Climatic niche divergence explains angiosperm diversification across clades in China

Diversification rates are critically important for understanding patterns of species richness among clades. However, the effects of climatic niche width on plant diversification rates remain to be elucidated. Based on the phylogenetic, climatic, and distributional information of angiosperms in China, a total of 26 906 species from 182 families were included in this study. We aimed to test relationships between diversification rate and climatic niche width and climatic niche width related variables (including climatic niche divergence, climatic niche position, geographic extent, and climatic niche evolutionary rate) using phylogenetic methods. We found that climatic niche divergence had the largest unique contribution to the diversification rate, while the unique effects of climatic niche width, climatic niche position, geographic extent, and climatic niche evolutionary rate on the diversification rate were negligible. We also observed that the relationship between diversification rate and climatic niche divergence was significantly stronger than the null assumption (artefactual relationship between diversification and clade-level climatic niche width by sampling more species). Our study supports the hypothesis that wider family climatic niche widths explain faster diversification rates through a higher climatic niche divergence rather than through higher geographic extent, higher climatic niche evolutionary rate, or separated climatic niche position. Hence, the results provide a potential explanation for large-scale diversity patterns within families of plants.     

Solid-phase microextraction and cuticular hydrocarbon differences related to reproductive activity in juniper bark borer Semanotus bifasciatus Motschulsky

Cuticular hydrocarbons of Cerambycidae species can function as signals for sex recognition. Little is known about the copulatory signals of the juniper bark borer Semanotus bifasciatus, a major economic threat to Platycladus orientalis Franco in China. Here, we investigated the cuticular hydrocarbons of both sexes of S. bifasciatus to determine the chemically mediated mating signals using the solid-phase microextraction (SPME) technique with carbowax/divinylbenzene fibers (CAR/DVB) and then analyzed by coupled gas chromatography-mass spectrometry (GC-MS). A series of aliphatic saturated straight-chain n-alkanes (n-C₂₃ to n-C₂₈), internally branched monomethylalkanes at carbons 3, 11, or 13, and dimethylalkanes were identified, which showed no qualitative differences in either sex and were similar in the samples with SPME fiber extraction and those with hexane extraction. The bioassay showed that 11-methylpentacosane (11-MeC₂₅), 11-methylhexacosane (11-MeC₂₆), and 11-methylheptacosane (11-MeC₂₇) have sex-specific recognition functions that triggered more mating attempts at a female-specific ratio of 100:4:60 than at a male-specific ratio of 100:85:50. In addition, the female-specific ratio of 11-methylalkanes can elicit about 70% of male mating attempts within about 60 s, whereas live females elicit about 98% of male mating attempts within 25 s. The discrepancy in the initiation of mating attempts by synthetic mixtures and live females suggests that the methyl isomers 3-MeC₂₅, 3-MeC₂₇, and/or 11,15-diMeC₂₇ may also be involved in the mating behavior of S. bifasciatus. These results suggest that 11-MeC₂₅, 11-MeC₂₆, and 11-MeC₂₇ constitute the contact sex pheromone of S. bifasciatus, with the presence or absence of 11-MeC₂₆ in particular playing an important role in mate recognition by males.     

Systematics of Mukdenia and Oresitrophe (Saxifragaceae): Insights from genome skimming data

Oresitrophe and Mukdenia (Saxifragaceae) are epilithic sister genera used in traditional Chinese medicine. The taxonomy of Mukdenia, especially of M. acanthifolia, has been controversial. To address this, we produced plastid and mitochondrial data using genome skimming for Mukdenia acanthifolia and Mukdenia rossii, including three individuals of each species. We assembled complete plastomes, mitochondrial CDS and nuclear ribosomal ETS/ITS sequences using these data. Comparative analysis shows that the plastomes of Mukdenia and Oresitrophe are relatively conservative in terms of genome size, structure, gene content, RNA editing sites and codon usage. Five plastid regions that represent hotspots of change (trnH-psbA, psbC-trnS, trnM-atpE, petA-psbJ and ccsA-ndhD) are identified within Mukdenia, and six regions (trnH-psbA, petN-psbM, trnM-atpE, rps16-trnQ, ycf1 and ndhF) contain a higher number of species-specific parsimony-informative sites that may serve as potential DNA barcodes for species identification. To infer phylogenetic relationships between Mukdenia and Oresitrophe, we combined our data with published data based on three different datasets. The monophyly of each species (Oresitrophe rupifraga, M. acanthifolia and M. rossii) and the inferred topology ((M. rossii, M. acanthifolia), O. rupifraga) are well supported in trees reconstructed using the complete plastome sequences, but M. acanthifolia and M. rossii did not form a separate clade in the trees based on ETS + ITS data, while the mitochondrial CDS trees are not well-resolved. We found low recovery of genes in the Angiosperms353 target enrichment panel from our unenriched genome skimming data. Hybridization or incomplete lineage sorting may be the cause of discordance between trees reconstructed from organellar and nuclear data. Considering its morphological distinctiveness and our molecular phylogenetic results, we strongly recommend that M. acanthifolia be treated as a distinct species.     

Charged-particle mutagenesis. 1. Cytotoxic and mutagenic effects of high-LET charged iron particles on human skin fibroblasts.

Cytotoxic and mutagenic effects of high-LET charged iron (56Fe) particles were measured quantitatively using primary cultures of human skin fibroblasts. Argon and lanthanum particles and gamma rays were used in comparative studies. The span of LETs selected was from 150 keV/microns (330 MeV/u) to 920 keV/microns (600 MeV/u). Mutations were scored at the hypoxanthine guanine phosphoribosyl transferase (HPRT) locus using 6-thio-guanine (6-TG) for selection. Exposure to these high-LET charged particles resulted in exponential survival curves. Mutation induction, however, was fitted by the linear model. The relative biological effectiveness (RBE) for cell killing ranged from 3.7 to 1.3, while that for mutation induction ranged from 5.7 to 0.5. Both the RBE for cell killing and the RBE for mutagenesis decreased with increasing LET over the range of 1.50 to 920 keV/microns. The inactivation cross section (sigma i) and the action cross section for mutation induction (sigma m) ranged from 32.9 to 92.0 microns2 and 1.45 to 5.56 X 10(-3) microns2; the maximum values were obtained by 56Fe with an LET of 200 keV/microns. The mutagenicity (sigma m/sigma i) ranged from 2.05 to 7.99 X 10(-5) with an inverse relationship to LET.