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Mon, 16 Nov 2009 15:30:11 PST

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Mon, 16 Nov 2009 15:30:11 PST

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Mon, 16 Nov 2009 15:30:11 PST

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Mon, 16 Nov 2009 15:30:11 PST

Species Tree Discordance Traces to Phylogeographic Clade Boundaries in North American Fence Lizards (Sceloporus)

Leache, A. D. — Mon, 16 Nov 2009 15:30:11 PST

I investigated the impacts of phylogeographic sampling decisions on species tree estimation in the Sceloporus undulatus species group, a recent radiation of small, insectivorous lizards connected by parapatric and peripatric distribution across North America, using a variety of species tree inference methods (Bayesian estimation of species trees, Bayesian untangling of concordance knots, and minimize deep coalescences). Phylogenetic analyses of 16 specimens representing 4 putative species within S. "undulatus" using complete (8 loci, >5.5 kb) and incomplete (29 loci, >23.6 kb) nuclear data sets result in species trees that share features with the mitochondrial DNA (mtDNA) genealogy at the phylogeographic level but provide new insights into the evolutionary history of the species group. The concatenated nuclear data and mtDNA data both recover 4 major clades connecting populations across North America; however, instances of discordance are localized at the contact zones between adjacent phylogeographic groups. A random sub-sampling experiment designed to vary the phylogeographic samples included across hundreds of replicate species tree inferences suggests that inaccurate species assignments can result in inferred phylogenetic relationships that are dependent upon which particular populations are used as exemplars to represent species and can lead to increased estimates of effective population size (). For the phylogeographic data presented here, reassigning specimens with introgressed mtDNA genomes to their prospective species, or excluding them from the analysis altogether, produces species tree topologies that are distinctly different from analyses that utilize mtDNA-based species assignments. Evolutionary biologists working at the interface of phylogeography and phylogenetics are likely to encounter multiple processes influencing gene trees congruence, which increases the relevance of estimating species trees with multilocus nuclear data and models that accommodate deep coalescence.

The Use and Validity of Composite Taxa in Phylogenetic Analysis

Campbell, V., Lapointe, F.-J. — Mon, 16 Nov 2009 15:30:11 PST

In phylogenetic analysis, one possible approach to minimize missing data in DNA supermatrices consists in sampling sequences from different species to obtain a complete sequence for all genes included in the study. We refer to those complete sequences as composite taxa because DNA sequences that are combined belong to different species. An alternative approach is to analyze incomplete supermatrices by coding unavailable DNA sequences as missing. The accuracy of phylogenetic trees estimated using matrices that include composite taxa has recently been questioned, and the best approach for analyzing incomplete supermatrices is highly debated. Through computer simulations, we compared the phylogenetic accuracy of the 2 competing approaches. We explored the effect of composite taxa when inferring higher level relationships, that is, relationships between monophyletic groups. DNA sequences were simulated on a 42-taxon model tree and incomplete supermatrices containing different percentages of missing data were generated. These incomplete supermatrices were analyzed either by coding the missing data with "?" or by reducing the amount of missing data through the combination of 2 or more taxa to generate composite taxa. Of 180 comparisons (18 simulation cases with 2 different inference methods and 5 levels of incompleteness), we observed significantly higher phylogenetic accuracies for composite matrices in 46 comparisons, whereas missing data matrices outperformed composites in 8 comparisons. In all other cases, the phylogenetic accuracy obtained with composite matrices was not significantly different from that of missing data matrices. This study demonstrates that composite taxa represent an interesting approach to minimize the amount of missing data in supermatrices and we suggest that it is the optimal approach to use in phylogenomic studies to reduce computing time.

Radiation of Extant Cetaceans Driven by Restructuring of the Oceans

Mon, 16 Nov 2009 15:30:11 PST

The remarkable fossil record of whales and dolphins (Cetacea) has made them an exemplar of macroevolution. Although their overall adaptive transition from terrestrial to fully aquatic organisms is well known, this is not true for the radiation of modern whales. Here, we explore the diversification of extant cetaceans by constructing a robust molecular phylogeny that includes 87 of 89 extant species. The phylogeny and divergence times are derived from nuclear and mitochondrial markers, calibrated with fossils. We find that the toothed whales are monophyletic, suggesting that echolocation evolved only once early in that lineage some 36–34 Ma. The rorqual family (Balaenopteridae) is restored with the exclusion of the gray whale, suggesting that gulp feeding evolved 18–16 Ma. Delphinida, comprising all living dolphins and porpoises other than the Ganges/Indus dolphins, originated about 26 Ma; it contains the taxonomically rich delphinids, which began diversifying less than 11 Ma. We tested 2 hypothesized drivers of the extant cetacean radiation by assessing the tempo of lineage accumulation through time. We find no support for a rapid burst of speciation early in the history of extant whales, contrasting with expectations of an adaptive radiation model. However, we do find support for increased diversification rates during periods of pronounced physical restructuring of the oceans. The results imply that paleogeographic and paleoceanographic changes, such as closure of major seaways, have influenced the dynamics of radiation in extant cetaceans.

Taxon Selection under Split Diversity

Minh, B. Q., Klaere, S., von Haeseler, A. — Mon, 16 Nov 2009 15:30:11 PST

The "phylogenetic diversity" (PD) measure of biodiversity is evaluated using a phylogenetic tree, usually inferred from morphological or molecular data. Consequently, it is vulnerable to errors in that tree, including those resulting from sampling error, model misspecification, or conflicting signals. To improve the robustness of PD, we can evaluate the measure using either a collection (or distribution) of trees or a phylogenetic network. Recently, it has been shown that these 2 approaches are equivalent but that the problem of maximizing PD in the general concept is NP-hard. In this study, we provide an efficient dynamic programming algorithm for maximizing PD when splits in the trees or network form a circular split system. We illustrate our method using a case study of game birds ("Galliformes") and discuss the different choices of taxa based on our approach and PD.

Estimating Trait-Dependent Speciation and Extinction Rates from Incompletely Resolved Phylogenies

FitzJohn, R. G., Maddison, W. P., Otto, S. P. — Mon, 16 Nov 2009 15:30:11 PST

Species traits may influence rates of speciation and extinction, affecting both the patterns of diversification among lineages and the distribution of traits among species. Existing likelihood approaches for detecting differential diversification require complete phylogenies; that is, every extant species must be present in a well-resolved phylogeny. We developed 2 likelihood methods that can be used to infer the effect of a trait on speciation and extinction without complete phylogenetic information, generalizing the recent binary-state speciation and extinction method. Our approaches can be used where a phylogeny can be reasonably assumed to be a random sample of extant species or where all extant species are included but some are assigned only to terminal unresolved clades. We explored the effects of decreasing phylogenetic resolution on the ability of our approach to detect differential diversification within a Bayesian framework using simulated phylogenies. Differential diversification caused by an asymmetry in speciation rates was nearly as well detected with only 50% of extant species phylogenetically resolved as with complete phylogenetic knowledge. We demonstrate our unresolved clade method with an analysis of sexual dimorphism and diversification in shorebirds (Charadriiformes). Our methods allow for the direct estimation of the effect of a trait on speciation and extinction rates using incompletely resolved phylogenies.

Reticulation, Data Combination, and Inferring Evolutionary History: An Example from Danthonioideae (Poaceae)

Pirie, M. D., Humphreys, A. M., Barker, N. P., Linder, H. P. — Mon, 16 Nov 2009 15:30:11 PST

We explore the potential impact of conflicting gene trees on inferences of evolutionary history above the species level. When conflict between gene trees is discovered, it is common practice either to analyze the data separately or to combine the data having excluded the conflicting taxa or data partitions for those taxa (which are then recoded as missing). We demonstrate an alternative approach, which involves duplicating conflicting taxa in the matrix, such that each duplicate is represented by one partition only. This allows the combination of all available data in standard phylogenetic analyses, despite reticulations. We show how interpretation of contradictory gene trees can lead to conflicting inferences of both morphological evolution and biogeographic history, using the example of the pampas grasses, Cortaderia. The characteristic morphological syndrome of Cortaderia can be inferred as having arisen multiple times (chloroplast DNA [cpDNA]) or just once (nuclear ribosomal DNA [nrDNA]). The distributions of species of Cortaderia and related genera in Australia/New Guinea, New Zealand, and South America can be explained by few (nrDNA) or several (cpDNA) dispersals between the southern continents. These contradictions can be explained by past hybridization events, which have linked gains of complex morphologies with unrelated chloroplast lineages and have erased evidence of dispersals from the nuclear genome. Given the discrepancies between inferences based on the gene trees individually, we urge the use of approaches such as ours that take multiple gene trees into account.

Heritability of Extinction Rates Links Diversification Patterns in Molecular Phylogenies and Fossils

Rabosky, D. L. — Mon, 16 Nov 2009 15:30:11 PST

Time-calibrated molecular phylogenies provide a valuable window into the tempo and mode of species diversification, especially for the large number of groups that lack adequate fossil records. Molecular phylogenetic data frequently suggest an initial "explosive speciation" phase, leading to widespread speculation that ecological niche-filling processes might govern the dynamics of species diversification during evolutionary radiations. However, these patterns are difficult to reconcile with the fossil record. The fossil record strongly suggests that extinction rates have been high relative to speciation rates, but such elevated background extinction should erase the signal of early, rapid speciation from molecular phylogenies. For this reason, extinction rates in molecular phylogenies are frequently estimated as zero under the widely used birth–death model. Here, I construct a simple model that combines phylogenetically patterned extinction with pulsed turnover dynamics and constant diversity through time. Using approximate Bayesian methods, I show that heritable extinction can easily explain the phenomenon of explosive early diversification, even when net diversification rates are equal to zero. Several assumptions of the model are more consistent with both the fossil record and neontological data than the standard birth–death model and it may thus represent a viable alternative interpretation of phylogenetic diversification patterns. These results suggest that variation in the absolute rate of lineage turnover through time, in conjunction with phylogenetically nonrandom extinction, may underlie the apparent diversity-dependent speciation observed in molecular phylogenies.

Testing Species-Level Diversification Hypotheses in Madagascar: The Case of Microendemic Brookesia Leaf Chameleons

Townsend, T. M., Vieites, D. R., Glaw, F., Vences, M. — Mon, 16 Nov 2009 15:30:11 PST

Madagascar's flora and fauna are remarkable both for their diversity and supraspecific endemism. Moreover, many taxa contain large numbers of species with limited distributions. Several hypotheses have been proposed to explain this high level of microendemism, including 1) riverine barrier, 2) mountain refuge, and 3) watershed contraction hypotheses, the latter 2 of which center on fragmentation due to climatic shifts associated with Pliocene/Pleistocene glaciations. The Malagasy leaf chameleon genus Brookesia is a speciose group with a high proportion of microendemic taxa, thus making it an excellent candidate to test these vicariance scenarios. We used mitochondrial and nuclear sequence data to construct a Brookesia phylogeny, and temporal concordance with Pliocene/Pleistocene speciation scenarios was tested by estimating divergence dates using a relaxed-clock Bayesian method. We strongly reject a role for Pliocene/Pleistocene climatic fluctuations in species-level diversification of Brookesia. We also used simulations to test the spatial predictions of the watershed contraction model in a phylogenetic context, independent of its temporal component, and found no statistical support for this model. The riverine barrier model is likewise a qualitatively poor fit to our data, but some relationships support a more ancient mountain refuge effect. We assessed support for the 3 hypotheses in a nonphylogenetic context by examining altitude and species richness and found a significant positive correlation between these variables. This is consistent with a mountain refuge effect but does not support the watershed contraction or riverine barrier models. Finally, we find repeated higher level east-west divergence patterns 1) between the 2 sister clades comprising the Brookesia minima group and 2) within the clade of larger leaf chameleons, which shows a basal divergence between western and eastern/northern sister clades. Our results highlight the central role of phylogeny in any meaningful tests of species-level diversification theories.

Stephen Jay Gould: Reflections on His View of Life

Morrison, D. A. — Mon, 16 Nov 2009 15:30:11 PST

Systematics and Taxonomy of Australian Birds

Chesser, R. T. — Mon, 16 Nov 2009 15:30:11 PST

Systematic Biology - current issue

Cover

Editorial Board

Subscriptions

Table of Contents

Announcements

Species Tree Discordance Traces to Phylogeographic Clade Boundaries in North American Fence Lizards (Sceloporus)

The Use and Validity of Composite Taxa in Phylogenetic Analysis

Radiation of Extant Cetaceans Driven by Restructuring of the Oceans

Taxon Selection under Split Diversity

Estimating Trait-Dependent Speciation and Extinction Rates from Incompletely Resolved Phylogenies

Reticulation, Data Combination, and Inferring Evolutionary History: An Example from Danthonioideae (Poaceae)

Heritability of Extinction Rates Links Diversification Patterns in Molecular Phylogenies and Fossils

Testing Species-Level Diversification Hypotheses in Madagascar: The Case of Microendemic Brookesia Leaf Chameleons

Stephen Jay Gould: Reflections on His View of Life

Systematics and Taxonomy of Australian Birds