Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis （Trin.） Tzvel.

Randomly amplified polymorphic DNA （RAPD） analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis （Trin.） Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% （P 〈 0.04）, and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% （P 〈 0.002）. A 21.06% RAPD variation among all 16 populations among two regions was found （P 〈 0.001）, as well as 72.59% variation within populations （P 〈 0.001）. Molecular variation within populations was significantly different among 16 populations.     

Distributional, morphological and genetic consequences of dispersal for temporary pond water mites

1. To determine the consequences of dispersal and gene flow for temporary pond water mites (Hydrachnida), we compared distributional, genetic and morphological characters in the closely related species Arrenurus angustilimbatus and A. rufopyriformis. The former has larvae that parasitise and disperse on adult mosquitoes, whereas larvae of the latter forego any association with hosts. 2. Allometrically adjusted egg size and gonopore size were found to be useful characters for distinguishing between females of the two species. 3. Arrenurus angustilimbatus possesses a broader and more continuous geographic distribution than its ‘direct developing’ counterpart. Allozyme heterozygosity was higher and population differentiation lower in A. angustilimbatus. In addition, populations of A. rufopyriformis were morphologically divergent, whereas populations of A. angustilimbatus were not. Isolation by distance analyses on both genetic and morphological characters indicated that the results were not biased by different sampling regimes for the two species. 4. These results demonstrate the importance of mosquito parasitism for maintaining ecological and genetic linkages between A. angustilimbatus populations. More broadly, we hypothesise that insect‐mediated dispersal has contributed to the ecological and evolutionary success of water mites, because the Hydrachnida lack other obvious adaptations for dispersing in space or time.     

Variation in life-history characteristics among populations of North American wood turtles: a view from the north

Life-history traits such as age at maturity, body size and clutch size tend to vary across a species' distribution. The purpose of our study was to describe the demography of a newly discovered population of North American wood turtles Glyptemys insculpta at the species' northern range limit, and to compare our findings to those of other studies to test hypotheses about adaptive life-history variation. Turtles were hand-captured from May to October 2005 and 2006 along a 4.5 km stretch of river located in the Sudbury District, ON, Canada (46°N). Fifty-five captured individuals provided a population density estimate of 1.3 turtles/100 m of river. Juveniles comprised 35% of wood turtles captured, and growth ring counts (i.e. age estimates) indicated recruitment in each of the past 11 years. Among populations, we found a nonlinear pattern in body size variation with the largest turtles in the north, smallest turtles in the centre of the range, and intermediate-sized turtles in the south. This nonlinear pattern in body size was reflected in clutch size variation. Selective pressures to overcome years of low recruitment may have resulted in larger body sizes and hence large clutch sizes at northern latitudes while conspecifics at southern latitudes can achieve larger body sizes because they live in a more productive environment. Population density decreased with latitude, likely as a result of a gradient in habitat productivity.     

REPEAT SEQUENCE PRIMER‐PCR STUDY ON DNA POLYMORPHISM OF GEOGRAPHIC POPULATIONS OF COTTON APHID,APHIS GOSSYPII,IN CHINA*

Abstract The repeat sequence primer‐PCR technique was used to determine DNA polymorphism of the aphid Aphis gossypii (Glover) collected from 8 different localites in China. Three primers were selected and used for similarity index (SI) and cluster analysis based on the data of Nei's genetic distance (D). We found that the populations in the north and northwest of China was linked before they were joined by those in southern China. A proposed explanation emphasizes the populations in the north and northwest of China were located near — 4 °C isotherm or lower in January with less than 200 frost‐free days per year, whereas populations in southern China were located near 0 °C isotherm or higher with more than 300 frost ‐ free days per year. So it may be the over‐winter host plants instead of the geographic distance or gene flow, exert pronounced influence on the geographic population differentiation of A. gossypii. Species on different over‐winter host plants may directly lead to the genetic differentiation of their summer offsprings.     

中国东南沿海弹涂鱼科常见鱼类的遗传多样性和DNA条形码

为了探究中国东南沿海海岸线经济开发、海水污染等对该区域生物遗传多样性的潜在影响,本文使用COI基因作为DNA条形码,对从中国东南沿海广东汕头、福建东山、福建云霄、福建泉州、福建霞浦、上海崇明6个地点采集的大弹涂鱼(Boleophthalmus pectinirostris)、弹涂鱼(Periophthalmus modestus)和青弹涂鱼(Scartelaos histophorus)进行种间和种内的遗传学分析。遗传多样性分析显示,青弹涂鱼的核苷酸多样性(0.0018)在3个种中最低;青弹涂鱼广东汕头种群的核苷酸多样性(0.0018)比福建云霄种群低;大弹涂鱼的上海崇明种群核苷酸多样性(0.0021)低于其他5个地理种群。物种水平分析表明,3个物种间分化明显,种间与种内遗传距离有明显差异;不同种的单倍型在系统发育树上聚成3个高度支持的独立分支。种群水平分析显示,大弹涂鱼的6个不同地理种群之间有共享单倍型,地理种群间与地理种群内的遗传距离重叠;各地理种群之间的基因流较频繁(Nm>4);青弹涂鱼的分析情况与大弹涂鱼基本一致。大弹涂鱼和青弹涂鱼的单倍型在系统发育树上均呈现多系或并系分布格局,并未按地理位置分成不同的单系群。本研究表明,应及时加强3种鱼类及其野生种群遗传多样性的保护,且COI基因对种一级的识别明确可靠,而在地理种群水平的识别则比较困难,有待进一步深入研究。     

Expressed mutational load increases toward the edge of a species’ geographic range

There is no general explanation for why species have restricted geographic distributions. One hypothesis posits that range expansion or increasing scarcity of suitable habitat results in accumulation of mutational load due to enhanced genetic drift, which constrains population performance toward range limits and further expansion. We tested this hypothesis in the North American plant, Arabidopsis lyrata. We experimentally assessed mutational load by crossing plants of 20 populations from across the entire species range and by raising the offspring of within- and between-population crosses at five common garden sites within and beyond the range. Offspring performance was tracked over three growing seasons. The heterosis effect, depicting expressed mutational load, was increased in populations with heightened genomic estimates of load, longer expansion distance or long-term isolation, and a selfing mating system. The decline in performance of within-population crosses amounted to 80%. Mutation accumulation due to past range expansion and long-term isolation of populations in the area of range margins is therefore a strong determinant of population-mean performance, and the magnitude of effect may be sufficient to cause range limits.     

我国烟蚜种群分化的RAPD分析

用RAPD-PCR技术研究了我国烟草上烟蚜Myzus persicae (Sulzer)的种群分化。结果表明：我国烟蚜的不同地理种群和不同体色之间DNA均呈现出多态性,且不同的引物可在不同水平上反应出烟蚜种群的DNA多态性。Nei的遗传距离表明我国烟草上烟蚜的分化仅在种群水平上,并未达到亚种水平。用相似性指数和Nei的遗传距离对所筛选的三个引物OPX-04、OPX-06和OPX-19的扩增结果进行聚类,虽然二者的结果不一致,但均可反应出烟蚜的地理种群和体色生物型的DNA差异。在DNA水平上,与完全周期生活史的烟蚜相比,完全周期和不完全周期生活史混合发生的烟蚜与不完全周期生活史的烟蚜更为接近,而两种生活史混合发生的烟蚜之间无明显差异。从体色看,红色比黄绿色更接近褐色。     

When are genetic methods useful for estimating contemporary abundance and detecting population trends?

The utility of microsatellite markers for inferring population size and trend has not been rigorously examined, even though these markers are commonly used to monitor the demography of natural populations. We assessed the ability of a linkage disequilibrium estimator of effective population size (N_e) and a simple capture-recapture estimator of abundance (N) to quantify the size and trend of stable or declining populations (true N = 100–10,000), using simulated Wright–Fisher populations. Neither method accurately or precisely estimated abundance at sample sizes of S = 30 individuals, regardless of true N. However, if larger samples of S = 60 or 120 individuals were collected, these methods provided useful insights into abundance and trends for populations of N = 100–500. At small population sizes (N = 100 or 250), precision of the N_e estimates was improved slightly more by a doubling of loci sampled than by a doubling of individuals sampled. In general, monitoring N_e proved a more robust means of identifying stable and declining populations than monitoring N over most of the parameter space we explored, and performance of the N_e estimator is further enhanced if the N_e/N ratio is low. However, at the largest population size (N = 10,000), N estimation outperformed N_e. Both methods generally required ≥ 5 generations to pass between sampling events to correctly identify population trend.     

Genetic differentiation within and between isolated Algerian subpopulations of Barbary macaques (Macaca sylvanus): evidence from microsatellites

This study of wild-living Algerian Barbary macaques ( Macaca sylvanus ) was designed to examine genetic variability in subpopulations isolated in residual forest patches, in an attempt to obtain data on the effects of habitat fragmentation. The wild population of this species (estimated at a maximum of 15 000) is vulnerable and this study therefore has direct relevance for conservation measures. Data from five microsatellite loci were analysed for 159 individuals from nine different groups living in four isolates in Algeria. Genetic polymorphism was found to be relatively high (4–12 alleles per locus) compared with other genetic markers used in previous studies of this species; mean expected heterozygosity was 65%. The four isolates are all genetically distinct ( F _ST = 0; P < 0.001). Indeed, the results suggest that dispersal is limited even between some social groups within a single isolate. Genetic distances based on models not assuming stepwise mutation ( F _ST and chord distance) gave very similar results and are highly correlated with geographical distances within one isolate but not between isolates. This may indicate that isolation by distance exerts a significant influence within an isolate but that genetic drift prevails between the four isolates. After allowing for variation in sample size, we found no evidence of reduced allelic diversity within small isolates that may have been separated for 250 years or more. The surviving population of Algerian Barbary macaques taken as a whole still shows marked variability in microsatellite alleles, but maintenance of genetic variability over the long term will surely require effective protection of all isolates.     

Low RAPD Variation and Female-Biased Sex Ratio Indicate Genetic Drift in Small Populations of the Dioecious Conifer Taxus Baccata in Switzerland

Small populations are prone to genetic drift as a consequence of random sampling effects. We investigated whether we could detect such random sampling effects in the English yew (Taxus baccata), a dioecious conifer species occurring in scattered populations in Switzerland. Seven pairs of small and large populations were analyzed using random amplified polymorphic DNA (RAPD) marker bands from 20 individuals per population. Several genetic parameters (mean marker band frequency deviation, molecular variance, population differentiation) indicated that small populations experienced genetic drift. These genetic differences between small and large populations of yew were paralleled by an increased sex ratio bias towards a higher number of females in the small populations. Our findings support earlier assumptions that the Swiss occurrences of yew may be described as metapopulation dynamics, characterized by local colonization and extinction events leading to the observed genetic drift.     

Genetic Diversity in Introduced Populations with an Allee Effect

A phenomenon that strongly influences the demography of small introduced populations and thereby potentially their genetic diversity is the demographic Allee effect, a reduction in population growth rates at small population sizes. We take a stochastic modeling approach to investigate levels of genetic diversity in populations that successfully overcame either a strong Allee effect, in which populations smaller than a certain critical size are expected to decline, or a weak Allee effect, in which the population growth rate is reduced at small sizes but not negative. Our results indicate that compared to successful populations without an Allee effect, successful populations with a strong Allee effect tend to (1) derive from larger founder population sizes and thus have a higher initial amount of genetic variation, (2) spend fewer generations at small population sizes where genetic drift is particularly strong, and (3) spend more time around the critical population size and thus experience more genetic drift there. In the case of multiple introduction events, there is an additional increase in diversity because Allee-effect populations tend to derive from a larger number of introduction events than other populations. Altogether, a strong Allee effect can either increase or decrease genetic diversity, depending on the average founder population size. By contrast, a weak Allee effect tends to decrease genetic diversity across the entire range of founder population sizes. Finally, we show that it is possible in principle to infer critical population sizes from genetic data, although this would require information from many independently introduced populations.     

The population ecology of rare species

There is no general theory of rarity, although one is sorely needed both to understand population dynamics and to determine conservation priorities. Here we suggest some of the strands that might be woven into such a theory. They include relationships between local abundance, geographic range size and body size of species, and the determinants of minimum viable population sizes. In each of these areas much can still be learnt from the classical 'compare and contrast' approach using assemblages of species from a variety of taxa. Freshwater fish have contributed relatively little to the broad ecological literature in this respect. We perform some tentative analyses for this group of species, and speculate on how they might fit into our current understanding of rarity.     

中国与欧洲高卢蜜环菌的遗传多样性

高卢蜜环菌(Armillaria gallica)为北半球广布种,不同大陆间的菌株遗传相似性和多样性水平能反映出该种在洲际大陆尺度上的地理遗传变异关系。作者用ISSR(inter-simple sequence repeat)分子标记技术,对从中国和欧洲收集到的高卢蜜环菌79个菌株进行了遗传多样性分析。用6个ISSR引物扩增得到210个位点,其中多态性位点(频率<0.95)为202个,占96.2%,平均每个引物多态位点多达33.6个,表明ISSR标记在蜜环菌中存在较高的多态性。根据非加权类平均法(UPGMA)聚类分析,中国53个菌株中的49个在0.773的相似性水平上聚成了中国类群(China group);而欧洲26个菌株遗传分化较大,分别在0.775和0.763的相似性水平上聚成了欧洲类群A(Europe group A)和B(Europe group B);2个欧洲类群间的相似性水平仅为0.738,而欧洲类群A与中国类群间的相似性却达到了0.770;两个大陆均有少数菌株表现出较为明显的遗传分化,个别菌株的种内遗传相似性甚至低于蜜环菌种间的遗传相似性。结果表明,中欧两个大陆间的A.gallica菌株因地理隔离已经表现出明显的遗传分化,处于异域物种形成过程中;欧洲大陆的菌株遗传分化更为明显,可能是两个大陆A.gallica菌株的起源地。