Quantifying the age of recent species divergence events can be challenging in the absence of calibration points within many groups. The katydid species Neoconocephalus lyristes provides the opportunity to calibrate a post-Pleistocene, taxa specific mutation rate using a known biogeographic event, the Mohawk-Hudson Divide. DNA was extracted from pinned museum specimens of N. lyristes from both Midwest and Atlantic populations and the mitochondrial gene COI sequenced using primers designed from extant specimens. Coalescent analyses using both strict and relaxed molecular clock models were performed in BEAST v1.8.2. The assumption of a strict molecular clock could not be rejected in favor of the relaxed clock model as the distribution of the standard deviation of the clock rate strongly abutted zero. The strict molecular clock model resulted in an intraspecific calculated mutation rate of 14.4-17.3 %/myr, a rate substantially higher than the common rates of sequence evolution observed for insect mitochondrial DNA sequences. The rate, however, aligns closely with mutation rates estimated from other taxa with similarly recent lineage divergence times.
Orchidaceae constitutes one of the largest families of angiosperms. Owing to the significance of orchids in plant biology, market needs and current sustainable technology levels, basic research on the biology of orchids and their applications in the orchid industry is increasing. Although chloroplast (cp) genomes continue to be evolutionarily informative, there is very limited information available on orchid chloroplast genomes in public repositories. Here, we report the complete cp genome sequence of Dendrobium nobile from Northeast India (Orchidaceae, Asparagales), bearing the GenBank accession number KX377961, which will provide valuable information for future research on orchid genomics and evolution, as well as the medicinal value of orchids. Phylogenetic analyses using Bayesian methods recovered a monophyletic grouping of all Dendrobium species (D. nobile, D. huoshanense, D. officinale, D. pendulum, D. strongylanthum and D. chrysotoxum). The relationships recovered among the representative orchid species from the four subfamilies, i.e., Cypripedioideae, Epidendroideae, Orchidoideae and Vanilloideae, were consistent within the family Orchidaceae.
Red algae comprise an anciently diverged, species-rich phylum with morphologies that span unicells to large seaweeds. Here, leveraging a rich red algal genome and transcriptome dataset, we used 298 single-copy orthologous nuclear genes from 15 red algal species to erect a robust multi-gene phylogeny of Rhodophyta. This tree places red seaweeds (Bangiophyceae and Florideophyceae) at the base of the mesophilic red algae with the remaining non-seaweed mesophilic lineages forming a well-supported sister group. The early divergence of seaweeds contrasts with the evolution of multicellular land plants and brown algae that are nested among multiple, unicellular or filamentous sister lineages. Using this novel perspective on red algal evolution, we studied the evolution of the pathways for isoprenoid biosynthesis. This analysis revealed losses of the mevalonate pathway on at least three separate occasions in lineages that contain Cyanidioschyzon, Porphyridium, and Chondrus. Our results establish a framework for in-depth studies of the origin and evolution of genes and metabolic pathways in Rhodophyta.
The ancestor of Paulinella chromatophora established a symbiotic relationship with cyanobacteria related to the Prochloroccocus/Synechococcus clade. This event has been described as a second primary endosymbiosis leading to a plastid in the making. Based on the rate of pseudogene disintegration in the endosymbiotic bacteria Buchnera aphidicola, it was suggested that the chromatophore in P. chromatophora has a minimum age of ~60 Myr. Here we revisit this estimation by using a lognormal relaxed molecular clock on the 18S rRNA of P. chromatophora. Our time estimates show that depending on the assumptions made to calibrate the molecular clock, P. chromatophora diverged from heterotrophic Paulinella spp. ~ 90 to 140 Myr ago, thus establishing a maximum date for the origin of the chromatophore.
The katydid genus Neoconocephalus is characterized by high diversity of the acoustic communication system. Both male signals and female preferences have been thoroughly studied in the past. This study used Bayesian character state reconstruction to elucidate the evolutionary history of diverse call traits, based on an existing, well supported phylogenetic hypothesis. The most common male call pattern consisted of continuous calls comprising one fast pulse rate; this pattern is the likely ancestral state in this genus. Three lines of call divergence existed among the species of the genus. First, four species had significantly slower pulse rates. Second, five species had alternating pulse periods, resulting in a double pulse rhythm. Third, several species had discontinuous calls, when pulses were grouped into rhythmically repeated verses. Bayesian character state reconstruction revealed that the double-pulse pattern likely evolved convergently five times; the slow pulse rate also evolved four times independently. Discontinuous calls have evolved twice and occur in two clades; each of which contains reversals to the ancestral continuous calls. Pairwise phylogenetically independent contrast analyses among the three call traits found no significant correlations among the character states of the different traits, supporting the independent evolution of the three call traits.
Phylogenetic trees are used by researchers across multiple fields of study to display historical relationships between organisms or genes. Trees are used to examine the speciation process in evolutionary biology, to classify families of viruses in epidemiology, to demonstrate co-speciation in host and pathogen studies, and to explore genetic changes occurring during the disease process in cancer, among other applications. Due to their complexity and the amount of data they present in visual form, phylogenetic trees have generally been difficult to render for publication and challenging to directly interact with in digital form. To address these limitations, we developed PhyloPen, an experimental novel multi-touch and pen application that renders a phylogenetic tree and allows users to interactively navigate within the tree, examining nodes, branches, and auxiliary information, and annotate the tree for note-taking and collaboration. We present a discussion of the interactions implemented in PhyloPen and the results of a formative study that examines how the application was received after use by practicing biologists — faculty members and graduate students in the discipline. These results are to be later used for a fully supported implementation of the software where the community will be welcomed to participate in its development.
Recently developed molecular methods enable geneticists to target and sequence thousands of orthologous loci and infer evolutionary relationships across the tree of life. Large numbers of genetic markers benefit species tree inference but visual inspection of alignment quality, as traditionally conducted, is challenging with thousands of loci. Furthermore, due to the impracticality of repeated visual inspection with alternative filtering criteria, the potential consequences of using datasets with different degrees of missing data remain nominally explored in most empirical phylogenomic studies. In this short communication, I describe a flexible high-throughput pipeline designed to assess alignment quality and filter exonic sequence data for subsequent inference. The stringency criteria for alignment quality and missing data can be adapted based on the expected level of sequence divergence. Each alignment is automatically evaluated based on the stringency criteria specified, significantly reducing the number of alignments that require visual inspection. By developing a rapid method for alignment filtering and quality assessment, the consistency of phylogenetic estimation based on exonic sequence alignments can be further explored across distinct inference methods, while accounting for different degrees of missing data.
Incomplete lineage sorting (ILS), modelled by the multi-species coalescent, is a process that results in a gene tree being different from the species tree. Because ILS is expected to occur for at least some loci within genome-scale analyses, the evaluation of species tree estimation methods in the presence of ILS is of great interest. Performance on simulated and biological data have suggested that concatenation analyses can result in the wrong tree with high support under some conditions, and a recent theoretical result by Roch and Steel proved that concatenation using unpartitioned maximum likelihood analysis can be statistically inconsistent in the presence of ILS. In this study, we survey the major species tree estimation methods, including the newly proposed “statistical binning” methods, and discuss their theoretical properties. We also note that there are two interpretations of the term “statistical consistency”, and discuss the theoretical results proven under both interpretations.
Phylogeneticists have long understood that several biological processes can cause a gene tree to disagree with its species tree. In recent years, molecular phylogeneticists have increasingly foregone traditional supermatrix approaches in favor of species tree methods that account for one such source of error, incomplete lineage sorting (ILS). While gene tree-species tree discordance no doubt poses a significant challenge to phylogenetic inference with molecular data, researchers have only recently begun to systematically evaluate the relative accuracy of traditional and ILS-sensitive methods. Here, we report on simulations demonstrating that concatenation can perform as well or better than methods that attempt to account for sources of error introduced by ILS. Based on these and similar results from other researchers, we argue that concatenation remains a useful component of the phylogeneticist’s toolbox and highlight that phylogeneticists should continue to make explicit comparisons of results produced by contemporaneous and classical methods.