Species diversity and population density affect genetic structure and gene dispersal in a subtropical understory shrub

Aims The dispersal of pollen and seeds is spatially restricted and may vary among plant populations because of varying biotic interactions, population histories or abiotic conditions. Because gene dispersal is spatially restricted, it will eventually result in the development of spatial genetic structure (SGS), which in turn can allow insights into gene dispersal processes. Here, we assessed the effect of habitat characteristics like population density and community structure on small-scale SGS and estimate historical gene dispersal at different spatial scales.Methods In a set of 12 populations of the subtropical understory shrub Ardisia crenata, we assessed genetic variation at 7 microsatellite loci within and among populations. We investigated small-scale genetic structure with spatial genetic autocorrelation statistics and heterogeneity tests and estimated gene dispersal distances based on population differentiation and on within-population SGS. SGS was related to habitat characteristics by multiple regression.Important findings The populations showed high genetic diversity (H e = 0.64) within populations and rather strong genetic differentiation (F ′ ST = 0.208) among populations, following an isolation-by-distance pattern, which suggests that populations are in gene flow–drift equilibrium. Significant SGS was present within populations (mean Sp = 0.027). Population density and species diversity had a joint effect on SGS with low population density and high species diversity leading to stronger small-scale SGS. Estimates of historical gene dispersal from between-population differentiation and from within-population SGS resulted in similar values between 4.8 and 22.9 m. The results indicate that local-ranged pollen dispersal and inefficient long-distance seed dispersal, both affected by population density and species diversity, contributed to the genetic population structure of the species. We suggest that SGS in shrubs is more similar to that of herbs than to trees and that in communities with high species diversity gene flow is more restricted than at low species diversity. This may represent a process that retards the development of a positive species diversity–genetic diversity relationship.     

Spatial genetic structure in Milicia excelsa (Moraceae) indicates extensive gene dispersal in a low-density wind-pollinated tropical tree

In this study, we analysed spatial genetic structure (SGS) patterns and estimated dispersal distances in Milicia excelsa (Welw.) C.C. Berg (Moraceae), a threatened wind-pollinated dioecious African tree, with typically low density (∼10 adults/km²). Eight microsatellite markers were used to type 287 individuals in four Cameroonian populations characterized by different habitats and tree densities. Differentiation among populations was very low. Two populations in more open habitat did not display any correlation between genetic relatedness and spatial distance between individuals, whereas significant SGS was detected in two populations situated under continuous forest cover. SGS was weak with a maximum S _p-statistic of 0.006, a value in the lower quartile of SGS estimates for trees in the literature. Using a stepwise approach with Bayesian clustering methods, we demonstrated that SGS resulted from isolation by distance and not colonization by different gene pools. Indirect estimates of gene dispersal distances ranged from σ _g = 1 to 7.1 km, one order of magnitude higher than most estimates found in the literature for tropical tree species. This result can largely be explained by life-history traits of the species. Milicia excelsa exhibits a potentially wide-ranging wind-mediated pollen dispersal mechanism as well as very efficient seed dispersal mediated by large frugivorous bats. Estimations of gene flow suggested no major risk of inbreeding because of reduction in population density by exploitation. Different strategy of seed collection may be required for reforestation programmes among populations with different extent of SGS.     

Population history and gene dispersal inferred from spatial genetic structure of a Central African timber tree,Distemonanthus benthamianus (Caesalpinioideae)

African rainforests have undergone major distribution range shifts during the Quaternary, but few studies have investigated their impact on the genetic diversity of plant species and we lack knowledge on the extent of gene flow to predict how plant species can cope with such environmental changes. Analysis of the spatial genetic structure (SGS) of a species is an effective method to determine major directions of the demographic history of its populations and to estimate the extent of gene dispersal. This study characterises the SGS of an African tropical timber tree species, Distemonanthus benthamianus, at various spatial scales in Cameroon and Gabon. Displaying a large continuous distribution in the Lower Guinea domain, this is a model species to detect signs of past population fragmentation and recolonization, and to estimate the extent of gene dispersal. Ten microsatellite loci were used to genotype 295 adult trees sampled from eight populations. Three clearly differentiated gene pools were resolved at this regional scale and could be linked to the biogeographical history of the region, rather than to physical barriers to gene flow. A comparison with the distribution of gene pools observed for two other tree species living in the same region invalidates the basic assumption that all species share the same Quaternary refuges and recolonization pathways. In four populations, significant and similar patterns of SGS were detected. Indirect estimates of gene dispersal distances (sigma) obtained for three populations ranged from 400 to 1200 m, whereas neighbourhood size estimates ranged from 50 to 110.     

Fragmentation can increase spatial genetic structure without decreasing pollen-mediated gene flow in a wind-pollinated tree

Fragmentation reduces population sizes, increases isolation between habitats and can result in restricted dispersal of pollen and seeds. Given that diploid seed dispersal contributes more to shaping fine-scale spatial genetic structure (SGS) than haploid pollen flow, we tested whether fine-scale SGS can be sensitive to fragmentation even if extensive pollen dispersal is maintained. Castanopsis sclerophylla (Lindley & Paxton) Schottky (Fagaceae), a wind-pollinated and gravity seed-dispersed tree, was studied in an area of southeast China where its populations have been fragmented to varying extents by human activity. Using different age classes of trees in areas subject to varying extents of fragmentation, we found no significant difference in genetic diversity between prefragmentation vs. postfragmentation C. sclerophylla subpopulations. Genetic differentiation among postfragmentation subpopulations was also only slightly lower than among prefragmentation subpopulations. In the most fragmented habitat, selfing rates were significantly higher than zero in prefragmentation, but not postfragmentation, cohorts. These results suggest that fragmentation had not decreased gene flow among these populations and that pollen flow remains extensive. However, significantly greater fine-scale SGS was found in postfragmentation subpopulations in the most fragmented habitat, but not in less fragmented habitats. This alteration in SGS reflected more restricted seed dispersal, induced by changes in the physical environments and the prevention of secondary seed dispersal by rodents. An increase in SGS can therefore result from more restricted seed dispersal, even in the face of extensive pollen flow, making it a sensitive indicator of the negative consequences of population fragmentation.     

Fine-scale genetic structure of the common Primula elatior (Primulaceae) at an early stage of population fragmentation

Many rare species are threatened by habitat fragmentation; however, less is known about effects of fragmentation on common species, despite their potential role in ecosystem productivity and functioning. We identified key factors and processes influencing gene flow in a large population of Primula elatior, a common distylous perennial herb, at an early stage of the fragmentation process, i.e., when fragmentation is taking place. Using 19 allozyme loci, we investigated genetic variation and fine-scale spatial genetic structure (SGS) at seedling and adult life stages in relation to fragmentation history (recent bottlenecks), selection, clonal propagation, sexual reproduction (seed and pollen dispersal, distyly), and patchy structure (patch size, plant density, and morph ratio). The main factors contributing to the strong SGS are seed and (to a lesser extent) pollen dispersal, through a spatial Wahlund effect and biparental inbreeding. Significant differences in allele frequencies between seedlings and adults indicate a temporal Wahlund effect. Patch plant density and biased morph ratio also affect the genetic patterns. Our results show that if P. elatior populations evolve into patchworks of small, isolated remnants, genetic erosion, reduced gene flow, and increased inbreeding can be expected, suggesting that such common plant species might require large population sizes to remain viable.     

Fine-Scale Spatial Genetic Structure in Emmer Wheat and the Role of Population Range Position

The extent of spatial genetic structure (SGS) within plant populations depends on seed and pollen dispersal distance, breeding type, level of self-fertilization and effective plant density. Self-fertilizing species with gravity-dispersed seeds are expected to have both small effective population sizes and low pollen movement leading to high genetic structure. Higher SGS can be expected in more patchy and peripheral populations because of lower plant density and population sizes, and lower intensity of gene flow. We tested these predictions analyzing SGS in two core and two peripheral populations of predominantly self-fertilizing emmer wheat. Analysis of SGS with 11 nuclear microsatellites revealed (1) a negative linear relationship between kinship coefficients, calculated for pairs of individuals, and the logarithm of geographical distance between members of the pairs, in all studied populations; and (2) a significant autocorrelation for a distance up to 5 m (core populations) or 20 m (peripheral populations). Pollen flow, estimated from comparison of nuclear and chloroplast variation, was spatially limited, as was seed dispersal. Our results support a hypothesized relationship between SGS intensity and breeding system, the mode of seed dispersal and the population range position (core vs. periphery).     

Genetic differentiation among populations of an oceanic island: The case of Metrosideros boninensis, an endangered endemic tree species in the Bonin Islands

Conservation of endemic species on oceanic islands is an essential issue for biodiversity conservation. Metrosideros boninensis (Myrtaceae) is an endangered tree species endemic to the Bonin Islands of the western North Pacific Ocean. This species is considered to be extremely rare with less than 400 adult individuals, a number that has fluctuated between the 1880s and 1980s through human influence. We analyzed the genetic diversity and genetic structure of this species using amplified fragment length polymorphism markers and microsatellite markers. Genetic diversity of M. boninensis was extremely low compared to related taxa and similar endemic species from small islands. This low genetic diversity might be attributed to a stepwise colonization process with repeated founder bottlenecks in the dispersal pathway to the Bonin Islands. Populations of M. boninensis showed significant genetic differentiation and isolation by distance over a small geographical scale, despite the fact that this species should have extensive gene dispersal ability. This genetic differentiation might be caused by limited gene flow via pollen and seed among populations and genetic drift amid a small number of remnant individuals. Taken together, these findings suggest that the genetic diversity and connectivity of tree populations on islands are more vulnerable to habitat fragmentation than previously thought. We offer some recommendations for management to ameliorate habitat fragmentation and biological invasion.     

Contrasting spatial genetic structure in Annona crassiflora populations from fragmented and pristine savannas

In continuous populations, fine-scale genetic structure tends to be stronger in species with restricted pollen and seed dispersal. However, habitat fragmentation and disturbances can affect genetic diversity and spatial genetic structure due to disruption in ecological processes, such as plant reproduction and seed dispersal. In this study, we compared the genetic diversity and fine-scale spatial genetic structure (SGS) in two populations of Annona crassiflora (Annonaceae) in a pristine savanna Reserve (ESECAE) and in a fragmented disturbed savanna area (PABE), both in Cerrado biome in Central Brazil. The analyses were based on the polymorphism at 10 microsatellite loci. Our working hypothesis was that SGS is stronger and genetic diversity is lower in population at fragmented area (PABE) than at pristine area (ESECAE). Both populations presented high levels of polymorphism and genetic diversity and showed no sign of bottleneck for both Wilcoxon sign-rank test for heterozygosity excess (p > 0.05) and coalescent analyses (growth parameter g not different from zero), but population at fragmented area showed higher fixation index and stronger SGS. Besides, populations are significantly differentiated (F _ST = 0.239, R _ST = 0.483, p < 0.001 for both). Coalescent analyses showed high historical effective population sizes for both populations, high gene flow between ESECAE and PABE and recent time to most recent common ancestor (~37 k year BP). Our results suggest that despite the high genetic diversity, fragmentation and disturbance may have been affecting populations of this species increasing mating between closely related individuals leading to high fixation index and strong SGS.     

Impact of selective logging on inbreeding and gene dispersal in an Amazonian tree population of Carapa guianensis Aubl

Selective logging may impact patterns of genetic diversity within populations of harvested forest tree species by increasing distances separating conspecific trees, and modifying physical and biotic features of the forest habitat. We measured levels of gene diversity, inbreeding, pollen dispersal and spatial genetic structure (SGS) of an Amazonian insect-pollinated Carapa guianensis population before and after commercial selective logging. Similar levels of gene diversity and allelic richness were found before and after logging in both the adult and the seed generations. Pre- and post-harvest outcrossing rates were high, and not significantly different from one another. We found no significant levels of biparental inbreeding either before or after logging. Low levels of pollen pool differentiation were found, and the pre- vs. post-harvest difference was not significant. Pollen dispersal distance estimates averaged between 75 m and 265 m before logging, and between 76 m and 268 m after logging, depending on the value of tree density and the dispersal model used. There were weak and similar levels of differentiation of allele frequencies in the adults and in the pollen pool, before and after logging occurred, as well as weak and similar pre- and post-harvest levels of SGS among adult trees. The large neighbourhood sizes estimated suggest high historical levels of gene flow. Overall our results indicate that there is no clear short-term genetic impact of selective logging on this population of C. guianensis.     

Bottlenecks, drift and differentiation: the population structure and demographic history of sika deer (Cervus nippon) in the Japanese archipelago

We assessed genetic differentiation and diversity in 14 populations of sika deer (Cervus nippon) from Japan and four populations of sika deer introduced to the UK, using nine microsatellite loci. We observed extreme levels of differentiation and significant differences in diversity between populations. Our results do not support morphological subspecies designations, but are consistent with previous mitochondrial DNA analyses which suggest the existence of two genetically distinct lineages of sika deer in Japan. The source of sika introduced to the UK was identified as Kyushu. The underlying structure of Japanese populations probably derives from drift in separate glacial refugia and male dispersal limited by distance. This structure has been perturbed by bottlenecks and habitat fragmentation, resulting from human activity from the mid-nineteenth century. Most current genetic differentiation and differences in diversity among populations probably result from recent drift. Coalescent model analysis suggests sika on each of the main Japanese islands have experienced different recent population histories. Hokkaido, which has large areas of continuous habitat, has maintained high levels of gene flow. In Honshu the population is highly fragmented and is likely to have been evolving by drift alone. In Kyushu there has been a balance between gene flow and drift but all the populations have experienced high levels of drift. Habitat fragment size was not significantly associated with genetic diversity in populations but there was a significant correlation between habitat fragment size and effective population size.     

鹅掌楸贵州烂木山居群的微卫星遗传多样性及空间遗传结构

濒危植物鹅掌楸(Liriodendron chinense)目前仅零散分布于我国亚热带及越南北部地区, 残存居群生境片断化较为严重。研究濒危植物片断化居群的遗传多样性及小尺度空间遗传结构(spatial genetic structure)有助于了解物种的生态进化过程以及制定相关的保育策略。本研究采用13对微卫星引物, 对鹅掌楸的1个片断化居群进行了遗传多样性及空间遗传结构的研究, 旨在揭示生境片断化条件下鹅掌楸的遗传多样性及基因流状况。研究结果表明: 鹅掌楸烂木山居群内不同生境斑块及不同年龄阶段植株的遗传多样性水平差异不显著(P>0.05), 居群内存在寨内和山林2个遗传分化明显的亚居群。烂木山居群个体在200 m以内呈现显著的空间遗传结构, 而2个亚居群内的个体仅在20 m的距离范围内存在微弱或不显著的空间遗传结构。鹅掌楸的空间遗传结构强度较低(Sp = 0.0090), 且寨内亚居群的空间遗传结构强度(Sp = 0.0067)要高于山林亚居群(Sp = 0.0053)。鹅掌楸以异交为主, 种子较轻且具翅, 借助风力传播, 在一定程度上降低了空间遗传结构的强度。此外, 居群内个体密度及生境特征也对鹅掌楸的空间遗传结构产生了一定影响。该居群出现显著的杂合子缺失, 近交系数(F_IS)为0.099 (P < 0.01), 表明生境片断化的遗传效应正逐渐显现。因此, 对鹅掌楸的就地保护应注意维护与强化生境的连续性, 促进基因交流。迁地保护时, 取样距离应不小于20 m, 以涵盖足够多的遗传变异。     

Multiscale spatial genetic structure within and between populations of wild cherry trees in nuclear genotypes and chloroplast haplotypes

Spatial genetic structure (SGS) of plants mainly depends on the effective population size and gene dispersal. Maternally inherited loci are expected to have higher genetic differentiation between populations and more intensive SGS within populations than biparentally inherited loci because of smaller effective population sizes and fewer opportunities of gene dispersal in the maternally inherited loci. We investigated biparentally inherited nuclear genotypes and maternally inherited chloroplast haplotypes of microsatellites in 17 tree populations of three wild cherry species under different conditions of tree distribution and seed dispersal. As expected, interpopulation genetic differentiation was 6–9 times higher in chloroplast haplotypes than in nuclear genotypes. This difference indicated that pollen flow 4–7 times exceeded seed flow between populations. However, no difference between nuclear and chloroplast loci was detected in within‐population SGS intensity due to their substantial variation among the populations. The SGS intensity tended to increase as trees became more aggregated, suggesting that tree aggregation biased pollen and seed dispersal distances toward shorter. The loss of effective seed dispersers, Asian black bears, did not affect the SGS intensity probably because of mitigation of the bear loss by other vertebrate dispersers and too few tree generations after the bear loss to alter SGS. The findings suggest that SGS is more variable in smaller spatial scales due to various ecological factors in local populations.     

Microsatellite diversity and genetic structure of fragmented populations of the rare,fire-dependent shrub Grevillea macleayana

Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2-4.2 alleles/locus; Hexp = 0.420-0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past.     

Fine-scale spatial genetic structure in predominantly selfing plants with limited seed dispersal: a rule or exception?

Gene flow at a fine scale is still poorly understood despite its recognized importance for plant population demographic and genetic processes. We tested the hypothesis that intensity of gene flow will be lower and strength of spatial genetic structure (SGS) will be higher in more peripheral populations because of lower population density. The study was performed on the predominantly selfing Avena sterilis and included: (1) direct measurement of dispersal in a controlled environment; and (2) analyses of SGS in three natural populations, sampled in linear transects at fixed increasing inter plant distances. We found that in A.sterilis major seed dispersal is by gravity in close (less than 2m) vicinity of the mother plant, with a minor additional effect of wind. Analysis of SGS with six nuclear SSRs revealed a significant autocorrelation for the distance class of 1m only in the most peripheral desert population, while in the two core populations with Mediterranean conditions, no genetic structure was found. Our results support the hypothesis that intensity of SGS increases from the species core to periphery as a result of decreased within population gene flow related to low plant density. Our findings also show that predominant self pollination and highly localized seed dispersal lead to SGS at a very fine scale, but only if plant density is not too high.     

Genetic Diversity and Spatial Genetic Structure of the Grassland Perennial Saxifraga granulata along Two River Systems

Due to changes in land use, the natural habitats of an increasing number of plant species have become more and more fragmented. In landscapes that consist of patches of suitable habitat, the frequency and extent of long-distance seed dispersal can be expected to be an important factor determining local genetic diversity and regional population structure of the remaining populations. In plant species that are restricted to riparian habitats, rivers can be expected to have a strong impact on the dynamics and spatial genetic structure of populations as they may enable long-distance seed dispersal and thus maintain gene flow between fragmented populations. In this study, we used polymorphic microsatellite markers to investigate the genetic diversity and the spatial genetic structure of 28 populations of Saxifraga granulata along two rivers in central Belgium. We hypothesized that rivers might be essential for gene flow among increasingly isolated populations of this species. Genetic diversity was high (H_S = 0.68), which to a certain extent can be explained by the octoploid nature of S. granulata in the study area. Populations along the Dijle and Demer rivers were also highly differentiated (G” _ST = 0.269 and 0.164 and D _EST = 0.190 and 0.124, respectively) and showed significant isolation-by-distance, indicating moderate levels of gene flow primarily between populations that are geographically close to each other. Along the river Demer population genetic diversity was higher upstream than downstream, suggesting that seed dispersal via the water was not the primary mode of dispersal. Overall, these results indicate that despite increasing fragmentation populations along both rivers were highly genetically diverse. The high ploidy level and longevity of S. granulata have most likely buffered negative effects of fragmentation on genetic diversity and the spatial genetic structure of populations in riparian grasslands.     

Genetic population structure, fitness variation and the importance of population history in remnant populations of the endangered plant Silene chlorantha (Willd.) Ehrh. (Caryophyllaceae)

Habitat fragmentation can lead to a decline of genetic diversity, a potential risk for the survival of natural populations. Fragmented populations can become highly differentiated due to reduced gene flow and genetic drift. A decline in number of individuals can result in lower reproductive fitness due to inbreeding effects. We investigated genetic variation within and between 11 populations of the rare and endangered plant Silene chlorantha in northeastern Germany to support conservation strategies. Genetic diversity was evaluated using AFLP techniques and the results were correlated to fitness traits. Fitness evaluation in nature and in a common garden approach was conducted. Our analysis revealed population differentiation was high and within population genetic diversity was intermediate. A clear population structure was supported by a Bayesian approach, AMOVA and neighbour-joining analysis. No correlation between genetic and geographic distance was found. Our results indicate that patterns of population differentiation were mainly caused by temporal and/or spatial isolation and genetic drift. The fitness evaluation revealed that pollinator limitation and habitat quality seem, at present, to be more important to reproductive fitness than genetic diversity by itself. Populations of S. chlorantha with low genetic diversity have the potential to increase in individual number if habitat conditions improve. This was detected in a single large population in the investigation area, which was formerly affected by bottleneck effects.     

Fine-scale spatial genetic structure and gene flow in a small, fragmented population of Sinojackia rehderiana (Styracaceae), an endangered tree species endemic to China

Populations of Sinojackia rehderiana are highly threatened and have small and scattered distribution due to habitat fragmentation and human activities. Understanding changes in genetic diversity, the fine-scale spatial genetic structure (SGS) at different life stages and gene flow of S. rehderiana is critical for developing successful conservation strategies for fragmented populations of this endangered species. In this study, 208 adults, 114 juveniles and 136 seedlings in a 50 × 100-m transect within an old-growth forest were mapped and genotyped using eight microsatellite makers to investigate the genetic diversity and SGS of this species. No significant differences in genetic diversity among different life-history stages were found. However, a significant heterozygote deficiency in adults and seedlings may result from substantial biparental inbreeding. Significant fine-scale spatial structure was found in different life-history stages within 19 m, suggesting that seed dispersal mainly occurred near a mother tree. Both historical and contemporary estimates of gene flow (13.06 and 16.77 m) indicated short-distance gene dispersal in isolated populations of S. rehderiana. The consistent spatial structure revealed in different life stages is most likely the result of limited gene flow. Our results have important implications for conservation of extant populations of S. rehderiana. Measures for promoting pollen flow should be taken for in situ conservation. The presence of a SGS in fragmented populations implies that seeds for ex situ conservation should be collected from trees at least 19-m apart to reduce genetic similarity between neighbouring individuals.     

Assessing the impact of hunting pressure on population structure of Guinea baboons (Papio papio) in Guinea-Bissau

Guinea baboons are heavily hunted for bushmeat consumption in Guinea-Bissau. We investigated whether hunting-driven mortality has affected population structure in this generalist primate using two genetic markers. Sampling was conducted in protected areas separated by anthropogenic landscape features. We predicted significant genetic differentiation between samples and investigated whether genetic discontinuities in the data were concordant with the location of human infrastructures. Genetic diversity was not significantly reduced when compared with a neighbouring population in Senegal and we inferred historically female-biased dispersal and recent contact between localities. Evidence was found for a contact zone between genetically differentiated populations where gene-flow is unidirectional, admixed individuals are at a higher proportion and individuals differentiated for both genetic markers co-exist within the same social units. Genetic discontinuities were, however, unrelated to anthropogenic dispersal barriers and we could not explain the existence of a contact zone by geographic distance, habitat type or the effect of social structure. We propose that hunting practices have affected the population structure by increasing dispersal distances, facilitating contact between previously separated gene pools within social groups. We suggest that hunting-related density sinks found in areas where the quality of the habitat remains adequate could precipitate the immigration of genetically distinct individuals from distant populations. Alternatively, migrants found in protected areas might be avoiding hunters, in locations they may perceive as less disturbed. This study suggests that hunting practices must be considered when investigating genetic patterns in primates and underlines the utility of molecular approaches to detect population perturbations due to bushmeat hunting.     

Fine-scale spatial genetic structure in predominantly selfing plants with limited seed dispersal:a rule or exception?

Gene flow at a fine scale is still poorly understood despite its recognized importance for plant population demographic and genetic processes.We tested the hypothesis that intensity of gene flow will be lower and strength of spatial genetic structure(SGS) will be higher in more peripheral populations because of lower population density.The study was performed on the predominantly selfing Avena sterilis and included:(1) direct measurement of dispersal in a controlled environment;and(2) analyses of SGS in three natural populations,sampled in linear transects at fixed increasing inter-plant distances.We found that in A.sterilis major seed dispersal is by gravity in close(less than 2 m) vicinity of the mother plant,with a minor additional effect of wind.Analysis of SGS with six nuclear SSRs revealed a significant autocorrelation for the distance class of 1 m only in the most peripheral desert population,while in the two core populations with Mediterranean conditions,no genetic structure was found.Our results support the hypothesis that intensity of SGS increases from the species core to periphery as a result of decreased within-population gene flow related to low plant density.Our findings also show that predominant self-pollination and highly localized seed dispersal lead to SGS at a very fine scale,but only if plant density is not too high.     

Endangered species in small habitat patches can possess high genetic diversity: the case of the Tana River red colobus and mangabey

We used mtDNA sequence data from the Tana River red colobus and mangabey to determine how their population genetic structure was influenced by dispersal and habitat fragmentation. The colobus and mangabey are critically endangered primates endemic to gallery forests in eastern Kenya. The forests are a Pliocene–Pleistocene refugium that has recently undergone significant habitat loss and fragmentation due to human activities. We expected both primates to exhibit low levels of genetic diversity due to elevated genetic drift in their small populations, and to show a strong correspondence between genetic and geographic distance due to disruption of gene flow between forests by habitat fragmentation. Additionally, because mangabey females are philopatric, we expected their mtDNA variation to be homogeneous within forest patches but to be heterogeneous between patches. In contrast, colobus have a female-biased dispersal and so we expected their mtDNA variation to be homogeneous within and between forest patches. We found high levels of haplotype and nucleotide diversity as well as high levels of sequence divergence between haplotype groups in both species. The red colobus had significantly higher genetic variation than the mangabey did. Most of the genetic variation in both primates was found within forest fragments. Although both species showed strong inter-forest patch genetic structure we found no correspondence between genetic and geographic distances for the two primates. We attributed the high genetic diversity to recent high effective population size, and high sequence divergence and strong genetic structures to long-term habitat changes in the landscape.