Biochemical assessment of the taxonomic diversity of the operculate land snail, Cyclophorus fulguratus (Gastropoda: Cyclophoridae), from Thailand

Allozyme variation was examined in 223 samples of the operculate land snail Cyclophorus fulguratus from 13 localities across three regions of Thailand. Using horizontal starch gel electrophoresis, 13 allozyme presumed loci (12 polymorphic) were screened. Heterozygosity was moderate in C. fulguratus (H_exp = 0.008–0.127) with a high genetic heterogeneity among samples (F_st = 0.734). Populations showed a greater genetic differentiation in central Thailand (F_st = 0.380) than in northeastern Thailand (F_st = 0.108), suggesting frequent gene flow among populations in northeastern Thailand. C. fulguratus exhibits a strong pattern of isolation by distance over the entire tested species range in Thailand and may potentially have been involved in an extensive local fragmentation. Results of the distance analysis revealed that large genetic divergence has occurred among the central, northeastern and eastern Thailand groups [D = 0.361–0.701], strongly suggesting populations from these three geographical regions may actually represent or else be evolving into separate species.     

Genetic structure of the common terrestrial pulmonate snail,Cryptozona siamensis (Pfeiffer, 1856), in Thailand

Allozyme variation was examined in 432 specimens of the pulmonate snail, Cryptozona siamensis, from 24 localities across three regions of Thailand plus an additional population from Malaysia. Although this snail is a cosmopolitan species it was predicted that C. siamensis should exhibit a large degree of genetic subdivision across these regions due to a low level of inter-population gene flow. To test this hypothesis, 10 enzyme systems were screened using horizontal starch gel electrophoresis, from which 14 presumed allozyme loci were scored and 13 found to be polymorphic. For these 13 polymorphic loci the expected heterozygosity levels were moderate (H_exp = 0.036–0.183, mean = 0.101). Genetic differentiation among the samples was low, with a low F_ST value (0.254) and genetic distance (D = 0.000–0.124, mean = 0.034) and no significant isolation by distance (IBD) across the whole sampled range of Thailand or Thailand plus Malaysia. However, an IBD pattern in the population substructure in the central Thailand region was detected. The low F_ST and moderate H_exp values in various populations of C. siamensis suggests a high degree of gene flow/migration between populations across the three geographic regions of Thailand (northern, central and southern) as well as the sampled population in Malaysia, perhaps associated with the anthropochoric effect of snail dispersal. The apparent IBD in the central Thailand region could be the consequence of local dynamics though this region.     

Low heterogeneity in populations of the terrestrial earthworm,Metaphire peguana (Rosa, 1890), in Thailand,as revealed by analysis of mitochondrial DNA COI sequences and nuclear allozymes

The genetic variation of a widely distributed terrestrial earthworm species, Metaphire peguana (Rosa, 1890), was examined in Thailand using allozyme and mitochondrial (mt)DNA cytochrome oxidase subunit 1 (COI) sequence analyses. A total of 274 individuals were collected from 13 localities in Thailand and scored for 12 enzyme systems (18 presumptive allozyme loci) using horizontal starch gel electrophoresis. Fourteen of these presumed loci were found to be polymorphic. In addition, a 660 bp fragment of the COI mtDNA gene was amplified and sequenced from one representative individual for each of the 13 geographical regions. The expected heterozygosity (H_exp) was relatively low, ranging from 0.059–0.147 with an overall mean of 0.092 ± 0.02 and there was no significant isolation by distance pattern for the 13 populations (localities) across the entire study area (P-value > 0.05). Genetic divergences among the samples were low, with a low genetic distance (mean = 0.048) and uncorrected p-distance (mean = 0.02) indicating frequent gene flow among these populations in Thailand. The monophyly of M. peguana across these regions was supported by Neighbor joining, Maximum likelihood and Bayesian inference based phylogenetic analysis of the mtDNA COI sequences with no geographic location dependent pattern. This may be due to anthropogenic movement of M. peguana in soil or with plant scions throughout this region.     

Genetic variation amongst viviparid snails in the genus Mekongia (Prosobranchia: Viviparidae) in Thailand

Allozyme variation in viviparid snails from the genus Mekongia in Thailand were examined across the different species, subspecies and geographical locations (river drainage systems). Using horizontal starch gel electrophoresis, 11 presumed allozyme loci (eight polymorphic) from eight enzyme systems were screened. Heterozygosity was moderately low (Hexp = 0.000–0.109, mean = 0.037). One population of Mekongia pongensis (Nong Khai) was monomorphic at all 11 examined loci in contrast to the other two populations, suggesting bottleneck within this population. Populations were more differentiated in the Mekongia sphaericula complex (F_ST = 0.587) than in either the Mekongia swainsoni complex (F_ST = 0.161) or M. pongensis species (F_ST = 0.073). Mekongia sphaericula sphaericula and Mekongia sphaericula extensa exhibited fixed allele differences at two loci, a high genetic distance (D = 0.265–0.300) and a potential polyphyletic relationship, suggesting two distinct lineages (species).     

MATING SYSTEM AND GENETIC STRUCTURE OF THE DISTYLOUS TROPICAL TREE PSYCHOTRIA FAXLUCENS (RUBIACEAE)

The population genetics and mating system of the understory tropical rain forest tree Psychotria faxlucens were studied at two plots in Los Tuxtlas, Veracruz, México, on the Gulf of México coast. This species is distylous and is pollinated by moths, mainly small hawkmoths. The seeds are dispersed by gravity and by frugivorous birds. Controlled pollinations indicate that the trees are self-incompatible and that intramorph pollinations have lower compatibilities than intermorph pollinations. The pollen: ovule ratio is high, suggesting obligate xenogamy. Using electrophoretic allozyme methods we found that eight out of 20 loci were polymorphic (P = 0.400), the observed heterozygosity (H) was 0.198, and the mean expected heterozygosity (H) was 0.495, both relatively high values compared with that reported for tropical trees. The genetic differentiation between the two plots is low, as shown by the heterogeneity in allele frequencies and the F_st (mean F_st seedlings = 0.031, mean F_st adults = 0.026), although for some loci the plot differentiation is statistically significant. The studied populations are near Hardy-Weinberg proportions, both for seedlings (mean F = 0.128) and adults (mean F = 0.075). From the fixation rate, an indirect estimate of the outcrossing rate at equilibrium gave a mean of t = 0.898 for plot 1 and 0.685 for plot 2. Direct single loci and multiloci outcrossing rate estimates were generally not statistically different from 1.0.     

Allozyme and mitochondrial DNA variability within the New Zealand damselfly genera Xanthocnemis,Austrolestes, and Ischnura (Odonata)

Abstract

We collected larval damselflies from 17 sites in the North, South and Chatham Islands, and tested the hypotheses that: (1) genetic markers (e.g., allozymes, mtDNA) would successfully discriminate taxa; and (2) the dispersal capabilities of adult damselflies would limit differentiation among locations. Four species from three genera were identified based on available taxonomic keys. Using 11 allozyme loci and the mitochondrial cytochrome c‐oxidase subunit I (COI) gene, we confirmed that all taxa were clearly discernible. We found evidence for low to moderate differentiation among locations based on allozyme (meani F _ST = 0.09) and sequence (COI) divergence (<0.034). No obvious patterns with respect to geographic location were detected, although slight differences were found between New Zealand's main islands (North Island, South Island) and the Chatham Islands for A. colensonis (sequence divergence 0.030–0.034). We also found limited intraspecific genetic variability based on allozyme data (H_exp < 0.06 in all cases). We conclude that levels of gene flow/dispersal on the main islands may have been sufficient to maintain the observed homogeneous population structure, and that genetic techniques, particularly the COI gene locus, will be a useful aid in future identifications.     

High genetic diversity but limited gene flow among remnant and fragmented natural populations of Liriodendron chinense Sarg

As a relic species, Liriodendron chinense is now recognized as an endangered species. To better understand the genetic structure and differentiation among remnant populations of L. chinense, we determined the genotypes of 14 simple sequence repeats (SSRs) loci across 318 individuals from 12 natural populations and 750 seedlings from five offspring populations. We found that L. chinense maintained high genetic diversity (H_e = 0.7385) within populations but moderate genetic differentiation (F_st = 0.1956) and low gene flow (N_m = 1.0283) between populations. The genetic diversity was slightly lower for offspring populations than for their corresponding natural populations. Moreover, using a two-phased model of mutation (TPM), we demonstrated that significant bottlenecks had occurred in six populations. A Mantel test revealed a statistically significant correlation between the geographic distances and genetic distances between populations (r = 0.5011, P = 0.002). Hence, we presume that geographical isolation and habitat fragmentation might contribute jointly to current population structure of L. chinense. We suggest that populations from southern Yunnan can be regarded as a variety of L. chinense, given their large deviation from other populations. Our findings may be of value for the conservation and use of L. chinense.     

Conservation genetics of Butte County meadowfoam (Limnanthes floccosa ssp. californica Arroyo), an endangered vernal pool endemic

The endangered annual plant Limnanthes floccosa ssp. californica Arroyo is restricted to vernal pools in Butte County, California. To identify populations with unique genetic resources, guide reintroduction efforts, and design seed collection scenarios for long-term ex situ seed storage we determined extant genetic diversity and structure by surveying 457 individuals from 21 distinct populations using nine polymorphic microsatellite markers. We found low within population genetic diversity: low allelic diversity (1.9 [0.06 SE] alleles/locus); low heterozygosity (H _obs = 0.10 ± 0.018, H _exp = 0.19 ± 0.015), and a high fixation index (0.556 ± 0.044). The number of polymorphic loci ranged between 11 and 89%. Bayesian ordination determined 20 distinct populations and we found high genetic structure among these (F _st = 0.65, P < 0.0001). We identified notable gene flow barriers across populations, confirming regional structuring between three previously defined population density centers and two outlying populations (F _st = 0.21, P < 0.0001). Population size estimates ranged between ~50 and >5,000 extant plants per site. Our study confirms previous isozyme-based results and suggests that the loss of any population would represent a significant loss in the species’ genetic diversity. Recovery requires active restoration of existing populations and permanent habitat protection. We recommend close comparison of microhabitats of declining populations with genetically similar populations, to determine the potential for human assisted gene flow via seed movement to recover declining populations.     

Were the main mountain ranges in the Korean Peninsula a glacial refugium for plants? Insights from the congeneric pair Lilium cernuum – Lilium amabile

The main Korean mountain range (the so-called “Baekdudaegan”), which stretches from north to south across most of the country, has been thought to harbor glacial refugia for boreal plant species, where they likely found relatively stable habitats and maintained large population sizes. Under this scenario, high levels of genetic variation and low or moderate degree of differentiation among populations within these species were expected. To test this hypothesis, we examined levels of allozyme diversity (14 loci) in eight populations of the boreal herb Lilium cernuum, which in Korea occurs largely along the Baekdudaegan and, as a reference, in eight populations of its congener Lilium amabile, a temperate species that is distributed on lower hillsides in peripheral regions of the Baekdudaegan. L. cernuum harbored higher levels of genetic variation within populations than L. amabile (%P = 49.1 vs. 25.0, A = 1.71 vs. 1.34, and H_e = 0.159 vs. 0.048). Genetic differentiation among populations was low for both species (F_ST = 0.119 and 0.014 for L. cernuum and L. amabile, respectively). A series of historical and ecological factors may explain the contrasting levels of genetic diversity between L. cernuum and L. amabile: occurrence within the main ranges of the Baekdudaegan (enduring the glacial periods in macrorefugia) vs. low elevation peripheral areas (in microrefugia) and shade-tolerant vs. shade-intolerant. This study, as well as previous population genetics studies, strongly suggests that the Baekdudaegan merits high priority for conservation given its proposed role as glacial refugia for montane species.     

Genetic diversity of the endangered endemic Microcycas calocoma (Miq.) A. DC (Zamiaceae, Cycadales): Implications for conservation

The diversity and genetic structure of seven populations of Microcycas calocoma (Miq.) A. DC, were analyzed by gel electrophoresis using 19 allozymes. The mean number of alleles per locus (A) was 1.49 and the percentage of polymorphic loci was relatively high (P = 48.09). The mean observed (H_o) and expected heterozygosity (H_e) were 0.20 and 0.17, respectively. The F-statistics revealed a high population structure (F_st = 0.34). Mean gene flow between population pairs was Nm = 0.96. Results were compared with those of other cycad species, and indicate that M. calocoma populations have become fragmented due to increasing pressures of habitat conversion and disturbance. Also, geographical isolation among populations has generated allele loss in relation to altitude. The establishment and maintenance of protected areas for in situ conservation is critical to preserve the high genetic diversity of M. calocoma. Conservation strategy guidelines have been specified.     

Genetic Structure and Gene Flow in Elymus glaucus (blue wildrye): Implications for Native Grassland Restoration

Interest in using native grass species for restoration is increasing, yet little is known about the ecology and genetics of native grass populations or the spatial scales over which seed can be transferred and successfully grown. The purpose of this study was to investigate the genetic structure within and among populations of Elymus glaucus in order to make some preliminary recommendations for the transfer and use of this species in revegetation and restoration projects. Twenty populations from California, Oregon, and Washington were analyzed for allozyme genotype at 20 loci, and patterns of variation within and among populations were determined. Allozyme variation at the species level was high, with 80% of the loci polymorphic and an average expected heterozygosity (an index of genetic diversity) of 0.194. All but two of the populations showed some level of polymorphism. A high degree of population differentiation was found, with 54.9% of the variation at allozyme loci partitioned among populations (F_st= 0.549). A lesser degree of genetic differentiation among closely spaced subpopulations within one of the populations was also demonstrated (F_st= 0.124). Self-pollination and the patchy natural distribution of the species both likely contribute to the low level of gene flow (N_m= 0.205) that was estimated. Zones developed for the transfer of seed of commercial conifer species may be inappropriate for transfer of E. glaucus germplasm because conifer species are characterized by high levels of gene flow. Limited gene flow in E. glaucus can facilitate the divergence of populations over relatively small spatial scales. This genetic differentiation can be due to random genetic drift, localized selective pressures, or both. In order to minimize the chances of planting poorly adapted germplasm, seed of E. glaucus may need to be collected in close proximity to the proposed restoration site.     

SPECSTAT: PC software for statistical data analysis in the field of population genetics

This set of applied programs, SPECSTAT, has been written in Turbo Pascal-5 and is adapted for an IBM compatible PC-XT/AT using MS-DOS. SPECSTAT is a small software package (approximately 300K) which has high efficacy when performing calculations. SPECSTAT provides some new computational opportunities not provided by the existing statistical packages for analyzing allozyme population genetic data. Furthermore, it is able to carry out some simple transformations of quantitative traits (QT) and the genotypic data matrix. These transformations are convenient for the investigation of QT and allele frequencies and for the analysis of the correlations between QT and allozyme genotypic codes. From the vectors of genotypic codes for each sample, the following parameters are computed: i) the allele frequencies with standard errors (SE), ii) chi-squared values of goodness-of-fit for the observed and expected Hardy-Weinberg genotype frequencies and iii) H_o, H_s and F_is values. The H_t, F_it, F_st, D_st′ and F_st′ statistics, chi-squared values in the heterogeneity test of the predominant alleles, and G-statistics of all-allelic heterogeneity among samples with Williams' correction (Sokal & Rolf, 1981) are also available. Calculations are performed to produce single-locus and combined matrices of Nei's genetic distances Dn and Dm (standard and minimal unbiased), and the matrix of combined Kalabushkin's similarity metrics, which maximize small differences. Other computational opportunities are provided as well. Output data are simple ASCII files and are organized in a compact mode which can either be used directly for publication or used after minor changes in further calculations.     

Conservation genetics of Heritiera littoralis (Sterculiaceae), a threatened mangrove in China,based on AFLP and ISSR markers

AFLP and ISSR markers were used to determine the genetic variations in eight mangrove and non-mangrove populations of Heritiera littoralis (Sterculiaceae), a threatened species in China. Our results showed a moderate to high level of genetic variation in this species (P = 63.69%, H_T = 0.20 for AFLP; P = 76.07%, H_T = 0.22 for ISSR), and a relatively high level of genetic differentiation among populations (G_ST = 0.24 for AFLP and 0.27 for ISSR). Life history traits, long-distance dispersal of floating seeds, and local environments may play important roles in shaping the genetic diversity and genetic structure of this species. Investigation of the plant’s reproductive capacity showed that the natural seed production of H. littoralis was low, as was the germination rate and the transformation rate from juvenile to adult. H. littoralis is seriously threatened and is in urgent need of conservation in China.     

Pattern of genetic structure of the common stream fish,Neolissochilus soroides (Pisces: Cyprinidae), addresses the importance of protected areas in eastern Thailand

The well-known presence of mahseers, Neolissochilus soroides (Cyprinidae), in forested streams in eastern Thailand has attracted many visitors to protected areas for several decades. Because of its historical high abundance, this species was never considered of conservation concern. In this study, the authors revealed that mahseers are very limited to upstream areas in mountains facing the Gulf of Thailand and are now solely confined to habitats within protected areas. The fish were sampled below seven waterfalls in four national parks. All individuals were analysed using a fragment of the mitochondrial DNA cytochrome b gene and eight nuclear microsatellite DNA loci to uncover spatial genetic patterns. Cytochrome b data showed very low genetic diversity but indicated strong genetic differentiation between the most distant Klong Kaeo (KK) population and the other populations. The more variable microsatellite DNA markers showed moderate level of genetic diversity compared to other mahseers but revealed limited gene flow among all locations (overall F_ST = 0.25, P < 0.05). In addition, significant correlation was found between genetic and geographic distances (P < 0.05). Genetic bottleneck analyses provided an insight into evolutionary history in N. soroides that may have experienced past reduction in population size. As eastern Thailand is a relatively heavily populated region, habitat modification in lowland areas is inevitable, and it will have consequences for species that prefer fast-flowing and clear water. Protected areas therefore provide valuable sanctuaries for N. soroides in headwater streams.     

Genetic diversity and differentiation of the Critically Endangered Hispaniolan palm Coccothrinax jimenezii M.M. Mejía & R.G. García based on novel SSR markers

Coccothrinax jimenezii M.M. Mejía & R.G. García is a Critically Endangered palm species restricted to Haiti (one population near the city of Gonaïves with 43 individuals) and the Dominican Republic (one population on the shores of Lago Enriquillo with 18 individuals). The species faces two major conservation challenges: (1) water level rise in the hypersaline Lago Enriquillo and (2) overexploitation of leaves for making brooms in Haiti. Six SSR microsatellite loci were used to access levels of genetic variation and the genetic structure of these two populations. Only the Gonaïves site had loci that deviated from Hardy–Weinberg Equilibrium (2 loci). Both populations exhibited a relatively large number of private alleles (13 in Lago Enriquillo and 14 in Gonaïves) and did not show evidence of genetic bottlenecks. Inbreeding coefficients were much larger in Gonaïves (F_is = 0.232) than in Lago Enriquillo (F_is = 0.093). We detected high genetic differentiation among these sites (F_st = 0.497) suggesting that additional taxonomic studies are needed to determine if individuals from these two sites should be recognized as belonging to two different taxa. Because of taxonomic uncertainties we recommend not to translocate individuals between sites in future conservation activities involving this species.     

Gene variation and genetic differentiation among populations of the solitary mud dauber wasp Trypoxylon (Trypargilum) albitarse Fabricius 1804 (Hymenoptera, Crabronidae)

Trypoxylon is a genus of solitary crabronid wasps whose population genetics is poorly known. The purpose of the present study was to investigate the genetic variation and differentiation among five populations of Trypoxylon albitarse, a species widely distributed throughout the Neotropics, with records from Panama to northern Argentina. Eight species-specific microsatellite loci were used for genotyping 96 adult wasps (one female per nest) sampled at five sites in Brazil. The analysis of allelic richness and private alleles indicated high genetic diversity in the populations sampled. Pairwise comparisons using the F _st and D _est indices revealed significant differentiation for all, but one pair of populations. F _st, D _est, AMOVA and assignment test values pointed to inter-population differentiation. Additionally, the analysis of population structure using Bayesian and PCA methods characterized two alternative genetic groups. The Mantel test indicated no correlation between genetic and geographic distances. Despite evidence of considerable dispersal capacity for T. albitarse, the data indicate low to moderate population structuring in this species.     

The genetic structure of populations of the sea urchin Strongylocentrotus intermedius from the northwestern Sea of Japan in connection with a shift in spawning time

Usin seven allozyme loci as gene markers, we studied the genetic structure of ten natural populations of the sea urchin Strongylocentrotus intermedius in the northwestern Sea of Japan that differ in the proportion of individuals with different spawning seasonality (early spawning at the end of May?CJune and late spawning in September-early October). This study revealed the spatial genetic heterogeneity of the sea-urchin populations (F _st = 0.051); its degree was independent of the geographic distance between populations. Out of the seven loci that were surveyed, four loci (peptidase Pep-1, Pep-2, mannose phosphate isomerase Mpi, and inorganic pyrophosphatase Ipp) accounted for the differences between pairs of samples; different loci contributed to the variation in each sample pair. The genetic similarity between pairs of populations ranged from 0.905 to 0.988. The genetic heterogeneity of the sea-urchin populations seems to be a result of both genetic drift and natural selection. At the same time, no significant genetic differences were found between specimens of S. intermedius with different spawning times (the genetic similarity was 0.988?C0.991). The shift in spawning season from autumn to early summer in the populations of S. intermedius inhabiting the areas of Peter the Great Bay adjacent to Vladivostok city can be explained by a phenotypic response of this species to environmental changes caused by chronic anthropogenic pollution of the bay.     

Evolutionary implications of allozyme and RAPD variation in diploid populations of dioecious buffalograss Buchloë dactyloides

Buffalograss, Buchloë dactyloides, is widely distributed throughout the Great Plains of North America, where it is an important species for rangeland forage and soil conservation. The species consists of two widespread polyploid races, with narrowly endemic diploid populations known from two regions: central Mexico and Gulf Coast Texas. We describe and compare the patterns of allozyme and RAPD variation in the two diploid races, using a set of 48 individuals from Texas and Mexico (four population samples of 12 individuals each). Twelve of 22 allozyme loci were polymorphic, exhibiting 35 alleles, while seven 10-mer RAPD primers revealed 98 polymorphic bands. Strong regional differences were detected in the extent of allozyme polymorphism: Mexican populations exhibited more internal gene diversity (H_e= 0.20, 0.19) than did the Texan populations (H_e= 0.08, 0.06), although the number of RAPD bands in Texas (n= 62) was only marginally smaller than in Mexico (n= 68). F-statistics for the allozyme data, averaged over loci, revealed strong regional differentiation (mean F_RT=+ 0.30), as well as some differentiation among populations within regions (mean F_PR=+ 0.09). In order to describe and compare the partitioning of genetic variation for multiple allozyme and RAPD loci, we performed an Analysis of Molecular Variance (AMOVA). AMOVA for both allozyme and RAPD data revealed similar qualitative patterns: large regional differences and smaller (but significant) population differences within regions. RAPDs revealed greater variation among regions (58.4% of total variance) than allozymes (45.2%), but less variation among individuals within populations (31.9% for RAPDs vs. 45.2% for allozymes); the proportion of genetic variance among populations within regions was similar (9.7% for RAPDs vs. 9.6% for allozymes). Despite this large-scale concordance of allozyme and RAPD variation patterns, multiple correlation Mantel techniques revealed that the correlations were low on an individual by individual basis. Our findings of strong regional differences among the diploid races will facilitate further study of polyploid evolution in buffalograss.     

Population genetic structure of the Korean threadsail filefish (Stephanolepis cirrhifer) based on microsatellite marker analysis

The threadsail filefish Stephanolepis cirrhifer is one of the most important commercial fish resources in Korea. However, its natural populations have declined drastically over the last several decades. To investigate the genetic characteristics of the threadsail filefish for conservation and management purposes, its genetic variation was analyzed in Korean fishing grounds using 11 microsatellite loci. All populations showed moderate genetic diversity (mean number of alleles (N_A) = 8.6, expected heterozygosity (He) = 0.73), representing a slightly lower level of genetic variability than other congeneric species. The presence of a weak genetic population substructure was detected (F_ST = 0.023, R_ST = 0.030, P < 0.001), but this substructure did not feature significant isolation based on the distance between populations. This differentiation may be primarily attributable to genetic differences between populations from Geomundo and other localities, based on relative low level of gene flow, a high level of pairwise F_ST and R_ST or the position of this population in a phylogenetic tree. An analysis of molecular variance (AMOVA) also revealed a greater part of the variation within the population and genetic differentiation among the samples analyzed and identified two genetic clusters. The possibility of a recent genetic bottleneck was observed in some populations of S. cirrhifer. Given the prevailing ocean currents and the intensity of threadsail filefish harvesting activities in Korea, the possibility that human harvest and stock enhancement activities may have partially contributed to our detected genetic pattern cannot be excluded. Management strategies that take these findings into account might lower the risk of harmful genetic change in the species.     

Geographic Influence on Genetic Structure in the Widespread Neotropical Tree Simarouba amara (Simaroubaceae)

This study aimed to assess the population genetic structure of a widespread Neotropical tree species, Simarouba amara, at local, regional and continental spatial scales. We used five microsatellite loci to examine genetic variation in 14 natural populations (N?=?478 individuals) of this vertebrate-dispersed rain forest tree species in Panama, Ecuador, and French Guiana. Estimates of genetic differentiation (F _st and R _st) were significant among all but one population pair and global differentiation was moderate (F _st?=?0.25, R _st?=?0.33) with 94% of genetic variation ascribed to differences among three main geographic regions (Central America, Western Ecuador, Amazon basin). There was no evidence of isolation by distance within regions. Allele-size mutations contributed significantly (R _ST > F _ST) to the divergences between cis- and trans-Andean populations, highlighting the role of the northern Andean cordilleras as an important geographic barrier for this species.