Effect of reproductive modes and environmental heterogeneity in the population dynamics of a geographically widespread clonal desert cactus

The dynamics of plant populations in arid environments are largely affected by the unpredictable environmental conditions and are fine-tuned by biotic factors, such as modes of recruitment. A single species must cope with both spatial and temporal heterogeneity that trigger pulses of sexual and clonal establishment throughout its distributional range. We studied two populations of the clonal, purple prickly pear cactus, Opuntia macrocentra, in order to contrast the factors responsible for the population dynamics of a common, widely distributed species. The study sites were located in protected areas that correspond to extreme latitudinal locations for this species within the Chihuahuan Desert. We studied both populations for four consecutive years and determined the demographic consequences of environmental variability and the mode of reproduction using matrix population models, life table response experiments (LTREs), and loop and perturbation analyses. Although both populations seemed fairly stable (population growth rate, λ∼1), different demographic parameters and different life cycle routes were responsible for this stability in each population. In the southernmost population (MBR) LTRE and loop and elasticity analyses showed that stasis is the demographic process with the highest contributions to λ, followed by sexual reproduction, and clonal propagation contributed the least. The northern population (CR) had both higher elasticities and larger contributions of stasis, followed by clonal propagation and sexual recruitment. Loop analysis also showed that individuals in CR have more paths to complete a life cycle than those in MBR. As a consequence, each population differed in life history traits (e.g., size class structure, size at sexual maturity, and reproductive value). Numerical perturbation analyses showed a small effect of the seed bank on the λ of both populations, while the transition from seeds to seedlings had an important effect mainly in the northern population. Clonal propagation (higher survival and higher contributions to vital rates) seems to be more important for maintaining populations over long time periods than sexual reproduction.     

Microsatellite identification of ramet genotypes in a clonal plant with phalanx growth: The case of Cirsium rivulare (Asteraceae)

Cirsium rivulare is a perennial plant that forms patches consisting of ramets resulting from sexual reproduction by seeds and asexual propagation by rhizome fragmentation. We examined the relationship between the size of patches and genetic differentiation of ramets within and between patches. Ramet genotypes were identified using microsatellites. From among 216 ramets examined in the studied population, 123 had a unique genotype, while 93 were clonal, i.e., their genotype was present in at least two ramets. The frequency of ramets with clonal genotypes was 43% and the frequency of unique genotypes was 57%. Ramets with identical genotypes were dominant in small patches. Large patches consisted of ramets with both unique and clonal genotypes, usually with the predominance of the latter. A molecular variance analysis showed the highest level of variance between ramets and the lowest between patches. Additionally, 21.02% of the total variance was recorded between ramets and within patches. The size of patches was correlated with the number of clonal ramets and the number of unique ramets, but it was not correlated with the clonality index. This population of C. rivulare is currently in a phase of decline from 30 years of vegetation transformation, and there appears to have been an increase in sexual propagation based growth over clonal propagation based growth. Hence, a predominance of ramets with unique genotypes was observed. This can happen as a result of disintegration of large patches and formation of gaps between them. These gaps become convenient places for seed germination and the subsequent development of seedlings.     

Historical vicariance and postglacial colonization effects on the evolution of genetic structure in Lophocereus,a Sonoran Desert columnar cactus

Distinguishing the historical effects of gene migration and vicariance on contemporary genetic structure is problematic without testable biogeographic hypotheses based on preexisting geological and environmental evidence. The availability of such hypotheses for North America's Sonoran Desert has contributed to our understanding of the effect of historical vicariance and dispersal events on the diversification of this region's vertebrate biota but have not yet been applied to its flora. In this paper we describe a detailed allozyme analysis of the population genetic structure and phylogeography of the Sonoran Desert columnar cactus, Lophocereus schottii (senita). Inferred phylogroup distributions reflect two historical vicariance events: (1) a middle Pliocene northward transgression of the Sea of Cortéz that is reflected in well-supported Baja California peninsular and continental phylogroups but not in current taxonomic treatments of the species; and (2) a late Pliocene transpeninsular seaway across southern Baja that is reflected in tentative support for peninsular and southern Cape Region phylogroups corresponding to taxonomic varieties L. schottii var. schottii and L. schottii var. australis, respectively. A middle Pleistocene midpeninsular seaway hypothesized to explain congruent phylogroup distributions in several vertebrate taxa is not reflected in L. s. var. schottii, nor is the distinction of a third variety, L. s. var. tenuis, from continental populations of L. s. var. schottii. Linear regression of pairwise estimates of interpopulation differentiation (M and F(ST)/[1 - F(ST)]) on interpopulation geographic distance revealed significant evidence of isolation by distance within peninsular and continental phylogroups but not between them, consistent with historical vicariance between but not within these regions. We also found significant evidence of isolation by distance between putative L. s. var. schottii and L. s. var. australis phylogroups, suggesting that reproductive isolation between peninsular and Cape Region forms is incomplete. Within peninsular, but not continental, phylogroups, northward range expansion from southern Pleistocene refugia is reflected in significant declines in genetic variation with increasing latitude and in an area phenogram in which populations are progressively nested from south (ancestral) to north (descendant) along the Baja peninsula. Although the geographic concordance of phylogenetic topologies suggests that ancient vicariance events, and not dispersal, have primarily influenced the biogeographic distributions of Baja's vertebrate biota, the phylogeographic structure of L. schottii suggests that Sonoran Desert plant species may exhibit genetic signatures of postglacial range expansion and gene flow as well as vicariance.     

Clonal growth and its effects on male and female reproductive success in <Emphasis Type="Italic">Prunus ssiori</Emphasis> (Rosaceae)

Clonal growth can increase not only floral display but also geitonogamy and may affect sexual reproduction both positively and negatively. A clonal woody species, Prunus ssiori, was partially self-incompatible according to a pollination experiment. Its main pollinators, bumble bees, were often observed to consecutively visit inflorescences within a tree. Clone identification revealed that its genets formed mutually exclusive patches. These features suggest frequent geitonogamous pollination. In a 6.24-ha plot, 212 trees belonged to 59 genets, and 42 genets consisted of a single tree, whereas the rest contained two or more clonal trees. The largest genet had 65 trees and occupied 0.4 of a hectare. Fruit set was measured in 127 inflorescences sampled from nine maternal trees at the center of the plot. Paternal genets of 107 of their 300 seeds were assigned in the plot using microsatellites. There were no selfed seeds. Male reproductive success (the probability that individual trees of each genet sired a seed) increased as tree size increased, as the distance between the trees and maternal trees decreased, when the genet did not contain the maternal trees, and when the genet consisted of a single tree. Female reproductive success (fruit set in individual inflorescences of each maternal tree) increased as the within-tree geitonogamy index, which reflected the frequency of pollination within the maternal tree, decreased. These results suggest that clonal growth reduces male reproductive success, at least, in P. ssiori, because of pollen discounting.     

野古草种群克隆的遗传变异和遗传结构

用酶电泳法和同工酶分析对东北松嫩草原西北部野古草种群克隆遗传变异性和种群遗传结构做了探讨。讨论了遗传多样性、地理距离和遗传距离之间的关系、大种群和小种群的遗传变异性和种群间的基因流 ;种群间 ,包括大种群和小种群间基因流、遗传和地理距离对遗传多样性的影响、昆虫和风传粉、种群籽苗的补充、遗传多样性的发生和保持 ,自交不亲和性和无性繁殖及体细胞突变     

Climate change may alter genetic diversity of Duchesnea indica,a clonal plant species

Climate change may alter the genetic diversity of plants. However, the relationship between genetic diversity in clonal plant species and climate change is unclear. To address this, we examined a representative clonal plant species, Duchesnea indica. We used microsatellite markers to analyze the genetic diversity of the species and used a correlation analysis to infer the relationship between climatic suitability and genetic diversity by using Maxent modeling. Then, we used a geographical information system approach to evaluate the change in genetic diversity of D. indica under climate change scenarios. There was a significantly negative relationship between climatic suitability and the genetic diversity of the clonal plant species. Using a proxy of genetic diversity, we found that climate change may alter the genetic diversity and even lead to a reduction in regional genetic diversity in D. indica. Annual precipitation, in particular, contributes to these changes in genetic diversity. Hence, climatic factors can be used as indicators of genetic diversity for clonal plant species, and studies should examine the impact of climate change on the maintenance of genetic diversity in plant species.     

The effect of local resource availability and clonal integration on ramet functional morphology in Hydrocotyle bonariensis

Summary Within a physiologically integrated clone, the structure and functioning of an individual ramet is determined by: 1) the response of that ramet to its local environment and 2) its response to resource integration within the clone. In a multifactorial experiment, Hydrocotyle bonariensis ramets were grown in limiting resource environments with and without the benefit of basipetal resource movement from another branch of the clone. Ramets were analyzed for their morphological responses to variation in local light, water and nitrogen availability and to the superimposed effect of resource integration on these conditions. The expression of ramet morphology, from induction to development, was highly plastic in response to variable local resource availability. Resource integration changed a ramet's local response in a variety of ways depending on the resource(s) being translocated and the character involved. Among leaf characteristics (leaf weight, petiole height, blade area), resource translocation into the shade resulted in an enhancement of the local response. Similarly, the translocation of nitrogen and water generally increased clonal proliferation and sexual reproduction among ramets. In contrast, the translocation of water reversed the effect of local low water conditions on ramets by inhibiting root production. Some characters such as internode distance and leaf allometry were unaffected by integration. The maintenance of connections between ramets as a Hydrocotyle clone expands allows for resource sharing among widely separated ramets and can result in an integrated morpological response to a resource environment that is patchy in time and space.     

Effects of kin-structured seed dispersal on the genetic structure of the clonal dioecious shrub ilex leucoclada

Nonrandom patterns of gene dispersal have been identified as possible causes of genetic structuring within populations. Attempts to model these patterns have generally focused solely on the effects of isolation by distance, but the processes involved are more complex than such modeling suggests. Here, we extend considerations of gene dispersal processes beyond simple isolation by distance effects by directly evaluating the effects of kin-structured gene dispersal mediated by the group dispersal of related seeds within fruits (i.e., kin-structured seed dispersal) by birds on genetic structure in Ilex leucoclada, a clonal dioecious shrub. To examine the genetic structure patterns, we established two 30x30 m plots (one with immature soils in old-growth forest and one in secondary forest, designated IM and SC, respectively) with different I. leucoclada stem densities. In these two plots 145 and 510 stems were found, representing 78 and 85 genets, respectively, identified by analyzing their genotypes at eight microsatellite loci. The clonal structure was stronger in the SC plot than in the IM plot. Correlograms of coancestry for genets in both plots exhibited significant, positive, high values in the shortest distance class, indicating the presence of strong genetic structure. However, Sp statistics revealed that the pattern of the genetic structure differed between the plots. In addition, to estimate the family structure within fruits, we sampled forty fruits, in total, from 15 randomly selected plants in the area around the IM and SC plots, and found that 80% of the fruits were multiseeded and 42-100% of the multiseeded fruits contained at least one pair of full sibs. Simulations based on these estimates demonstrated that the group dispersal of related seeds produced through correlated mating both within and across fruits, but not unstructured half-sib dispersal, could generate the observed magnitude and trends of genetic structure found in the IM plot. Furthermore, in addition to kin-structured seed dispersal, isolation by distance processes is also likely to promote genetic substructuring in the SC plot. After discussing possible ecological factors that may have contributed to the observed genetic structure, we contrast our results with those predicted by general isolation by distance models, and propose that kin-structured seed dispersal should promote some evolutionary phenomena, and thus should be incorporated, where appropriate, in models of gene dispersal in natural plant populations.     

分子标记在食（药）用真菌遗传多样性研究中的应用

食（药）用真菌在经济和生态方面都具有重要意义,其遗传多样性研究是资源可持续利用和生物保护学研究的基础,有利于食（药）用真菌种质资源的收集、保存、评价和利用,也有助于其分类学、系统学及进化等的研究。遗传多样性的研究方法很多,分子标记是目前最常用最有效的方法之一。综合分析了分子标记在食（药）用真菌遗传多样性研究中的应用,比较了各种标记的应用范围、优缺点,探讨了分子标记用于食（药）用真菌遗传多样性评价的前景及问题。     

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m²) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ _ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.     

Rapid clonal propagation of Saccharum officinarum L. Vars. CO-6907 and CO-86249 and to assess the genetic uniformity through molecular markers

Abstract

An efficient protocol was developed for in vitro clonal propagation of Saccharum officinarum Vars. CO-6907 and CO-86249 through axillary meristem culture. Maximum meristem elongation was achieved on Murashige and Skoog's (MS) medium supplemented with 0.5 mg/L 6-benzyladenine (BA) and 0.5 mg/L kinetin (Kn) within 15 days of culture. Multiple shoots were induced from meristems on MS basal medium supplemented with 1.0 mg/L BA, 0.5 mg/L Kn, 0.25 mg/L 1-napthaleneacetic acid (NAA) and 3% (w/v) sucrose. Addition of 0.1–0.25 mg/L gibberellic acid into the multiplication medium found the better shoot elongation. Repeated subculture on multiplication medium induces higher rate of shoot multiplication. The root induction from excised microshoots was achieved on half-strength MS medium supplemented with 1.0–2.0 mg/L NAA or indole-3-butyric acid and 6% (w/v) sucrose. While either decreasing or increasing of sucrose concentration in the rooting medium, the percentage of rooting was reduced. Maximum percentage of rooting was achieved on medium having 2.0 mg/L NAA with 6% (w/v) sucrose. About 80% of micropropagated plantlets were hardened in the greenhouse and successfully established in the soil. Random Amplified Polymorphic DNA marker was used to detect the variability among the micropropagated plants developed through in vitro. The results showed that there was no polymorphism among the micropropagated plants. This study will help for propagation of quality planting material of high-yielding variety of sugarcane for commercialization.     

Low genetic diversity and high genetic differentiation in the critically endangered Omphalogramma souliei (Primulaceae):implications for its conservation

Omphalogramma souliei Franch. Is an endangered perennial herb only distributed in alpine areas of SW China. ISSR markers were applied to determine the genetic variation and genetic structure of 60 individuals of three populations of O. Souliei in NW Yunnan, China. The genetic diversity at the species level is low with P= 42.5% (percentage of polymorphic bands) and Hsp=0.1762 (total genetic diversity). However, a high level of genetic differentiation among populations was detected based on different measures (Nei's genetic diversity analysis: Gst=0.6038; AMOVA analysis: Fst=0.6797). Low level of genetic diversity within populations and significant genetic differentiation among populations might be due to the mixed mating system in which xenog-amy predominated and autogamy played an assistant role in O. Souliei. The genetic drift due to small population size and limited current gene flow also resulted in significant genetic differentiation. The assessment of genetic variation and differentiation of the endangered species provides important information for conservation on a genetic basis. Conservation strategies for this rare endemic species are proposed.     

栖息条件对中华蜜蜂遗传多样性的影响

为了评估不同栖息条件对中华蜜蜂(简称中蜂)种群遗传多样性的影响,本研究运用微卫星标记的方法,对皖南山区4个不同采样点120个中华蜜蜂群体的2400只工蜂样本进行了分析.结果表明:与天然林野生中蜂群相比,单一茶树种植结构下,皖南中蜂群的等位基因数、平均期望杂合度和多态信息含量的差异均不显著;人工驯养中蜂群的等位基因数、多态信息含量差异显著,平均期望杂合度差异不显著;2006年采集的野生中蜂群与天然林野生中蜂群的等位基因数、平均期望杂合度和多态信息含量均差异显著.各种群间存在极显著的遗传分化,平均分化系数为0.32.说明皖南地区茶树单一化种植不会影响中蜂的遗传结构与资源保护.     

Growth and demography of a declining,endangered cactus in the Sonoran Desert

Increases in the incidence and severity of drought threaten the viability of rare plants in arid regions. The endangered Nichol's Turk's head cactus (Echinocactus horizonthalonius Lemaire var. nicholii L. Benson) occurs only in four small, isolated populations in the Sonoran Desert of North America. Since 1995 we have monitored a population in southeastern Arizona (USA). Here we report 23 years of observations on abundance, growth, mortality, flowering and recruitment. Abundance of plants decreased from 132 in 1996 to 40 in 2017, with 100 individuals recruited and 203 dying during the study. Individual plants grew slowly, increasing annually by an average of 0.22 cm (95% confidence interval, 0.18–0.26 cm) in diameter and 0.27 cm (0.20–0.33 cm) in height. Growth was slowest when drought was most severe and slowed as plants reached maximum size. Annual mortality increased markedly across the study period and did not vary with plant size. Annual probability of flowering increased as plants increased in diameter but not in height, and varied with precipitation and drought but not with mean annual temperature. Recruitment was higher when average temperature was higher and the number of recruits per capita increased across the study period. The annual rate of change in abundance averaged −6%, but shifted markedly from −1% during 1995–2008 to −11% during 2008–2017. Our results indicate that the population's decline was not a consequence of failed recruitment but of increased mortality, which we discuss in the context of climate and herbivory.     

分子标记及其在核桃遗传多样性研究中的应用

核桃是我国重要的坚果和木本油料树种之一,具有重要的学术研究和经济价值。现代分子标记技术的迅速发展为核桃的种质鉴定、遗传育种、遗传多样性分析、亲缘鉴定等提供了崭新途径。本文主要介绍RFLP、RAPD、AFLP及SSR等几种分子标记技术的主要原理、特点以及在核桃遗传多样性方面的研究进展,分析了分子标记在核桃遗传多样性研究中的主要问题,并对其发展提出了展望。     

Retrospective investigation of captive red wolf reproductive success in relation to age and inbreeding

The critically endangered red wolf (Canis rufus) has been subject to a strictly managed captive breeding program for three decades. A retrospective demographic analysis of the captive population was performed based on data from the red wolf studbook. Data analyses revealed a decrease in the effective population size relative to the total population size, and changes in age structure and inbreeding coefficients over time. To varying degrees, the probability of successful breeding and litter sizes declined in association with increasing dam age and sire inbreeding coefficients. Neonate survival also declined with increasing dam age. Recent changes in strategies regarding breed-pair recommendations have resulted in moderate increases in reproductive success. Zoo Biol 28:214–229, 2009. © 2009 Wiley-Liss, Inc.     

Low genetic diversity and high genetic differentiation in the critically endangered Omphalogramma souliei (Primulaceae): implications for its conservation

Omphalogramma souliei Franch. is an endangered perennial herb only distributed in alpine areas of SW China. ISSR markers were applied to determine the genetic variation and genetic structure of 60 individuals of three populations of O. souliei in NW Yunnan, China. The genetic diversity at the species level is low with P=42.5% (percentage of polymorphic bands) and Hsp=0.1762 (total genetic diversity). However, a high level of genetic differentiation among populations was detected based on different measures (Nei's genetic diversity analysis: Gst=0.6038; AMOVA analysis: Fst=0.6797). Low level of genetic diversity within populations and significant genetic differentiation among populations might be due to the mixed mating system in which xenogamy predominated and autogamy played an assistant role in O. souliei. The genetic drift due to small population size and limited current gene flow also resulted in significant genetic differentiation. The assessment of genetic variation and differentiation of the endangered species provides important information for conservation on a genetic basis. Conservation strategies for this rare endemic species are proposed.     

Patterns and causes of spatial variation in the reproductive success of a desert annual

Summary This study examines patterns and causes of variation in the reproductive success of the desert annual Stipa capensis. Three nested scales of variation were analyzed: variation between individuals of the same plot, variation between different plots of the same habitat, and variation between different habitats in the same region. Perturbation experiments (irrigation and neighbors removal) were performed to test the effects of heterogeneity in soil water and neighborhood competition on the magnitude of variation in each scale. The results demonstrate that variation of reproductive success was highest within plots, lowest between plots, and moderate between habitats. Soil water heterogeneity contributed to spatial variation in all scales but was most important for differences between habitats. Neighborhood competition increased the variation within plots, but decreased the variation between habitats. The results further demonstrate that water limitation was negatively correlated with the position of the habitat along the run-off/run-on gradient. An opposite trend was obtained for the effect of competition.