Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years.
Thamnochortus (ca. 32 species) is an ecologically diverse genus of Restionaceae. Restionaceae comprise a major component of the southern African Cape flora, wherein eco-diversification might have been important in the generation of high levels of species richness. In an attempt to reconstruct the macroecological history of Thamnochortus, it was found that standard procedures for character state optimization make two inappropriate assumptions. The first is that ancestors are monomorphic (i.e., ecologically uniform) and the second is that eco-diversification follows, or is slower than, lineage diversification. We demonstrate a variety of coding schemes with which the assumption of monomorphy can be avoided. For unordered discrete ecological characters, presence coding and generalized frequency coding (GFC) are suboptimal because they occasionally yield illogical assignments of no state to ancestors. Polymorphism coding or use of the program DIVA are preferable in this respect but are applicable only with parsimony. For continuous eco-characters (e.g., a rainfall gradient, where individual species occur in ranges), GFC and MaxMin coding provide equally valid solutions to optimizing ranges with parsimony. However, MaxMin can be extended to likelihood approaches and is therefore preferable. With respect to rates and timing, all algorithms currently employed for ancestral ecology reconstruction bias toward slow rates of eco-diversification relative to lineage diversification. An alternative to this bias is provided by DIVA, which biases toward accelerated rates of eco-diversification and thus inferences of ecology-driven speciation. We see no way of choosing between these biases; however, phylogeneticists should be aware of them. Applying these methods to Thamnochortus, we find there to be important differences in details, yet general congruence, regarding the historical ecology of this clade. We infer the most recent common ancestor of Thamnochortus to have been a post-fire resprouting species distributed on rocky, well-drained, sandstone-derived soils at lower-middle elevations, in regions of moderate levels of yearly (primarily winter) rainfall. This species would have been distributed in habitats much like those of the southwestern Cape mountains today. Major ecological trends include shifts to lower rainfall regimes and shifts from sandstone to limestone-derived alkaline soils at lower altitudes.
The Cape Floristic Region ('fynbos biome') has very high levels of plant species diversity and endemism. Much of this diversity is concentrated in a relatively small number of clades centered in the region (Cape clades), and these form a vegetation called 'fynbos'. The general explanation for the origin of this diversity is that much of it evolved in the Pliocene and Late Miocene in response to progressive aridification. We present a phylogenetic analysis of an almost complete species sample of the largest clade of Restionaceae, the third largest Cape clade. This indicates that the radiation of the Restionaceae started between 20 and 42 Myr ago, and since then there were no, or at most gradual, changes in the speciation rate in this clade. For seven other clades, the estimated starting dates for their radiation ranges from 7 to 20 Myr ago. Combining the radiation patterns for these clades shows that ca. 15% of the modern species evolved during the Pleistocene, and almost 40% since the beginning of the Pliocene. We suggest that these clades might have radiated in response to the fynbos vegetation increasing its extent in the Cape as a result of climatic change.
Mitochondrial sequences are an important source of data in animal phylogenetics, equivalent in importance to plastid sequences in plants. However, in recent years plant systematists have begun exploring the mitochondrial genome as a source of phylogenetically useful characters. The plant mitochondrial genome is renowned for its variability in size, structure, and gene organization, but this need not be of concern for the application of sequence data in phylogenetics. However, the incorporation of reverse transcribed mitochondrial genes ("processed paralogs") and the recurring transfer of genes from the mitochondrion to the nucleus are evolutionary events that must be taken into account. RNA editing of mitochondrial genes is sometimes considered a problem in phylogenetic reconstruction, but we regard it only as a mechanism that may increase variability at edited sites and change the codon position bias accordingly. Additionally, edited sites may prove a valuable tool in identifying processed paralogs. An overview of genes and sequences used in phylogenetic studies of angiosperms is presented. In the monocots, a large amount of mitochondrial sequence data is being collected together with sequence data from plastid and nuclear genes, thus offering an opportunity to compare data from different genomic compartments. The mitochondrial and plastid data are incongruent when organelle gene trees are reconstructed. Possible reasons for the observed incongruence involve sampling of paralogous sequences and highly divergent substitution rates, potentially leading to longbranch attraction. The above problems are addressed in Acorales, Alismatales, Poales, Liliaceae, the "Anthericum clade" (in Agavaceae), and in some achlorophyllous taxa.
Hardy, C R; Moline, P ; Linder, H P Hardy, C R; Moline, P; Linder, H P (2008 Difficulties with obtaining complete species-level phylogenies include (1) the accurate identification and sampling of species, (2) obtaining a complete species sampling, and (3) resolving relationships among closely related species.We addressed these in a study of 317 species and subspecies of the African Restionaceae. Accurate species identification and collection in the field was facilitated by a morphology-based interactive key to all species. Despite intensive fieldwork, however, material for DNA extraction could not be obtained for 20 of the 292 species of the focal Restio subclade. Furthermore, the 6831 aligned nucleotides and 1685 parsimonyinformative sequence characters were insufficient to resolve relationships fully within the clade. A simulation indicated that an additional 5000-7000 bases may have been needed to achieve supported resolution in the neighborhood of 95%-100%. Instead of further sequencing, we investigated the phylogenetic utility of the large set of characters contained within the interactive key data set, exploiting recent advances in parsimony and Bayesian programs that allow multistate and supermultistate (including continuous for parsimony) morphological characters. On doing so, parsimony resolution increased 17% to nearly 100%, and overall support increased in both parsimony (bootstrap) and Bayesian (posterior probability) frameworks. Taxa for which DNA data were lacking could be placed in fully resolved positions. Experiments using the parsimony ratchet indicated that placement of these morphology-only taxa may have been completely accurate 30% of the time, to within three nodes of accuracy 60% of time, and accurate to genus 96% of the time. Accurate placement of morphology-only taxa through Bayesian analysis may require extensive effort devoted toward exploring tree and parameter space. We conclude that the increasingly available large morphological data sets associated with interactive keys or informatics initiatives represent convenient yet potentially powerful tools in overcoming many of the commonly encountered obstacles in molecular-based species-level phylogenetics. Difficulties with obtaining complete species-level phylogenies include (1) the accurate identification and sampling of species, (2) obtaining a complete species sampling, and (3) resolving relationships among closely related species. We addressed these in a study of 317 species and subspecies of the African Restionaceae. Accurate species identification and collection in the field was facilitated by a morphology-based interactive key to all species. Despite intensive fieldwork, however, material for DNA extraction could not be obtained for 20 of the 292 species of the focal Restio subclade. Furthermore, the 6831 aligned nucleotides and 1685 parsimonyinformative sequence characters were insufficient to resolve relationships fully within the clade. A simulation indicated that an additional 5000-7000 bases may have been needed to achieve s...
There are several ways to extract information about the evolutionary ecology of clades from their phylogenies. Of these, character state optimization and 'ancestor reconstruction' are perhaps the most widely used despite their being fraught with assumptions and potential pitfalls. Requirements for robust inferences of ancestral traits in general (i.e. those applicable to all types of characters) include accurate and robust phylogenetic hypotheses, complete species-level sampling and the appropriate choice of optimality criterion. Ecological characters, however, also require careful consideration of methods for accounting for intraspecific variability. Such methods include 'Presence Coding' and 'Polymorphism Coding' for discrete ecological characters, and 'Range Coding' and 'MaxMin Coding' for continuously variable characters. Ultimately, however, historical inferences such as these are, as with phylogenetic inference itself, associated with a degree of uncertainty. Statistically based uncertainty estimates are available within the context of model-based inference (e.g. maximum likelihood and Bayesian); however, these measures are only as reliable as the chosen model is appropriate. Although generally thought to preclude the possibility of measuring relative uncertainty or support for alternative possible reconstructions, certain useful non-statistical support measures (i.e. 'Sharkey support' and 'Parsimony support') are applicable to parsimony reconstructions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
334 Leonard St
Brooklyn, NY 11211
Copyright © 2023 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.