Resistance to locust leafminer (Coleoptera: Chrysomelidae) in black locust

Locust leafminer, Odontota dorsalis (Thunberg), activity was observed for 2 yr on 70 black locust, Robinia pseudoacacia L., trees grown from seed collected from its native range. Four black locust seedlings from Tennessee had low numbers of eggs, larvae, pupae, and mines, and were selected for clonal propagation. These clonal propagules were resistant to locust leafminers collected from three different counties in Maryland. This resistance was also observed in controlled choice and no-choice tests in outdoor screen houses. Adults showed different ovipositional preferences for black locust trees from different seed sources, which were reflected in lower numbers of larvae, pupae, and mines in resistant clones. It was concluded that antixenosis and antibiosis were involved in the mechanisms of resistance to the locust leafminer in black locust.     

An isozyme study of clone diversity and relative importance of sexual and vegetative recruitment in the grass Brachypodium pinnatum

We asked whether differences in abundance and seed prodtiction of Brachypodium pinnatum after 16 yr of four different experimental land use regimes were reflected in differences in vegetative dispersal distance, clone diversity, clone area, and the proportions of sexual and vegetative recruitment. Mean vegetative dispersal distance was 5.5 mm yr'. Electrophoresis of 5 polymorphic isozyme loci of 20 tillers sampled at defined positions in each of twelve 1 × 6 m sampling areas (3 per treatment) revealed considerable clonal diversity. Per sampling area we found on average 9.98 enzyme phenotypes (clones), mean Simpson index was 0.825. and mean Shannon index 0.801. The mean ratio of sexual vs vegetative recruitment was about 1:32000. Despite this low ratio, clonal diversity within the population of" B. pinnatum was higher than reported for other clonal plant populations, possibly because of its high ramet densities. Moan clone area was 5.73 m²-. i.e. mean clone radius was 1.35 m. None of the 10 pairwise correlations between abundance and seed production on the one hand, and number of clones per plot sample, plot Simpson index, plot Shannon index, ratio of vegetative vs sexual recruitment, and clone area on the other, was significant. Mean clone radius was 245 times larger than the mean distance of yearly vegetative dispersal which suggests old ages and low turnover rates of clones. The time scale of the inert response of clonal diversity of B. pinnatum to changes in land use appears to largely exceed the experimental period of 16 yr.     

The clonal root system of balsam poplar in upland sites of Quebec and Alberta

Balsam poplar seeds are short‐lived and require moist seedbeds soon after they are released to germinate. In addition to sexual reproduction, balsam poplar stands can regenerate clonally by root suckering. The origin of stands will in turn affect their genetic structure and root system architecture, which are poorly understood for upland forest stands. Three stands were hydraulically excavated in Quebec (moist) and Alberta (dry) to determine the origin of trees and to characterize root systems with respect to presence of parental roots and root grafts connections. Clones were identified using single‐nucleotide polymorphism (SNPs), and all stems, roots and root grafts were aged using dendrochronology techniques. All 82 excavated trees were of sucker origin, and four of the six stands contained a single clone. Parental root connections were found between 22% and 25% of excavated trees, and 53% and 48% of trees were linked with a root graft between the same or different clones, in Alberta and Quebec, respectively. Mean distance between trees connected by parental root was significantly lower than the distance between unconnected trees (0.47 ± 0.25 m vs. 3.14 ± 0.15 m and 1.55 ± 0.27 m vs. 4.25 ± 0.13 m) in Alberta and in Quebec, respectively. The excavations also revealed many dead stumps with live roots, maintained through root connections with live trees. This research highlights that balsam poplar growing in upland stands is a clonal species that can maintain relatively high genotypic diversity, with frequent root connections between trees at maturity. Maintaining an extensive root system through root connections increases the chances of a clone surviving when the above ground tree is dead and may also enhance the resilience of balsam poplar stands after disturbance.     

Effects of black locust (Robinia pseudoacacia) on soil properties in the loessial gully region of the Loess Plateau, China

Black locust (Robinia pseudoacacia) has been widely planted in the Loess Plateau for soil and water conservation. The effects of black locust on soil properties has significant role in land use and ecosystem management. However, this beneficial effect has been little studied in the Loess Plateau. The soil properties below black locust and native grass growing in Nanxiaohe and Wangdonggou watersheds, located in the loessial gully region of the Loess Plateau, were studied for changes in soil properties after establishment of black locust. The black locust significantly increased soil cation exchange capacity, organic carbon, total nitrogen, nitrate, and carbon:nitrogen and carbon:phosphorus (P) ratios, as well as some enzymes like alkaline phosphatase and invertase in 0–20 cm or 0–80 cm depths of soil compared to the native grassland in Nanxiaohe and Wangdonggou watersheds. However, the effects on ammonium, total P, and extractable P and potassium were not consistent in both watersheds. There were more obvious differences in soil properties between black locust land and grassland for Nanxiaohe watershed than for Wangdonggou watershed, suggesting that the effects of black locust on most soil properties increase with black locust age. The results indicate that black locust has potential to improve soil properties in the loessial gully region of the Loess Plateau and the improvements were greater in long-term than middle-term black locust stands.     

Effects of male fecundity, interindividual distance and anisotropic pollen dispersal on mating success in a Scots pine (Pinus sylvestris) seed orchard

Quantifying the effect of pollen dispersal and flowering traits on mating success is essential for understanding evolutionary responses to changing environments and establishing strategies for forest tree breeding. This study examined, quantitatively, the effects of male fecundity, interindividual distance and anisotropic pollen dispersal on the mating success of Scots pine (Pinus sylvestris), utilizing a well-mapped Scots pine seed orchard. Paternity analysis of 1021 seeds sampled from 87 trees representing 28 clones showed that 53% of the seeds had at least one potential pollen parent within the orchard. Pronounced variation in paternal contribution was observed among clones. Variations in pollen production explained up to 78% of the variation in mating success, which was 11.2 times greater for clones producing the largest amount of pollen than for clones producing the least pollen. Mating success also varied with intertree distance and direction, which explained up to 28% of the variance. Fertilization between neighboring trees 2.3 m apart was 2.4 times more frequent than between trees 4.6 m apart, and up to 12.4 times higher for trees downwind of the presumed prevailing wind direction than for upwind trees. The effective number of pollen donors recorded in the seed orchard (12.2) was smaller than the theoretical expectation (19.7). Based on the empirical observations, a mating model that best describes the gene dispersal pattern in clonal seed orchards was constructed.     

蚂蚁对澜沧舞花姜种子散布及种苗空间分布格局的影响

 在野外系统观测了澜沧舞花姜（Globba lancangensis）18个果实共216粒种子的散布过程。共有10种蚂蚁参与了澜沧舞花姜的种子散布,距离为0.01～3.35 m,平均距离(0.47±0.03) m（平均值±SE,n=216）。其中最重要的３种蚂蚁是横纹齿猛蚁（Odontoponera transversa）、大头蚁(Pheidole sp.)和黄足厚结猛蚁(Pachycondyla luteipes),其出现频率分别为61%、50%和28%,散布的平均距离分别为(0.60±0.09) m、(0.20±0.01) m和(0.32±0.05) m。从总体上看,蚂蚁促进了种子的分散,降低了种子的聚集程度。横纹齿猛蚁对于种子上的油质体最为敏感,对人工去除了油质体的种子不搬运,对种子散布距离较远,暗示了其与澜沧舞花姜之间可能存在更紧密的互惠关系。野外样方调查结果表明,在3种舞花姜属植物中,以种子繁殖为主的澜沧舞花姜种苗之间的平均最近距离为(36.8±1.45) cm（平均值±SE,n=74）,显著大于以珠芽繁殖为主的毛舞花姜（Globba barthiri）的(29.8±2.70) m（n=34）（t73,33=2.11,p=0.037）和异果舞花姜（Globba racemosa）的(28.7±3.16) cm（n=32）（t73,31=2.33,p=0.022）;澜沧舞花姜的种苗聚集程度（Z=-1.70±0.19）显著小于毛舞花姜（Z=-2.58±0.37,t73,33=2.36,p=0.020）和异果舞花姜（Z=-3.28±0.53）（t73,31=3.54,p=0.001）。这说明相对于毛舞花姜和异果舞花姜,蚂蚁对种子的散布作用显著增加了澜沧舞花姜种苗间的平均最近距离,降低了居群的聚集度。     

Population structure, genetic diversity, and clone formation in Quercus chrysolepis (Fagaceae)

Stands of canyon live oak (Quercus chrysolepis, Fagaceae) are maintained for fuelwood, fire management, recreation, and as habitat for wildlife. Information about the link between the oak's reproductive ecology and its extent of genetic diversity is important in developing land management policies that will maintain the long-term viability of populations. Basal sprouting is the primary means of reproduction following fire or cutting, and stands frequently include groups of visibly connected trees in a clustered distribution that suggests cloning. We determined the extent to which clusters of trees were clonal and defined the spatial pattern and diversity of genotypes for six populations across nearly the entire east-west extent of the San Bernardino Mountains in southern California. We mapped over 100 trees at each of five sites and genotyped each tree for allozymes at seven polymorphic loci. We identified clones using these multilocus genotypes and detected an average of 34.4 ± 7.3 (SD) clones per site, most of which had unique genotypes. In general, clustered trees belong to single clones and most clones consist of few trees (mean = 3.4 ± 0.6 trees per clone). However, clone size increased significantly with increased individual heterozygosity, suggesting that selection may favor highly heterozygous clones. Clonal diversity and evenness were high relative to reports for most other clonal species; an average of 97% of clones had distinct genotypes, and Simpson's index of diversity averaged 0.95 ± 0.02. Population genetic analyses of 319 clones from six sites revealed high genetic diversity within sites (mean HS = 0.443). Only a small proportion of the total genetic diversity was explained by variation among sites (mean GST = 0.018), which is consistent with high gene flow among sites (Nm = 9.5). We found no significant substructure among plots within sites, and fixation indices within sites were generally small, suggesting that either little inbreeding occurs, and/or few inbred progeny survive. However, spatial autocorrelation analysis of clones indicated fine-scale genetic structure at distances under 4 m, possibly due to limited seed dispersal. Our data suggest that guidelines for seed collection of canyon live oak for use in restoration can be specified in a manner similar to that recommended for conifer species within the region studied.     

Microgeographic variation in recruitment under adult trees: arrival of new genotypes or perpetuation of the existing ones?

• Investigating spatial variation in the relative importance of sexual reproduction and clonal propagation is critical to obtain more accurate estimates of future effective population sizes and genetic diversity, as well as to identify ecological correlates of clonality.
• We combined a stratified sampling scheme with microsatellite genetic analyses to estimate variation in the proportion of sexual versus clonal recruits among saplings in five populations of the tree Pyrus bourgaeana. Using a likelihood framework, we identified clones among the genotypes analysed and examined variation among populations regarding the proportion of saplings coming from clonal propagation. We also examined the relationship between the relative abundance of clonal shoots across the studied populations and their herbivory levels.
• Our results revealed that one third of the saplings examined (N = 225 saplings) had a probability above 0.9 of being clones of nearby (<10 m) trees, with the ratio between clonal propagation and sexual recruitment varying up to eight‐fold among populations. A small portion of these putative clonal shoots reached sexual maturity. Relative abundance of clonal shoots did not significantly relate to the herbivory by ungulates.
• Our results call into question optimistic expectations of previous studies reporting sufficient levels of recruitment under parental trees without animal seed dispersal services. Nevertheless, given that some of these clonal shoots reach sexual maturity, clonal propagation can ultimately facilitate the long‐term persistence of populations during adverse periods (e.g. environmental stress, impoverished pollinator communities, seed dispersal limitation).

     

Pollen limitation and distance-dependent fecundity in females of the clonal gynodioecious herb Glechoma hederacea (Lamiaceae)

Summary Pollen movement is often restricted in natural populations, and insufficient pollination is a potential constraint on sexual reproduction in outcrossing species. Seed-set should decrease with increased distance from the pollen source in outcrossing plants. This prediction was tested using females of the clonal, gynodioecious herb Glechoma hederacea in three natural populations. In controlled pollinations, both hermaphrodites and females had similar high percentages of fruit-set and seed-set. In a natural population where a female clone was isolated from the nearest hermaphroditic clone by c. 100 m, fruit-set was low (1%). In another population where hemaphroditic clones were rare and female clones had a patchy distribution, fruit-and seed-set in females were pollen-limited and decreased with increased distance from the nearest pollen source. The estimated mean pollen dispersal distance was 5.9 m when calculated on fruit-set and 5.3 m when calculated on seed-set. The most frequent pollinators were bumblebees. The mean and median distances moved by pollinators between ramets were 0.13 m and 0.05 m. In a third population where female clones were isolated from the nearest hermaphrodites by more than 200 m, fruit-set was 0%. After introduction of 16 hermaphroditic ramets in the center of the female clone, fruit-set varied between 0% and 100% in individual female ramets. Fruit-set decreased with increased distance from the pollen source. The mean and median pollen movement distances were 1.06 m and 0.54 m.     

Nitrogen stocks in a riparian area invaded by N-fixing black locust (Robinia pseudoacacia L.)

Fixation of river flow passages and riverbed degradation may facilitate the development of higher floodplains with the establishment of exotic species such as black locust (Robinia pseudoacacia L.). We quantitatively evaluated the relationship between nitrogen (N) levels in black locust trees and in sediments under different flood disturbance regimes in a riparian area of the Chikuma River. In this study, allometric equations were developed for relating leaf N content to diameter at breast height of black locust. The amount of leaf N in black locust increased with distance from the river, reaching 159 kg N ha⁻¹ at 180 m from the river. There was a small difference in N content between green and fallen leaves (0.2%), and so the leaf N was almost equivalent to N input to riparian sediments. Fine sediments accumulated on the riparian area, where the amount of sediments N increased with distance from the river, ranging from 1091 ± 767 to 4953 ± 2953 kg N ha⁻¹. The N accumulation rates also increased with distance from the river, corresponding with the amount of leaf N in black locust per unit area, but the former exceeded the latter. The sediment N accumulation might be accelerated by sediment trapping effect due to riparian vegetation itself. A large input of N provided by invaded black locust might alter nutrient dynamics and native plant community structure in the riparian area.     

马尾松二代无性系种子园子代父本分析及花粉散布

目前国内较早建立的马尾松(Pinus massoniana)二代种子园正陆续进入正常开花结实期。研究马尾松二代种子园花粉散布和自由授粉子代的父本组成, 可为生产上指导马尾松高世代种子园的规划设计和遗传管理提供理论依据。该文利用筛选的11对SSR引物, 对马尾松二代无性系种子园内8个无性系单株的320个自由授粉子代和48个候选父本进行了扩增, 并采用最大似然法对子代进行父本分析。结果表明: 11个位点共检测到61个等位基因, 每个位点的等位基因数在2-11之间, 平均为5.55个。试验亲本和子代群体的总平均观测杂合度(H_o)、期望杂合度(H_e)及多态信息含量(PIC)分别为0.428、0.433和0.387。在80%的可信度水平下可为232 (72.50%)个子代确定其父本。平均每个采种母树与19个父本产生子代。在自由授粉状态下, 马尾松二代种子园自交率为1.72%, 自交现象很弱, 其交配方式以异交为主。绝大多数亲本无性系的雄性繁殖适合度在1.00%-4.00%之间, 候选父本平均繁殖适合度为2.17%, 平均形成5个后代。马尾松有效花粉的散布距离和固定交配距离的父本繁殖适合度均符合正态分布, 两者呈极显著负相关, 其主要散布距离集中在0-100 m, 而检测到的最大散布距离为192 m。种子园花粉污染率较低, 仅为4.06%。总体看来, 树冠南面子代亲本交配距离较北面有增加的趋势, 但树冠南、北面子代父本组成数并未表现明显的规律。     

Within-population genetic structure and clonal diversity of a threatened endemic metallophyte, Viola calaminaria (Violaceae)

We studied the within-population genetic structure and the clonality extent of Viola calaminaria, a rare endemic species of calamine soils, by means of RAPD markers in two populations (one recent and one ancient) with expected harsh and heterogeneous heavy-metal stress. At a very local scale (0.2-3 m), clonal propagation was detected in both populations, but the levels of clonal diversity were high (number of genets/number of ramets sampled = 0.9 [recent] and 0.76 [ancient]) and the maximal observed extension of the clones was 0.4 m. This indicated that clonality is not, for the species, an important mode of propagation and that clonal growth cannot be interpreted as a strategy for propagating or perpetuating adapted genotypes under harsh ecological constraints. Spatial autocorrelations revealed a significant (P < 0.001) negative value of correlogram slope in the two populations even when a single individual per clone was considered (i.e., analysis at the genet level). We conclude that spatial genetic structure at a very local scale reflects limited gene flow due to restricted seed dispersal rather than variation in clonal pattern in response to environmental heterogeneity. At a larger scale (2-30 m), spatial autocorrelations revealed a positive (P < 0.001) correlation at < 3 m and a random pattern at larger distances for the two populations. This suggested a patchy distribution of the genetically linked individuals associated with a disrupted pattern at a longer distance probably due to gene flow by pollen dispersal and a seed bank effect. The implications for the conservation of V. calaminaria are discussed.     

佛坪国家级自然保护区秦岭箭竹克隆结构的SSR分析

利用SSR分子标记技术分析了佛坪国家级自然保护区秦岭箭竹(Fargesia qinlingensis)的克隆多样性和克隆结构,以探讨小尺度范围内秦岭箭竹自然居群遗传变异的分布特征,对该种开花特性、高山地区生态环境维护和大熊猫的保护提供重要依据。结果表明7对SSR引物共扩增出79个位点,其中多态性位点77个,多态位点百分率(PPB)为97.47%。秦岭箭竹的142个分株共形成107个克隆,最大克隆可达5 m。克隆多样性略高于其他克隆植物的平均值(D=0.62,G/N=0.17,E=0.68),基因型比率(G/N)、Simpson指数(D)、平均克隆大小(N/G)和Fager均匀性指数(E)分别为0.7535、0.9680、1.3271和0.5109。克隆空间结构分析表明秦岭箭竹的克隆构型为密集型,各克隆呈镶嵌性分布,同一克隆的分株排列紧密。克隆聚类分析表明各克隆之间聚类不明显,总体上来自同一样地的克隆被聚为一类。空间自相关分析显示在空间距离为36 m范围内,分株比基株有更显著的空间遗传结构,空间自相关系数r的取值范围分别为0.084—0.626和0.024—0.288,说明克隆繁殖在一定程度上限制了空间遗传结构的范围。样地内秦岭箭竹个体在空间距离小于44 m时存在显著的正相关空间结构,特别是在4 m处表现出最大的空间自相关系数(r=0.626),表明空间距离相距4 m内的个体最有可能属于同一克隆,4 m比5 m更能表现出清晰的克隆结构,X-轴截距为52.280,代表了秦岭箭竹不规则克隆的平均最小长度。秦岭箭竹的克隆多样性和克隆结构与初始苗补充、花粉散播方式和微环境差异有关。     

Genetic differentiation between clone collections and natural populations of European black poplar (<Emphasis Type="Italic">Populus nigra</Emphasis> L.) in turkey

The European black poplar (Populus nigra L.) is an ecologically and economically important tree species for Turkey. The important and major genetic resources of species for future breeding and ex situ conservation purposes have been archived in a clone bank in Ankara by selecting clones from natural populations and old plantations throughout Turkey. There is no study to date assessing genetic composition these materials. Two-hundred-thirty-three P. nigra clones from six geographic region of Turkey (clone collection populations), and 32 trees from two natural populations (Tunceli and Melet) were genotyped by using 12 nuclear microsatellite DNA markers. There were nine clones which duplicated in various frequencies. The analysis carried out with removal of the duplicated clones revealed a moderately high genetic diversity in studied populations. The observed heterozygosities ranged from 0.59 in Tunceli natural to 0.69 in Central Anatolia clone collection populations. In general, there was excess of heterozygosity in the studied populations. Populations composed of clone collections were significantly differentiated from natural populations (F _ST = 0.17), while there was little differentiation among those populations in the clone collection (F _ST = 0.03). Two distantly located natural populations with small sizes also differed from each other (F _ST = 0.17). Genetic structure analysis revealed two distinct groups (clone collection vs natural populations) with very high membership values (>92%). Clone collection populations had high level of admixture while natural populations had homogenous genetic structure. The presence of large number of clonal duplication, reduced genetic differentiation, and high level of admixture in clone collection populations indicate that genetic resources of European black poplar were highly degraded through genetic erosion and pollution caused by intensive cultural practices and extensive dispersal of clonal materials. To understand genetic diversity and its structural pattern thoroughly in the six clone collection populations, a further study with extensive and systematic sampling of European black poplar populations in major river ecosystems in Turkey will be useful.     

Three-gene identity coefficients demonstrate that clonal reproduction promotes inbreeding and spatial relatedness in yellow-cedar, Callitropsis nootkatensis

Asexual reproduction has the potential to promote population structuring through matings between clones as well as through limited dispersal of related progeny. Here we present an application of three-gene identity coefficients that tests whether clonal reproduction promotes inbreeding and spatial relatedness within populations. With this method, the first two genes are sampled to estimate pairwise relatedness or inbreeding, whereas the third gene is sampled from either a clone or a sexually derived individual. If three-gene coefficients are significantly greater for clones than nonclones, then clonality contributes excessively to genetic structure. First, we describe an estimator of three-gene identity and briefly evaluate its properties. We then use this estimator to test the effect of clonality on the genetic structure within populations of yellow-cedar (Callitropsis nootkatensis) using a molecular marker survey. Five microsatellite loci were genotyped for 485 trees sampled from nine populations. Our three-gene analyses show that clonal ramets promote inbreeding and spatial structure in most populations. Among-population correlations between clonal extent and genetic structure generally support these trends, yet with less statistical significance. Clones appear to contribute to genetic structure through the limited dispersal of offspring from replicated ramets of the same clonal genet, whereas this structure is likely maintained by mating among these relatives.     

Clonal diversity and spatial genetic structure of Potamogeton pectinatus in managed pond and river populations

Higher levels of genetic diversity of river macrophytes are expected in downstream parts because of potential accumulation of various genotypes from upstream sites. We assessed the clonal diversity and spatial genetic structure of fennel pondweed (Potamogeton pectinatus or Stuckenia pectinata) populations with emphasis on the estimation of dispersal via clonal propagules along a river in connection to upstream ponds. We analysed genetic diversity of 354 plant shoots sampled in 2005 and 2006 at three pond and five river sites in the Woluwe river catchment (Belgium). Nine microsatellite DNA markers revealed 88 genets of which 89% occurred in only one site. Clonal propagule dispersal was detected up to 10 km along the river. Few multilocus genotypes were repeatedly present along a major part of the river indicating vegetative spread. Populations of ponds contained a higher amount of clonal diversity, indicating the importance of local seed recruitment. A fine-scaled spatial genetic structure indicated that most seedling recruitment occurred at a distance <5 m in pond populations whereas clones in river sites were unrelated and showed no spatial autocorrelation. The clonal diversity decreased along the river from upstream to downstream due to establishment of few large clones.     

Short-distance pollen dispersal and high self-pollination in a bat-pollinated neotropical tree

We investigated pollen dispersal and breeding structure in the tropical tree species Caryocar brasiliense Camb. (Caryocaraceae), using genetic data from ten microsatellite loci. All adult trees (101) within a patch of 8.3 ha were sampled, and from these adults 18 open-pollinated maternal progeny arrays were analyzed (280 seeds from 265 fruits). Most fruits presented only one seed (median equal to 1.000) and mean number of ripened seeds per fruit was 1.053 (SD?=?0.828). Our results showed that C. brasiliense presents a mixed-mating system, with 11.4% of self-pollination, multilocus outcrossing rate of t _m?=?0.891?±?0.025, and high probability of full-sibship within progeny arrays (r _p?=?0.135?±?0.032). Outcrossing rate and self-pollination varied significantly among mother trees. We could detect a maximum pollen dispersal distance of ～500 m and a mean pollen dispersal distance of ～132 m. However, most pollination events (80%) occurred at distances less than 200 m. Our results also indicated that pollen dispersal is restricted to a neighborhood of 5.4 ha with rare events of immigration (～1% N _e m?=?0.35). C. brasiliense also presents a significant but weak spatial genetic structure (Sp?=?0.0116), and extension of pollen dispersal distance was greater than seed dispersal (N _b?=?86.20 m). These results are most likely due to the foraging behavior of pollinators that may have limited flight range. The highly within-population synchronous flowering, high population density, and clumped distribution reinforce pollinator behavior and affect residence time leading to a short-distance pollen dispersal.     

Landscape Genetics of American Beaver in Coastal Oregon

American beaver (Castor canadensis) have been translocated for population restoration, reduction of human-wildlife conflict, and enhancement of ecosystem function. Yet few studies have assessed dispersal of beaver, making it difficult to determine at what scale translocations are appropriate. Genetic studies can provide inferences about gene flow, and thus dispersal. We used a landscape genetic approach to evaluate whether landscape features influenced gene flow among beaver in the Coast Range of western Oregon, USA, using samples collected April–September 2014. We collected genetic samples from live-captured (n = 232), road-killed (n = 2) and trapper-provided (n = 58) tissue samples and genotyped them at 10 microsatellite loci. We mapped records of beaver translocations into or within the study area during the twentieth century to consider the effect of those movements on genetic structure. We used population assignment tests to delimit genetic clusters, evaluated correspondence of those clusters with watershed boundaries and translocation history, and then estimated differentiation between clusters and between watersheds using model-based and model-free approaches. We evaluated how individual genetic differences varied with geographic distance, and investigated related pairs within clusters. We developed landscape resistance models incorporating slope, distance to water, and watershed boundaries at 2 scales, and estimated effective distances between sample locations with least cost path and circuit theoretic analyses. We evaluated the correlation of individual genetic distances with effective distances using a pseudo-bootstrapping approach. Landscape genetic models did not explain spatial variation in genetic structure better than geographic distance, but hierarchical genetic structure corresponded with watershed boundaries and suggested influences from historical translocations. Pairwise individual genetic distances were positively correlated with geographic distances to 61 km; highly-related pairs mostly were detected <1 km apart (median = 1.0 km, = 14.6 ± 2.3 [SE] km, n = 77). We concluded that slope and distance to water did not strongly limit dispersal and gene flow by beaver in this system, but concordance of genetic structure with watershed boundaries suggests that dispersal is more common within than between watersheds. Genetic differentiation of beaver within this topographically complex system was much greater than reported in a study at similar spatial scales in relatively flat topography. We recommend that translocation efforts of American beaver in topographically complex landscapes occur within watersheds when possible but conclude that dispersal can occur across watersheds. © 2021 The Wildlife Society. This article is a U.S. Government work and is in the public domain in the USA.     

Clonal spread of invasive Ludwigia hexapetala and L. grandiflora in freshwater wetlands of California

Ludwigia hexapetala and L. grandiflora are recent, aggressive invaders of freshwater wetlands in California. To assess the relative role of sexual versus clonal reproduction in invasive spread, we used AFLP markers to genotype 794 ramets of L. hexapetala sampled from 27 populations in three watersheds of California, and 150 ramets of L. grandiflora from five populations in a fourth watershed. We then used two analytical methods, similarity thresholds and character incompatibilities, to distinguish genotypic variation within genets (clones) from variation between genets. Our analyses revealed extremely limited genotypic and genet variation in invasive L. hexapetala and L. grandiflora within California. Within L. hexapetala, 95% of the ramets analyzed represented a single genet. The genet was the only one detected in 20 populations. The remaining seven populations contained two to nine genets. Within L. grandiflora, all ramets were of only one genotype. Thus, invasive spread within and between populations, and across watersheds, appears to be almost exclusively clonal and brought about by the dispersal of vegetative propagules. The extremely low seedling recruitment indicates that management should target vegetative dispersal and growth.     

Distribution and fine-scale spatial-genetic structure in British wild cherry (Prunus avium L.)

Insights into the within-population spatial-genetic structure (SGS) of forest tree species, where little is known regarding seed and pollen dispersal patterns, enhance understanding of their ecology and provide information of value in conservation and breeding. This study utilised 13 polymorphic simple sequence repeat loci to investigate the impact of asexual recruitment, management regime and tree size on the development of SGS in wild cherry (Prunus avium L). Only 246 genotypes were identified in the 551 trees sampled, reflecting significant levels of clonal reproduction in both managed and unmanaged populations. Naturally regenerated wild cherry was spatially aggregated under both management regimes. However, in the managed population, sexually derived trees accounted for a greater proportion of the smaller size classes, whereas vegetatively produced trees dominated the smaller size classes in the unmanaged population. High overall SGS values (Sp 0.030-Sp 0.045) were observed when considering only sexually derived genets and kinship coefficients were significant up to the 120 m distance class for both populations. The inclusion of clonal ramets in the analysis significantly increased the overall SGS (Sp 0.089-Sp 0.119) as well as kinship coefficients in the 40-80 m distance classes, illustrating the dramatic impact of vegetative propagation on SGS in this species. Increased spatial aggregation and regeneration appeared to be concomitant with increased SGS in the 40 m distance class in the unmanaged population. Neighbourhood size estimates were relatively small for both populations and kinship coefficients were found to decline with distance under both management regimes, suggesting that common mechanisms may restrict gene dispersal in wild cherry.