Miles J. McKenna

Delimitation of the Segregate Genera of Maytenus s. l. (Celastraceae) Based on Morphological and Molecular Characters

Abstract Maytenus s. l. (including Gymnosporia) is a morphologically diverse genus of about 300 species that is widely distributed in the tropics and subtropics of both the Old and New Worlds. Its delimitation has been extensively debated and despite the segregation of Gymnosporia, Maytenus s. s. remains a heterogeneous, polyphyletic group. To delimit natural segregate genera we increased taxon sampling and generated sequences from two nuclear gene regions (ITS and 26S rDNA) and two plastid loci (matK and trnL-F) to analyze together with morphological characters. Both Moya and Tricerma were found to be nested within the New World Maytenus and are recognized as synonyms of Maytenus s. s.. In contrast, the three New World species of Gymnosporia are recognized as a new genus that is closely related to Gyminda. Haydenia is erected for these three species: H. gentryi, H. haberiana , and H. urbaniana . One or more previously proposed or novel genera are required to accommodate the systematically difficult African Maytenus. Putterlickia, and most likely Gloveria, are nested within Gymnosporia and should be synonymized with that genus. New binomials are required for four Chinese and one Rapan species of Gymnosporia that have been previously treated only as Maytenus: Gymnosporia austroyunnanensis, G. confertiflora, G. dongfangensis, G. guangxiensis , and G. pertinax . Austral-Pacific Maytenus are transferred to Denhamia, requiring eight new binomials: Denhamia bilocularis, D. cunninghamii, D. cupularis, D. disperma, D. fasciculiflora, D. ferdinandii, D. fournieri , and D. silvestris . Existing intrageneric classifications of Gymnosporia and Maytenus s. s. were not supported in their entirety. Gymnosporia is inferred to have had an African origin followed by dispersals to Madagascar, southeast Asia and the Austral-Pacific.

Evaluating multiple criteria for species delimitation: an empirical example using Hawaiian palms (Arecaceae: Pritchardia).

BackgroundRobust species delimitations are fundamental for conservation, evolutionary, and systematic studies, but they can be difficult to estimate, particularly in rapid and recent radiations. The consensus that species concepts aim to identify evolutionarily distinct lineages is clear, but the criteria used to distinguish evolutionary lineages differ based on the perceived importance of the various characteristics of evolving populations. We examined three different species-delimitation criteria (monophyly, absence of genetic intermediates, and diagnosability) to determine whether currently recognized species of Hawaiian Pritchardia are distinct lineages.ResultsData from plastid and nuclear genes, microsatellite loci, and morphological characters resulted in various levels of lineage subdivision that were likely caused by differing evolutionary rates between data sources. Additionally, taxonomic entities may be confounded because of the effects of incomplete lineage sorting and/or gene flow. A coalescent species tree was largely congruent with the simultaneous analysis, consistent with the idea that incomplete lineage sorting did not mislead our results. Furthermore, gene flow among populations of sympatric lineages likely explains the admixture and lack of resolution between those groups.ConclusionsDelimiting Hawaiian Pritchardia species remains difficult but the ability to understand the influence of the evolutionary processes of incomplete lineage sorting and hybridization allow for mechanisms driving species diversity to be inferred. These processes likely extend to speciation in other Hawaiian angiosperm groups and the biota in general and must be explicitly accounted for in species delimitation.

Phylogeny of Celastraceae tribe Euonymeae inferred from morphological characters and nuclear and plastid genes

The phylogeny of Celastraceae tribe Euonymeae (≈ 230 species in eight genera in both the Old and New Worlds) was inferred using morphological characters together with plastid (matK, trnL-F) and nuclear (ITS and 26S rDNA) genes. Tribe Euonymeae has been defined as those genera of Celastraceae with generally opposite leaves, isomerous carpels, loculicidally dehiscent capsules, and arillate seeds (except Microtropis). Euonymus is the most diverse (129 species) and widely cultivated genus in the tribe. We infer that tribe Euonymeae consists of at least six separate lineages within Celastraceae and that a revised natural classification of the family is needed. Microtropis and Quetzalia are inferred to be distinct sister groups that together are sister to Zinowiewia. The endangered Monimopetalum chinense is an isolated and early derived lineage of Celastraceae that represents an important component of phylogenetic diversity within the family. Hedraianthera is sister to Brassiantha, and we describe a second species (Brassiantha hedraiantheroides A.J. Ford) that represents the first reported occurrence of this genus in Australia. Euonymus globularis, from eastern Australia, is sister to Menepetalum, which is endemic to New Caledonia, and we erect a new genus (Dinghoua R.H. Archer) for it. The Madagascan species of Euonymus are sister to Pleurostylia and recognized as a distinct genus (Astrocassine ined.). Glyptopetalum, Torralbasia, and Xylonymus are all closely related to Euonymus sensu stricto and are questionably distinct from it. Current intrageneric classifications of Euonymus are not completely natural and require revision.

Geographic and taxonomic disparities in species diversity: dispersal and diversification rates across Wallace's line.

Broad‐scale patterns of species diversity have received much attention in the literature, yet the mechanisms behind their formation may not explain species richness disparities across small spatial scales. Few taxa display high species diversity on either side of Wallaces Line and our understanding of the processes causing this biogeographical pattern remains limited, particularly in plant lineages. To understand the evolution of this biogeographical pattern, a time‐calibrated molecular phylogeny of Livistoninae palms (Arecaceae) was used to infer the colonization history of the Sahul tectonic plate region and to test for disparities in diversification rates across taxa and across each side of Wallaces Line. Our analyses allowed us to examine how timing, migration history, and shifts in diversification rates have contributed to shape the biogeographical pattern observed in Livistoninae. We inferred that each of the three genera found in Sahul crossed Wallaces Line only once and relatively recently. In addition, at least two of the three dispersing genera underwent an elevation in their diversification rate leading to high species richness on each side of Wallacea. The correspondence of our results with Southeast Asian geologic and climatic history show how palms emerge as excellent models for understanding the historical formation of fine‐scale biogeographic patterns in a phylogenetic framework.

Phylogeny of Celastraceae Subfamilies Cassinoideae and Tripterygioideae Inferred from Morphological Characters and Nuclear and Plastid Loci

Abstract The phylogeny of Celastraceae subfamilies Cassinoideae (120 species in 17 genera in both the Old and New World tropics and subtropics) and Tripterygioideae (39 species in seven genera) was inferred using plastid (matK, trnL-F) and nuclear (ITS and 26S rDNA) loci together with morphological characters. Subfamily Cassinoideae include those Celastraceae genera with drupes, berries, or nuts that have one to five locules and one to two seeds per locule, while Tripterygioideae include those genera with one to two seeded samaras that lack arillate seeds. We infer that both subfamilies are grossly polyphyletic groups, with Cassinoideae consisting of ≥ eight separate lineages and Tripterygioideae consisting of ≥ six separate lineages. Crossopetalum, from tropical America, is part of an early derived lineage sister to a taxonomically diverse Austral-Pacific clade. Myginda is not distinct from Crossopetalum. Gyminda + Orthosphenia + Rzedowskia + Schaefferia are a clade that is only distantly related to Crossopetalum. The monotypic Hartogiopsis is in a clade with other Madagascan genera and sister to the more widely distributed Pleurostylia. Fraunhofera and Plenckia are a clade nested within New World Maytenus; taxonomic changes are required for ≥ one of these genera. Platypterocarpus is part of a primarily African clade and is only distantly related to Tripterygium and Wimmeria.

Telomeres and Telomerase in the Radiation Response: Implications for Instability, Reprograming, and Carcinogenesis

Telomeres are nucleoprotein complexes comprised of tandem arrays of repetitive DNA sequence that serve to protect chromosomal termini from inappropriate degradation, as well as to prevent these natural DNA ends from being recognized as broken DNA (double-strand breaks) and triggering of inappropriate DNA damage responses. Preservation of telomere length requires telomerase, the specialized reverse transcriptase capable of maintaining telomere length via template-mediated addition of telomeric repeats onto the ends of newly synthesized chromosomes. Loss of either end-capping function or telomere length maintenance has been associated with genomic instability or senescence in a variety of settings; therefore, telomeres and telomerase have well-established connections to cancer and aging. It has long been recognized that oxidative stress promotes shortening of telomeres, and that telomerase activity is a radiation-inducible function. However, the effects of ionizing radiation (IR) exposure on telomeres per se are much less well understood and appreciated. To gain a deeper understanding of the roles, telomeres and telomerase play in the response of human cells to IRs of different qualities, we tracked changes in telomeric end-capping function, telomere length, and telomerase activity in panels of mammary epithelial and hematopoietic cell lines exposed to low linear energy transfer (LET) gamma(γ)-rays or high LET, high charge, high energy (HZE) particles, delivered either acutely or at low dose rates. In addition to demonstrating that dysfunctional telomeres contribute to IR-induced mutation frequencies and genome instability, we reveal non-canonical roles for telomerase, in that telomerase activity was required for IR-induced enrichment of mammary epithelial putative stem/progenitor cell populations, a finding also suggestive of cellular reprograming. Taken together, the results reported here establish the critical importance of telomeres and telomerase in the radiation response and, as such, have compelling implications not only for accelerated tumor repopulation following radiation therapy but also for carcinogenic potential following low dose exposures as well, including those of relevance to spaceflight-associated galactic cosmic radiations.

Chromosomal and telomeric biomarkers of normal tissue injury to evaluate risk of degenerative health effects (secondary malignancy, cardiovascular disease) post radiation therapy

An overall intent of radiotherapy is to precisely target tumor cells, while minimizing exposures to surrounding normal tissue. Despite successes in this area, there is growing concern that an unacceptably large volume of normal tissue is unavoidably exposed. Chromosome aberrations provide a direct measure of ionizing radiation (IR)-induced DNA damage, as well as an indirect measure of future risk since they are associated with virtually all known cancers. Such structural variants (SVs) include translocations (rearrangements between chromosomes) and inversions (rearrangements within chromosomes), the latter being recently identified as part of a distinctive mutational signature associated with radiation therapyinduced second malignancies. Directional Genomic Hybridization (dGH), is a strand-specific cytogenomicsbased methodology for cell-by-cell, high-resolution detection of all SVs—particularly inversions—which when combined with compatible telomere probes, can also be used to assess telomere length dynamics, as well as validate a variety of changes involving chromosomal termini. Telomeres are critical structural elements that serve to protect the physical ends of chromosomes. Dysfunctional telomeres are associated with instability and carcinogenesis, as well as with a variety of other age-related degenerative pathologies, including cardiovascular disease (CVD). We introduce Telomere-dGH (Telo-dGH) as a prospective “personalized” approach for monitoring of radiation oncology patients, in order to evaluate chromosomal and telomeric alterations as biomarkers of normal tissue injury. Such a strategy has the potential to improve both evaluation and management of risk associated with degenerative late effects across a variety of cancer types (e.g., prostate, pediatric brain), and in connection with various radiation treatment modalities [e.g., intensity-modulated radiation therapy (IMRT), protons, carbon ions].

Telomeres and NextGen CO-FISH: Directional Genomic Hybridization (Telo-dGH™).

The cytogenomics-based methodology of Directional Genomic Hybridization (dGH™) emerged from the concept of strand-specific hybridization, first made possible by Chromosome Orientation FISH (CO-FISH), the utility of which was demonstrated in a variety of early applications, often involving telomeres. Similar to standard whole chromosome painting (FISH), dGH™ is capable of identifying inter-chromosomal rearrangements (translocations between chromosomes), but its distinctive strength stems from its ability to detect intra-chromosomal rearrangements (inversions within chromosomes), and to do so at higher resolution than previously possible. dGH™ brings together the strand specificity and directionality of CO-FISH with sophisticated bioinformatics-based oligonucleotide probe design to unique sequences. dGH™ serves not only as a powerful discovery tool-capable of interrogating the entire genome at the megabase level-it can also be used for high-resolution targeted detection of known inversions, a valuable attribute in both research and clinical settings. Detection of chromosomal inversions, particularly small ones, poses a formidable challenge for more traditional cytogenetic approaches, especially when they occur near the ends or telomeric regions. Here, we describe Telo-dGH™, a strand-specific scheme that utilizes dGH™ in combination with telomere CO-FISH to differentiate between terminal exchange events, specifically terminal inversions, and an altogether different form of genetic recombination that often occurs near the telomere, namely sister chromatid exchange (SCE).