Journal of Evolutionary Biology最新文献

Many hypotheses in the field of phylogenetic comparative biology involve specific changes in the rate or process of trait evolution. This is particularly true of approaches designed to connect macroevolutionary pattern to microevolutionary process. We present a method to test whether the rate of evolution of a discrete character has changed in one or more clades, lineages, or time periods. This method differs from other related approaches (such as the "covarion" model) in that the "regimes" in which the rate or process is postulated to have changed are specified a priori by the user, rather than inferred from the data. Similarly, it differs from methods designed to model a correlation between two binary traits in that the regimes mapped onto the tree are fixed. We apply our method to investigate the rate of dewlap colour and/or caudal vertebra number evolution in Caribbean and mainland clades of the diverse lizard genus Anolis. We find little evidence to support any difference in the evolutionary process between mainland and island evolution for either character. We also examine the statistical properties of the method more generally and show that it has acceptable type I error, parameter estimation, and power. Finally, we discuss some general issues of frequentist hypothesis testing and model adequacy, as well as the relationship of our method to existing models of heterogeneity in the rate of discrete character evolution on phylogenies.

Insular biodiversity hotspots of Southeast Asia are remarkable for their biodiverse faunas. With a marine larval phase lasting up to several months, the freshwater fish subfamily Sicydiinae has colonized most islands of these hotspots. However, Sicydiinae diversity is still poorly understood in Southeast Asia. With the objective of estimating intraspecific genetic diversity and inferring past demography, we conducted the molecular inventory of Sicydiinae species in Sundaland and Wallacea using 652 bp of the mitochondrial cytochrome oxidase I gene, species delimitation methods, and Bayesian Skyline plot reconstructions. In total, 24 Molecular Operational Taxonomic Units are delimited among the 603 sequences belonging to 27 species and 5 genera. Two cases of discordance between morphology and mitochondrial sequence are observed, suggesting ongoing speciation and/or introgression in 2 genera. Multiple new occurrences are reported, either for a single biodiversity hotspot or both, some of which correspond to observations of a few individuals far from the range distribution of their conspecifics. Among the 10 species or species groups whose intraspecific diversity was examined, high levels of genetic diversity and past population expansion are revealed by Tajima's D tests and Bayesian Skyline Plot reconstructions. Together, these results indicate that long-distance dispersal is common and suggest that most endemic species originated through founder events followed by population expansion. Patterns of sexual dimorphism and males' coloration among diverging species pairs seem to point to sexual selection as an important mechanism contributing to speciation in the Sicydiinae of Sundaland and Wallacea.

Intraspecific processes impact macroevolutionary patterns through individual variation, selection, and ecological specialization. According to the niche variation hypothesis, the broader ecological niche of generalist species results in an increased morphological variation among individuals either because they are constituted of diversified specialized individuals each exploiting a fraction of the species' niche or because they are constituted of true generalist individuals that experience relaxed selection. To test this hypothesis, we surveyed the individual floral morphology of species of Antillean Gesneriaceae, a group that has transitioned between specialization for hummingbird pollination and generalization multiple times throughout its evolutionary history. We characterized the profiles of corollas using geometric morphometrics and compared the intraspecific shape variance of specialists and generalists in a phylogenetic context. We used three approaches that differently accounted for the high dimensionality of morphological traits, the ancestral reconstruction of pollination syndromes over time, and the error associated with the estimation of the intraspecific variance. Our findings provide partial support for the niche variation hypothesis. If considering the whole shape in the analysis corroborated this idea, decomposing the shape into principal components indicated that not all aspects of the corolla exhibit the same pattern of variation. Specifically, pollination generalists tend to display greater intraspecific variation than specialists in terms of tubularity, but not of curvature. Accounting for the error in the variance estimation also reduced the support for the hypothesis, suggesting that larger sample sizes may be required to reach stronger conclusions. This study emphasizes the reciprocal influence between plants and their pollinators on floral morphology at different biodiversity scales and suggests that ecological strategies of species can affect patterns of morphological variation at macroevolutionary scales.

The processes that generate biodiversity start on a microevolutionary scale, where each individual's history can impact the species' history. This manuscript presents a theoretical study that examines the macroevolutionary patterns that emerge from the microevolutionary dynamics of populations inhabiting two patches. The model is neutral, meaning that neither survival nor reproduction depends on a fixed genotype, yet individuals must have minimal genetic similarity to reproduce. We used historical sea level oscillation over the past 800 thousand years to hypothesize periods when individuals could migrate from one patch to another. In our study, we keep track of each speciation and extinction event, build the complete and extant phylogenies, and characterize the macroevolutionary patterns regarding phylogeny balance, acceleration of speciation, and crown age. We also evaluate ecological patterns: richness, beta diversity, and species distribution symmetry. The balance of the complete phylogeny can be a sign of the speciation mode, contrasting speciation induced by migration and isolation (vicariance). The acceleration of the speciation process is also affected by the geographical barriers and the duration of the isolation period, with high isolation times leading to accelerated speciation. We report the correlation between ecological and macroevolutionary patterns and show it decreases with the time spent in isolation. We discuss, in light of our results, the challenge of integrating present-time community ecology with macroevolutionary patterns.

Rates of evolution get smaller when they are measured over longer time intervals. As first shown by Gingerich, rates of morphological change measured from fossil time series show a robust minus-one scaling with time span, implying that evolutionary changes are just as large when measured over a hundred years as when measured over a hundred-thousand years. On even longer time scales, however, the scaling shifts toward a minus-half exponent consistent with evolution behaving as Brownian motion, as commonly observed in phylogenetic comparative studies. Here, I discuss how such scaling patterns arise, and I derive the patterns expected from standard stochastic models of evolution. I argue that observed shifts cannot be easily explained by simple univariate models, but require shifts in mode of evolution as time scale is changing. To illustrate this idea, I present a hypothesis about three distinct, but connected, modes of evolution. I analyze the scaling patterns predicted from this, and use the results to discuss how rates of evolution should be measured and interpreted. I argue that distinct modes of evolution at different time scales act to decouple micro- and macroevolution, and criticize various attempts at extrapolating from one to the other.

Quantitative genetic theory on multivariate character evolution predicts that a population's response to directional selection is biased towards the major axis of the genetic covariance matrix G-the so-called genetic line of least resistance. Inferences on the genetic constraints in this sense have traditionally been made by measuring the angle of deviation of evolutionary trajectories from the major axis or, more recently, by calculating the amount of genetic variance-the Hansen-Houle evolvability-available along the trajectories. However, there have not been clear practical guidelines on how these quantities can be interpreted, especially in a high-dimensional space. This study summarizes pertinent distribution theories for relevant quantities, pointing out that they can be written as ratios of quadratic forms in evolutionary trajectory vectors by taking G as a parameter. For example, a beta distribution with appropriate parameters can be used as a null distribution for the squared cosine of the angle of deviation from a major axis or subspace. More general cases can be handled with the probability distribution of ratios of quadratic forms in normal variables. Apart from its use in hypothesis testing, this latter approach could potentially be used as a heuristic tool for looking into various selection scenarios, like directional and/or correlated selection, as parameterized with the mean and covariance of selection gradients.

The evolution of sexual dimorphism is widely acknowledged as a manifestation of sex-specific genetic architecture. Although empirical studies suggested that sexual dimorphism evolves as a joint consequence of constraints arising from genetic architecture and sexually divergent selection, it remains unclear whether and how these established microevolutionary processes scale up to the macroevolutionary patterns of sexual dimorphism among taxa. Here, we studied how sexual selection and parental care drive sexual dimorphism in cichlid fishes from Lake Tanganyika. We found that male-male competition, female choice, and maternal mouthbrooding are associated with sexual dimorphism in body length, body colour, and head length, respectively, despite strong allometric relationships between body length and head length. Within-species (static) allometry of head length on body length evolved as sex-specific responses to mouthbrooding, where females evolved higher intercepts while males evolved steeper slopes. Thus, selection to increase mouth size in mouthbrooders may have broken down and reorganized the pattern of allometric constraints that are inherently strong and concordant between sexes. Furthermore, sex-specific responses to mouthbrooding left a remarkably clear signature on the macroevolutionary pattern, resulting in a decoupling of co-evolution in parameters of static allometries between sexes observed exclusively within maternal mouthbrooders. Our study provides multiple lines of evidence that are consistent with the idea that macroevolutionary patterns of sexual dimorphism in Lake Tanganyika cichlids result from sexually divergent selection. Our approach illustrates that an examination of within-population phenotypic variance in the phylogenetic comparative framework may facilitate nuanced understandings of how macroevolutionary patterns are generated by underlying microevolutionary processes.

Ever since the Modern Synthesis, a debate about the relationship between microevolution and macroevolution has persisted-specifically, whether they are equivalent, distinct, or explain one another. How one answers these questions has become shorthand for a much broader set of theoretical debates in evolutionary biology. Here, we examine microevolution and macroevolution in the context of the vast proliferation of data, knowledge, and theory since the advent of the Modern Synthesis. We suggest that traditional views on microevolution and macroevolution are too binary and reductive given current empirical and theoretical advances in biology. For example, patterns and processes are interconnected at various temporal and spatial scales and among hierarchical entities, rather than defining micro- or macro-domains. Further, biological entities have variably fuzzy boundaries, resulting in complex evolutionary processes that influence macroevolution occuring at both micro- and macro-levels. In addition, conceptual advances in phylodynamics have yet to be fully integrated with contemporary macroevolutionary approaches. Finally, holding microevolution and macroevolution as distinct domains thwarts synthesis and collaboration on important research questions. Instead, we propose that the focal entities and processes considered by evolutionary studies be contextualized within the complexity of the multidimensional, multimodal, multilevel phylogenetic system.

In the last two decades, lineage-based models of diversification, where species are viewed as particles that can divide (speciate) or die (become extinct) at rates depending on some evolving trait, have been very popular tools to study macroevolutionary processes. Here, we argue that this approach cannot be used to break down the inner workings of species diversification and that "opening the species box" is necessary to understand the causes of macroevolution, but that too detailed speciation models also fail to make robust macroevolutionary predictions. We set up a general framework for parsimonious models of speciation that rely on a minimal number of mechanistic principles: (a) reproductive isolation is caused by excessive dissimilarity between genotypes; (b) dissimilarity results from a balance between differentiation processes and homogenizing processes; and (c) dissimilarity can feed back on these processes by decelerating homogenization. We classify such models according to the main homogenizing process: (a) clonal evolution models (ecological drift), (b) models of genetic isolation (gene flow), and (c) models of isolation by distance (spatial drift). We review these models and their specific predictions on macroscopic variables such as species abundances, speciation rates, interfertility relationships, or phylogenetic tree structure. We propose new avenues of research by displaying conceptual questions remaining to be solved and new models to address them: the failure of speciation at secondary contact, the feedback of dissimilarity on homogenization, and the emergence in space of breeding barriers.