On the use of genetic divergence for identifying species

Degree of genetic divergence is frequently used to infer that two populations belong to separate species, or that several populations belong to a single species. I explore the logical framework of this approach, including the following assumptions: (i) speciation takes place over very long periods of time; (ii) reproductive isolation is based on the slow accumulation many genetic differences throughout the genome; (iii) genetic divergence automatically leads to reproductive isolation between species; and (iv) pre-mating and post-mating reproductive isolation have a similar genetic basis. I argue that so many exceptions to these assumptions have been demonstrated that they cannot be used with any reliability to distinguish different species. In addition, genetic distance as a species criterion is mostly used within the framework of Mayr's Biological Species Concept and is not free of assumptions about the nature of species or of speciation. The use of genetic distance to infer separate species (or the lack of these) is not parsimonious, its theoretical foundations are not well understood, and it cannot be applied over a wide range of plants and animals. I explore alternative approaches towards solving the species problems normally solved using genetic distance. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 509–516.     

梨不同DNA提取方法的效果研究

以7个梨品种为实验材料,比较分析了SDS法、CTAB法、SDSCTAB法、改良的CTAB法、高盐低pH值法、分步离心法对梨总DNA提取的效果。结果表明:利用以上6种方法提取的梨总DNA在纯度和量上有很大的差别。所得到的平均DNA量从大到小依次为:分步离心法、SDS法、SDSCTAB法、改良的CTAB法、CTAB法、高盐低pH值法。DNA提取纯度依次为分步离心法、SDSCTAB法、改良的CTAB法、高盐低pH值法、CTAB法、SDS法。RAPD和自交不亲和基因(S基因)特异性引物扩增实验结果都比较理想,但分步离心法和SDSCTAB法提取的DNA双酶切效果较好。分步离心法提取的梨总DNA更适用于后续的分子生物学实验操作。     

Homogeneous detection of cyanobacterial DNA via polymerase chain reaction

Aims: To design a primer set enabling the identification through PCR of high‐quality DNA for routine and high‐throughput genomic screening of a diverse range of cyanobacteria. Methods and Results: A codon‐equivalent multiple alignment of the phycocyanin alpha‐subunit coding sequence (cpcA) of 22 cyanobacteria was generated and analysed to produce a single degeneracy primer set with virtually uniform product size. Also, an 18S ribosomal RNA detection set is proposed for rejecting false positives. The primer sets were tested against five diverse cyanobacteria, Chlorella vulgaris, Saccharomyces cerevisiae, and Escherichia coli. All five cyanobacteria showed positive amplification of cpcA product with homogeneous fragment length, and no products were observed for any other organism. Additionally, the only product formation observed for the 18S rRNA set was in C. vulgaris and S. cerevisiae. Conclusions: The newly proposed primer set served as effective check primers for cyanobacteria. Cyanobacteria gDNA had a positive, homogenous result, while other bacteria, eukaryotes and alga tested were negative. Significance and Impact of the Study: These novel, broad‐spectrum primers will greatly increase the utility of PCR on newly discovered cyanobacterial species.     

浙江晚稻稻种非致病细菌多样性初步研究

为了解特定生态环境中晚稻稻种的非致病细菌多样性以更有效地治理水稻主要病害,于1996－2001年间对采自浙江平原、丘陵及山区的606份稻种样本进行了非致病细菌种类、频率及对水稻纹枯病和恶苗病的抑菌作用研究。从中分离出9605个菌株,经致病性测定、菌落形态及部分细菌学特征（革兰氏染色、KMB培养基上的荧光色素和扩散性非荧光色素、YDC培养基上黄色菌落的产生、好气性、鞭毛及芽孢的染色镜检等）测定后,选出代表菌株622个,连同80个对照菌株用Biolog及脂肪酸分析法（FAME）进行测试。鉴定出Pseudomonas属11个种或型及其他14属的23种非致病细菌,并发现Pseudomonas属中55％的种及其他属中49％的种存在对水稻纹枯病或恶苗病的拮抗菌株,但不同种间的抑菌率存在较大差异。3类稻区均以Bacillus spp.、Acinetobacter spp.和P.putida等3个种群为主导并同时存在许多其他相似种,其中7个常见种的分离频率在不同稻区有显著差异。     

Phenylalanine tRNA of Lupinus luteus seeds

Two isoaccepting tRNA^Phe were isolated from yellow lupin seeds by DEAE-cellulose, BD-cellulose and reversed phase chromatography. The products obtained were characterized by aminoacylation and fluorescence. The chromatographic behaviour and some properties of the isolated tRNAs are discussed and compared with the known tRNA^Phe from other sources.     

红曲菌代谢产物中低极性组分的分离及表征

以石油醚∶醋酸乙酯 =4∶1(V/V)作为洗脱剂 ,采用柱层层析粗分离醇溶性红曲菌代谢产物中的低极性组分。经浓缩、结晶除去白色结晶后的浓缩液 ,用正己烷∶醋酸乙酯 =9∶1(V/V)作为展开剂进行薄层层析分离 ,在紫外灯下观察 ,从低极性组分中分离出六个组分 ,分别为 :具荧光组分、两个相隔较近的黄色组分、淡黄色具荧光组分、具浅蓝绿色荧光组分、具荧光组分。各组分的Rf 值分别为 :0 2 9、0 15、0 12、0 0 9、0 0 6、0 0 4。MS测定结果表明 ,Rf 值最大的具荧光组分可能为含有 OH及Br的共轭烯烃或脂肪酮 ,而在紫外灯下呈淡黄色组分为含有 OH的环状化合物。     

Do allopatric male Calopteryx virgo damselflies learn species recognition?

There is a growing amount of empirical evidence that premating reproductive isolation of two closely related species can be reinforced by natural selection arising from avoidance of maladaptive hybridization. However, as an alternative for this popular reinforcement theory, it has been suggested that learning to prefer conspecifics or to discriminate heterospecifics could cause a similar pattern of reinforced premating isolation, but this possibility is much less studied. Here, we report results of a field experiment in which we examined (i) whether allopatric Calopteryx virgo damselfly males that have not encountered heterospecific females of the congener C. splendens initially show discrimination, and (ii) whether C. virgo males learn to discriminate heterospecifics or learn to associate with conspecifics during repeated experimental presentation of females. Our experiment revealed that there was a statistically nonsignificant tendency for C. virgo males to show initial discrimination against heterospecific females but because we did not use sexually naïve individuals in our experiment, we were not able to separate the effect of innate or associative learning. More importantly, however, our study revealed that species discrimination might be further strengthened by learning, especially so that C. virgo males increase their association with conspecific females during repeated presentation trials. The role of learning to discriminate C. splendens females was less clear. We conclude that learning might play a role in species recognition also when individuals are not naïve but have already encountered potential conspecific mates.     

THE GENETICS OF AN ISOLATING MECHANISM BETWEEN TWO SIBLING SPECIES OF DROSOPHILA

Matings between Drosophila simulans females and males of the sibling species D. mauritiana are of abnormally short duration. These rapid matings interrupt the transfer of sperm, leading to substantial reproductive isolation in interspecific as compared to intraspecific copulations. Genetic analysis of this behavior shows that it is influenced much more by the male than the female genotype, with genes from D. simulans being dominant. In males, shortened copulation is caused by interspecific divergence at a minimum of three loci, with one gene on each of the major chromosomes. This is an underestimate of the true number of loci affecting the trait, which could be much larger. The two autosomes have the largest effect, whereas that of the X chromosome is much smaller. The genetic architecture of copulation duration and the larger effect of male than female genotype suggest that females can detect and discriminate against differences in male genitalia.     

Zonation pattern of an isolated mangrove community at Playa Medina,Venezuela

This study focuses on a mangrove system which is completely isolated from the sea, lacking any connecting tidal channels or creeks and far enough from the coastline to prevent tidal flushing. The reason why it has become isolated remains unclear. But it is obvious that this situation may have introduced important changes in soil salinity and hydrological patterns, which might be reflected in the present composition and zonation patterns of the mangrove community. Main findings of this study suggest that: (1) Plant species distribution is affected mainly by water logging and mineral content of soils. (2) Ground water is the only permanent supply of water and salts to the isolated mangrove. (3) Soils are subjected to different degrees of leaching of salts. (4) The K: Na ratios support that mangrove community is not subjected to salinity stress. (5) Continuous leaching of salts favor the advance of terrestrial non-halophytes plants.     

Reproductive isolation among geographically and temporally isolated marine Brachionus strains

Using a polyclonal antibody against the mate recognition pheromone (MRP) of Brachionus rotundiformis Koshiki strain, we investigated the behavioral reproductive isolation and the similarity of MRP among geographically and temporally isolated B. rotundiformis strains. Males of the Koshiki strain did not discriminate in mating attempts among females of the Koshiki strain and those of conspecific allopatric strains from Hamana, Fiji, Thailand and Spain. Likewise, Koshiki males attempted mating with statistically indistinguishable frequency with Koshiki females and B. plicatilis strains. However, copulation was not consummated between Koshiki males and B. plicatilis females. The amount of anti-MRP binding to three allopatric B. rotundiformis strains was similar to that of the Koshiki strain, but binding to Hamana and the B. plicatilis strain was significantly lower. Four temporally separated B. rotundiformis populations were hatched from resting eggs collected from 0, 5, 10 and 15 cm depth in the sediment of Kai-ike pond in Koshiki island, Japan. Sediment age was determined using the ²¹⁰Pb method, allowing us to estimate that resting eggs from 15 cm depth were produced 65 years ago. Results of mating assays and anti-MRP binding showed that no behavioral reproductive isolation exists among the four temporally isolated Koshiki strains. B. rotundiformis appears to be reproductively isolated from B. plicatilis, but heterospecific matings are still attempted between B. plicatilis and B. rotundiformis, suggesting that the MRP remains sufficiently similar to elicit circling behavior.