Genetic variation of microsatellite loci in a bottlenecked species: the northern hairy-nosed wombat Lasiorhinus krefftii

We investigate the utility of hypervariable microsatellite loci to measure genetic variability remaining in the northern hairy-nosed wombat, one of Australia's rarest mammals. This species suffered a dramatic range and population reduction over the past 120 years and now exists as a single colony of about 70 individuals at Epping Forest National Park, central Queensland. Because our preliminary research on mitochondrial DNA and multilocus DNA fingerprints did not reveal informative variation in this population, we chose to examine variation in microsatellite repeats, a class of loci known to be highly polymorphic in mammals. To assess the suitability of various wombat populations as a reference for comparisons of genetic variability and subdivision we further analysed mitochondrial DNA cytochrome b sequence, using phylogenetic methods. Our results show that appreciable levels of variation still exist in the Epping Forest colony although it has only 41% of the heterozygosity shown in a population of a closely-related species. From museum specimens collected in 1884, we also assessed microsatellite variation in an extinct population of the northern hairy-nosed wombat, from Deniliquin, New South Wales, 2000 km to the south of the extant population. The apparent loss of variation in the Epping Forest colony is consistent with an extremely small effective population size throughout its 120-year decline.     

云贵鹅耳枥群落乔木种群生态位初探

木文应用Ｌｅｖｉｎ公式和王刚改进公式分别计测了贵阳喀斯特山地云贵鹅耳枥群落中乔木种群的生态位宽度和生态位重叠,并对这些种群的生态位关系及其对群落结构和动态的影响进行了分析。     

Host-plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract.

• 1 Newly-emerged, second-instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb.
• 2 Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect.
• 3 In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring.
• 4 Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k-values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones.
• 5 Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones.
• 6 We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density-dependent factor governing the density of early-stage jack pine budworm.
• 7 The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

     

Wild pearl millet population (Pennisetum glaucum,Poaceae) integrity in agricultural Sahelian areas. An example from Keita (Niger)

Morphometric and isozymic analyses of adjacent cultivated and spontaneous populations of pearl millet in Niger revealed in the field a unique continuous distribution of phenotypes ranging from the most cultivated one to a typical cultivated × wild hybrid. The natural population was subdivided into a major wild group and a hybrid wild × cultivated group. Cultivated millet displayed an equilibrium state between recombined domesticated and wild genes. The natural population, in spite of a high rate of immigration by pollen from cultivated plants, retained its structure by apparently reproducing itself exclusively from the major wild group.     

水稻品种对白背飞虱种群增长的影响

白背飞虱在不同类型水稻品种上的分布、趋性、发育和繁殖力是不同的。它喜欢在杂交稻（汕优6号）上生活和繁殖,取食后成虫寿命最长,取食量、产卵趋性、产卵量、田间虫量均最大,种群增长快;在粳稻上却相反;常规灿稻和糯稻介于二者之间。在同一类型品种中,抗虫品种比感虫品种在上述特性方面差异明显。说明抗虫育种和种植抗虫品种是对该害虫综合治理的一项关键技术。     

THE POPULATION DYNAMICS OF NORTHERN SEA LIONS, 1975-1985

Abstract: Populations of northern sea lions ( Eumetopias jubatus ) in the vicinity of Marmot Island, Alaska declined during 1975–1985 at about 5% per year (Merrick et al. 1987). The cause of this decline is not known. A life table for the northern sea lion was calculated assuming that life spans follow a Weibull distribution. Samples of northern sea lions taken in the vicinity of Marmot Island, Alaska during 1975–1978 and 1985–1986 indicate that the average age of females older than 3 yr increased about 1.55 yr (SD = 0.35 yr) while the population was declining at about 5% per year. Fecundity rates decreased by 10% over the same period, but the decrease was not statistically significant (Calkins and Goodwin 1988). Possible causes of the population decline and the change in age structure were examined by writing the Leslie matrix population equation in terms of changes in juvenile and adult survival rates and fecundity, and examining the short–term behavior of the trajectories of the average age of adult females, total number of females, and total number of pups with respect to those changes in the vital parameters. From the observed rate of declines of adults and the changes in average age of adult females and fecundity, estimates of the changes in adult and juvenile survival were calculated; estimates of the standard deviations of these changes were estimated via a bootstrap procedure. One purpose of this exercise is to aid in setting priorities for research for determining the cause of the decline. An explanation for the observed declines in numbers of adult sea lions consistent with the observed fecundity rates, a rate of decrease of 5% in the number of adults, and the corresponding increase in average age (of females age 3 yr and older) was a 10%–20% decrease in the survival of juveniles (age 0-3 yr) coupled with an insignificant change in adult survival (0.03%, SD = 1%).     

Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Annual survival rate and age structure of habu,Trimeresurus flavoviridis (Viperidae), on Minna island,Japan: Estimation from removal trapping

A population of a viperid snake,Trimeresurus flavoviridis, was studied over 10 years by removal trapping on a small subtropical island in Japan. The sex ratio of trapped individuals changed seasonally, but was not biased to either sex in the whole sample of 258 individuals. The age of each individual was estimated through the size structure and the age-size relationship. The minimum number of individuals at the beginning of the study was estimated through accumulating older individuals trapped in the subsequent years. By assuming an annual natural survival rate in the course of this accumulation, an age structure was simulated which led to calculate a resulted natural survival rate. The assumed rate of 0.62 fitted best to the resulted one. The annual trapped proportion estimated on the simulated absolute number of individuals was higher in older individuals than in younger ones with the overall mean of 16%.     

寄生蜂种群繁殖分布时间特征的研究

运用１０种寄生蜂的２３张生殖力表资料,分析比较了这些种群繁殖分布的特征．结果表明,寄生蜂种群繁殖具有相似的分布特征,种群繁殖集中分布在生殖头ｄ天内,在生殖头ｄ／２天内繁殖分布更为集中．在生殖头ｄ天内种群繁殖对种群增长的贡献几乎均达到１００％,其中大部分贡献是在生殖头ｄ／２天内实现的．这种繁殖分布特征对于寄生蜂种群内禀增长率的测定和掌握种群数量动态的时间特性十分重要．本文结合Ｉｗａｏ零频率法和Ｇｅｒｒａｒｄ阈限密度法,提出一种改进的种群密度估计方法──“综合阈限密度估计法”,并由此探讨了苹果树上山楂叶螨成螨的密度估计及其抽样技术．采用零样频率来估计成螨的平均密度,并得到用概率保证的理论抽样数模型．比较结果表明,零频率法所需的理论抽样数少于直接计数法．综合阈限密度估计法的拟合效果更为显著．     

山楂叶螨种群空间格局及其应用的研究Ⅱ．成螨种群密度综合估计及其抽样技术

本文结合Ｉｗａｏ零频率法和Ｇｅｒｒａｒｄ阈限密度法,提出一种改进的种群密度估计方法──“综合阈限密度估计法”,并由此探讨了苹果树上山楂叶螨成螨的密度估计及其抽样技术．采用零样频率来估计成螨的平均密度,并得到用概率保证的理论抽样数模型．比较结果表明,零频率法所需的理论抽样数少于直接计数法．综合阈限密度估计法的拟合效果更为显著．