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1.
Inbreeding depression constitutes a significant threat to the viability of small populations. In addition to small size and isolation of populations, short distance dispersal may elevate risk of inbreeding, but empirical evidence is scarce. Inbreeding depression has been demonstrated in the highly endangered red-cockaded woodpecker Picoides borealis. It has been suggested that conservation efforts to support extant populations should aim at spatially aggregating territories to enhance dispersal success. This however may aggravate inbreeding risk because distance between territories and hence dispersal distances become short. We analysed empirical data from a long-term study of the demography of the red-cockaded woodpecker and found that inbreeding risk varied inversely with natal dispersal distance of the mother. Using an individual-based, spatially explicit population model that incorporates simulations of environmental and demographic stochasticity and an empirically derived, species-specific estimate of inbreeding costs, we demonstrated that inbreeding depression significantly elevated extinction risk in this species. On the other hand, even though dispersal distances in populations with spatially aggregated territories were shorter and the proportion of inbred individuals was higher than in other populations of the same size, such populations were still more persistent. Despite the overall adverse effect of inbreeding depression on viability of red-cockaded woodpecker populations, lowering interterritorial distances can be viewed as a valuable conservation tool. Given the small size and isolated location of most extant red-cockaded woodpecker populations however, our findings suggest that inbreeding depression represents a significant threat to the survival of this species. 相似文献
2.
An initial survey of breeding records of captive ungulates showed that juvenile mortality was higher in inbred than in non-inbred young in 15 of 16 species. Because of recent scepticism regarding the deleterious effects of inbreeding, we conducted a more detailed analysis of the 12 species for which adequate records were available to examine the possibility that the trend of higher mortality rates in inbred young was not due to inbreeding but rather to some other factor often associated with inbreeding.The factors considered were: birth season; birth order; management changes; population density; and differences between captive-born and wild-caught, and inbred and non-inbred dams.None of these possibly confounding factors could account for the higher mortality rates of inbred young. These results demonstrate the reality of the effects of inbreeding and emphasize that an awareness of the consequences of inbreeding is vital to the sound genetic management of small captive populations. 相似文献
3.
European bison (Bison bonasus) became extinct in the wild at the beginning of the 20th century. The contemporary Lowland line of bison was founded by seven individuals that survived in captivity. The largest population of Lowland bison live in the Bia?owie?a Forest, but the forest and the population are divided by a border fence between Poland and Belarus. This fence is a barrier to the movement of ungulates. In this study, we used population genetic models to predict the future viability of the Polish and Belarusian bison populations. We determined the founder contribution, founder equivalent, mean inbreeding coefficient, mean kinship, and the proportion of genetic diversity retained in the Belarusian bison population. Although the founding group of the Belarusian population was larger than that of the Polish population, the latter had more favourable genetic parameters. We assessed inbreeding depression for fecundity in free-ranging European bison compared to captive individuals. Using population viability analysis (PVA) we modelled both bison populations with or without gene exchange, and with or without incorporating the kinship of the founders. When founder kinship was included, in both populations the mean number of alleles and the gene diversity retained within extant populations decreased substantially compared to PVA models in which founders were not related. The worst genetic parameters were obtained for the Belarusian population under a scenario in which the founders are related and gene exchange is lacking, which is the closest to the real situation. Creation of passages for animals by partial removal of the border fence would have a favourable effect on the genetic variation and viability of both bison populations, especially the Belarusian. 相似文献
4.
Inbreeding is common in plants and can have considerable effects on population viability, because of inbreeding depression. Understanding what determines the magnitude of inbreeding depression is of fundamental importance for conservation biology. We used meta-analysis of 116 studies and 107 plant species to investigate the effects of population size, test environment, life history characteristics and stage on the magnitude of inbreeding depression in 13 different fitness traits. We found that inbreeding depression levels significantly increase with population size. This may be a consequence of either, or both, a higher baseline of the level of inbreeding or increased impact of purging in small populations; unfortunately the available data did not allow distinguishing between these potential explanations. In general, inbreeding depression was found to be common across species and environments, and was significant in all traits examined. Yet, the magnitude of inbreeding depression was significantly influenced by plant longevity and life-history stage, and varied depending on how plant fitness was measured. Our findings highlight the fundamental role of population size in influencing the magnitude of inbreeding depression in plants. This clearly has important implications for conservation biology. Moreover, our findings on the overall generality of inbreeding depression confirm that inbreeding depression is one of the key factors reducing plant population fitness and viability. Hence, we need a better understanding on the architecture of inbreeding depression, how different ecological and historical conditions influence the levels of inbreeding depression in natural plant populations, and its impacts on community dynamics. 相似文献
5.
Carlos Vilas 《Biological conservation》2006,129(1):124-133
Loss of genetic variation in populations may have other effects than inbreeding depression and loss of adaptive potential. In the case of the numerous gynodioecious plant species having cytonuclear systems of sex determination with dominant nuclear restorers of the male function, reduced genetic variation and increased inbreeding would increase the proportion of non-restorer recessive genes found in homozygosity, and therefore that of female plants producing pistillate flowers. This could have opposite effects on the extinction risk of the population. Female plants produce no pollen and may cause pollen limitation, but at the same time they may reduce average homozygosity and inbreeding depression because they are forced outcrossers. We observed that inbreeding indeed increased the frequency of female plants and pistillate flowers in the population, and that this effect was accompanied by reductions in population recruitment independent of inbreeding depression and likely due to pollen limitation. These results suggest that dominant nuclear restorers of pollen production speed up the extinction of small populations of Silene littorea, and that sex determination mechanisms might be an important factor to consider in the conservation of many plant species. 相似文献
6.
Populations with small effective sizes are at risk for inbreeding depression and loss of adaptive potential. Variance in reproductive success is one of several factors reducing effective population size (Ne) below the actual population size (N). Here, we investigate the effects of polygynous (skewed) mating and variation in female breeding success on the effective size of a small population of the Gunnison sage-grouse (Centrocercus minimus), a ground nesting bird with a lek mating system. During a two-year field study, we recorded attendance of marked birds at leks, male mating success, the reproductive success of radio-tagged females, and annual survival. We developed simulations to estimate the distribution of male reproductive success. Using these data, we estimated population size () and effective population size Ne for the study population. We also simulated the effects of population size, skewed vs. random mating, and female breeding failure on Ne. In our study population, the standardized variance in seasonal reproductive success was almost as high in females as in males, primarily due to a high rate of nest failure (73%). Estimated Ne (42) was 19% of in our population, below the level at which inbreeding depression is observed in captive breeding studies. A high hatching failure rate (28%) was also consistent with ongoing inbreeding depression. In the simulations, Ne was reduced by skewed male mating success, especially at larger population sizes, and by female breeding failure. Extrapolation of our results suggests that six of the seven extant populations of this species may have effective sizes low enough to induce inbreeding depression and hence that translocations may be needed to supplement genetic diversity. 相似文献
7.
Genetic consequences of silvicultural management of Leucaena esculenta subsp. esculenta were analyzed from eight allozyme loci in half-sib families of one wild and one managed in situ (selectively cleared) population from La Montaña de Guerrero region, Central Mexico. A reference sample (including wild, feral and cultivated individual plants) from the states of Morelos, Puebla and Guerrero, Mexico was also analyzed. Genetic variation, population structure and mating system were analyzed. All loci showed high variation (75–87.5% polymorphic loci at 95% level; 2.4–2.8 mean number of alleles per locus). All progenies showed heterozygous deficiency, but both wild and managed parental inbreeding coefficients were negative, suggesting heterosis. Progenies of managed populations differed from those of the wild and reference samples (Nei’s unbiased identities 0.874–0.934). Biparental inbreeding is suggested by Wright’s-statistics ( f = 0.313), and by outcrossing rate estimates: tm = 0.644 (SE 0.094), and 0.645 (SE 0.193); ts = 0.576 (SE 0.189), and 0.523 (SE 0.182), for managed and wild samples respectively. Population differentiation is significant (Θ = 0.210). The species is self-incompatible and deviations from the mixed mating model were found. Indirect estimates of products of effective population size (Ne) by the proportion of migrants (Nm) were moderate, as were the N evalues. Variation due to ecotypic differentiation (related to altitude), prolonged artificial selection, and introduction from other areas is supported. A model of domestication of seed-propagated trees is suggested, based on extensive and in situ selection of locally adapted populations, and their diffusion to other areas. 相似文献
8.
Forest restoration programmes aim to use material for re-planting that is genetically diverse and not inbred. However, restricted seed sampling, high variance in reproductive output, and the production of inbred seeds that survive in the nursery but not in the wild can lead to forest restoration stock being genetically compromised. The aim of this study was to evaluate whether the reproductive biology of the New Caledonian endemic conifer Araucaria nemorosa makes it susceptible to these genetic problems and to assess whether there is evidence for genetic bottlenecks and elevated inbreeding in nursery stock compared to seedlings and adults from wild source populations. Reproductive output was low with high variance among trees (only 14% of adult trees surveyed produced mature cones, >50% of examined cones had <10 viable seeds). Evidence for an extreme genetic bottleneck was detected in a nursery population established from cones collected from adult trees. A second nursery population established with seed collected from the forest floor showed no evidence of a genetic bottleneck, but was inbred compared to its wild source population. In light of these results, we do not recommend collecting cones directly from A. nemorosa as an efficient means of establishing genetically diverse stock for restoration programmes. Collecting seed from the forest floor is likely to be more effective, but the planting stock may contain a high proportion of inbred individuals. Collecting established wild seedlings already subjected to natural selection is suggested as an alternative method of maximising the diversity captured, whilst minimising sampling effort and proportion of inbred individuals. 相似文献
9.
Levels of genetic variation and intrapopulation genetic structures of Leontice microrhyncha S. Moore (Berberidaceae) were assessed for six populations in South Korea, representing the southern most range of a species found in Northeast China and the Korean peninsula. Detected genetic diversity (Hes) was very low (0.024) and FIS values showed large heterozygote deficiencies. The small percentage of polymorphic loci and numbers of alleles per locus suggest that L. microrhyncha has a history of severe or long-lasting population bottlenecks that have eroded genetic diversity. This study suggests that the Korean population appears to consist of two historically isolated and independently evolving populations. It seems likely that these groups have been isolated and unstable for a significant period of time. However, the effects of recent habitat fragmentation on the historically disjunct and fragmented population system found in L. microrhyncha were not those predicted from the lack of significant relationships between population-level patterns of genetic variation and population sizes. Most non-unique genotypes were shared by most individuals and the lower level of diversity, high levels of inbreeding and population differentiation as well as high rate of seed production indicated that this species is autogamous and self-compatible and probably largely selfing. Therefore, to preserve extant genetic variation, all populations must be protected across the small geographic range of the species to retain both allelic and genotypic diversity. 相似文献
10.
We investigated how genetic factors and pollen shortage affect seed production in a small population of Magnolia stellata, a threatened insect-pollinated tree. We used microsatellite and manual pollination techniques, and compared a small population to a large one. Compared to the large population, the small population showed low allelic variation and had an FIS significantly greater than 0 in adults, indicating that genetic deterioration, including genetic drift and inbreeding, may have occurred in adults. Manual self-pollination lowered seed production relative to manual cross-pollination to a different extent between populations: δ (the magnitude of inbreeding depression due to self-fertilization) was lower in the small population than in the large population. However, under natural pollination, the estimated embryo mortality rates after ovules self-fertilized were similar between the two populations because the primary selfing rate was higher in the small population. The ovule mortality rate due to pollen shortage and that due to factors independent of pollen shortage and selfing were both approximately 10% higher in the small population, suggesting that pollen transfer may have decreased and genetic deterioration effects may have increased in that population. These factors reduced seed production in the small population (female reproductive success = 0.3%) compared to the large population (2.6%). Our results suggest that seed production in the small population of M. stellata is strictly limited by elevated pollen shortage, selfing, and genetic deterioration in adults, which accelerate the risk of extinction. 相似文献
11.
低磷胁迫下不同基因型玉米籽粒磷含量及品质性状分析 总被引：3，自引：2，他引：1
从我国北方和西南各地共收集129个自交系玉米品种,通过田间试验,研究了正常磷（120kg P2O5/hm2）和低磷（0kg P2O5/hm2）2种施磷水平下,依据百粒重筛选出的15个耐低磷基因型玉米品种及5个磷敏感基因型玉米品种的籽粒磷含量及品质性状的变化情况。结果表明,低磷胁迫对于磷敏感基因型玉米籽粒中磷含量、粗淀粉、粗油分含量变异程度的影响明显大于耐低磷基因型玉米,对粗蛋白含量变异程度的影响则低于后者。相关性分析结果表明,在2种施磷水平下的籽粒粗淀粉与籽粒粗蛋白质含量都呈极显著负相关,籽粒粗淀粉与籽粒粗油分含量不相关。低磷胁迫下,各典型自交系玉米品种的磷含量与粗淀粉、粗油分、粗蛋白之间,粗蛋白与粗油分之间的相关性都比正常施磷水平增加。通过研究筛选出的20个典型自交系玉米品种,籽粒中粗淀粉、粗油分、粗蛋白含量在不同磷水平下的变化有着极显著的基因型差异（P＜0.01）,具有进一步的研究价值。 相似文献
12.
玉米自交系苗期磷营养特性评价 总被引：2，自引：0，他引：2
利用一元线性回归模型对9种基因型玉米自交系在6叶龄苗期的磷(P)营养特性进行了评价。以幼苗的全株或地上部生物量(mg/plant)分别与培养介质对其供磷量(P.mg)建立线性模型,其回归系数作为全株或地上部磷效率的指标;以幼苗的全株或地上部生物量分别与相应的全株或地上部磷含量(P.mg/plant)建立线性模型,其回归系数作为全株或地上部磷利用效率的指标;以幼苗全株磷含量与培养介质对其供磷量建立线性模型的回归系数作为幼苗磷吸收效率的指标。结果表明,9种玉米基因型的磷效率,磷利用效率和磷吸收效率的平均值分别为53.95(全株)和42.61(地上部)、131.84(全株)和124.45(地上部)、0.41。自交系04419的磷效率比平均值约高出45%(全株)和59%(地上部),属于磷效率高效型;而自交系04065和04088的磷效率分别比平均值约低43%、38%(全株)和55%、51%(地上部),属于磷效率低效型;其余自交系的磷效率介于两者之间,为磷效率中间型。玉米自交系苗期的磷效率与磷吸收效率呈显著正相关,与磷利用效率关系不明显;磷吸收效率可作为苗期磷效率预筛选的生理指标。 相似文献
13.
Stuart G. Field 《Soil biology & biochemistry》2006,38(6):1334-1339
The earthworm Lumbricus terrestris has relatively low dispersal rates. This can represent a challenge for the internal gregarine parasite Monocystis, the dispersal of which often depends on the host. Mating of Monocystis can also be restricted to parasite stages within the current host individual. Adaptations, including host behavioural modification, that improve parasite transmission and simultaneously avoid inbreeding within a single host individual should be favoured by selection. We used a correlative approach to investigate the question of parasitic manipulation in this Gregarine-Lumbricid system. We observed mature earthworms (n=24) for 3 weeks while recording various measures of activity (surface activity, burrowing activity, surfacing delay, number of surface visits) and correlated parasite load with these activity measures. We found a significant positive correlation between surface activity and midden (or cast) production, which suggests a simple method for assessing the overall activity of local earthworm populations. However, we found no evidence of behavioural manipulation of any measure of host activity. We discuss these results in the context of inbreeding depression and host-parasite coevolution. 相似文献
14.
采用基因枪法将Bt基因(GFM CrylA)导入东北春玉米自交系铁7922的幼胚中,获得转基因植株。经过连续3年的田间接卵、室内饲喂玉米螟鉴定,获得稳定抗虫转基因系。以此为亲本与常规自交系配制了四密25Bt、通单24Bt、吉单209Bt3个杂交种。转基因自交系和杂交种的抗螟性鉴定结果表明：转基因系间抗虫性差异极显著,同一转基因系单株间和配制的3个杂交种间抗虫性也存在差异;与对照相比,转基因系配制的杂交种抗虫性明显提高,差异显著。农艺性状鉴定结果显示,转基因系配制的杂交种与对照在株高、穗长、穗行数、行粒数、百粒重上无显著差异。本研究认为,GFM CrylA(Bt)基因可用于玉米的抗螟性改良,也为转Bt基因玉米自交系能够直接用于育种提供了依据。 相似文献
15.
A. C. B. Sousa M. A. Carvalho T. Campos D. A. Sfor?a M. I. Zucchi L. Jank A. P. Souza 《Genetic Resources and Crop Evolution》2012,59(7):1449-1464
Calopogonium mucunoides Desv. is a species native of South and Central America that is used as green manure and a pasture crop. The molecular genetic diversity was characterized in 195 C. mucunoides accessions from a germplasm collection using 17 microsatellite markers. Outcrossing rate was estimated after the evaluation of six microsatellite loci in 200 genotypes originated from 10 open-pollinated progenies (20 genotypes per progeny). Six genetic clusters were identified in the germplasm collection by the STRUCTURE software analysis, neighbor-joining tree comparisons and principal component analysis, which highly correlated with the geographic locations where these accessions were originated or collected. These results were confirmed using AMOVA. The largest portion of the genetic variation was observed among clusters (64.38%). The results indicated that: multilocus outcrossing rate (t m ) was 16.3%, suggesting a mixed mating system with a predominance of autogamy; single locus outcrossing rate (t s ) was 11%; difference (t m ?t s ) was 0.054, indicating that only 5.4% of outcrossing occurred among related individuals; paternity correlation (r p ) was 33% suggesting a low probability of finding full sibs among the progeny; parental coefficient of inbreeding (F m ) was 5.0%, indicating a low degree of inbreeding in each parent. A core collection for C. mucunoides was assembled to capture the allelic diversity found in this study. The complete allelic diversity was represented by only 15 accessions. These results should be useful for exploiting the genetic resources of C. mucunoides and could influence future conservation efforts and breeding programs. 相似文献
16.
Endangered birds in insular environments like New Zealand are often translocated to predator-free offshore islands for conservation purposes. Some translocated populations however exhibit reduced fecundity, and it has been suggested that either inbreeding (due to small number of founders) or resource shortages (due to high population density) may limit reproductive success. For example, the South Island robin (Petroica a. australis) population on Motuara Island (59 ha) was founded by only five birds but has increased to ∼600 individuals, or a density >10 times that of the mainland. Despite this apparent success, the rate of hatching failure in this population is three times higher than in mainland populations, with more than a third of eggs failing to hatch. To test if elevated hatching failure is the result of food limitation, we carried out a food supplementation experiment by providing females with mealworms equivalent to ∼50% of their daily energy requirements. Food supplementation had no effect on hatching success, clutch size, incubation attentiveness or nest size. Egg volume increased with food supplementation in one of the two years of this study, but both egg volume and incubation attentiveness were unrelated to rate of hatching failure. As previous genetic analyses confirmed that the bottlenecked population of robins on Motuara Island have significantly less genetic variation than their source population, we conclude that inbreeding depression, and not food limitation, is the most likely explanation for their high rate of hatching failure. We suggest that the experimental translocation of genetically dissimilar individuals be considered as a possible remedy for low productivity in island populations that were initiated with few founders. 相似文献
17.
Edward J. Boza Cecile L. Tondo Noris Ledesma Richard J. Campbell Jay Bost Raymond J. Schnell Osman A. Gutiérrez 《Genetic Resources and Crop Evolution》2018,65(4):1195-1215
Avocado (Persea americana Mill.) is a subtropical domesticated fruit tree indigenous to Mesoamerica. It is a member of the Lauraceae family and is separated into three horticultural races (Guatemalan, Mexican, and West Indian) mainly corresponding to their ecological adaptation, botanical, and physiological traits. Main objectives of this study were to characterize the population structure, genetic diversity, and horticultural race of a total of 354 Persea spp. trees whose origin is as follow: 221 trees [P. americana, (218), P. nubigena (2) and P. krugii (1)] from the USDA-ARS-Subtropical Horticultural Research Station, Miami; 105 trees from the Fairchild Farm [P. americana (104) and P. schiedeana (1)], and 28 trees collected in Mexico [P. schiedeana (23) and P. americana (5)]. The complexity of their interracial admixture; as well as mislabeling frequency was also evaluated. Molecular marker analysis utilizing a set of 55 simple sequence repeat (SSR) markers amplified a total of 869 alleles with a mean number of alleles per locus of 15.8 and average polymorphism information content value of 0.71, indicating a high variability in the allele frequency for the collection. Significant deviations from Hardy–Weinberg equilibrium were identified after Bonferroni correction for a large number of loci (48; 87%) due to the presence of null alleles. The main source of variation for this population was found to be within individuals (66.84%), with 19.30% variation among populations, and 13.86% variation among individuals within populations. Moreover, population specific inbreeding indices (F IS ) were calculated for West Indian, Guatemalan, and Mexican [(0.1918; p value 0.0000), (0.1879; p-value 0.0000), (0.0925; p-value 0.0022)], respectively. Bayesian analysis divided the individual genotypes into groups associated with the Guatemalan, Mexican, West Indian races; interracial admixture; complex hybrids and P. schiedeana species. Also, results of the multivariate clustering method (PCA) and genetic distance analyses calculated among all possible individual combinations within the SSR diversity data agreed with Bayesian or Structure analyses results. The 55 SSRs provided complete resolution of all individuals and the estimated mislabeling error was approximately 0.28%. 相似文献
18.
不同磷效率玉米自交系根系形态与根际特征的差异 总被引：5，自引：0，他引：5
通过三室根袋栽培试验,对3种磷高效型和3种磷低效型的玉米自交系在2种不同磷水平下的植株生物量、吸磷量、根系形态、根际pH值以及根际磷酸酶进行研究,比较不同磷利用率基因型玉米自交系的根系形态及根际特征的差异。结果表明,在低磷情况下,磷利用率高的玉米自交系其植株生物量中的根干重、植株的吸磷量、根系形态中的根尖数与根长以及根际磷酸酶的活性方面均高于磷利用率低的玉米自交系。植株的根部干重:磷高效的1号品种（hp1）显著高于磷低效的2号品种（lp2）,hp2显著高于lp1、lp2、lp3;hp1、hp2的地上部与根系的吸磷量均显著高于lp2、lp3。hp1、hp2根尖数、根长显著高于磷低效型的lp2、lp3。hp1、hp2、hp3根际土壤的酸性磷酸酶活性显著高于lp2、lp3。其他指标如植株地上部分干重、pH值,磷高效型玉米自交系也存在一定优势。所有品种中hp2与lp3的差异最为显著。 相似文献
19.
用SSR对60个玉米自交系的DNA进行分子标记和杂种优势群划分研究。利用14对SSR引物在供试材料中检测出57个等位基因变异,每对引物检测等位基因2～7个,平均为4．07个,多态信息量变化范围为0．389～0．832,平均为0．692。自交系间遗传相似系数变幅为0．058～0．756,UPGMA聚类分析表明,供试自交系可分为五个类群。利用这14对具有较高多态性信息量的引物,可以对供试材料进行初步鉴定。 相似文献
20.
Aleck Kondwakwenda Julia Sibiya Assefa B. Amelework Rebecca Zengeni 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2020,70(4):265-271
ABSTRACTThe success of a breeding programme can be determined by the level of genetic diversity that exists among breeding materials. This study was carried out to (i) determine the level of genetic diversity that exist among the collection of tropical provitamin A maize inbred lines and (ii) evaluate the genetic structure and divergence of provitamin A maize inbred lines. Forty-six advanced provitamin A inbred lines obtained from the International Maize and Wheat Improvement Centre (CIMMYT) and International Institute of Tropical Agriculture (IITA) were genotyped using 3047 single nucleotide polymorphism (SNP) markers. Genotyping was done following an Illumina Infinium HD Assay Ultra protocol. Eight six percent of the SNPs were polymorphic with the mean polymorphic information content of 0.36. Cluster analysis displayed two distinct clusters. The average pairwise genetic distance among the inbred lines was 0.60. The average gene diversity was 0.359. Variation was partitioned into among individuals (78%), among populations (12%) and within individuals (10%). Overall results suggest the inbred lines are genetically diverse. The key implication of this study is that selection should be done from genetically diverse inbred lines in order to exploit heterosis when developing hybrids. 相似文献