Table of Contents

24 July 2017, Volume 55 Issue 4
Cover illustration: Biodiversity Cyberbank as the world's primary biodiversity data repository and containing important cybertaxonomy tools, proposed by Wen et al., pp. 308–321 in this issue.
  • Reviews
  • Richard J. Abbott
    J Syst Evol. 2017, 55(4): 238-258.
    Environmental gradients are very common and many plant species respond to them through adaptive genetic change. This can be a first step along a continuum of change that leads ultimately to the origin of fully reproductively isolated forms, i.e., ‘biological species’. Before complete reproductive isolation is achieved, hybrid zones may form between divergent lineages either through primary intergradation or secondary contact. Here, I review the literature on plant hybrid zones between native species and highlight: mode of origin (primary intergradation versus secondary contact); distribution among plant families, genera and life form; type and genotypic composition related to strength and type of reproductive isolation between parental lineages; nature of prezygotic and postzygotic reproductive barriers; level and direction of gene flow; and the stability of hybrid zones in the face of climate change. The total number of plant hybrid zones detected in a literature search was surprisingly small (137). This was the case even for areas of the world with a long history of research into plant evolution, ecology and systematics. Reasons for this are discussed, including the possibility that plant hybrid zones are naturally rare in the wild. Only for a few hybrid zones have attempts been made to distinguish between formation by primary intergradation or secondary contact, and it is assumed that most hybrid zones originate through secondary contact. From the limited information available, it appears that plant hybrid zones may frequently move in response to climate change, but long-term studies are required to confirm this.
  • Robert J. Soreng, Paul M. Peterson, Konstantin Romaschenko, Gerrit Davidse, Jordan K. Teisher, Lynn G. Clark, Patricia Barberá, Lynn J. Gillespie, Fernando O. Zuloaga
    J Syst Evol. 2017, 55(4): 259-290.
    We present a new worldwide phylogenetic classification of 11 506 grass species in 768 genera, 12 subfamilies, seven supertribes, 52 tribes, five supersubtribes, and 90 subtribes; and compare two phylogenetic classifications of the grass family published in 2015 (Soreng et al. and Kellogg). The subfamilies (in descending order based on the number of species) are Pooideae with 3968 species in 202 genera, 15 tribes, and 30 subtribes; Panicoideae with 3241 species in 247 genera, 13 tribes, and 19 subtribes; Bambusoideae with 1670 species in 125 genera, three tribes, and 15 subtribes; Chloridoideae with 1602 species in 124 genera, five tribes, and 26 subtribes; Aristidoideae with 367 species in three genera, and one tribe; Danthonioideae with 292 species in 19 genera, and one tribe; Micrairoideae with 184 species in eight genera, and three tribes; Oryzoideae with 115 species in 19 genera, four tribes, and two subtribes; Arundinoideae with 40 species in 14 genera, two tribes, and two subtribes; Pharoideae with 12 species in three genera, and one tribe; Puelioideae with 11 species in two genera, and two tribes; and the Anomochlooideae with four species in two genera, and two tribes. We also include a radial tree illustrating the hierarchical relationships among the subtribes, tribes, and subfamilies. Newly described taxa include: supertribes Melicodae and Nardodae; supersubtribes Agrostidodinae, Boutelouodinae, Gouiniodinae, Loliodinae, and Poodinae; and subtribes Echinopogoninae and Ventenatinae.
  • W. John Kress
    J Syst Evol. 2017, 55(4): 291-307.
    DNA barcodes have provided a new biological tool for organismal biologists to increase their understanding of the natural world. Over the last decade four plant DNA barcode markers, rbcL, matK, trnH-psbA, and ITS2, have been developed, tested, and used to address basic questions in systematics, ecology, evolutionary biology and conservation, including community assembly, species interaction networks, taxonomic discovery, and assessing priority areas for environmental protection. Forensic investigators have also applied these plant DNA barcodes in the regulatory areas of traffic in endangered species and monitoring commercial products, such as foods and herbal supplements. Major challenges ahead will focus on building the global plant DNA barcode library and adopting genomic sequencing technologies for a more efficient and cost-effective workflow in applying these genetic identification markers to additional fields of biological and commercial endeavors.
  • Jun Wen, AJ Harris, Stefanie M. Ickert-Bond, Rebecca Dikow, Kenneth Wurdack, Elizabeth A. Zimmer
    J Syst Evol. 2017, 55(4): 308-321.
    Systematics is the science of discovering, organizing and interpreting the diversity of all living organisms. Recent developments in genomics and biodiversity informatics are transforming systematics and have opened up many new opportunities. Major digitization efforts and developments in biodiversity informatics have helped the systematics community explore ways to enhance the efficiency in organizing, publishing, and utilizing systematic information. At the same time, genomics is rapidly facilitating construction of the tree of life, improving taxonomic classification, and disentangling complex evolutionary histories. In the informatics and genomics era, systematics has an incredible capacity to integrate with computational and exploratory platforms for discovery as well as with other, related disciplines while maintaining its core strengths in biological collections and morphology. We call for the establishment of a new global cyberinfrastructure or Biodiversity Cyberbank that will function as the main repository of many types of biodiversity data to ensure the long-term sustainability of the vast and growing amount of systematic data. This Biodiversity Cyberbank will contain new and efficient analytical pipelines for systematics research, especially for efficiently generating taxonomic treatments (revisions, e-monographs and floras). Integrative systematics requires the training of the next-generation systematists with taxonomic, phylogenomic and informatics skills to address grand questions about biodiversity and its assembly and continue to develop the Biodiversity Cyberbank. Integrative systematics must also proactively educate the public and policy makers on the importance of systematics and collections for addressing the biodiversity crisis of the Anthropocene, and a Biodiversity Cyberbank may represent one powerful tool for outreach.
  • Ling Fang, Frederik Leliaert, Zhen-Hua Zhang, David Penny, Bo-Jian Zhong
    J Syst Evol. 2017, 55(4): 322-332.
    Green plants comprise two main clades: the Streptophyta, which include charophyte green algae and the embryophytic land plants, and the Chlorophyta including a wide diversity of marine, freshwater, and terrestrial green algae. Establishing a robust phylogeny is important to provide an evolutionary framework for comparative and functional studies. During the last two decades our understanding of the evolution of green algae has profoundly changed, first by phylogenetic analyses of nuclear ribosomal sequence data (mainly 18S), and more recently by analyses of multi-gene and chloroplast genomic data. The phylogenetic relationships among the main streptophytan lineages have been extensively studied and are now relatively well resolved. Although a lot of progress has been made in the last few years, the phylogenetic relationships in the Chlorophyta are still less well established. Here we review how chloroplast genomic data have contributed to address relationships among the main chlorophytan lineages. We highlight recent progress and conflicts among different studies, and discuss future directions in chloroplast phylogenomics of green algae.
  • Susanne S. Renner, Jochen Heinrichs,Aretuza Sousa
    J Syst Evol. 2017, 55(4): 333-339.
    The three bryophyte lineages have long-lived gametophytes that are either bisexual, producing both male- and female gametes, or sexually specialized and then producing only one type of gamete. Phylogenies suggest repeated evolutionary switches between these systems, implying that bryophyte sex chromosomes may have been gained and lost repeatedly. How this occurred is poorly understood, even though plant sex chromosomes were first discovered in liverworts. We explain how the sex chromosomes of haploid-dominant organisms are distinct from the better-studied X-Y and Z-W systems in the tree of life, summarise what is known about their distribution and genetic composition, and present new cytogenetic data for Frullania dilatata and Plagiochila asplenioides, the former with two U chromosomes and one V chromosome, the latter with one U chromosome and two V chromosomes; male and female C-values in F. dilatata are correspondingly asymmetric (the C-value of P. asplenioides is only known for female nuclei). So far, there is a lack of high-throughput sequencing, quantification, and in situ study of the repetitive DNA, organellar DNA, and transposable elements, and it is therefore not known what causes the size difference of U and V chromosomes from the autosomes or each other. Heterochromatin was also first discovered in bryophytes, but its function in their sex regulation has not been addressed. Studies of bryophyte sex chromosomes with combined cytogenetic and genomic approaches are fundamental for a fuller understanding of sex chromosome evolution across the tree of life.
  • Jonathan P. Spoelhof, Pamela S. Soltis, Douglas E. Soltis
    J Syst Evol. 2017, 55(4): 340-352.
    Polyploidy (whole-genome duplication, WGD) is an integral feature of eukaryotic evolution with two main forms typically recognized, autopolyploidy and allopolyploidy. In plants, a growing body of research contradicts historical assumptions that autopolyploidy is both infrequent and inconsequential in comparison to allopolyploidy. However, the legacy of these assumptions still persists through a lack of research on central facets of autopolyploid evolution. This review highlights recent research that has significantly increased scientific understanding of autopolyploidy. Key advances include: 1) unreduced female gametes contribute disproportionally to polyploidization through the formation of triploids, 2) niche divergence in autopolyploids can occur immediately or gradually after WGD through a diverse set of mechanisms, but broad niche overlap is also common between diploids and autopolyploids, and 3) the degree of genomic and transcriptomic changes following WGD is lower in autopolyploids than allopolyploids, but is highly variable both within and between species in both types of polyploids. We discuss the implications of these and other recent findings, present promising systems for future research, and advocate for expanded research in diverse areas of autopolyploid evolution.
  • Research Articles
  • Harald Schneider, Hong-Mei Liu, Yan-Fen Chang, Daniel Ohlsen, Leon R. Perrie, Lara Shepherd, Michael Kessler, Dirk Karger, Sabine Hennequin, Jeannine Marquardt, Stephen Russell, Stephen Ansell, Ngan Thi Lu, Peris Kamau, Josmaily Lóriga Pineiro, Ledis Regalado, Jochen Heinrichs, Atsushi Ebihara, Alan R. Smith, Mary Gibby
    J Syst Evol. 2017, 55(4): 353-364.
    Polyploidy is widely considered as a major process in the evolution of plants but the accumulation of polyploid species diversity is still controversial. Some recent studies proposed increased extinction risk in neopolyploids compared with their diploid ancestors. The high proportion of polyploid ferns is expected to be formed mainly by neopolyploids, whereas paleopolyploid species are predicted to be clustered in clades founded by whole genome duplications. Here, we test this prediction by exploring the evolution of polyploidy in the derived fern family Aspleniaceae. The family has a global distribution and shows the highest frequency of polyploid taxa among all ferns. To test the hypothesis, we obtained a comprehensive phylogeny using chloroplast DNA sequences of 883 specimens representing 292 species. All published chromosome counts were mapped onto this phylogenetic framework in order to explore the evolution of polyploids. We recovered evidence for several whole genome duplications in the history of Aspleniaceae. Phylogenetic relationships of polyploids exceeding the tetraploid level suggest that tetraploid Asplenium species may have replaced their diploid ancestors as the main evolutionary players in some clades of this family.
  • Sue Sherman-Broyles, Aureliano Bombarely, Jeff Doyle
    J Syst Evol. 2017, 55(4): 365-376.
    Allopolyploidy is a common feature in many angiosperm genera. The perennial wild relatives of soybean in the genus Glycine include at least nine recently formed (within the last million years) allopolyploid taxa. This study examined three allopolyploid and four diploid progenitor taxa using genome-wide single nucleotide polymorphisms (SNPs) and network analysis. Genotyping by sequencing (GBS) was used to generate SNPs and results were compared with previous analyses from transcriptome data. Three lanes of Illumina sequencing produced genotypes for 70 accessions and an alignment of 22 806 SNPs across eight taxa with no missing data. The alignment combined with network analysis confirmed results from previous studies. In addition, the extended sampling made possible by GBS identified accessions that have either been misclassified or samples that came from mixed seed stocks. The most intriguing results are the discovery of previously unrecognized substructure within diploid taxa, and the likelihood that allopolyploids were derived from particular subgroups. Separation of allopolyploid SNPs into SNPs derived from homoeologous progenitor species indicate that allopolyploids no longer share genotypes with their diploid progenitors but have evolved separately long enough for signals from direct progenitor genotypes to be obscured.
  • Zhe Cai, Song Ge
    J Syst Evol. 2017, 55(4): 377-384.
    Phytoliths, as one of the important sources of microfossils, have been widely used in paleobotany-related studies, especially in the grass family (Poaceae) where abundant phytoliths are found. Despite great efforts, several challenges remain when phytoliths are used in various studies, including the accurate description of phytolith morphology and the effective utilization of phytolith traits in taxon identification or discrimination. In this study, we analyzed over 1000 phytolith samples from 18 taxa representing seven main genera in the tribe Oryzeae (subfamily Ehrhartoideae) and five taxa in the subfamilies Bambusoideae and Pooideae. By focusing on Oryzeae, which has been extensively investigated in terms of taxonomy and phylogeny, we were able to evaluate the discrimination power of phytoliths at lower taxonomic levels in grasses. With the help of morphometric analysis and by introducing several machine learning algorithms, we found that 87.7% of the phytolith samples could be classified correctly at the genus level. In spite of slightly different performances, all four machine learning algorithms significantly increased the resolving power of phytolith evidence in taxon identification and discrimination compared with the traditional phytolith analysis. Therefore, we propose a pipeline of phytolith analyses based on machine learning algorithms, including data collection, morphometric analysis, model building, and taxon discrimination. The methodology and pipeline presented here should be applied to various studies across different groups of plants. This study provides new insights into the utilization of phytoliths in evolutionary and ecology studies involving grasses and plants in general.
  • Robabeh Shahi Shavvon, Shahrokh Kazempour Osaloo, Ali Asghar Maassoumii, Farideh Moharrek, Seher Karaman Erkul, Alan R. Lemmon, Emily Moriarty Lemmon, Ingo Michalak, Alexandra N. Muellner-Riehl, Adrien Favre
    J Syst Evol. 2017, 55(4): 385-404.
    The origin and evolution of alpine biota are not yet fully understood, particularly in the vast Asian mountain regions. In addition, in these regions, most studies have concentrated on taxa occurring in areas benefitting from relatively generous rainfall from the summer monsoon. In this study, we collected a large number of Oxytropisspecies throughout their distribution range, and investigated the taxonomy and evolution of this diverse legume genus, which also occurs in mountainous areas prone to drought. Using nuclear (ITS) and plastid (trnL-F) markers, we reconstructed phylogenetic relationships within Oxytropis, conducting maximum parsimony, fasttree-like, maximum likelihood, Bayesian, and BEAST analyses. We also used Anchored Hybrid Enrichment (AHE) to test the power of this method to resolve relationships among a small subset of Oxytropis species. For AHE, we sampled eight species and obtained 527 low-copy and orthologous nuclear loci. We show that the taxonomy of this genus that radiated explosively in Asian mountains will remain recalcitrant based on conventional molecular methods. Because of a severe lack of resolution, none of the available taxonomic treatments for Oxytropis could either be confirmed or refuted based upon ITS and trnL-F. Nevertheless, we confirm the status of several species, and identify morphological or genetic particularities for some groups of species. The AHE approach yielded a highly supported phylogenetic tree, suggesting that increased taxon sampling coupled with AHE methods promise advances in the study of the taxonomy and evolution of Oxytropis, thus providing further analytical opportunities, such as diversification rate and biogeographical analyses.
  • Short Communication
  • Jennifer R. Mandel, Michael S. Barker, Randall J. Bayer, Rebecca B. Dikow, Tian-Gang Gao, Katy E. Jones, Sterling Keeley, Norbert Kilian, Hong Ma, CarolinaM. Siniscalchi, Alfonso Susanna, Ramhari Thapa, Linda Watson, Vicki A. Funk
    J Syst Evol. 2017, 55(4): 405-410.
    Comprising more than 25 000 species, the Sunflower Family (Compositae or Asteraceae) is the largest family of flowering plants. Many of its lineages have experienced recent and rapid radiations, and the family has a deep and widespread history of large-scale gene duplications and polyploidy. Many of the most important evolutionary questions about the family's diversity remain unanswered due to poor resolution and lack of support for major nodes of the phylogeny. Our group has employed a phylogenomics approach using Hyb-Seq that includes sequencing ∼1000 low-copy number nuclear markers, plus partial plastomes for large numbers of species. Here we discuss our progress to date and present two phylogenies comprising nine subfamilies and 25 tribes using concatenated and coalescence-based analyses. We discuss future plans for incorporating high-quality reference genomes and transcriptomes to advance systematic and evolutionary studies in the Compositae. While we have made great strides toward developing tools for employing phylogenomics and resolving relationships within Compositae, much work remains. Recently formed global partnerships will work to solve the unanswered evolutionary questions for this megafamily.