Influence of spatial structure on the maintenance of sexual reproduction

We include spatial extension into a model for the maintenance of sexual reproduction introduced recently. The model is based on a broad spectrum of resources, which regrow slowly. Other key features of the model are that sexual reproduction sets in when resources become scarce and that only a few genotypes can coexist locally. The extension of the model to several patches in space is done in two different ways. Model A is based on central egg deposition and allows migration of juveniles into all patches. Model B has a one-dimensional array of patches with migration only between neighboring patches. The main findings are that wide dispersal favors asexuals, while for slower migration there is a wide range of parameter values for which sexually reproducing species always win against asexuals. These results are conform with major patterns for the distribution of parthenogenesis in animals and plants, i.e. the prevalence of parthenogenetic reproduction in minute species, which are easily dispersed by physical forces, such as protists and small metazoans including e.g. bdelloid rotifers, tardigrades and nematodes.     

Molecular phylogeny of oribatid mites (Oribatida, Acari): evidence for multiple radiations of parthenogenetic lineages

Nucleotide sequences of the D3 expansion segment and its flanking regions of the 28S rDNA gene were used to evaluate phylogenetic relationships among representative sexual and asexual oribatid mites (Oribatida, Acariformes). The aim of this study was to investigate the hypothesis that oribatid mites consist of species-rich clusters of asexual species that may have radiated while being parthenogenetic. Furthermore, the systematic position of the astigmate mites (Astigmata, Acariformes) which have been hypothesised to represent a paedomorphic lineage within the oribatid mites, is investigated. This is the first phylogenetic tree for oribatid mites s.l. (incl. Astigmata) based on nucleotide sequences. Intraspecific genetic variation in the D3 region was very low, confirming the hypothesis that this region is a good species marker. Results from neighbour joining (NJ) and maximum parsimony (MP) algorithms indicate that several species-rich parthenogenetic groups like Camisiidae, Nanhermanniidae and Malaconothridae are monophyletic, consistent with the hypothesis that some oribatid mite groups diversified despite being parthenogenetic. The MP and maximum likelihood (ML) method indicated that the D3 region is a good tool for elucidating the relationship of oribatid mite species on a small scale(genera, families) but is not reliable for large-scale taxonomy, because branches from the NJ algorithm collapsed in the MP and ML tree. In all trees calculated by different algorithms the Astigmata clustered within the oribatid mites, as proposed earlier.     

Fertilized eggs obtained from transplantation of frozen ovaries and parthenogenesis in combination with artificial insemination of frozen semen of the silkworm,Bombyx mori

A reliable method is reported for the long-term preservation of ovaries and spermatozoa of the silkworm (Bombyx mori). Three studies are presented. In the first, ovaries were removed from larvae at either 3rd, 4th, or 5th instar, cryopreserved, and stored in liquid nitrogen. Thawed ovaries were transplanted to surgically castrated female larvae at the same or a different developmental stage. The highest percentage of recipient females producing eggs resulted into either 3rd or 4th instar larvae (respectively, 22.1 and 8.7%). Similarly, the highest levels of other measurements of successful cryopreservation and transplanted ovary, and number of eggs laid, occurred with the same combination of donor and recipient developmental stages. Other combinations of ovary/recipient developmental stages yielded lower results. In the second experiment, semen was collected from male moths, cryopreserved, and then thawed semen was diluted with trypsin solution and artificially inseminated into females obtained from the best conditions of first experiment. A small percentage of inseminated moths laid eggs (8-10.3%) compared to that of controls (100%). In addition, the fertility of eggs from experimental moths was lower than that of control females (respectively, 40.3-88% and 97.5%). In the third experiment, eggs were surgically removed from ovarian tubules of moth following transplantation of thawed ovaries and subjected to parthenogenetic activation and artificial hatching. As expected, all resulting moths were female and, following natural mating or artificial insemination with thawed semen, yielded normal offspring at high rates.     

Radiation in sexual and parthenogenetic oribatid mites (Oribatida, Acari) as indicated by genetic divergence of closely related species

The D3 domain and its flanking regions of 28S rRNA of four pairs of closely related sexual species (Eupelops hirtus and E. torulosus; Oribatella calcarata and O. quadricornuta; Chamobates voigtsi and Ch. borealis; Liacarus coracinus and L. subterraneus) and four pairs of closely related parthenogenetic species (Nanhermannia nana and Na. coronata; Nothrus silvestris and No. palustris; Tectocepheus sarekensis and T. minor; Camisia spinifer and Ca. segnis) of oribatid mites were sequenced to investigate (1) if the D3 region can be used as a species marker and (2) if there is genetic variation among closely related species pairs and if its magnitude is related to reproductive mode. Furthermore, we investigated the world-wide genetic variation of the D3 region from the oribatid mite species Platynothrus peltifer. There was no intraspecific genetic variation in the D3 region in any of the species studied; it was even identical in two closely related parthenogenetic species (Na. nana and Na. coronata) and two closely related sexual species (E. hirtus and E. torulosus). The genetic differences of the other species pairs indicated that both parthenogenetic and sexual lineages have various ages. On average, however, the differences between the closely related parthenogenetic species were larger than those between closely related sexual species, indicating that parthenogenetic lineages exist historically and may radiate slower than sexual species. The findings of this study support the hypothesis that some of the parthenogenetic oribatid mite taxa (Tectocepheus, Nothrus) are ‘ancient asexuals’. The absence of intraspecific or intra-individual variation in the D3 region of parthenogenetic species is consistent with the presence of concerted evolution in the 28S rRNA gene. From this we infer the existence of a meiotic process, which is consistent with the automixy known from several other parthenogenetic oribatid species. This revised version was published online in July 2006 with corrections to the Cover Date.     

标记辅助选择在水稻改良中的应用前景

标记辅助选择在水稻改良中的应用前景郑康乐（中国水稻研究所,杭州３１０００６）黄宁（国际水稻研究所,马尼拉１０９９）ＯｕｔｌｏｏｋｏｎｔｈｅＡｐｐｌｉｃａｔｉｏｎｏｆＭａｒｋｅｒ－ａｓｉｓｔｅｄＳｅｌｅｃｔｉｏｎｉｎＲｉｃｅＩｍｐｒｏｖｅｍｅｎｔＺｈｅ...     

韭菜未传粉子房培养中单倍体的胚胎发生和植株再生

在自然生长条件下,韭菜反足细胞可与合子同时分裂形成多细胞原胚,但很快退化,种子成熟时仅含有合子胚。在未传粉子房培养条件下,反足细胞和卵细胞可经相似的早期胚胎发生过程再生单倍体植株。高频率的胚胎发生为韭菜单倍体育种提供了一条新途径。文中讨论了反足细胞无配子生殖的有关问题。     

Inheritance of parthenogenesis in Poa pratensis L.: auxin test and AFLP linkage analyses support monogenic control

 Gametophytic apomixis in Kentucky bluegrass (Poa pratensis L.) involves the parthenogenetic development of unreduced eggs from aposporic embryo sacs. Attempts to transfer the apomictic trait beyond natural sexual barriers require further elucidation of its inheritance. Controlled crosses were made between sexual clones and apomictic genotypes, and the parthenogenetic capacity of (poly)diploid hybrids was ascertained by the auxin test. A bulked segregant analysis with RAPD and AFLP markers was then used to identify a genetic linkage group related to the apomictic mode of reproduction. This approach enabled us to detect both an AFLP marker located 6.6 cM from the gene that putatively controls parthenogenesis and a 15.4-cM genomic window surrounding the target locus. A map of the P. pratensis chromosome region carrying the gene of interest was constructed using additional RAPD and AFLP markers that co-segregated with the parthenogenesis locus. Highly significant linkage between parthenogenesis and a number of AFLP markers that also appeared to belong to a tight linkage block strengthens the hypothesis of monogenic inheritance of this trait. If a single gene is assumed, apomictic polyploid types of P. pratensis would be simplex for a dominant allele that confers parthenogenesis, and this genetic model would be further supported by the bimodal distribution of the degree of parthenogenesis exhibited in the (poly)diploid progenies from sexual x apomictic matings. The molecular tagging of apomixis in P. pratensis is an essential step towards marker-assisted breeding and map-based cloning strategies aimed at investigating and manipulating its mode of reproduction. Received: 13 January 1998 / Accepted: 19 January 1998     

Differential effects of protein synthesis inhibitors on porcine oocyte activation

This study was designed to evaluate the effects of cycloheximide and puromycin on activation and protein synthesis of porcine oocytes. When matured oocytes were electrostimulated, then cultured in the presence of cycloheximide (5 μ/ml) for 6 or 24 hr, 92% of oocytes were activated as indicated by pronuclear formation, vs. 2.8% for untreated oocytes, 5.3% for oocytes not electrostimulated but cultured with cycloheximide, and 60.0% for those only electrostimulated. When cultured with L-[³⁵S]methionine in the presence of cycloheximide, puromycin (100 μg/ml), or no protein synthesis inhibitor for 24 hr, oocytes had mean radiolabeled incorporation rates of 36.5, 2.21, and 32.0 fmol/4 hr/oocyte, respectively. Thus, cycloheximide had little effect on protein synthesis after 24 hr of culture. A 1D-SDS PAGE showed that oocytes cultured with puromycin or cycloheximide are not activated, while electrostimulated oocytes are activated, as characterized by the conversion of a 25-kDa polypeptide to a 22-kDa polypeptide. The radiolabeling experiment was repeated, except that oocytes were cultured for 4 or 24 hr. At 4 hr, mean incorporation rates were lower in the cycloheximide group (2.34 fmol/4 hr/oocyte), but similar in the puromycin (15.7 fmol/4 hr/oocyte) and control groups (18.9 fmol/4 hr/oocyte). At 24 hr, the puromycin group (5.73 fmol/4 hr/oocyte) had a lower rate of incorporation, while the cycloheximide (22.6 fmol/4 hr/oocyte) and control (26.0 fmol/4 hr/oocyte) groups were similar. Cycloheximide was more effective earlier during culture, while puromycin was more effective later. When combined with ES, puromycin did have a higher rate (P = 0.10) of activation (87.8%) than with electrostimulation alone (73.0%). A final experiment evaluated the development to blastocyst after transfer to a ligated oviduct. Cycloheximide treatment in conjunction with an electric pulse did not increase the rate of compact morula or blastocyst formation. In conclusion, puromycin and cycloheximide have differential effects on protein synthesis, and although cycloheximide alone will not induce activation in porcine oocytes, it is very effective in generating activated oocytes in combination with electrostimulation. © 1995 Wiley-Liss, Inc.     

激光诱发家蚕孤雌生殖的研究：Ⅲ单性一号及单性二号性状表现

采用CO_2激光扩束辐照诱发家蚕孤雌生殖,从获得的单性蚕中,选择出单性一号和单性二号两个类型,单性一号由血色限性突变为斑纹限性,体质强健好养,单性二号仍保持亲本的血色限性,但茧丝质有了提高。     

草地早熟禾无融合生殖现象的研究

本文应用石蜡切片和子房整体染色透明法研究了草地早熟禾(Poa pratensisL.)的无融合生殖现象,结果表明,草地早熟禾的胚胎发育分为两种类型。一种是由孤雌生殖形成胚,即卵细胞分裂较早形成幼胚,少数胚囊中的一个或两个助细胞也分裂较早,同时形成幼胚,但两个极核并不融合,三个反足细胞明显增大。由孤雌生殖形成胚的约占观察总数的66%,其中3%为双胚,仅一个是三胚。在成熟种子中也有两个成熟胚并生的现象。另一种是形成胚和胚乳,约占34%。34%中形成种子有两种可能的途径,一是通过有性生殖形成种子,二是由孤雌生殖形成的胚和极核受精形成的胚乳共同组成的无融合生殖种子。本研究还首次观察到早熟禾完整的双胚囊结构。