Species delimitation and hybridization history of a hazel species complex

Background and AimsHybridization increases species adaptation and biodiversity but also obscures species boundaries. In this study, species delimitation and hybridization history were examined within one Chinese hazel species complex (Corylus chinensis–Corylus fargesii). Two species including four varieties have already been described for this complex, with overlapping distributions.MethodsA total of 322 trees from 44 populations of these four varieties across their ranges were sampled for morphological and molecular analyses. Climatic datasets based on 108 geographical locations were used to evaluate their niche differentiations. Flowering phenology was also observed for two co-occurring species or varieties.Key ResultsFour statistically different phenotypic clusters were revealed, but these clusters were highly inconsistent with the traditional taxonomic groups. All the clusters showed statistically distinct niches, with complete or partial geographical isolation. Only two clusters displayed a distributional overlap, but they had distinct flowering phenologies at the site where they co-occurred. Population-level evidence based on the genotypes of ten simple sequence repeat loci supported four phenotypic clusters. In addition, one cluster was shown to have an admixed genetic composition derived from the other three clusters through repeated historical hybridizations.ConclusionsBased on our new evidence, it is better to treat the four clusters identified here as four independent species. One of them was shown to have an admixed genetic composition derived from the other three through repeated historical hybridizations. This study highlights the importance of applying integrative and statistical methods to infer species delimitations and hybridization history. Such a protocol should be adopted widely for future taxonomic studies.     

Overdominant epistatic loci are the primary genetic basis of inbreeding depression and heterosis in rice. I. Biomass and grain yield

To understand the genetic basis of inbreeding depression and heterosis in rice, main-effect and epistatic QTL associated with inbreeding depression and heterosis for grain yield and biomass in five related rice mapping populations were investigated using a complete RFLP linkage map of 182 markers, replicated phenotyping experiments, and the mixed model approach. The mapping populations included 254 F(10) recombinant inbred lines derived from a cross between Lemont (japonica) and Teqing (indica) and two BC and two testcross hybrid populations derived from crosses between the RILs and their parents plus two testers (Zhong 413 and IR64). For both BY and GY, there was significant inbreeding depression detected in the RI population and a high level of heterosis in each of the BC and testcross hybrid populations. The mean performance of the BC or testcross hybrids was largely determined by their heterosis measurements. The hybrid breakdown (part of inbreeding depression) values of individual RILs were negatively associated with the heterosis measurements of their BC or testcross hybrids, indicating the partial genetic overlap of genes causing hybrid breakdown and heterosis in rice. A large number of epistatic QTL pairs and a few main-effect QTL were identified, which were responsible for >65% of the phenotypic variation of BY and GY in each of the populations with the former explaining a much greater portion of the variation. Two conclusions concerning the loci associated with inbreeding depression and heterosis in rice were reached from our results. First, most QTL associated with inbreeding depression and heterosis in rice appeared to be involved in epistasis. Second, most ( approximately 90%) QTL contributing to heterosis appeared to be overdominant. These observations tend to implicate epistasis and overdominance, rather than dominance, as the major genetic basis of heterosis in rice. The implications of our results in rice evolution and improvement are discussed.     

Microbiological Processes in a High-Temperature Oil Field

Thermophilic sulfate-reducing bacteria (SRB) oxidizing lactate, butyrate, and C₁₂–C₁₆ n-alkanes of oil at a temperature of 90°C were isolated from samples of water and oil originating from oil reservoirs of the White Tiger high-temperature oil field (Vietnam). At the same time, no thermophiles were detected in the injected seawater, which contained mesophilic microorganisms and was the site of low-temperature processes of sulfate reduction and methanogenesis. Thermophilic SRB were also found in samples of liquid taken from various engineering reservoirs used for oil storage, treatment, and transportation. These samples also contained mesophilic SRB, methanogens, aerobic oil-oxidizing bacteria, and heterotrophs. Rates of bacterial production of hydrogen sulfide varied from 0.11 to 2069.63 at 30°C and from 1.18 to 173.86 at 70°C g S/(l day); and those of methane production, varied from 58.4 to 100 629.8 nl CH₄/(l day) (at 30°C). The sulfur isotopic compositions of sulfates contained in reservoir waters and of hydrogen sulfide of the accompanying gas indicate that bacterial sulfate reduction might be effective in the depth of the oil field.     

Molecular phylogeny of Old World monkeys (Cercopithecidae) as inferred from gamma-globin DNA sequences

DNA sequence data of the nuclear-encoded gamma1-gamma2-globin duplication region were used to examine the phylogenetic relationships of 16 cercopithecid (Old World monkey) species representing 12 extant genera. Morphology- and molecular-based hypotheses of Old World monkey branching patterns are generally congruent, except for generic relationships within the subtribe Papionina. The cercopithecids divide into colobines (leaf-eating monkeys) and cercopithecines (cheek-pouched monkeys). The colobines examined by the DNA data divide into an Asian clade (Nasalis, proboscis monkeys; Trachypithecus, langurs) and an African clade (Colobus, colobus monkeys). The cercopithecines divide into tribes Cercopithecini (Erythrocebus, patas monkey; Chlorocebus, green monkeys; Cercopithecus, guenons) and Papionini. Papionins divide into subtribes Macacina (Macaca, macaques) and Papionina (Papio, hamadryas baboons; Mandrillus, drills and mandrills; Theropithecus, gelada baboons; Lophocebus, arboreal mangabeys; Cercocebus, terrestrial mangabeys). In a morphologically based classification, Mandrillus is a subgenus of Papio, whereas Lophocebus is a subgenus of Cercocebus. In contrast, the molecular evidence treats Mandrillus as a subgenus of Cercocebus, and treats both Theropithecus and Lophocebus as subgenera of Papio. Local molecular clock divergence time estimates were used as a yardstick in a "rank equals age" system to propose a reduction in taxonomic rank for most clades within Cercopithecidae.     

小鼠原生殖细胞的研究进展

在动物的整个生命周期中,生殖细胞提供了各代间的连续性。对于多数动物来说,其生殖细胞不是在生殖腺中产生的,其前身原生殖细胞（ＰｒｉｍｏｒｄｉａｌＧｅｒｍＣｅｌ简称ＰＧＣ）是迁移到正在发育着的生殖腺中的。近年来,由于ＰＧＣ体外培养技术的不断完善,ＰＧＣ的...     

Structure and diversity of the mitochondrial gene pool of the aboriginal population of Tuva and Buriatia from restriction polymorphism data

The populations of Tuvinians (N = 36) and Buryats (N = 105) were characterized by using the data on mitochondrial DNA (mtDNA) polymorphism. The gene pools of both ethnic groups possessed the mtDNA types belonging to the four main haplogroups, A, B, C, and D, found only in the indigenous populations of Asia and America. The total frequencies of the A, B, C, and D haplogroups in Tuvinians and Buryats were 72.3% and 52.4%, respectively. These values, along with the frequency for Altai populations (57.2%), were highest in the Asian populations studied, indicating that the populations Southern and Eastern Siberia can be considered as ancestral relatives to the ethnic groups of the New World. Analysis of the mtDNA region V polymorphism showed the presence of 9-bp deletion and 4-bp insertion in both populations with frequencies respectively of 13.9 and 5.56% in Tuvinians and 4.8 and 1.9% in Buryats. The frequency of the +AvaII/8249 variant was 11.1% in Tuvinians and 3.81% in Buryats. Analysis of the association between the region V deletion-insertion polymorphism and certain restriction haplogroups pointed to repeated and independent emergence of the 4-bp insertion in Siberia.