Comparison of quantitative and molecular variation in agroforestry populations of the shea tree (Vitellaria paradoxa C.F. Gaertn) in Mali

In this study we investigated the within- and between-population genetic variation using microsatellite markers and quantitative traits of the shea tree, Vitellaria paradoxa, an important agroforestry tree species of the Sudano–Sahelian region in Africa. Eleven populations were sampled across Mali and in northern Côte d’Ivoire. Leaf size and form and growth traits were measured in a progeny test at the nursery stage. Eight microsatellites were used to assess neutral genetic variation. Low levels of heterozygosity were recorded (1.6–3.0 alleles/locus; H_E = 0.25–0.42) and the fixation index (F_IS = −0.227–0.186) was not significantly different from zero suggesting that Hardy–Weinberg equilibrium is encountered in all populations sampled. Quantitative traits exhibited a strong genetic variation between populations and between families within populations. The degree of population differentiation of the quantitative traits (Q_ST = 0.055–0.283, Q_STmean = 0.189) strongly exceeds that in eight microsatellite loci (F_ST = −0.011–0.142, F_STmean = 0.047). Global and pairwise F_ST values were very low and not significantly different from zero suggesting agroforestry practices are amplifying gene flow (Nm = 5.07). The population means for quantitative traits and the rainfall variable were not correlated, showing variation was not linked with this climatic cline. It is suggested that this marked differentiation for quantitative traits, independent of environmental clines and despite a high gene flow, is a result of local adaptation and human selection of shea trees. This process has induced high linkage disequilibrium between underlying loci of polygenic characters.     

Population structure of rice (Oryza sativa) landraces from high altitude area of Indian Himalayas

This study examined the genetic diversity in 20 rice landrace populations from parts of traditional farming areas of the Indian Himalayas using 11 mapped simple sequence repeats (SSR) loci. Twenty‐four individuals sampled from each of the 20 landraces (480 individuals), which were collected from farmers from Northwest to Northeast Himalaya, showed that all landraces showed within population variation and none were homogeneous. The number of polymorphic loci in a landrace population ranged from 5 to 11. A total of 71 alleles were recorded of which 58 were common and 13 were rare. Of the 71 alleles, 46 were common to both Northwest and Northeast regions, whereas 9 were unique to the former and 16 were unique to the latter. The mean number of alleles per locus was 6.45 and for landrace populations from Northwest and Northeast regions were 5.0 and 5.64, respectively. Population differentiation, as shown by a high F_ST value (0.61), was greater for Northeast populations. The unweighted pair group method with arithmetic mean (UPGMA) dendrogram classified the populations into three major clusters: cluster I comprised seven populations from the Northwest region, cluster II comprised seven populations from the Northeast region and cluster III comprised populations from both regions. Investigating the population genetic structure can help monitor change in diversity over time and space, and also help devise a rational plan for management of crop landraces on‐farm under farmer management.     

Genetic variation in island populations of tuatara (<Emphasis Type="Italic">Sphenodon</Emphasis> spp) inferred from microsatellite markers

Tuatara (Sphenodon spp) populations are restricted to 35 offshore islands in the Hauraki Gulf, Bay of Plenty and Cook Strait of New Zealand. Low levels of genetic variation have previously been revealed by allozyme and mtDNA analyses. In this new study, we show that six polymorphic microsatellite loci display high levels of genetic variation in 14 populations across the geographic range of tuatara. These populations are characterised by disjunct allele frequency spectra with high numbers of private alleles. High F _ST (0.26) values indicate marked population structure and assignment tests allocate 96% of all individuals to their source populations. These genetic data confirm that islands support genetically distinct populations. Principal component analysis and allelic sequence data supplied information about genetic relationships between populations. Low numbers of rare alleles and low allelic richness identified populations with reduced genetic diversity. Little Barrier Island has very low numbers of old tuatara which have retained some relictual diversity. North Brother Island’s tuatara population is inbred with fixed alleles at 5 of the 6 loci.     

POPULATION GENETIC STRUCTURE IN DIPLOID BLUEBERRY VACCINIUM SECTION CYANOCOCCUS (ERICACEAE)

Vaccinium section Cyanococcus comprises diploid, tetraploid, and hexaploid species (x = 12) all of which are highly self-sterile. In order to assess the distribution of genetic variation within and among the diploids, population genetic analyses of allozyme data were conducted on three species: V. elliottii, V. myrtilloides, and V. tenellum. Populations were located throughout the range of these taxa in eastern North America. Data were collected at 20 loci, 12 of which are mendelian based on formal genetic analyses. Consistent with expectations for out-crossing taxa, these species exhibited high levels of variation within populations. Eighteen loci were polymorphic with the number and frequency of alleles varying among taxa. Mean values for the number of alleles per polymorphic locus, proportion of polymorphic loci, and expected heterozygosity were 2.8, 48.2, and 0.148, respectively. High infraspecific genetic identities exceeding 0.9 indicated that these taxa are homogeneous. All populations were in Hardy-Weinberg equilibrium with slight heterozygote excess observed in V. myrtilloides and V. tenellum. Although total genetic diversity was lower than that observed for other predominantly out-crossing species, it was apportioned similarly. The majority could be attributed to differences among individuals within populations. Conspecific populations were relatively undifferentiated with genetic differentiation similar to other self-incompatible species.     

Contrasting levels of genetic diversity between the historically rare orchid Cypripedium japonicum and the historically common orchid Cypripedium macranthos in South Korea

Many terrestrial orchids are historically rare and occur in small, spatially isolated populations. Theory predicts that such species will harbour low levels of genetic variation within populations and will exhibit a high degree of population genetic divergence, primarily as a result of genetic drift. If the origin of the present‐day populations is relatively recent from the same genetically depauperate source population, a complete lack of genetic differentiation between conspecific populations is expected. If a terrestrial orchid was historically common with moderate or high levels of genetic diversity, but has experienced more recent anthropogenic disturbance as a result of over‐collection, it would still exhibit initial levels of genetic variation within populations and a low degree of genetic divergence between populations. To test these predictions, we examined the genetic diversity in six populations (N = 131) of the historically and currently rare Cypripedium japonicum and in four populations (N = 94) of the historically common but now rare C. macranthos from South Korea. Fourteen putative allozyme loci resolved from eight enzyme systems revealed no variation either within or among populations of C. japonicum, which supports the first prediction. In contrast, populations of C. macranthos harboured high levels of genetic variation (mean percentage of polymorphic loci %P = 46.7; mean expected heterozygosity H_e = 0.185) and exhibited a low degree of population genetic divergence (G_ST = 0.059), supporting the second prediction. The lack of genetic variation both within and among conspecific populations of C. japonicum may suggest that populations originated from the same genetically depauperate ancestral population. The high levels of genetic diversity maintained in populations of C. macranthos suggest that the collection‐mediated decrease in the number of individuals is still too recent for long‐term effects on genetic variation. Based on current demographic and genetic data, in situ and ex situ conservation strategies should be provided to preserve genetic variation and to ensure the long‐term survival of the two species in the Korean Peninsula. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 119–129.     

A population genetic evaluation of ecological restoration with the case study on <Emphasis Type="Italic">Cyclobalanopsis myrsinaefolia</Emphasis> (Fagaceae)

The ultimate goal of ecological restoration is to create a self-sustaining ecosystem that is resilient to perturbation without further assistance. Genetic variation is a prerequisite for evolutionary response to environmental changes. However, few studies have evaluated the genetic structure of restored populations of dominant plants. In this study, we compared genetic variation of the restored populations with the natural ones in Cyclobalanopsis myrsinaefolia, a dominant species of evergreen broadleaved forest. Using eight polymorphic microsatellite loci, we analyzed samples collected from restored populations and the donor population as well as two other natural populations. We compared the genetic diversity of restored and natural populations. Differences in genetic composition were evaluated using measurements of genetic differentiation and assignment tests. The mean number of alleles per locus was 4.65. Three parameters (A, A _R, and expected heterozygosity) of genetic variation were found to be lower, but not significantly, in the restored populations than they were in the natural populations, indicating a founder effect during the restoration. Significant but low F _ST (0.061) was observed over all loci, indicating high gene flow among populations, as expected from its wind-pollination. Differentiation between the two restored populations was smallest. However, differences between the donor population and the restored populations were higher than those between other natural populations and the restored populations. Only 13.5% and 25.7% individuals in the two restored populations were assigned to the donor population, but 54.1 and 40% were assigned to another natural population. The genetic variation of the donor population was lowest, and geographic distances from the restoration sites to the donor site were much higher than the other natural populations, indicating that the present donor likely was not the best donor for these ecological restoration efforts. However, no deleterious consequences might be observed in restored populations due to high observed heterozygosity and high gene flow. This study demonstrates that during the restoration process, genetic structures of the restored populations may be biased from the donor population. The results also highlight population genetic knowledge, especially of gene flow-limited species, in ecological restoration.     

Genetic diversity and structure of natural fragmented Chamaecyparis obtusa populations as revealed by microsatellite markers

The genetic diversity and population structure of hinoki (Chamaecyparis obtusa) in Japan were investigated by examining the distribution of alleles at 13 microsatellite loci in 25 natural populations from Iwaki in northern Japan to Yakushima Island in southern Japan. On average, 26.9 alleles per locus were identified across all populations and 4.0% of the genetic variation was retained among populations (G _ST = 0.040). According to linkage disequilibrium analysis, estimates of effective population size and detected evidence of bottleneck events, the genetic diversity of some populations may have declined as a result of fragmentation and/or over-exploitation. The central populations located in the Chubu district appear to have relatively large effective population sizes, while marginal populations, such as the Yakushima, Kobayashi and Iwaki populations, have smaller effective population sizes and are isolated from the other populations. Microsatellite analysis revealed the genetic uniqueness of the Yakushima population. Although genetic differentiation between populations was low, we detected a gradual cline in the genetic structure and found that locus Cos2619 may be non-neutral with respect to natural selection.     

Genetic diversity and hierarchical population structure of a rare autotetraploid plant,Aster kantoensis (Asteraceae)

We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems.     

Population estimators or progeny tests: what is the best method to assess null allele frequencies at SSR loci?

Nuclear SSRs are notorious for having relatively high frequencies of null alleles, i.e. alleles that fail to amplify and are thus recessive and undetected in heterozygotes. In this paper, we compare two kinds of approaches for estimating null allele frequencies at seven nuclear microsatellite markers in three French Fagus sylvatica populations: (1) maximum likelihood methods that compare observed and expected homozygote frequencies in the population under the assumption of Hardy-Weinberg equilibrium and (2) direct null allele frequency estimates from progeny where parent genotypes are known. We show that null allele frequencies are high in F. sylvatica (7.0% on average with the population method, 5.1% with the progeny method), and that estimates are consistent between the two approaches, especially when the number of sampled maternal half-sib progeny arrays is large. With null allele frequencies ranging between 5% and 8% on average across loci, population genetic parameters such as genetic differentiation (F _ST) may be mostly unbiased. However, using markers with such average prevalence of null alleles (up to 15% for some loci) can be seriously misleading in fine scale population studies and parentage analysis.     

GENETIC STRUCTURE OF NORWAY SPRUCE (PICEA ABIES): CONCORDANCE OF MORPHOLOGICAL AND ALLOZYMIC VARIATION

This study describes the population structure of Norway spruce (Picea abies) as revealed by protein polymorphisms and morphological variation. Electrophoretically detectable genetic variability was examined at 22 protein loci in 70 populations from the natural range of the species in Europe. Like other conifers, Norway spruce exhibits a relatively large amount of genetic variability and little differentiation among populations. Sixteen polymorphic loci (73%) segregate for a total of 51 alleles, and average heterozygosity per population is 0.115. Approximately 5% of the total genetic diversity is explained by differences between populations (G_ST = 0.052), and Nei's standard genetic distance is less than 0.04 in all cases. We suggest that the population structure largely reflects relatively recent historical events related to the last glaciation and that Norway spruce is still in a process of adaptation and differentiation. There is a clear geographic pattern in the variation of allele frequencies. A major part of the allelefrequency variation can be accounted for by a few synthetic variables (principal components), and 80% of the variation of the first principal component is “explained” by latitude and longitude. The central European populations are consistently depauperate of genetic variability, most likely as an effect of severe restrictions of population size during the last glaciation. The pattern of differentiation at protein loci is very similar to that observed for seven morphological traits examined. This similarity suggests that the same evolutionary forces have acted upon both sets of characters.     

Genetic variation and population structure ofCarex breviculmis (Cyperaceae) in Korea

We determined the genetic diversity and population structures ofCarex breviculmis (Cyperaceae) populations in Korea, using genetic variations at 23 allozyme loci.C. breviculmis is a long-lived herbaceous species that is widely distributed in eastern Asia. A high level of genetic variation was found in 15 populations. Twelve enzymes revealed 23 loci, of which 11 were polymorphic (47.8%). Genetic diversity at the speciesand population levels were 0.174 and 0.146, respectively. Total genetic diversity (H_T = 0.363) and within-population genetic diversity (H_s = 0.346) were high, whereas the extent of the population divergence was relatively low (G_ST = 0.063). Deviation from random mating (Fis) within the 15 populations was 0.206. An indirect estimate of the number of migrants per generation(Nm = 3.69) indicated that gene flow was extensive among Korean populations of this species. Analysis of fixation indices revealed a substantial heterozygote deficiency in some populations and at some loci. Genetic identity between popu-lations was high, exceeding 0.956.     

Variation in MHC genotypes in two populations of house sparrow (Passer domesticus) with different population histories

Small populations are likely to have a low genetic ability for disease resistance due to loss of genetic variation through inbreeding and genetic drift. In vertebrates, the highest genetic diversity of the immune system is located at genes within the major histocompatibility complex (MHC). Interestingly, parasite‐mediated selection is thought to potentially maintain variation at MHC loci even in populations that are monomorphic at other loci. Therefore, general loss of genetic variation in the genome may not necessarily be associated with low variation at MHC loci. We evaluated inter‐ and intrapopulation variation in MHC genotypes between an inbred (Aldra) and a relatively outbred population (Hestmannøy) of house sparrows (Passer domesticus) in a metapopulation at Helgeland, Norway. Genomic (gDNA) and transcribed (cDNA) alleles of functional MHC class I and IIB loci, along with neutral noncoding microsatellite markers, were analyzed to obtain relevant estimates of genetic variation. We found lower allelic richness in microsatellites in the inbred population, but high genetic variation in MHC class I and IIB loci in both populations. This suggests that also the inbred population could be under balancing selection to maintain genetic variation for pathogen resistance.     

High population differentiation and genetic variation in the endangered Mexican pine Pinus Rzedowskii (Pinaceae)

Pinus rzedowskii is an endangered pine species from Michoaca´n (central Me´xico), which has been previously reported from only three localities. Classified within the subgenus Strobus, it exhibits intermediate morphological characters between subgenera Strobus and Pinus. We analyzed genetic aspects that could shed light on the evolution and conservation of this species. The genetic structure of nine populations was examined using 14 isozyme loci. Pinus rzedowskii has a relatively high level of genetic variation with 46.8% of the loci assayed being polymorphic, a total of 35 alleles, and a mean heterozygosity per population of 0.219. We calculated Wright's F_ST statistic to estimate gene flow indirectly and to evaluate whether or not there was genetic structuring among populations. We found a marked differentiation among populations (F_ST = 0.175) and significant inbreeding (F_IS = 0.247). No pattern of isolation by distance was found. We also constructed a dendrogram based on a genetic distance matrix to obtain an overview of the possible historical relationships among populations. Finally, we found a convex relationship between the genetic distance among populations and the number of ancestral lineages, suggesting that demographically this species has not been at risk recently. Although endangered, with small and fragmented populations, P. rzedowskii shows higher levels of genetic variation than other conifer species with larger populations or similar conservation status.     

High genetic divergence characterizes populations of the endemic plant Lithophragma maximum (Saxifragaceae) on San Clemente Island

Narrowly-ranging species frequently harbor less genetic variability relative to widespread relatives and face graver extinction threats due to the heightened impacts of stochastic events on ecological and genetic diversity. In this study, we examined the impact of historical and current threats to the maintenance of genetic variation in Lithophragma maximum (Saxifragaceae), a perennial herb endemic to San Clemente Island, California. This species exists as small populations confined to canyons along 4 km of the southeast coastline of the island. In 15 populations analyzed with 10 microsatellite markers, we identified an average of 2.05 alleles per locus and 58.7% polymorphic loci. Significant departures from Hardy–Weinberg equilibrium existed in six populations; five of these exhibited heterozygote deficiency. Bayesian inference of genetic structure indicated a significant amount of structure among populations and canyons and infrequent gene flow even over very short distances. We also identified a significant and positive correlation between genetic and geographic distances, indicative of isolation by distance. There was no evidence of recent bottlenecks in any of the sampled populations, but older bottlenecks were detected in two populations. These results suggest that populations of L. maximum have historically been small and isolated, which is likely due to the rugged habitat in which this species occurs and limited pollen and seed dispersal. Given the high degree of structure observed across populations, we suggest that conservation efforts should focus on preserving populations in multiple canyons, maintaining large population sizes to preserve genetic variation, and controlling the spread of invasive species in areas where L. maximum occurs.     

Population Genetic structure ofPotentilla fragariodes var.major (Rosaceae) in Korea

The genetic diversity and population structure of eighteenPotentilla fragariodes var.major (Rosaceae) populations in Korea were determined using genetic variations at 22 allozyme loci. The percent of polymorphic loci within the enzymes was 66.7%. Genetic diversity at the species level and at the population level was high (Hes = 0.203; Hep = 0.185, respectively), whereas the extent of the population divergence was relatively low (G_ST = 0.069). F_IS, a measure of the deviation from random mating within the 18 populations, was 0.075. An indirect estimate of the number of migrants per generation (Nm = 3.36) indicated that gene flow was high among Korean populations of the species. In addition, analysis of fixation indices revealed a slight heterozygote deficiency in some populations and at some loci. Wide geographic ranges, perennial herbaceous nature and the persistence of multiple generations are associated with the high level of genetic variation. AlthoughP. fragariodes var.major usually propagated by asexually-produced ramets, we could not rule out the possibility that sexual reproduction occurred at a low rate because each ramet may produce terminal flowers. Mean genetic identity between populations was 0.983. It is highly probable that directional movement toward genetic uniformity in a relatively homogeneous habitat operates among Korean populations ofP. fragariodes var.major.     

Landscape discontinuities influence the population structure of Acer opalus ssp. obtusatum Waldst. & Kit. ex Willdenow

The major goal of landscape genetics is to understand how landscape structure genetic variation in natural populations. We investigated molecular diversity in Acer opalus subsp. obtusatum sampled from 95 sites using 14 nuclear microsatellite loci. The average number of alleles per nuclear microsatellite locus differed among sampling sites; the number was high (4.9 alleles) in populations from the Basilicata and Molise regions, where heterozygosity was also high (0.679, Molise; 0.669, Basilicata). Differentiation between sites was often low (mean F_ST = 0.220), indicating few genetic differences between most sites. There was a clear excess of homozygotes (mean H_o = 0.450, mean H_e = 0.513) and a relatively high F_IS (mean = 0.451), suggesting a consistent level of inbreeding in many A. opalus subsp. obtusatum populations. There was a significant pattern of isolation by distance across the study area (Mantel test; R² = 0.0662, P < 0.001). Two assignment methods (Structure and Geneland) produced some similarities in their definitions of population structure, especially for populations from the Campania and Tuscany regions. These two important genetic discontinuities were not associated with any physical barriers.     

Genetic diversity and morphological differentiation in Liatris helleri (Asteraceae), a threatened plant species

Liatris helleri (Asteraceae) is an insect-pollinated herbaceous perennial endemic to several high-elevation sites in the Blue Ridge Mountains of North Carolina. Allozymes were used to describe the genetic diversity and population structure in nine populations of this rare, federally listed species. Differences in leaf morphology were also examined for greenhouse-grown plants representing several populations. The proportion of the total genetic diversity found among populations, as indicated by the allozyme data, was 16%. Higher levels of population differentiation were found for differences in leaf shape; population of origin accounted for 37% of the variation in maximum leaf width, while families within populations accounted for 7%. In contrast to many endemic species, L. helleri maintains fairly high levels of genetic diversity. For the species, the percent polymorphic loci was 87.5, the average number of alleles at variable loci was 3.00 and the gene diversity was 0.276. Mean population values were percent polymorphic loci =58.4, mean number of alleles per polymorphic locus =2.59 and gene diversity =0.219. The estimated gene flow was low (Nm=0.85–1.32) and a relatively high correlation (r=0.55; p<0.005) was found between linear geographic and genetic distance. This suggests that the populations are partially isolated by distance, despite the limited range (<60 km) of the species. We recommend that population distinetiveness be maintained in restoration efforts.     

Genetic variation and differentiation in Nordic populations of Elymus alaskanus (Scrib. ex Merr.) Löve (Poaceae)

 To gain information on the extent and nature of genetic variation in Elymus alaskanus, levels and distribution of genetic variation were assessed within and among 13 populations originating from Iceland, Norway, Sweden and Russia using allozymes. The results showed that four (30.7%) of the 13 loci were polymorphic within the species, while the mean percentage of polymorphic loci within the populations was 1.9%. The mean number of alleles per locus for the species was 1.8 and 1.02 across the populations. Genetic diversity at the species level was low (H _es=0.135), and mean population diversity was notably lower (H _ep=0.005). A high degree of genetic differentiation was observed among populations. The salient points emerging from this study are: (1) statistically significant differences were found in allele frequencies among populations for every polymorphic locus (P<0.001), (2) the high mean coefficient of gene differentiation (G _ST) showed that 95% of the total allozyme variation was attributable to differences among populations, and (3) relatively high genetic distances between the populations were obtained (mean D=0.16). The Norwegian populations had the highest genetic diversity as compared with the other populations. Geographical comparisons revealed three different groups of populations clearly differentiated, i.e. Scandinavia (Norway and Sweden), Iceland and Russia. Cluster and principal coordinates analyses revealed the same genetic patterns of relationships among populations. Generally, this study indicates that E. alaskanus contains low allozymic variation in its populations. The implications of these results for the conservation of the species are discussed. Received: 23 October 1998 / Accepted: 19 December 1998     

Allelic diversity of high-molecular-weight glutenin protein subunits in natural populations of Dasypyrum villosum (L.) Candargy

Dasypyrum villosum (L.) Candargy (2n=14, V genome) is a wild, allogamous, diploid grass species that is a potential genetic resource for wheat improvement. The diversity of high-molecular-weight (HMW) glutenin subunits of the seed storage proteins of this species was examined in populations sampled in their natural habitats in Italy and Yugoslavia where the species is widely distributed. The results of selfed progeny tests confirmed that the allelic variation of HMW-glutenin subunits in D. villosum is controlled by a single locus (Glu-V1). Fourteen alleles at Glu-V1 were found among 982 individuals representing 12 populations from Italy and two from Yugoslavia, with a mean of seven alleles per population. Among the 14 Glu-V1 alleles, one produced no HMW-glutenin subunits, ten coded for a single subunit, and three for two subunits. The mobilities of all the subunits in SDS-PAGE gels were greater than that of reference subunit 7 of Triticum aestivum cv Chinese Spring. Eight of the alleles were relatively abundant (mean frequency over all populations ranged from 0.08 to 0.17) and distributed widely among the 14 populations (8 to 14); five of the alleles were rare (0.003 to 0.021) and found in only 1 to 5 populations. The frequencies of two alleles could not be individually estimated because of the similar electrophoretic mobility of their subunits. The multiple-allelic diversity at Glu-V1 was high (H_e ranged from 0.700 to 0.857) but similar from population to population. Overall, about 7% of the total allelic variation was distributed among populations (G_st=0.072), and more than 90% within populations. Whether the allelic variation at Glu-V1 is subject to natural selection is unknown, but the discovery of the homozygous null Glu-V1 alleles in the present study may be useful in pursuing this question. The multiple-allelic diversity in Glu-V1 presents the plant breeder with an opportunity to evaluate and select the most useful alleles for transfer to wheat. The importance of an evaluation genetic diversity in a wild species before interspecific gene transfers are attempted is well illustrated in this study.     

POPULATION VARIATION,OUTCROSSING, AND COLONIZATION OF DISTURBED AREAS BY CALAMAGROSTIS CANADENSIS: EVIDENCE FROM ALLOZYME ANALYSIS

Calamagrostis canadensis (a rhizomatous grass) exists in temperate forest sites of different successional age. It can rapidly colonize disturbed sites to form dense swards. We examined allozyme variation in: four populations (mature forest, intermediate aged forest, forest cutblock, wetland); nine small plots (2 m × 4 m) within the cutblock; and progeny of several families from three populations; in order to assess the mode of colonization of disturbed areas and the effect of successional changes on population genetic structure. All four populations showed equal and extensive genetic variation (1.5 to 1.7 alleles per locus [K], 41.7% to 50% polymorphic loci [PPL], H_st = 0.155 to 0.208) and were not genetically differentiated (G_st = 0.0193, 1 = 0.986 to 0.997). The cutblock subpopulations also showed considerable genetic variation (K = 1.6 to 1.8, PPL = 50% to 58.3%, H_st = 0.151 to 0.278) and no microdifferentiation (G_st = 0.034, I = 0.967 to 0.997). We found 14 different genotypes among the 30 individuals sampled from the cutblock as a whole (based on five polymorphic loci). The cutblock subpopulations had from nine to 14 different genotypes each (same five loci, 18 individuals per subpopulation). Seed produced was primarily outcrossed (multilocus estimate 0.888 to 0.900). We concluded that disturbed sites are colonized primarily by sexually produced seedlings. Potential genetic drift and natural selection, which occur during subsequent successional changes, do not result in reduced genetic variation or population differentiation.