三种外来入侵斑潜蝇种间竞争研究进展

美洲斑潜蝇、南美斑潜蝇、三叶斑潜蝇是危害蔬菜、花卉的世界性大害虫。不同种间相互更替或取代的现象时有发生。根据国内外相关研究报道,综述了对近年来3种斑潜蝇种间竞争的研究。对斑潜蝇种间更替和取代现象的分析显示,生殖干扰、新生物型的出现、天敌、生态位、寄主植物以及抗药性等因素可能是影响它们种间竞争的关键。以期为斑潜蝇种群演替研究及防治策略制定提供参考。     

Recovery of Bacillus thuringiensis in vegetative form from the phylloplane of clover (Trifolium hybridum) during a growing season

Two media were developed which specifically allow the cultivation of Bacillus thuringiensis while it is in the vegetative as opposed to the spore form. Using these media B. thuringiensis was shown conclusively for the first time to exist in an active form on the phylloplane. The profile of its appearance in vegetative and spore form was followed over a growing season on clover (Trifolium hybridum) in the field. Three simultaneous and sudden rises and declines of both spore and vegetative cell densities were observed. The most common other spore-former on these leaves was Bacillus cereus but the fluctuations in appearance of these two very closely related species were not co-incident. Using specific PCR primers a considerable diversity of cry toxin gene types was found in isolates that had been recovered in vegetative form ('vegetative isolates') with the majority possessing multiple delta-endotoxin genes while some had only one of those tested. Bioassays against a lepidopteran insect of purified delta-endotoxins showed that they were no more potent than those from a laboratory-adapted strain. PCR primers for an internal region of the vip3A gene produced amplification in 70% of the vegetative isolates compared to 25% of the laboratory-adapted strains tested.     

Asexual propagation in the coral reef macroalga Halimeda (Chlorophyta, Bryopsidales): production, dispersal and attachment of small fragments

Siphonous, green macroalgae of the genus Halimeda are ubiquitous and ecologically important in tropical and subtropical marine environments. It has been hypothesized that the abundance of Halimeda on coral reefs is in part due to the ability of this genus to propagate asexually via vegetative fragmentation. However, vegetative fragmentation has only been documented for H. discoidea in a laboratory setting. To test the hypothesis that vegetative fragmentation contributes to field populations of Halimeda, we examined three aspects of fragmentation by H. tuna (Ellis and Solander) Lamouroux, H. opuntia (Linneaus) Lamouroux and H. goreaui Taylor on Conch Reef in the Florida Keys: (1) short-term (8 days) and long-term (14 weeks) fragment survival and rhizoid production in the laboratory and field (7 and 21 m), (2) size of the fragment pool and (3) influences of herbivory and water motion on production and dispersal of fragments. Although morphologically similar to H. discoidea, only a small percentage of H. tuna fragments survived. Fragments of H. opuntia and H. goreaui were more robust, and survival and rhizoid production were positively correlated with size in short-term trials. In 14-week field trials, one-third or fewer fragments of any species survived at 7 m, potentially because fragments were covered by large amounts of sediment. Survivors included some buried, seemingly dead individuals that turned green when exposed to light, highlighting the remarkable ability of this genus to survive disturbances. There was much less sediment accumulation at 21 m, where more fragments survived. Most (93%) eight-segment fragments of H. opuntia produced attachment rhizoids by the end of the 14-week trial. Overall, a range of 4.7-9.4 fragments of Halimeda m⁻² day⁻¹ were found on Conch Reef; most fragments were generated by H. goreaui. Fish bite marks were evident on 75-85% of the individuals of H. tuna and the number of bites per thallus ranged from 1 to 23. Herbivorous reef fish commonly fed on all three species of Halimeda. Some fish consumed the biomass, while others rejected most bites. For example, 83% of bites were rejected by the blue-striped grunt. Dispersal distances for rejected bites ranged from 0 to 31 m. Water motion was also responsible for fragment dispersal; experimentally produced fragments moved up to 48 cm day⁻¹. Results presented here suggest that asexual propagation of fragments of Halimeda is an important component of the life-history of this genus and vegetative fragmentation contributes to the abundance of this genus on coral reefs.     

Mycoplasma feriruminatoris sp. nov., a fast growing Mycoplasma species isolated from wild Caprinae

Five Mycoplasma strains from wild Caprinae were analyzed: four from Alpine ibex (Capra ibex) which died at the Berlin Zoo between 1993 and 1994, one from a Rocky Mountain goat collected in the USA prior to 1987. These five strains represented a population different from the populations belonging to the ‘Mycoplasma mycoides cluster’ as tested using multi locus sequence typing, Matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis and DNA–DNA hybridization. Analysis of the 16S rRNA gene (rrs), genomic sequence based in silico as well as laboratory DNA–DNA hybridization, and the analysis of phenotypic traits in particular their exceptionally rapid growth all confirmed that they do not belong to any Mycoplasma species described to date. We therefore suggest these strains represent a novel species, for which we propose the name Mycoplasma feriruminatoris sp. nov. The type strain is G5847^T (= DSM 26019^T = NCTC 1362^T).     

Genetic relationship among Paspalum species of the subgenus Anachyris: Taxonomic and evolutionary implications

Paspalum is one of the most important genera of the Poaceae family due to its large number of species and diversity. The subgenus Anachyris comprises six species mainly from South America grouped together by sharing rare spikelet characteristics. A genetic analysis using ISSR markers, compared with the morphological and phenotypic variation observed in each one species, was used to establish genetic relationships among 40 accessions with several ploidy levels, belonging to 5 species of the subgenus Anachyris. Fourteen accessions of Paspalum malacophyllum (2x and 4x), 12 of P. simplex (2x, 3x, 4x and 6x), 4 of P. procurrens (2x and 4x), 4 of P. usterii (4x) and 6 of P. volcanensis (4x) were analysed. A total of 227 ISSR loci (98.7% polymorphic) were detected among all accessions, with variable loci number and percentages of polymorphism according to species delimitations. Six main groups were identified by cluster analysis based on Jaccard's genetic distance and UPGMA, four of which matched all the respective accessions of P. simplex, P. procurrens, P. usterii and P. volcanensis, while the other two were consistent with two different groups of accessions of P. malacophyllum, one involving most tetraploid accessions, and the other one grouping together a tetraploid and two diploid accessions. The distinctive morphological characteristics and the separate clustering of these tetraploid and diploid cytotypes suggest to consider a new multiploid species complex inside the subgenus Anachyris. Both cytotypes of P. procurrens, and the four co-specific cytotypes of P. simplex consistently clustered together forming two specific groups for the two multiploid taxons. This is in agreement with the existence of high phenotypic similarities between diploid and tetraploid cytotypes of P. procurrens, and among diploid, triploid, tetraploid and hexaploid cytotypes of P. simplex. Since the polyploid cytotypes of these species are reproduced by apomixis, the specific genetic clustering by ISSR markers and morphological and cytological results support the hypothesis that the two multiploid species were originated by autopolyploidy. Our results confirm previous studies suggesting a monophyletic origin for the subgenus Anachyris and are concordant with previous data regarding genomic homologies and phylogenetic analyses in the genus.     

Hebeloma species associated with Cistus

The genus Hebeloma has a number of species highly specific to Cistus and others that occur with several host genera. This paper discusses the species of Hebeloma that appear to be ectomycorrhizal with Cistus, judging from their occurrence when Cistus is the only available host. The previously unknown species H. plesiocistum spec. nov. is described. We also provide a key to the known Hebeloma associates of Cistus. Molecular analyses based on ITS sequence data further illustrate the distinctness of the newly described species and difficulties in the species delimitation with view to H. erumpens. Specific associations with Cistus may have evolved more than once within the genus Hebeloma.     

The importance of vegetative and sexual dispersal of Luronium natans

Luronium natans (L.) Rafin. is a very rare macrophyte even though it has the ability to grow in a wide variety of habitat types. Previous studies leave two possibilities for this pattern: the species has a poor ability to disperse and establish or it is unable to grow and develop a sustainable population after colonization.     

The het-c heterokaryon incompatibility gene in Aspergillus niger

Heterokaryon incompatibility among Aspergillus niger strains is a widespread phenomenon that is observed as the inability to form stable heterokaryons. The genetic basis of heterokaryon incompatibility reactions is well established in some sexual filamentous fungi but largely unknown in presumed asexual species, such as A. niger. To test whether the genes that determine heterokaryon incompatibility in Neurospora crassa, such as het-c, vib-1 and pin-c, have a similar function in A. niger, we performed a short in silico search for homologues of these genes in the A. niger and several related genomes. For het-c, pin-c and vib-1 we did indeed identify putative orthologues. We then screened a genetically diverse worldwide collection of incompatible black Aspergilli for polymorphisms in the het-c orthologue. No size variation was observed in the variable het-c indel region that determines the specificity in N. crassa. Sequence comparison showed only minor variation in the number of glutamine coding triplets. However, introduction of one of the three N. crassa alleles (het-c2) in A. niger by transformation resulted in an abortive phenotype, reminiscent of the heterokaryon incompatibility in N. crassa. We conclude that although the genes required are present and the het-c homologue could potentially function as a heterokaryon incompatibility gene, het-c has no direct function in heterokaryon incompatibility in A. niger because the necessary allelic variation is absent.     

Ent-kaurane derivatives from the root cortex of yacon and other three Smallanthus species (Heliantheae,Asteraceae)

The metabolites produced by the secretory canals of the root cortex from four Smallanthus species belonging to the yacon group were identified as ent-kaurane-type diterpenes. The dichloromethane root cortex extracts of the four species were treated with diazomethane and analyzed comparatively by GC–MS using a simple and rapid procedure which is very sensitive and reproducible permitting detection of minor components. In all cases, ent-16-kauren-19-oic acid (kaurenoic acid) methyl ester was the main component, differences being observed only in the minor components. The minor components identified were grandiflorenic acid methyl ester, ent-16-kauren-19-al, 16α,17-epoxy-15α-angeloyloxy-kauran-19-oic acid methyl ester and several O-acyl derivatives at C-15 or C-18 of kaurenoic acid. One of the minor components, 18-isobutyroyloxy-ent-kaur-16-en-19-oic acid is a new kaurenoic acid derivative. Grandiflorenic acid and 15-α-angeloyloxy-16,17-α-epoxy-ent-16-kauren-19-oic acid were present only in Smallanthus sonchifolius and Smallanthus siegesbeckius which showed very similar GC traces. The different GC profile of RC diterpenes from Smallanthus connatus and Smallanthus macroscyphus supports the view that they are different taxa. Some chemotaxonomic aspects of the genus Smallanthus and the subtribe Milleriinae are briefly discussed.     

Hybridizations and genetic relationships among Lindernia species (Scrophulariaceae): L. procumbens and two subspecies of L. dubia

Lindernia procumbens and L. dubia are common annual weeds in flooded rice fields of Japan. Two subspecies of L. dubia, subsp. major and subsp. dubia, are usually recognized in Japan but they are both regarded as synonyms of L. dubia elsewhere. In a cluster analysis based on AFLP, most L. dubia subsp. major formed a separate cluster from L. dubia subsp. dubia although 11% of haplotypes classified using AFLP were not coincident with classification using the shape of leaf bases, which is the commonly used identification trait. Artificial F₁ plants between L. procumbens and L. dubia subsp. major, and between L. procumbens and L. dubia subsp. dubia did not produce seed. Forty percent of capsules produced by F₁ plants from these two subspecies were slimmer and 80% pollen were sterile in slimmer capsules. However, seed number of most F₁ capsules was not different from that of self-fertilized plants, suggesting that there was no complete reproductive isolation between the subspecies. Natural hybridization of these subspecies may have occurred but we are not aware of it because F₁ plants are rare and F₂ plants are indistinguishable from these subspecies.     

A new role for the SHATTERPROOF genes during Arabidopsis gynoecium development

Gynoecium development is a complex process which is regulated by key factors that control the spatial formation of the apical, medial and basal parts. SHATTERPROOF1 (SHP1) and SHP2, two closely related MADS-box genes, redundantly control the differentiation of the dehiscence zone and promote the lignification of adjacent cells. Furthermore, SHP1 and SHP2 have shown to play an important role in ovule identity determination. The present work identifies a new function for these two genes in promoting stigma, style and medial tissue development. This new role was discovered by combining the shp1 shp2 double mutant with the aintegumenta (ant) and crabs claw (crc) mutants. In quadruple mutant flowers, the inner whorl is composed of unfused carpels which lack almost completely apical and medial tissues, a phenotype similar to the previously reported fil ant and lug ant double mutants.     

Phylogenetic diversity of Rhizobium strains nodulating diverse legume species growing in Ethiopia

The taxonomic diversity of thirty-seven Rhizobium strains, isolated from nodules of leguminous trees and herbs growing in Ethiopia, was studied using multilocus sequence analyses (MLSA) of six core and two symbiosis-related genes. Phylogenetic analysis based on the 16S rRNA gene grouped them into five clusters related to nine Rhizobium reference species (99–100% sequence similarity). In addition, two test strains occupied their own independent branches on the phylogenetic tree (AC86a2 along with R. tibeticum; 99.1% similarity and AC100b along with R. multihospitium; 99.5% similarity). One strain from Milletia ferruginea was closely related (>99%) to the genus Shinella, further corroborating earlier findings that nitrogen-fixing bacteria are distributed among phylogenetically unrelated taxa. Sequence analyses of five housekeeping genes also separated the strains into five well-supported clusters, three of which grouped with previously studied Ethiopian common bean rhizobia. Three of the five clusters could potentially be described into new species. Based on the nifH genes, most of the test strains from crop legumes were closely related to several strains of Ethiopian common bean rhizobia and other symbionts of bean plants (R. etli and R. gallicum sv. phaseoli). The grouping of the test strains based on the symbiosis-related genes was not in agreement with the housekeeping genes, signifying differences in their evolutionary history. Our earlier studies revealing a large diversity of Mesorhizobium and Ensifer microsymbionts isolated from Ethiopian legumes, together with the results from the present analysis of Rhizobium strains, suggest that this region might be a potential hotspot for rhizobial biodiversity.     

RPB2 sequences reveal a close phylogenetic relationship between tetraploid Hordelymus and diploid Hordeum species in Triticeae (Poaceae)

The origin of Hordelymus genome has been debated for years, and no consensus conclusion was reached. In this study, we sequenced and analyzed the RPB2 (RNA polymerase subunit II) gene from Hordelymus europaeus (L.) Harz, and its potential diploid ancestor species those were suggested in previous studies. The focus of this study was to examine the phylogenetic relationship of Hordelymus genomes with its potential donor Hordeum, Psathyrostachys, and Taeniatherum species. Two distinguishable copies of sequences were obtained from H. europaeus. The obvious difference between the two copies of sequences is a 24 bp indel (insertion/deletion). Phylogenetic analysis showed a strong affinity between Hordeum genome and Hordelymus with 85% bootstrap support. These results suggested that one genome in tetraploid H. europaeus closely related to the genome in Hordeum species. Another genome in H. europaeus is sister to the genomes in Triticeae species examined here, which corresponds well with the recently published EF-G data. No obvious relationship was found between Hordelymus and either Ta genome donor, Taeniatherum caput-medusae or Ns genome donor, Psathyrostachys juncea. Our data does not support the presence of Ta and Ns genome in H. europaeus, and further confirms that H. europaeus is allopolyploid.     

On the roles of Notch, Delta, kuzbanian, and inscuteable during the development of Drosophila embryonic neuroblast lineages

The generation of cellular diversity in the nervous system involves the mechanism of asymmetric cell division. Besides an array of molecules, including the Par protein cassette, a heterotrimeric G protein signalling complex, Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells. In this context, Notch is required to be active in one sibling and inactive in the other. Here, we investigated the requirement of genes previously known to play key roles in sibling cell fate specification such as members of the Notch signalling pathway, e.g., Notch (N), Delta (Dl), and kuzbanian (kuz) and a crucial regulator of asymmetric cell division, inscuteable (insc) throughout lineage progression of 4 neuroblasts (NB1-1, MP2, NB4-2, and NB7-1). Notch-mediated cell fate specification defects were cell-autonomous and were observed in all neuroblast lineages even in cells born from late ganglion mother cells (GMC) within the lineages. We also show that Dl functions non-autonomously during NB lineage progression and clonal cells do not require Dl from within the clone. This suggests that within a NB lineage Dl is dispensable for sibling cell fate specification. Furthermore, we provide evidence that kuz is involved in sibling cell fate specification in the central nervous system. It is cell-autonomously required in the same postmitotic cells which also depend on Notch function. This indicates that KUZ is required to facilitate a functional Notch signal in the Notch-dependent cell for correct cell fate specification. Finally, we show that three neuroblast lineages (NB1-1, NB4-2, and NB7-1) require insc function for sibling cell fate specification in cells born from early GMCs whereas insc is not required in cells born from later GMCs of the same lineages. Thus, there is differential requirement for insc for cell fate specification depending on the stage of lineage progression of NBs.     

Extension of the breeding season and its effects on fertilization and development in two species of lugworm (Arenicola marina and A. defodiens)

In the autumn/winter breeding polychaetes, Arenicola marina and A. defodiens, spawning can be advanced or delayed by a number of months through temperature manipulation of the adults. However, this manipulation may have significant consequences for fertilization rates and embryo developmental success and so in vitro fertilizations were performed to assess the impact of manipulation. Firstly, we used oocytes and sperm obtained from advanced or delayed individuals. For both species, using gametes from 4 weeks advanced individuals did not result in a significant reduction in development, however, gametes from individuals advanced (A. marina only) or delayed by 8 weeks resulted in significantly fewer embryos developing normally. Reciprocal crosses of temperature-manipulated A. marina gametes (from 4 weeks advanced and 4 weeks delayed individuals) with those at the natural spawning time confirmed that the reduction in developmental success in both was attributable to the oocytes. After 5 h post-fertilization, the majority of oocytes from advanced individuals had fertilized, but by 24 h most were abnormal. For fertilizations with gametes from delayed individuals, nearly 100% of the embryos were developing normally after 24 h, but after 144 h significantly more were abnormal in crosses involving oocytes from delayed females. Although both species have reproductive plasticity to extend their breeding season, the significant reduction in the numbers of competent larvae produced as the spawning is delayed or advanced further may be a significant bottleneck in aquaculture and it may also have considerable implications for the long-term reproductive success of a population in response to environmental change.Sympatric populations of the species exist in many locations and the inherent variability in the breeding seasons could allow spawning times to overlap. Artificially delaying A. marina individuals enabled fertilizations to be performed with A. defodiens at the natural spawning time in the laboratory. Both conspecific fertilizations produced 100% trochophore larvae after 120 h, but A. defodiens oocytes failed to fertilize after incubation with A. marina sperm, in comparison to the A. marina oocytes incubated with A. defodiens sperm where 40% developed to the trochophore stage. This asymmetric gamete incompatibility may be one of a suite of mechanisms to minimise hybridisation.     

Enhanced ultraviolet radiation can terminate sexual reproduction in the broadcasting coral species Acropora cervicornis Lamarck

The effects of enhanced ultraviolet radiation (280-400 nm: UVR) on the fecundity of Acropora cervicornis were measured in field-transplanted colonies from 20 m to 1 m depth and vice versa at La Parguera, Puerto Rico. Fecundity was estimated from histological sections made from tissue samples obtained at different time intervals during the experimental period (March - August 2003). All colonies transplanted from 20 m to 1 m showed a 100% reduction in gonads per mesentery per polyp one month after transplantation, while those transplanted from 1 m to 20 m did not show any significant reduction in fecundity throughout the experimental period. The latter colonies did show however, a delay in the spawning times by releasing their gamete bundles approximately two-three weeks after the controls at 1 m and two months after the controls at 20 m suggesting an induced response as a consequence of changes in their daily light cycle due to less radiation (PAR and UVR) available at 20 m compared to 1 m. Control colonies at 20 m spawned after the full moon of June 2003, while the controls at 1 m spawned 5-6 days after the full moon of July 2003. While a possible reabsorption of the gametes occurred in A. cervicornis colonies transplanted from 20 m to 1 m, the expulsion of these gametes due to the sudden stress caused by the transplantation is not discarded. The results suggest that sudden increases in UVR can completely stop sexual reproduction in ramose broadcasting coral species, which in turn can affect the dominance of the species and the composition and structure of shallow reef environments.