Evolution Of Phenotypic Traits Research Articles

Coping with extremes: convergences of habitat use, territoriality, and diet in summer but divergences in winter between two sympatric snow finches on the Qinghai-Tibet Plateau.

On the Qinghai-Tibet Plateau, extreme environmental conditions have imposed intense selective pressure on the evolution of phenotypic traits of wild animals. To date, limited information is available on behavioral and ecological traits concerning niche differentiation among sympatric animals on the Qinghai-Tibet Plateau, especially during winter when the environments are most severe. Here, we studied the seasonal variations in habitat occurrence, territorial behavior, and diet in two sympatric snow finches (the white-rumped snow finch, Onychostruthus taczanowskii, WRSF; and the rufous-necked snow finch, Pyrgilauda ruficollis, RNSF) to determine convergence and divergence of ecological traits in such severe climatic conditions. Our results showed that: (i) WRSF occupied rural areas as a dominant species throughout the annual cycle while RNSF occupied the rural areas in summer and then shifted to human-occupied areas in winter and spring; (ii) WRSFs exhibited robust aggressive behavior and territoriality during winter relative to RNSFs; (iii) the diets of both species varied with the season but did not vary between species except that WRSF ate significantly more seeds but RNSF consumed more starchy material derived from human food waste during winter. Therefore, the separations in the spatial niche and territoriality between WRSF and RNSF, especially in winter, may contribute to alleviating the pressure of interspecific competition, and promoting the coexistence of the two sympatric snow finches in the extreme environments on the Qinghai-Tibet Plateau.

Selection on fruit traits is mediated by the interplay between frugivorous birds, fruit flies, parasitoid wasps and seed-dispersing ants.

Every organism on Earth must cope with a multitude of species interactions both directly and indirectly throughout its life cycle. However, how selection from multiple species occupying different trophic levels affects diffuse mutualisms has received little attention. As a result, how a given species amalgamates the combined effects of selection from multiple mutualists and antagonists to enhance its own fitness remains little understood. We investigated how multispecies interactions (frugivorous birds, ants, fruit flies and parasitoid wasps) generate selection on fruit traits in a seed dispersal mutualism. We used structural equation models to assess whether seed dispersers (frugivorous birds and ants) exerted phenotypic selection on fruit and seed traits in the spiny hackberry (Celtis ehrenbergiana), a fleshy-fruited tree, and how these selection regimes were influenced by fruit fly infestation and wasp parasitoidism levels. Birds exerted negative correlational selection on the combination of fruit crop size and mean seed weight, favouring either large crops with small seeds or small crops with large seeds. Parasitoids selected plants with higher fruit fly infestation levels, and fruit flies exerted positive directional selection on fruit size, which was positively correlated with seed weight. Therefore, higher parasitoidism indirectly correlated with higher plant fitness through increased bird fruit removal. In addition, ants exerted negative directional selection on mean seed weight. Our results show that strong selection on phenotypic traits may still arise in perceived diffuse species interactions. Overall, we emphasize the need to consider diverse direct and indirect partners to achieve a better understanding of the mechanisms driving phenotypic trait evolution in multispecies interactions.

Coping with extremes: Remarkably blunt adrenocortical responses to acute stress in two sympatric snow finches on the Qinghai-Tibet Plateau during winter relative to other seasons

The extreme climatic conditions (ECCs) of the Qinghai-Tibet Plateau impose strong selective pressures on the evolution of phenotypic traits in free-living animals. It is not well understood how animals on the Qinghai-Tibet Plateau modify their adrenocortical functions in response to both predictable and unpredictable events of ECCs, especially when the available resources are lowest during the wintering life-history stage. To uncover potential physiological mechanisms, we studied the life history stage dependent features of morphology, the plasma corticosterone response to acute stress and brain glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA expression in two sympatric snow finches: the white-rumped snow finch (Onychostruthus taczanowskii, WRSF); and the rufous-necked snow finch, Pyrgilauda ruficollis, RNSF) in Qinghai Province, China. Our results showed that (a) baseline corticosterone and stressor-induced corticosterone levels significantly varied with life history stage, but not between the species; (b) in WRSF, GR mRNA expression in the paraventricular nucleus was higher in the wintering stage compared to the pre-basic molt stage. There were no differences in hippocampus MR mRNA expression between stages in either species; (c) in the wintering stage, the suppression of corticosterone secretion in both species was an unexpected strategy in free-living animals. Both convergent and divergent phenotypic traits of adrenocortical responses to acute stress in two sympatric snow finches contribute to our understanding of the coping mechanisms of closely related species in the severe winter on the Qinghai-Tibet Plateau.

Historical biogeography and multi-trait evolution in miniature toadlets of the genus Brachycephalus (Anura: Brachycephalidae)

AbstractEvolutionary changes towards a miniaturized body plan may directly affect other important phenotypic traits related to the physiology, behaviour and ecology of organisms. The frog genus Brachycephalus is an outstanding example of a radiation of miniaturized species endemic to the Brazilian Atlantic Forest. We inferred ancestral states and historical changes in body size, body colour and hyperossification to test hypotheses about diversification and selective environmental mechanisms leading to the evolution of these specialized traits. The ancestral distribution was associated with high-elevation regions in the northern Serra do Mar mountain range, and diversification in the genus was coincident with important geological and climatic events during the history of the Atlantic Forest. The dynamic historical changes provided an opportunity for multiple lowland lineages and for speciation via dispersal and vicariance in multiple invasions of the highlands. The ancestral Brachycephalus was reconstructed as miniaturized and dull coloured, without hyperossification in the skin, skull or postcranial skeleton. A parallel evolution of phenotypic traits has occurred in northern and southern Atlantic Forest lineages, beginning in the Miocene. Shifts in body size are not related to elevation range or latitude. However, we found a significant correlation between the evolution of hyperossification and aposematism with increasing body size.

A multivariate phylogenetic comparative method incorporating a flexible function between discrete and continuous traits

One major challenge of using the phylogenetic comparative method (PCM) is the analysis of the evolution of interrelated continuous and discrete traits in a single multivariate statistical framework. In addition, more intricate parameters such as branch-specific directional selection have rarely been integrated into such multivariate PCM frameworks. Here, originally motivated to analyze the complex evolutionary trajectories of group size (continuous variable) and social systems (discrete variable) in African subterranean rodents, we develop a flexible approach using approximate Bayesian computation (ABC). Specifically, our multivariate ABC-PCM method allows the user to flexibly model an underlying latent evolutionary function between continuous and discrete traits. The ABC-PCM also simultaneously incorporates complex evolutionary parameters such as branch-specific selection. This study highlights the flexibility of ABC-PCMs in analyzing the evolution of phenotypic traits interrelated in a complex manner.

Evaluating Chromatin Accessibility Differences Across Multiple Primate Species Using a Joint Modeling Approach.

Changes in transcriptional regulation are thought to be a major contributor to the evolution of phenotypic traits, but the contribution of changes in chromatin accessibility to the evolution of gene expression remains almost entirely unknown. To address this important gap in knowledge, we developed a new method to identify DNase I Hypersensitive (DHS) sites with differential chromatin accessibility between species using a joint modeling approach. Our method overcomes several limitations inherent to conventional threshold-based pairwise comparisons that become increasingly apparent as the number of species analyzed rises. Our approach employs a single quantitative test which is more sensitive than existing pairwise methods. To illustrate, we applied our joint approach to DHS sites in fibroblast cells from five primates (human, chimpanzee, gorilla, orangutan, and rhesus macaque). We identified 89,744 DHS sites, of which 41% are identified as differential between species using the joint model compared with 33% using the conventional pairwise approach. The joint model provides a principled approach to distinguishing single from multiple chromatin accessibility changes among species. We found that nondifferential DHS sites are enriched for nucleotide conservation. Differential DHS sites with decreased chromatin accessibility relative to rhesus macaque occur more commonly near transcription start sites (TSS), while those with increased chromatin accessibility occur more commonly distal to TSS. Further, differential DHS sites near TSS are less cell type-specific than more distal regulatory elements. Taken together, these results point to distinct classes of DHS sites, each with distinct characteristics of selection, genomic location, and cell type specificity.

Automatic generation of evolutionary hypotheses using mixed Gaussian phylogenetic models

Phylogenetic comparative methods are widely used to understand and quantify the evolution of phenotypic traits, based on phylogenetic trees and trait measurements of extant species. Such analyses depend crucially on the underlying model. Gaussian phylogenetic models like Brownian motion and Ornstein-Uhlenbeck processes are the workhorses of modeling continuous-trait evolution. However, these models fit poorly to big trees, because they neglect the heterogeneity of the evolutionary process in different lineages of the tree. Previous works have addressed this issue by introducing shifts in the evolutionary model occurring at inferred points in the tree. However, for computational reasons, in all current implementations, these shifts are "intramodel," meaning that they allow jumps in 1 or 2 model parameters, keeping all other parameters "global" for the entire tree. There is no biological reason to restrict a shift to a single model parameter or, even, to a single type of model. Mixed Gaussian phylogenetic models (MGPMs) incorporate the idea of jointly inferring different types of Gaussian models associated with different parts of the tree. Here, we propose an approximate maximum-likelihood method for fitting MGPMs to comparative data comprising possibly incomplete measurements for several traits from extant and extinct phylogenetically linked species. We applied the method to the largest published tree of mammal species with body- and brain-mass measurements, showing strong statistical support for an MGPM with 12 distinct evolutionary regimes. Based on this result, we state a hypothesis for the evolution of the brain-body-mass allometry over the past 160 million y.

Gene expression profiling suggests differences in molecular mechanisms of fin elongation between cichlid species

Comparative analyses of gene regulation inform about the molecular basis of phenotypic trait evolution. Here, we address a fin shape phenotype that evolved multiple times independently across teleost fish, including several species within the family Cichlidae. In a previous study, we proposed a gene regulatory network (GRN) involved in the formation and regeneration of conspicuous filamentous elongations adorning the unpaired fins of the Neolamprologus brichardi. Here, we tested the members of this network in the blockhead cichlid, Steatocranus casuarius, which displays conspicuously elongated dorsal and moderately elongated anal fins. Our study provided evidence for differences in the anatomy of fin elongation and suggested gene regulatory divergence between the two cichlid species. Only a subset of the 20 genes tested in S. casuarius showed the qPCR expression patterns predicted from the GRN identified in N. brichardi, and several of the gene-by-gene expression correlations differed between the two cichlid species. In comparison to N. brichardi, gene expression patterns in S. casuarius were in better (but not full) agreement with gene regulatory interactions inferred in zebrafish. Within S. casuarius, the dorsoventral asymmetry in ornament expression was accompanied by differences in gene expression patterns, including potential regulatory differentiation, between the anal and dorsal fin.

Rapid evolution of invasive traits facilitates the invasion of common ragweed, Ambrosia artemisiifolia

Abstract Invasive alien plants, together with organisms introduced for biological control, are ideal study systems with which to address questions of whether, and how fast, organisms adapt to changing environments. We compared populations of common ragweed, Ambrosia artemisiifolia, from native (USA) and introduced (China) ranges at similar latitudes, together with herbivores introduced for biological control, to understand the rate of evolutionary adaptive response of an invasive plant to novel environments. Evolution of phenotypic traits associated with invasiveness was assessed by comparing differentiation in quantitative traits (QST) to that of neutral microsatellite genetic loci (FST) and through climate data. A common‐garden experiment estimated quantitative genetic variation associated with competition with grasses and biological control history by beetles. Three growth traits (height, total and stem biomass) and plasticity associated with additional nutrients were significantly greater in invasive compared to native populations and differed from expectations from genetic drift alone. Native, but not invasive, populations exhibited traits showing evidence of past selection and correlations with climate, consistent with the recent timing of introductions. Competition experiments between invasive populations and a US bunch grass showed reduced competitive ability in populations with a history of biological control that might indicate a trade‐off between competitive ability and herbivore resistance in invasive populations. Synthesis. Our results demonstrate the rapid rate at which traits favouring invasion can evolve in invasive weeds, such as A. artemisiifolia, but also that adaptation may reflect joint effects of release from specialist herbivores and novel climatic conditions.

Evolutionary relationships among life-history traits in Caninae (Mammalia: Carnivora)

AbstractOver the last few years, a debate about the relative roles of distinct factors on the evolution of lineages has gained prominence. The family Canidae is an excellent group for exploring this idea, owing to its rich fossil history. One of the most intriguing traits in canids is social organization, which varies from highly social to solitary species. However, we do not have a complete understanding of how sociality evolved in this clade. Here, we use a combination of phylogenetic analyses, ancestral character reconstructions and comparative methods on the only extant subfamily, Caninae, to understand how traits expressing ecological features evolved over the last 12.6 Myr. Our findings suggest that the evolution of low, medium and high sociality forms was abrupt and highly correlated with the evolution of hypo-, meso- and hypercarnivorous forms, respectively. In addition, our results suggest that the evolution of phenotypic traits in Caninae occurred through a sequential cause–effect relationship, where changes in habitat use and body size probably triggered changes in social behaviour, which in turn drove the evolution of diet.

Females mate with males with diminished pheomelanin‐based coloration in the Eurasian nuthatch Sitta europaea

Sexual selection can drive the evolution of phenotypic traits because of female preferences for exaggerated trait expression in males. Sexual selection can also lead to the evolutionary loss of traits, a process to which female preferences for diminished male trait expression are hypothesized to contribute. However, empirical evidence of female preferences for diminished male traits is virtually lacking. Eurasian nuthatches Sitta europaea provide an opportunity to test this possibility, as a chestnut flank patch produced by the pigment pheomelanin is present since the first plumage of these birds and its color is more intense in nestlings in poor condition in our study population. It has been proposed that developing birds in poor condition may increase their production of pheomelanin as a detoxifying strategy. Female nuthatches may thus prefer mating with males showing flank feathers of diminished color, as this could indicate that males experienced good conditions early in development, which can positively affect the fitness of future generations. Here we show results according with this prediction in a wild population of Eurasian nuthatches, as adult males with lighter chestnut feathers paired earlier in the season, while chestnut coloration had no effect on female mating success. Chestnut color expression was not affected by the body condition of birds, suggesting that females obtain information on the body condition in early life of their potential mates and not on their current body condition. This constitutes one of the few examples of females mating with males showing diminished traits and provides the only explanation so far by which this process can occur.

Using the Ornstein–Uhlenbeck process to model the evolution of interacting populations

The Ornstein–Uhlenbeck (OU) process plays a major role in the analysis of the evolution of phenotypic traits along phylogenies. The standard OU process includes random perturbations and stabilizing selection and assumes that species evolve independently. However, evolving species may interact through various ecological process and also exchange genes especially in plants. This is particularly true if we want to study phenotypic evolution among diverging populations within species. In this work we present a straightforward statistical approach with analytical solutions that allows for the inclusion of adaptation and migration in a common phylogenetic framework, which can also be useful for studying local adaptation among populations within the same species. We furthermore present a detailed simulation study that clearly indicates the adverse effects of ignoring migration. Similarity between species due to migration could be misinterpreted as very strong convergent evolution without proper correction for these additional dependencies. Finally, we show that our model can be interpreted in terms of ecological interactions between species, providing a general framework for the evolution of traits between “interacting” species or populations.

Natural selection on immune defense: A field experiment.

Predicting the evolution of phenotypic traits requires an understanding of natural selection on them. Despite its indispensability in the fight against parasites, selection on host immune defense has remained understudied. Theory predicts immune traits to be under stabilizing selection due to associated trade-offs with other fitness-related traits. Empirical studies, however, report mainly positive directional selection. This discrepancy could be caused by low phenotypic variation in the examined individuals and/or variation in host resource level that confounds trade-offs in empirical studies. In a field experiment where we maintained Lymnaea stagnalis snails individually in cages in a lake, we investigated phenotypic selection on two immune defense traits, phenoloxidase (PO)-like activity and antibacterial activity, in hemolymph. We used a diverse laboratory population and manipulated snail resource level by limiting their food supply. For six weeks, we followed immune activity, growth, and two fitness components, survival and fecundity of snails. We found that PO-like activity and growth were under stabilizing selection, while antibacterial activity was under positive directional selection. Selection on immune traits was mainly driven by variation in survival. The form of selection on immune defense apparently depends on the particular trait, possibly due to its importance for countering the present parasite community.

Evolution of kin recognition mechanisms in a fish.

Both selection and phylogenetic history can influence the evolution of phenotypic traits. Here we used recently characterized variation in kin recognition mechanisms among six guppy populations to explore the phylogenetic history of this trait. Guppies can use two different kin recognition mechanisms: either phenotype matching, in which individuals are identified based on comparison with a recognition template, or familiarity, in which individuals are remembered based on previous interactions. Across the six populations, we identified four transitions in recognition mechanism: phenotype matching evolved once and was subsequently lost in a single population, whereas familiarity evolved twice. Based on a molecular clock, these transitions occurred among populations that had diverged on a timescale of hundreds of thousands of years, which is two orders of magnitude faster than previously documented transitions in recognition mechanisms. A randomization test provided no evidence that recognition mechanisms were constrained by phylogeny, suggesting that recognition mechanisms have the capacity to evolve rapidly, although the specific selection pressures that may be contributing to variation in recognition mechanisms across populations remain unknown.

Bridging Inter- and Intraspecific Trait Evolution with a Hierarchical Bayesian Approach.

The evolution of organisms is crucially dependent on the evolution of intraspecific variation. Its interactions with selective agents in the biotic and abiotic environments underlie many processes, such as intraspecific competition, resource partitioning and, eventually, species formation. Nevertheless, comparative models of trait evolution neither allow explicit testing of hypotheses related to the evolution of intraspecific variation nor do they simultaneously estimate rates of trait evolution by accounting for both trait mean and variance. Here, we present a model of phenotypic trait evolution using a hierarchical Bayesian approach that simultaneously incorporates interspecific and intraspecific variation. We assume that species-specific trait means evolve under a simple Brownian motion process, whereas species-specific trait variances are modeled with Brownian or Ornstein-Uhlenbeck processes. After evaluating the power of the method through simulations, we examine whether life-history traits impact evolution of intraspecific variation in the Eriogonoideae (buckwheat family, Polygonaceae). Our model is readily extendible to more complex scenarios of the evolution of inter- and intraspecific variation and presents a step toward more comprehensive comparative models for macroevolutionary studies.

Evolution of the fish heart by sub/neofunctionalization of an elastin gene.

The evolution of phenotypic traits is a key process in diversification of life. However, the mechanisms underlying the emergence of such evolutionary novelties are largely unknown. Here we address the origin of bulbus arteriosus (BA), an organ of evolutionary novelty seen in the teleost heart outflow tract (OFT), which sophisticates their circulatory system. The BA is a unique organ that is composed of smooth muscle while the OFTs in other vertebrates are composed of cardiac muscle. Here we reveal that the teleost-specific extracellular matrix (ECM) gene, elastin b, was generated by the teleost-specific whole-genome duplication and neofunctionalized to contribute to acquisition of the BA by regulating cell fate determination of cardiac precursor cells into smooth muscle. Furthermore, we show that the mechanotransducer yap is involved in this cell fate determination. Our findings reveal a mechanism of generating evolutionary novelty through alteration of cell fate determination by the ECM.

An increase in transmission‐related traits and in phenotypic plasticity is documented during a fungal invasion

The adaptive rapid evolution of phenotypic traits is potentially a key contributor to invasiveness, but has been relatively little studied for the fungi, even though these organisms are responsible for devastating losses in agriculture and natural resources. In this study, we compare biologically relevant phenotypic characters of spore‐generated individuals from two native and two invasive populations of the fungal pathogen Seiridium cardinale to infer which traits may be adaptive and rapidly evolving during an ongoing biological invasion. Results show that: (1) lower growth rate and smaller spore size are selected for in invasive populations, independent of the stage of invasion; (2) there is no selection evident towards increased rapid sporulation, but overall reproductive potential increases in later stages of the invasions; and (3) demographic plasticity of most traits increases during the initial stages of invasion, but decreases in a later phase. Comparisons against levels of neutral genetic variation (Qst‐Fst comparisons) showed that the decrease in spore size is strongly adaptive, despite the trade‐off of reduced viability. Lesion size of isolates inoculated on the naïve Italian cypress host was not correlated with their growth rate, and was significantly lower in invasive than in native populations. This last result indicates that rate of host colonization is a complex trait affected both by host and pathogen, which may not be necessarily adaptive and/or which may not easily evolve. In summary, the success of S. cardinale as an invasive in the Mediterranean basin is associated with reduced spore size and increased plasticity of almost all traits in initial phases, followed by further decreased spore size, increased overall sporulation, and decreased plasticity in a second phase of the invasion. Interestingly, growth rate by population results show that invasive populations are well adapted only to moderate temperatures, while native populations fare well also when exposed to relative extremes in temperature. This different adaptation suggests a “master‐of‐some” specialization scenario for the invasion by S. cardinale in the Mediterranean.

The importance of mechanisms for the evolution of cooperation.

Studies aimed at explaining the evolution of phenotypic traits have often solely focused on fitness considerations, ignoring underlying mechanisms. In recent years, there has been an increasing call for integrating mechanistic perspectives in evolutionary considerations, but it is not clear whether and how mechanisms affect the course and outcome of evolution. To study this, we compare four mechanistic implementations of two well-studied models for the evolution of cooperation, the Iterated Prisoner's Dilemma (IPD) game and the Iterated Snowdrift (ISD) game. Behavioural strategies are either implemented by a 1 : 1 genotype-phenotype mapping or by a simple neural network. Moreover, we consider two different scenarios for the effect of mutations. The same set of strategies is feasible in all four implementations, but the probability that a given strategy arises owing to mutation is largely dependent on the behavioural and genetic architecture. Our individual-based simulations show that this has major implications for the evolutionary outcome. In the ISD, different evolutionarily stable strategies are predominant in the four implementations, while in the IPD each implementation creates a characteristic dynamical pattern. As a consequence, the evolved average level of cooperation is also strongly dependent on the underlying mechanism. We argue that our findings are of general relevance for the evolution of social behaviour, pleading for the integration of a mechanistic perspective in models of social evolution.

Navigating natural variation in herbivory-induced secondary metabolism in coyote tobacco populations using MS/MS structural analysis

Natural variation can be extremely useful in unraveling the determinants of phenotypic trait evolution but has rarely been analyzed with unbiased metabolic profiling to understand how its effects are organized at the level of biochemical pathways. Native populations of Nicotiana attenuata, a wild tobacco species, have been shown to be highly genetically diverse for traits important for their interactions with insects. To resolve the chemodiversity existing in these populations, we developed a metabolomics and computational pipeline to annotate leaf metabolic responses to Manduca sexta herbivory. We selected seeds from 43 accessions of different populations from the southwestern United States--including the well-characterized Utah 30th generation inbred accession--and grew 183 plants in the glasshouse for standardized herbivory elicitation. Metabolic profiles were generated from elicited leaves of each plant using a high-throughput ultra HPLC (UHPLC)-quadrupole TOFMS (qTOFMS) method, processed to systematically infer covariation patterns among biochemically related metabolites, as well as unknown ones, and finally assembled to map natural variation. Navigating this map revealed metabolic branch-specific variations that surprisingly only partly overlapped with jasmonate accumulation polymorphisms and deviated from canonical jasmonate signaling. Fragmentation analysis via indiscriminant tandem mass spectrometry (idMS/MS) was conducted with 10 accessions that spanned a large proportion of the variance found in the complete accession dataset, and compound spectra were computationally assembled into spectral similarity networks. The biological information captured by this networking approach facilitates the mining of the mass spectral data of unknowns with high natural variation, as demonstrated by the annotation of a strongly herbivory-inducible phenolic derivative, and can guide pathway analysis.

Experimental systematics: sensitivity of cladistic methods to polarization and character ordering schemes

Phenotypic characters are essential to study the evolution of extant and extinct life forms and to reconstruct the tree of life. Inside the cladistics theory, parsimony is used by a large majority of systematists working on phenotypic characters, whereas 3ta is much less widespread but has triggered important debates. Many important differences in the interpretation of the cladistic theory exist between these methods, e.g. meaning and treatment of reversals, character representation as ‘data-matrices’ in parsimony (ordered and unordered), and as rooted trees (hierarchies) in 3ta. Although 3ta has received severe criticism, mostly focused in the use of software intended to be used in parsimony, only a few empirical studies have compared these methods so far. We present the results of simulations of the evolution of phenotypic traits under a Brownian motion model to characterize differences in sensitivity between parsimony and 3ta to (1) outgroup branch length, which affects the reliability of ancestral character state estimates, (2) character state ordering scheme, and (3) ingroup branch lengths that reflect the geological age of studied taxa. Our results show that the ‘nihilistic’ attitude of leaving multistate characters unordered when criteria to order are available (e.g. , similarity, ontogeny, etc…) can decrease resolving power of the method (by 13.4% to 29.3%) and increase the occurrence of artefactual clades (by 5% to 15.6%). Increasing outgroup branch length significantly decreases resolving power and increases artefactual resolution, at least for paleontological trees. All simulations show that ordered parsimony is always superior to 3ta in tested parameter space. These results depend on the assumption in parsimony that reversals (as implied by the Brownian motion, as in most other models) can be evidence for the support of a clade a posteriori from an analysis or a priori on simulations with a known pattern. We discuss implications of these points of view compared to the assumption inherent in 3ta (i.e. , that reversals should not support a clade as other synapomorphies do) on evolutionary models.