INBREEDING AND VARIANCE EFFECTIVE SIZES FOR NONRANDOM MATING POPULATIONS

Following an inbreeding approach and assuming discrete generations and autosomal inheritance involving genes that do not affect viability or reproductive ability, I have derived expressions for the inbreeding effective size, N_eI, for a finite diploid population with variable census sizes for three cases: monoecious populations with partial selfing; dioecious populations of equal numbers of males and females with partial sib mating; and unequal numbers of males and females with random mating. For the first two cases, recurrence equations for the inbreeding coefficient are also obtained, which allow inbreeding coefficients to be predicted exactly in both early and late generations. Following the variance of change in gene frequency approach, a general expression for variance effective size, N_eV, is obtained for a population with unequal numbers of male and female individuals, arbitrary family size distribution, and nonrandom mating. All the parameters involved are allowed to change over generations. For some special cases, the equation reduces to the simple expressions approximately as derived by previous authors. Comparisons are made between equations derived by the present study and those obtained by previous authors. Some of the published equations for N_eI and N_eV are shown to be incomplete or incorrect. Stochastic simulations are run to check the results where disagreements with others are involved.     

THE INFLUENCE OF THE MATING SYSTEM ON SEED SIZE VARIATION IN CRINUM ERUBESCENS (AMARYLLIDACEAE)

We present evidence that extreme seed size variation in fruits of Crinum erubescens (range: 0.1 to 66.5 g per seed) occurs when mating pairs are inbred, either from selfing or biparental inbreeding. Several relatively uniform seeds of intermediate size are produced when pollen from several pollen donors is applied simultaneously to a flower. Selfed fruits and some fruits pollinated with a single pollen donor produce both large and small seeds, although selfed fruits produce fewer seeds than outcrossed fruit. These results are contrary to the hypothesis that variation in seed size is attributable to either pollen competition or differential allocation of maternal resource to seeds of different genotypes.     

ASSORTATIVE MATING AND THE ADAPTIVE LANDSCAPE

The ability of a population to shift from one adaptive peak to another was examined for a two-locus model with different degrees of assortative mating, selection, and linkage. As expected, if the proportion of the population that mates assortatively increases, so does its ability to shift to a new peak. Assortative mating affects this process by allowing the mean fitness of a population to increase monotonically as it passes through intermediate gene frequencies on the way to a new, higher, homozygotic peak. Similarly, if the height of the new peak increases or selection against intermediates becomes less severe, the population becomes more likely to shift to a new peak. Close linkage also helps the shift to a new adaptive peak and acts similarly to assortative mating, but it is not necessary for such a shift as was previously thought. When a population shifts to a new peak, the number of generations required is significantly less than that needed to return to the original peak when that happens. The short period of time required may be an explanation for rapid changes in the geological record. Under extremely high degrees of assortative mating, the shift takes longer, presumably because of the difficulty of breaking up less favored allelic combinations.     

THE INFLUENCE OF DISPERSAL PATTERNS AND MATING SYSTEM ON GENETIC DIFFERENTIATION WITHIN AND BETWEEN POPULATIONS OF THE RED HOWLER MONKEY (ALOUATTA SENICULUS)

The relationship between social structure and partitioning of genetic variance was examined in two red howler monkey populations (W and G) in Venezuela, one of which (G) was undergoing rapid growth through colonization by new troops. Rates and patterns of gene flow had been determined through radiotelemetry and direct observation data on solitary migrants, and 10 years of troop censusing. Standard electrophoresis techniques were used to examine 29 loci in blood samples taken from 137 of the study animals. Analysis of genetic variance demonstrated: (1) a significantly high level of genetic variation among troops within populations (F_ST = 0.225 for W and 0.142 for G), and (2) a significant excess of heterozygosity within troops relative to expected (F_IS = -0.136 for W and -0.064 for G), despite relatively high levels of observed and inferred inbreeding in W. Differences between the populations in F_ST values conformed to those predicted based on differences in colonization rate. Comparison of partitioning of genetic variance among different genealogical subsets of troops demonstrated that the pattern of genetic differentiation observed among troops within populations was promoted by an essentially single-male harem breeding structure, a very low rate of random exchange of breeding males among troops, and a high degree of relatedness among troop females. Between-troop genetic differentiation (F_ST) was thereby increased relative to that expected from other types of social organization, while the correlation between uniting gametes within troops (F_IS) was decreased. Genetic differentiation between populations (2%) corresponded to that predicted from migration rates. Such a mosaic of genetic variation, combined with differences in reproductive success observed among troops and a high troop failure rate, create conditions in which interdemic selection could result in more rapid spread of advantageous gene combinations than would be expected in a panmictic population, particularly in a colonizing situation in which the founder population is small.     

THE EFFECTS OF POPULATION SIZE AND PLANT DENSITY ON OUTCROSSING RATES IN LOCALLY ENDANGERED SALVIA PRATENSIS

Multilocus outcrossing rates were estimated in natural and experimental populations of Salvia pratensis, an entomophilous, gynodioecious, protandrous perennial. Male steriles were used to check the estimation procedure of outcrossing rates in hermaphrodites. Estimates of outcrossing rates in hermaphroditic plants ranged from 38.2% to 81.8% in natural populations and from 71.5% to 95.5% in experimental populations. No correlations were found between outcrossing rates and population size. However, outcrossing in hermaphrodites was promoted by high plant densities and low frequencies of male steriles. It is argued that effective management to preserve genetic variation in populations of S. pratensis should provide for the maintenance of high plant densities.     

SEXUAL DIMORPHISM,MATING SYSTEM AND BODY SIZE IN NEW WORLD BLACKBIRDS (ICTERINAE)

Although sexual selection is widely accepted as a primary functional cause of sexual size dimorphism in birds and mammals, results from some comparative studies have cast doubt on this conclusion. Chief among these contradictory results is the widespread association between body size and size dimorphism—large species tend to be more dimorphic than small species. This correlation is not directly predicted by the normal sexual selection scenario, and many hypotheses have been advanced to explain it. This paper reviews these hypotheses and evaluates them using data for the New World blackbirds (Icterinae). In this avian subfamily, (1) body size correlates with the intensity of sexual selection (as measured by mean harem size), and (2) size does not correlate with dimorphism if the effects of mating system are removed. Similar results are obtained when controlling for the confounding influence of phylogeny. Further, body size and mating system are associated with nesting dispersion. These results strongly argue that sexual dimorphism is a product of sexual selection in this subfamily, and suggest that either: (1) large body size itself, or the ecology of large species, promotes the development of coloniality and a polygynous mating system; or (2) polygyny and/or coloniality lead to the evolution of large size in both males and females. None of the other hypotheses examined predict an association between size and mating system, and all predict that size will correlate with dimorphism after the effects of mating system are removed. Thus, none of the other hypotheses seem applicable in this case. These results are compared to those obtained for other avian and mammalian taxa. Difficulties of analysis present in previous studies are discussed. I argue that it is inappropriate to assume that associations between a trait and body size or phylogeny are evidence of nonadaptive evolutionary “constraints.”     

ESTIMATED POPULATION SIZE OF THE CALIFORNIA GRAY WHALE

Abstract: The 1987-1988 counts of gray whales passing Monterey are reanalyzed to provide a revised population size estimate. The double count data are modeled using iterative logistic regression to allow for the effects of various covariates on probability of detection, and a correction factor is introduced for night rate of travel. The revised absolute population size estimate is 20,869 animals, with CV = 4.37% and 95% confidence interval (19,200, 22,700). In addition the series of relative population size estimates from 1967-1968 to 1987-1988 is scaled to pass through this estimate and modeled to provide variance estimates from interannual variation in population size estimates. This method yields an alternative population size estimate for 1987-1988 of 21,296 animals, with CV = 6.05% and 95% confidence interval (18,900, 24,000). The average annual rate of increase between 1967-1968 and 1987-1988 was estimated to be 3.29% with standard error 0.44%.     

温度对桃蚜、萝卜蚜体重及种群参数的影响

桃蚜Myrus perslcae、萝卜蚜Lipaphis crystml在能正常产仔的整个恒温范围内,成蚜和新产仔蚜体重随温度的变化都符合二次抛物线,但体重最高值出现较低的温度下．即体重变化主要表现为随温度升高而下降的趋势．在组建蚜虫的生命生殖力表时,以新产仔蚜体重对其在各温度下的生殖事进行校正。并未对计算所得的内禀增长能力rm值及其随温度的变化情况产生明显的影响,不仅没有提供新的信息。相反。这一方法使计算所得rm的值含义模糊。故建议不予采用。     

MATING PATTERN AND FITNESS-COMPONENT ANALYSIS ASSOCIATED WITH INVERSION POLYMORPHISM IN A NATURAL POPULATION OF DROSOPHILA BUZZATII

Direct studies of mating success or mating pattern associated with Mendelian factors rarely have been carried out in nature. From the samples taken for the standard analyses of selection components, it is not usually possible to obtain the mating table, and only directional selection for male mating success can be detected. Both processes, mating pattern and differential mating probability, together with other fitness components, have been investigated for the inversion polymorphism of a natural population of the cactophilic species Drosophila buzzatii. Two independent samples of adult flies were collected: nonmating or single individuals (base population) and mating pairs (mating population). All individuals were karyotyped for the second and fourth chromosomes. A sequence of models with increasing simplicity was fitted to the data to test null hypotheses of no selection and random union of gametes and karyotypes. The main results were (1) no deviations from random mating were found; (2) differential mating probability was nonsignificant in both sexes; (3) inversion and karyotypic frequencies did not differ between sexes; and (4) karyotypic frequencies did not depart from Hardy-Weinberg expectations. These results are discussed in light of complementary evidence showing the need for interpreting with caution no-effect hypotheses such as the ones tested here. The use of complementary selective tests in these studies is suggested.     

不同配种方式对大熊猫产仔效果的影响

１９８７－１９９３年,我国人工圈养的大熊猫先后有３１只雌性受配１０８只次,产仔胎,获幼仔４５只。有１６只雄性参加配种,其中７只能进行自然交配,９只没有自然交配能力。从３只雄性采出的良好精液,能使雌怀孕产仔,怀孕率为１９．１２％。在雄性自然交恿前后再给雌兽化人工授精,能提高雌兽怀孕产仔效果,来自不同山系大熊猫的繁殖能力有不同程序的差异,尤以岷山山系大熊猫的繁殖效果较差。     

MOLECULAR DEMOGRAPHIC HISTORY OF THE ANNUAL SUNFLOWERS HELIANTHUS ANNUUS AND H. PETIOLARIS—LARGE EFFECTIVE POPULATION SIZES AND RATES OF LONG-TERM GENE FLOW

Hybridization between distinct species may lead to introgression of genes across species boundaries, and this pattern can potentially persist for extended periods as long as selection at some loci or genomic regions prevents thorough mixing of gene pools. However, very few reliable estimates of long-term levels of effective migration are available between hybridizing species throughout their history. Accurate estimates of divergence dates and levels of gene flow require data from multiple unlinked loci as well as an analytical framework that can distinguish between lineage sorting and gene flow and incorporate the effects of demographic changes within each species. Here we use sequence data from 18 anonymous nuclear loci in two broadly sympatric sunflower species, Helianthus annuus and H. petiolaris , analyzed within an "isolation with migration" framework to make genome-wide estimates of the ages of these two species, long-term rates of gene flow between them, and effective population sizes and historical patterns of population growth. Our results indicate that H. annuus and H. petiolaris are approximately one million years old and have exchanged genes at a surprisingly high rate (long-term N_efm estimates of approximately 0.5 in each direction), with somewhat higher rates of introgression from H. annuus into H. petiolaris than vice versa. In addition, each species has undergone dramatic population expansion since divergence, and both species have among the highest levels of genetic diversity reported for flowering plants. Our results provide the most comprehensive estimate to date of long-term patterns of gene flow and historical demography in a nonmodel plant system, and they indicate that species integrity can be maintained even in the face of extensive gene flow over a prolonged period.     

POPULATION SIZE AND BREEDING SEASON OF THE ANTARCTIC FUR SEAL ARCTOCEPHALUS GAZELLA AT HEARD ISLAND—1987/88

Breeding colonies of the antarctic fur seal Arctocephalus gazella on Heard Island (53°10'S, 73°30'E) are situated on the sheltered northern and eastern coasts on flat vegetated terrain near streams and pools. Pupping in the 1987/88 summer began on 21 November, with 90% of births in 26 d. The median birth date was 11 December. Pup counts at Heard Island made in seven breeding seasons from 1962/63 to 1987/88 show an exponential rate of increase of 21%, which may be inflated due to undercounting in early years. The total of 248 births in 1987/88 represents an exponential increase of 37% since the previous year, but pups may have been undercounted then. Based on the number of pups born, the breeding population is estimated at 870–1,120. During the breeding season, the largest number of animals ashore was 835. Many non-breeding fur seals began hauling out from early January and 15,000 animals were estimated to be ashore by late February, a fat larger number than expected from the size of the breeding population. Both the breeding and non-breeding components of the population may be augmented by immigration. The source of immigrants may be undiscovered breeding colonies of this species in the northwestern sector of the Kerguelen Archipelago or the concentration at South Georgia. Further censuses are required at Heard Island to monitor the population growth.     

人为因素导致的盐度变化对Kinneret湖水细菌种群的影响

由于Ｋｉｎｎｅｒｅｔ湖周围的诸多盐泉被人为地导入其下游的约旦河,使得Ｋｉｎｎｅｒｅｔ湖水的盐度逐渐下降,这对作为主要工家业用水和饮用水资源的Ｋｉｎｎｅｒｅｔ湖来说是非常有价值的。然而,对湖水中的细菌来说则可能产生不同的影响。作者通过实验研究发有水盐度的变化导致细菌种群的改变,从而使我们观察到盐度与细菌之间的关系。这些结果表明,盐度变化对湖水水质保护对策和将来一段时间内湖水管理政策的制定都具有重要的     

川西平原大足鼠的种群生态学Ⅰ.种群动态和个体大小

我们利用标志重捕、夹捕解剖和笼养等三种方法于１９８９年１月至１９９５年６月对川西平原的大足鼠的种群密度、个体大小、生长和生物量进行了研究。种群密度最高１１．３只／ｈａ,最低０．７只／ｈａ,平均３．６只／ｈａ,并显示出与农作物相同的季节变动特征。雌雄性比由幼年组和亚成体组约１：１到成体组１：０．７８到老年组１：０．５３。雌雄个体的平均质量分别为１３６ｇ和１１４ｇ,两性的个体质量和后足长有明显差异,体长和耳长差异不明显。饲养的幼体及亚成体个体质量和尾长均持续增长,并可分别用Ｌｏｇｉｓｔｉｃ和对数方程较好地拟合。生物量则显示出比种群密度和个体质量更稳定的特征。