and its associated dominance was investigated by analysing 12 quantitative traits in crosses between a mutant conferring resistance to the herbicide 2,4-D and nine different natural genetic backgrounds. Fitness cost values were found to be more affected by intraspecific genetic diversity than fitness cost dominance, even though this effect depends on the quantitative trait measured. This observation has implications for the choice of the best strategy for preventing herbicide resistance development. In addition, our results pinpoint a potential compensatory improvement of the resistance fitness cost and its associated dominance by the genetic diversity locally present within a species.