中国4种蝗虫不同种群的遗传分化

采用水平淀粉凝胶电泳技术,应用等位酶分析方法对采自我国山西、江苏、河北等地不同蝗区优势蝗虫种类3科4种8个种群的12种酶18个酶位点进行了检测,比较了4种蝗虫种群水平的等位基因频率变化和它们之间的遗传距离。等位基因频率分析表明：中华稻蝗和笨蝗各位点等位基因丰富,而长翅素木蝗和短额负蝗各位点等位基因较少。在所研究的4种蝗虫8个种群中,多态位点百分率普遍较高(P＝53．3％—100．0％),由于杂合子数目较少而使每个位点的平均杂合度观察值偏低(H。＝0．034—0．139)。受迁飞能力、繁殖方式和活动范围的限制,4种蝗虫的平均杂合度观察值表现出一定的差异：笨蝗较高(H。＝0．089—0．139),其次是中华稻蝗(H。＝0．073—0．090),而长翅素木蝗(H。＝0．0488—0．068)和短额负蝗(H。＝0．034—0．050)相对较低。除Adk-1、Ao-1、Idh-1、Ldh-1、Ldh-2和Me-1在部分蝗虫种群符合Hardy-Weinberg平衡外,其余绝大多数位点的基因型频率显著偏离H—W平衡,但短额负蝗的多个位点符合或接近H—W平衡,表明该种蝗虫在自然种群结构方面明显有别于其他种类。从4种蝗虫的F—统计量(Fst)看,笨蝗种群间基因分化程度最高(Fst＝0．32),其次是短额负蝗(Fst＝0．31),而中华稻蝗相对较低(Fsl＝0．20),长翅素木蝗种群间基因分化程度最低(Fsl＝0．18),利用非加权算术平均法(UPGMA)对I值和D值进行聚类,所得聚类树也证实了这种遗传分化差异,上述结果反映了迁飞能力、适应性和环境因子对不同蝗虫遗传分化的影响。Nei的遗传距离(D)和遗传一致度(I)进行的聚类分析基本符合传统形态学、细胞学等研究结果：即同属于斑腿蝗科的中华稻蝗和长翅素木蝗遗传距离最小(D＝0．559),遗传一致度最高(I＝0．576)。在3个科中,癞蝗科和锥头蝗科之间呈现较小的遗传距离(D＝0．776)和较高的遗传一致度(I＝0．776),而这两科与斑腿蝗科之间的遗传距离相对较大(D＝0．908),遗传一致度相对较低(I＝0．406)。等位酶分析能较好地反映蝗虫不同物种的亲缘关系和种内不同种群之间的遗传分化程度。     

宽翅曲背蝗两个地理种群等位酶的比较

采用水平淀粉凝胶电泳技术及应用等位酶分析方法,研究我国河北黄骅、辽宁葫芦岛宽翅曲背蝗两个自然种群的遗传多样性和遗传分化。在检测的11种酶15个酶基因座位中,Adk-I、Fbp-I、Mdh-2和G3pd-I基因座位的等位基因少,而Fbp-2、Mdh-I和Me-I基因座位的等位基因多。对每个基因座位的各基因型进行χ^2检验,除Mdh-I在辽宁葫芦岛种群、Adk-I在河北黄骅种群分别符合Hardy-Weinberg平衡外,其余绝大多数基因座位的基因型频率显著偏离Hardy-Weinberg平衡。两个种群之间存在明显的遗传多样性和分化：多态位点百分率分别为100％和93．3％,等位基因平均数分别为3．1和2．5,平均杂合度观测值分别为0．086和0．061。与其他非迁飞性蝗虫如中华稻蝗(Oxya chinensis)比较,这种蝗虫种群的平均杂合度较低但遗传多态性较高。结果表明：该蝗虫较强的跳跃能力可使个体暴露于各种不同环境,有利于维持种内遗传多态性的动态平衡,而种群保持较高的遗传多态性能增强该物种在不同栖息地的生存和繁殖能力。F-统计量表明两个种群之间的遗传分化相对较小,但这种分化显著高于迁飞性蝗虫如东亚飞蝗(Locusta migratoria manilensis)。Nei的遗传一致度(I)和Roger的遗传距离(D)的结果分析揭示了两个种群之间较高的遗传一致度(I=0．904)和较小的遗传距离(D=0．256)。然而,在一些酶基因座位如Aep-I(Fst=0．462)和Pgi-I(Fst=0．182),F-统计值相对较大,遗传分化比较明显。     

亚洲小车蝗不同地理种群遗传多样性的等位酶分析

采用等位酶电泳技术对亚洲小车蝗8个地理种群遗传多样性和遗传分化进行了研究,并对8种等位酶系统:苹果酸脱氢酶(MDH)、苹果酸酶(ME)、乙醇脱氢酶(ADH)、谷氨酸脱氢酶(GDH)、谷氨酸-草酰乙酸转氨酶(GOT)、异柠檬酸脱氢酶(IDH)、腺苷酸激酶(AK)和己糖激酶(HK)进行聚丙烯酰胺凝胶电泳分析。结果表明:在亚洲小车蝗8个地理种群中共检测到14个基因位点,其中7个位点为多态位点,检测到25个等位基因;种群总体水平多态位点比率P=42.86%,平均有效基因数A=1.786,平均期望杂合度He=0.072,种群平均遗传距离为0.069～0.235。聚类分析表明,遗传距离与地理距离存在一定相关性。亚洲小车蝗8个种群的遗传分化系数Fst=0.086,基因流Nm=3.142,表明亚洲小车蝗种群间有一定程度的遗传分化及基因交流。     

极濒危植物中华水韭休宁居群的遗传结构

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对极濒危蕨类植物中华水韭(Isoetes sinensis)现存于安徽休宁的5个亚居群的等位酶多样性和遗传结构进行了研究。结果表明：中华水韭居群每位点平均等位基因数A=1．7,平均多态位点比率P=55．56％,平均预期杂合度He=0．201。居群中半数的多念位点表现为等位基因的“固定杂合”,5个亚居群的遗传多样性无显著差异,但都表现出严重偏离Hardy—Weinberg平衡的杂合子过昔;其遗传变异主要发生于亚居群内(94．27％),亚居群之间的遗传分化较小(Gsl=0．0573),亚居群间遗传一致度较高(I=0．960—0．999)。我们推断这可能是由于居群构建之初的奠基者效应或者原种群曾经历了较为严重的遗传瓶颈所导致;此外亚居群间便利的基因交流也可能起到了很大作用(Nm=4．5062)。取自休宁居群的75株样品由13个专一多位点基因型(18个位点等位酶基因型)组成,亚居群及个体间高度遗传均质。本文还就中华水韭休宁野生居群濒危的遗传因素进行了探讨,并提出了相应的保育策略。     

华北2蝗区东亚飞蝗种群遗传结构的比较研究

利用水平淀粉凝胶电泳对采自天津北大港和河北黄骅两个相临蝗区的东亚飞蝗（Locusta migratoria manilensis)种群进行等位酶基因频率分析,比较了这两个种群的遗传结构,等位酶酶谱分析表明,19个基因座中4个基因座（Mdh-l,Pgm,Adk,G3pd)的等位基因频率变化很小,常见等位基因的频率均高于0．95,其他基因座有2－4个等位基因,但是两个种群的等位基因频率除两个基因座（Fbp,Got-2)外都很相似,多态位点的27个χ2检验表明,由于常见等位基因纯合子的高频率的和相应杂合子的缺乏,仅有北大港种群的2个基因座（Pgi,Got-1)符合Hardy-Weinberg平衡,在每个种群内的蝗虫存在明显的遗传变异,但在种群间遗传结构极为相似,多态位点的百分数P分别为73．7％和78．9％,每个基因座的平均等位基因数A为2．9和3．1,平均每个基因座的实际杂合度几乎相等（约为0．138）,F－统计量（FST＝0．053）也表明了两个种群间的遗传 一致性,遗传相似性系数（I）高达0．938,这些结果提示,这两个种群可能属于1 个大种群,在两个种群的一定位点上的遗传多态性和分化可能都与迁飞因素有关,因为东亚飞蝗的高度扩散能力有利于遗传结构的连续分布,高度的迁飞能力也导致个体暴露于各种不同的环境,而在种群水平上的遗传为异能增强种群在各种生态条件生存和繁殖能力,因此,迁飞有利于维持东亚飞蝗种群的遗传多态性的动态平衡。     

缙云山特有植物缙云黄芩的遗传多样性研究

采用聚丙烯酰胺凝胶垂直平板电泳检测了重庆缙云山特有植物缙云黄芩7个居群70个个体的过氧化物酶、细胞色素氧化酶、超氧化物歧化酶、淀粉酶和酯酶5种等位酶,获得20个基因位点的资料,由此分析了其遗传分化水平。结果表明：缙云黄芩遗传多样性水平较高,多态位点比率P为45．7％,平均每个多态位点的等位基因数目A为1．46,平均预期杂合度He为0．205,平均观察杂合度Ho为0．352。缙云黄芩居群间遗传分化水平较高,Gst=0．401,居群间遗传一致度和遗传距离的平均值分别为0．741和0．300。缙云黄芩遗传多样性的40．1％来源于居群之间的基因差异,59．9％属于居群内的遗传分化,因而对缙云黄芩遗传多样性的保护,应保护其较多的居群。     

海南粗榧(Cephalotaxus mannii Hk.f.) 5个种群遗传多样性及分化研究

采用垂直板型聚丙烯酰胺凝胶电泳测定了海南粗榧5个种群遗传多样性和遗分化程度。结果表明：海南粗榧种群遗传多样性水平较低,多态位点比率P＝0．33,等位基因平均数A＝1．33,平均期望杂合度为He=0．135,观察杂合度为Ho＝0139。种群间遗传分化程度较低,基因分化系数Gst=0.123,种群间遗传一致度和遗传距离的均值分别为0．9719、9．0288。黎母山种群与其它种群分化最大,其原因可能与传粉时盛行的风向有关。     

九种杜鹃属植物的遗传分化研究

采用水平淀粉凝胶电泳技术 ,对 9种杜鹃属 ( Rhododendron)植物的遗传分化进行了初步研究。对 10个酶系统的 14个等位酶位点的检测表明 ,9种杜鹃花在种内个体间的遗传变异水平较高 ,多态位点比率数为 P=2 8.6%～ 57.1% ,等位基因平均数 A=1.3～ 1.9,平均预期杂合度 He=0 .111～ 0 .319,平均观察杂合度 Ho=0 .0 83～ 0 .381。种间的多态位点比率非常高 P=10 0 % ,这说明杜鹃属种间的遗传分化较高 ,具有丰富的遗传多样性。杂合性基因多样化比率 Fst=0 .683,表明各种间存在明显的遗传分化现象     

不同地理飞蝗种群的遗传多样性

用GenBank中飞蝗Locusta migratoriaL.的序列来设计微卫星引物,并对这些引物的有效性进行验证。结果表明,在所设计的3对引物中,只有1对为有效引物,可扩增出微卫星位点。序列分析表明本位点是一个不连续的重复微卫星位点。该多态微卫星位点含有14个等位基因,不同飞蝗地理种群的等位基因数目、大小和频率都存在较大的差异。对该位点各等位基因型进行χ2检验,基因型频率的观察和期望杂合度分别为0.4578和0.8836,该位点不属于Hardy-Weinberg平衡位点(χ2=733.12,P=0.0000)。该微卫星位点表现出高度的多态性说明是分析飞蝗种群遗传多样性的优良分子遗传标记。     

用SSR研究栲树群体遗传结构

利用微卫星（SSR）分子标记对福建省内4个栲树（Castanopsis fargesii Franch.）群体遗传结构进行了研究。SSR标记揭示了栲树群体丰富的遗传变异：平均等位基因数A＝9.0,平均有效等位基因数Ne=4.8,平均期望杂合度He=0.65,而群 具有较低的Fst值（Fst=0.031）。SSR每个位点的等位基因频率分布在栲树群体间都存在显或极显差异,表明根据SSR等位基因频率分布亦能了解各体的分化。SSR标记使栲树群体中一些稀有等位基因得以表现,54个SSR等位基因中有15个等位基因仅出现在1个或2个群体中,且频率较低,在遗传多样性保护中更应注重保护这些稀有的等位变异。     

中国东亚飞蝗四个地理种群遗传结构的比较研究

利用水平切片淀粉凝胶电泳技术,分析了不同蝗区东亚飞蝗四个地理种群的遗传结构。在检测的20个酶基因座位中,四个种群均表现出一定的遗传多态性, 多态位点的百分率普遍偏高 (P=70%～80%),但由于杂合子数目较少而使每个位点的平均杂合度观察值偏低(H_o=0.023～0.032)。对每个基因座位的各基因型进行χ²检验, 除 Adk-1、Gdh-1、G3pd-1和Pgm-1在部分种群符合Hardy-Weinberg平衡外,其余绝大多数基因座位的基因型频率显著偏离Hardy-Weinberg平衡。从F统计量看,四个种群之间的遗传分化较低(F_st=0.0606 )。它表明： 东亚飞蝗较强的长距离迁飞行为增加了种群之间的基因交流, 降低了种群之间的遗传分化。根据Nei的遗传一致度（I）和Roger的遗传距离（D）进行分析, 在山西临猗与山西永济(I=0.964, D=0.175)、河南中牟与江苏沛县种群(I=0.957, D=0.160)之间,呈现出较高的遗传一致度和较小的遗传距离。结果表明： 迁飞性蝗虫东亚飞蝗种群之间的遗传分化与地理距离呈正相关。     

New methods employing multilocus genotypes to select or exclude populations as origins of individuals

A new method for assigning individuals of unknown origin to populations, based on the genetic distance between individuals and populations, was compared to two existing methods based on the likelihood of multilocus genotypes. The distribution of the assignment criterion (genetic distance or genotype likelihood) for individuals of a given population was used to define the probability that an individual belongs to the population. Using this definition, it becomes possible to exclude a population as the origin of an individual, a useful extension of the currently available assignment methods. Using simulated data based on the coalescent process, the different methods were evaluated, varying the time of divergence of populations, the mutation model, the sample size, and the number of loci. Likelihood-based methods (especially the Bayesian method) always performed better than distance methods. Other things being equal, genetic markers were always more efficient when evolving under the infinite allele model than under the stepwise mutation model, even for equal values of the differentiation parameter F(st). Using the Bayesian method, a 100% correct assignment rate can be achieved by scoring ca. 10 microsatellite loci (H approximately 0.6) on 30-50 individuals from each of 10 populations when the F(st) is near 0.1.     

中华稻蝗四个种群的遗传分化

采用水平淀粉凝胶电泳技术研究中华稻蝗(Oxya chinensis)四个种群的12个基因座位,探讨其遗传分化.这四个种群分别采自内蒙古呼和浩特、山西代县、山西太原和陕西西安.Ck和Mdh-2在四个种群中均为单态,其余的基因座位至少在一个种群内有两个以上的等位基因;在Ldh和Mdh-1的等位基因频率呈现梯度分布趋势.多态基因座位百分率(P)和平均每个基因座位的等位基因数目(A)分别为58.3%-66.7%和2.2-2.8,平均杂合度为Ho=0.173-0.240.除Gpi,Hk-2,Idh,Ldh和Mdh-1在部分蝗虫种群符合Hardy-Weinberg平衡外,其余绝大多数基因座位的基因型频率显著偏离Hardy-Weinberg平衡.四个种群间FST平均值不存在显著差异(FST=0.0510,P＞0.05),结合高的Nei's遗传一致度(I＞0.97)可知,种群之间遗传分化不明显.我们认为人类的农业活动可能促进了种群间的基因交流,从而降低了分化程度[动物学报50(2)187-192,2004].     

Genetic diversity of six populations of Atractomorpha sinensis and Atractomorpha peregrina in Shanxi Province, China

Ten enzymes (AAT,CK,G3PDH,HEX,IDH,LDH,MDH,ME,PGI,PGM)were examined using horizontal starch gel electrophoresis to estimate the levels of genetic variation within and among six natural populations of two grasshopper species Atractomorpha sinensis and A.peregrina from Shanxi,China.The collecting sites were geographically distant from each other from south to north:Quwo district,Linfen city;Xiangyuan county,Changzhi;Jinyuan district,Taiyuan city;Yuanping county,Xinzhou city and Fanshi county of Xinzhou.A.sinensis showed 43 alleles at 16 loci but A.peregrine showed 39 alleles at 15 loci (ldh-1 was deficient).The zymograms showed that some common alleles were shared at several loci in these two species (Aat-1-b,Aat-2-b,G3pdh-a,Ck-1-b and Ldh-b).However,Hex-1-a,Hex-2-a,Hex-3-a,Idh-2-b,Mdh-2-b,Mdh-1-f Pgi-b,Pgm-b had common alleles in A.sinensis and Hex-1-b,Hex-2-b,Hex-3-b,Idh-2-a,Mdh-2-a,Mdh-1-d,Pgi-a,Pgm-c were of high frequency in A.peregrine instead.Most of the observed genotype frequencies were found to significantly deviate from the Hardy-Weinberg expectations in both species.A tendency of clinal distribution of allele frequency was observed at three loci.The frequency of the moderately migrating allele Me-c (0.318-0.740)in A.peregrina,Hex-1-a (0.800-1.000)and Ldh-b (0.487-0.750)in A.sinensis demonstrated increased frequency from north to south.Such tendency suggests that the allele frequency in these three loci may be correlated with the species'geographic distributions.A.sinensis showed higher genetic diversity than A.peregrina as indicated by higher mean number of alleles per locus (A=1.9-2.3 in A.sinensis and 1.7-2.2 in A.peregrina),percentage of polymorphic loci (56.3%-68.8%in A.sinensis and 43.8%-56.3%in A.peregrina),and the observed heterozygosities (Ho=0.072-0.096 in A.sinensis and 0.070-0.107 in A.peregrina).The observed heterozygosities of the six populations were all noticeably lower than the Hardy-Weinberg expectations,mostly due to heterozygote deficiency in the populations of both species.The overall mean Fsr were small (FST=0.045,P＞0.05 in A.sinensis populations and 0.087,P＞0.05 in A.peregrina populations).Nei's genetic identity (I)estimates indicate low intraspecific (＞0.95)but higher interspecific (0.377-0.447)genetic diversity.The cluster analysis based on modified Roger's genetic distance (D)showed that the two species were divided into two branches.Both species are of limited dispersal capacity and a moderate geographical barrier might significantly restrict the gene exchange among populations,resulting in accumulation of local genetic differentiations.The A.sinensis populations used in this study were separated from each other by 155.2 to 271.4 km and the A.peregrina populations were separated from each other by 78.8 to 174.9 km with observable physical barriers.The aUozyme data showed only minimal genetic differentiation at population level,most likely as a result of gene exchange.It is reasoned that natural factors and human agricultural activities might have facilitated migration and dispersal for the two species.     

Microsatellite Variation in Two Populations of Free-Ranging Yellow Baboons (Papio hamadryas cynocephalus)

We investigated genetic variation at six microsatellite (simple sequence repeat) loci in yellow baboons (Papio hamadryas cynocephalus) at two localities: the Tana River Primate Reserve in eastern Kenya and Mikumi National Park, central Tanzania. The six loci (D1S158, D2S144, D4S243, D5S1466, D16S508, and D17S804) were all originally cloned from and characterized in the human genome. These microsatellites are polymorphic in both baboon populations, with the average heterozygosity across loci equal to 0.731 in the Tana River sample and 0.787 in the Mikumi sample. The genetic differentiation between the two populations is substantial. Kolmogornov–Smirnov tests indicate that five of the six loci are significantly different in allele frequencies in the two populations. The mean F _ST across loci is 0.069, and Shriver's measure of genetic distance, which was developed for microsatellite loci (Shriver et al., 1995), is 0.255. This genetic distance is larger than corresponding distances among human populations residing in different continents. We conclude that (a) the arrays of alleles present at these six microsatellite loci in two geographically separated populations of yellow baboons are quite similar, but (b) the two populations exhibit significant differences in allele frequencies. This study illustrates the potential value of human microsatellite loci for analyses of population genetic structure in baboons and suggests that this approach will be useful in studies of other Old World monkeys.     

Genetics of Brazil nut (Bertholletia excelsa Humb. & Bonpl.: Lecythidaceae)

Summary We provide an estimate of genetic variation within and between two populations of Bertholletia excelsa (Brazil nut), a large canopy tree found in the rain forests of South America. Average heterozygosity is 0.190, and 54.3% of the sampled loci are polymorphic. The population structure deviates significantly from Hardy-Weinberg expectations for Fest2 and Pgm2 (F =0.405 and 0.443, respectively) in one population, and highly significantly (F=-0.341) for Gdh in the other population. Although allele frequencies of the two populations differ significantly for Aat2, Est5, Mdh1, and Mdh2B, Nei's coefficient of gene differentiation (G_st) indicates that the between-population component (D_st) of genic diversity represents only 3.75% of the size of the within-population component (H_s). The implications of these findings in terms of conservation genetics are that much of the genetic diversity of this species may be preserved within one or a few populations. However, such populations must be very large because it appears that the large amount of genetic variation in Brazil nut populations is maintained by extensive gene flow and bonds of mating over a large area. The genetic architecture of Bertholletia excelsa is similar to that expected for an extensively diploidized paleopolyploid species.     

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant

We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0. 48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy-Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440-5000. The overall genetic differentiation among eelgrass populations, assessed as rho (a standardized estimate of Slatkin's RST) was 0.384 (95% CI 0.34-0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12-42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (rho = 0.029-0. 053) at scales of 15-35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation-by-distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise rho = 0.03-0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour-joining tree based on Cavalli-Sforza's chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity.     

A population genetic study of six VNTR loci in three ethnically defined populations.

To investigate the population genetic characteristics of VNTR polymorphisms in human populations, we have studied the allele frequency distribution of six VNTR loci (D1S57, RB1, D1S77, D1S61, alpha-globin 5'HVR, D1S76) in three well-defined populations (Kachari of Northeast India; Dogrib Indian of Canada; and New Guinea Highlander of Papua New Guinea). Even though the number of alleles sampled is limited, 48 to 92 alleles per locus per population, significant variation is noticed in the number of alleles per locus for all the populations. Using alternate summary measures, we have observed that genotype distributions at the six VNTR loci apparently conform to their respective Hardy-Weinberg predictions. Multilocus genotype profiles of the individuals in each of the three populations suggest that the VNTR alleles are independently segregating with the exception of the two linked loci D1S76 and D1S77. Lack of fit of all VNTR loci to one particular model of mutational change, either the Infinite Allele Model or the Stepwise Mutation Model, suggests more than one mechanism for production of new VNTR alleles. This study also indicates that increased heterozygosity at VNTR loci in comparison to protein and blood group loci may lead to more accurate estimates of genetic distance.     

High levels of genetic polymorphism in the insular endemic herb Jepsonia malvifolia.

Jepsonia malvifolia is a long-lived perennial herb endemic to the Channel Islands of southern California and Guadalupe Island, Mexico. Twelve populations of J. malvifolia on San Clemente Island were surveyed for their genotype at 21 allozyme loci, revealing high levels of genetic polymorphism. For all individuals across San Clemente Island, 95.2% of loci are polymorphic with A(p) = 2.90 and H(e) = 0.179. Populations averaged 60.2% polymorphic loci with A(p) = 2.42 and H(e) = 0.158. Most variation is found within rather than among populations (G(ST) = 0.101), although differentiation among populations is significant. Genetic identities range from 0.936 to 0.999 with mean I = 0.975. There is no significant relationship between genetic and geographic distance. Gene flow among populations is Nm = 9.5 based on private alleles and Nm = 2.2 based on F(ST). Outcrossing rates based on fixation indices average t = 0.753, indicating a primarily outcrossed mating system. The genetic variation observed is unusually high for an insular endemic herb and indicates that J. malvifolia is unlikely to be endangered by genetic factors.