Population structure in the Connecticut Valley: II. A comparison of multidimensional scaling solutions of migration matrices and isonymy

In a previous paper (Swedlund et al., 1984) we have described the population structure of the historical Connecticut River Valley of Massachusetts in terms of matrimonial migration matrices. Using procedures described by Morton (1973), Harpending and Jenkins (1974), Jorde (1980), and others the exchanges between subdivisions which make up the matrices are made column stochastic and analyzed to predict genetic kinship. Subsequently the kinship estimates within and between subdivisions can be interpreted as genetic covariance and compared to the actual geographic distances between the respective subdivisions using a principal components analysis. In the present paper we extend these results by applying nonmetric multidimensional scaling to the migration matrices, and to isonymy matrices based on the same communities. We demonstrate that the multidimensional scaling configurations of marital migration represent the actual geographic relationships between the communities quite effectively for this particular case study from historical Massachusetts. Moreover, we argue that while these migration data may provide good estimates of social and genetic exchange between the subdivisions, surname analysis may also be informative of processes not revealed in the migration matrices alone.     

Density-dependent migration and human population structure in historical Massachusetts

Studies of population structure often focus on the effects of population size and migration rates on genetic variation. Few studies, however, have investigated the relationship between these two factors. The purpose of this paper is to determine the extent to which migration (and gene flow) is density-dependent (that is, affected by population size) for populations in historical Massachusetts. Data from 4,859 marriage records were analyzed from four populations in north-central Massachusetts during the time period 1741 to 1849. These data were placed into 29 samples defined in terms of population and time cohort. Within each cohort the overall exogamy rate was computed along with three estimates of gene flow based on marital migration: local migration (k), long-distance migration (m), and effective migration rate (me). Three samples show unusually low rates that reflect the history of settlement. Regression analyses were used with the remaining samples, and they show nonlinear density-dependent migration that is unrelated to temporal trends. Migration is highest in samples with small population sizes (less than 800) and large population sizes (greater than 1,600). Migration is lowest in medium-sized populations. Two processes are suggested to explain this curvilinear relationship of migration and population size. In small populations, the lack of suitable potential mates and/or availability of settled land leads to an increase in migration into the population. As population size increases, this migration decreases. After populations reach a certain size, migration increases again, most likely reflecting the economic pull of larger populations. These patterns could act to enhance, or counter, genetic drift, depending on the direction of density dependence.     

Population structure and genetic heterogeneity in the Upper Markham Valley of New Guinea.

An analysis is presented of the standardized Wahlund's variances (f) in gene frequencies of the ABO, Rh and MNS blood group systems among 19 villages of the Atsera isolate of the upper Markham Valley, Papua New Guinea. In the past, there has been some disagreement over the relative importance of population structure and natural selection in the determination of these variances. The Lewontin-Krakauer test is presented as a means of resolving this disagreement. According to this test, selectively neutral variation in gene frequencies should generate essentially homogeneous values of f for all loci, a homogeneity which can be tested by comparing the value of (formula: see text) to a theoretical (formula: see text) expected when variations in (formula: see text) are due solely to sampling error. The observed value of (formula: see text) for the Atsera isolate is 2.9 x 10(-5), which is not significantly different from the expected values that range from 1.23 x 10(-5) to 2.46 x 10(-5) depending on the constant used in calculating (formula: see text). Therefore it appears that nonselective aspects of population structure such as genetic drift and intervillage migration are responsible for the recorded genetic variation in this isolate.     

Corridors for migration between large subdivided populations, and the structured coalescent

We study the ancestral genetic process for samples from two large, subdivided populations that are connected by migration to, from, and within a small set of subpopulations, or demes. We consider convergence to an ancestral limit process as the numbers of demes in the two large, subdivided populations tend to infinity. We show that the ancestral limit process for a sample includes a recent instantaneous adjustment to the sample size and structure followed by a more ancient process that is identical to the usual structured coalescent, but with different scaled parameters. This justifies the application of a modified structured coalescent to some hierarchically structured populations.     

Marital mobility in populations of the High Aran Valley

The analysis of 2.623 marriage certificates in the towns in the High Aran Valley shows marriage mobility between the years 1650 and 1990 and indicates the level of population's endogamy. The results from the data collected in the town of Arties are presented as an example. The distribution of the places of origin of spouses and a factor analysis show a remarkable geographical endogamy until 1940. The results from marriage mobility are confirmed by data from blood polymorphism studies, matrimonial dispensations and surnames.     

Seed migration and the structure of plant populations

Summary We use chemical typing to compare sub-populations of thyme (Thymus vulgaris L.) growing in the channels of several ravines where seed migration is expected from sub-populations on the plateu to associated basin subpopulations. The results indicate that seed migration does occur. However, there is little effective gene flow between sub-populations. We discuss the implications of restricted gene flow for population dynamics and structure.     

Population genetics of the people of Iran II. Genetic differentiation and population structure

The genetic structure of six populations of Iran (Turks, Kurds, Lurs, Zabolis, Baluchis and Zoroastrians) was examined using data on blood groups, serum proteins and cell enzymes. Our results show conclusively that there are genetic differences among the six populations and the analysis of superimposed R and S matrices defined Harpending & Jenkins (1973) show by that the dispersion of some of the alleles correspond to the dispersion of the populations. The F_ST estimates are not large enough to favour selection on any of the loci studied. The F_IT and F_IS estimates are positive and moderately high suggesting that the genetic differentiation to some extent is influenced by inbreeding.     

黑嘴鸥种群的遗传分化与迁徙模式

用分子生物学方法研究了黑嘴鸥(Larus saundersi)种群的遗传结构和分化.对我国黑嘴鸥现存的3个地方种群50个样本的线粒体DNA控制区部分片段进行了序列测定,结合已公布的的两个韩国样本的序列,比对后所获得的550 bp的序列中,共发现49个变异位点,定义了37种线粒体单元型,其中仅1种为我国3个地方种群间共享单元型,多数为各地方种群内特有.我国3个地方种群内的单元型多样性和核苷酸多态性都很高;4个地方种群合并成一个大种群时, 其线粒体单元型多样性与核苷酸多样性仍很高,分别为0.974%±0.012%和0.510%±0.042%.进一步分析表明,4个地方种群间核苷酸歧异度在0.433%-0.585%之间,种群分化程度FST在-0.03176-0.48063之间,基因流Nm在1.03-33.79之间,平均遗传距离为0.0051±0.0011.UPGMA系统发生树及最大简约网络图表明, 黑嘴鸥的演化关系呈现星状辐射,单元型之间呈现一种混杂的分布格局,地方种群没有形成明显的系统地理结构.同时运用彩色旗标技术,初步掌握了4个地方种群迁徙规律.对比分子研究结果,验证了不同地方种群间的遗传分化与其迁徙模式基本一致,同时认为黑嘴鸥不同地方繁殖种群从越冬地返回繁殖地的过程中会发生交叉.最后,鉴于黑嘴鸥不同地方种群间的遗传分化不显著,其迁徙行为具有差异性,建议在保护和遗传管理中应分别对待.     

Kin-structured migration and the rate of advance of an advantageous gene

Hemoglobin E, an allele generally considered to confer malarial resistance in heterozygotes, is found in high frequencies across a wide area of Southeast Asia. Apparently it originated as a single-point mutation which was spread by gene flow. The rate of diffusion of this adaptive allele is studied using four computer simulation models. It is shown that in small populations deterministic equations for gene flow may overestimate rates of diffusion. Other aspects of population structure, however, such as kin-structuring of migrant groups, increase the rate of advance. Finally, population growth coupled with the spread of the allele leads to much more rapid diffusion. These results suggest that population structure can be an important factor affecting the diffusion of advantageous genes.     

Social policy,economics, and demographic change in Nanticoke-Moor ethnohistory

The Nanticoke-Moors of Delaware are an ethnic group of Native American, Afro-American, and Euro-American descent. Their physiognomic and ethnic marginality has subjected them to a limited range of social and economic options under the influence of American racial policies. This article concerns their ethnic formation in the colonial period and the demographic effects (changes in fertility, mortality, and structure) of their 19th- and 20th-century social history. The demographic sample consists of 406 headstones from three community cemeteries. Each cemetery represents a socially and economically distinct unit, including a group that identifies with its traditional Indian heritage, an Afro-American acculturated group, and a migrant community of marginal ethnic affiliation. Variation and change in life expectancy is shown. Relationships between the political and economic processes affecting Nanticoke-Moor social affiliation, and those affecting color caste-class formation among mainstream Afro-Americans, are discussed.     

The distribution of the coalescence time and the number of pairwise nucleotide differences in the "isolation with migration" model

This paper is concerned with the “isolation with migration” model, where a panmictic ancestral population gave rise to a symmetric n-island model, time τ ago. Explicit analytical expressions are derived for the probability density function of the coalescence time of a pair of genes sampled at random from the same subpopulation or from different subpopulations, and for the probability distribution of the number of pairwise nucleotide differences.     

Cross-cultural analysis of migration rates: effects of geographic distance and population size.

A model is developed that treats migration rates among populations as a function of the geographic distance between them and the size of both sources and recipient population. Specifically, mij/mjj = a(Ni/Nj)pe-bd, where mij/mjj is the relative migration rate into population j from population i, Ni is the size of the source population, Nj is the size of the recipient population, d is the geographic distance between populations i and j, p is a measure of differential density-dependence, b is a measure of distance decay, and a is an adjustment parameter with little demographic meaning. Methods of parameter estimation and hypothesis testing using maximum likelihood are outlined. These methods are applied to migration matrix data from 13 samples obtained from the literature representing a wide range of ecological settings. All samples show a significant effect of geographic distance on migration, and all but one show a significant effect of differential population size. All but one sample show an overall tendency for migration to be negative density-dependent; that is, the relative migration rate is greater from larger populations to smaller populations than the reverse.     

Demographic Analysis of a Disjunct Population of Froelichia floridana in the mid-Ohio River Valley

Froelichia floridana (cottonweed) occurs as a disjunct population along the Ohio River in southeastern Ohio. The anomalous occurrence of F. floridana in this area has led to its designation as a state endangered species and a management regime to maintain the habitat conditions in which it occurs. As part of this effort, a restoration site was established on public lands in 1984 from seed collected in areas threatened by development. This study seeks to determine the demographic characteristics of this species in the restored and non‐restored managed sites to provide basic ecological information regarding life history parameters and to judge the effectiveness of the restoration. For two years (1997–1998) we collected information on seed bank abundance, field seed germination, plant survivorship, and seed production to create a stage‐based transition matrix model. The model suggests that population growth and abundance as assayed by λ (rate of increase) are stable to declining and are similar between the restoration and natural sites. A reduction in competition had a positive effect on population growth. Elasticity analysis showed that plants germinating earlier in the spring and becoming established as an early cohort contributed a greater level of reproductive output than plants germinating in late spring. Lowered population growth for 1997 is attributed to a cooler and dryer than average early spring that delayed germination and subsequent seed production. Elasticity analysis also suggested that the presence of a persistent seed bank was crucial for long‐term population maintenance and may allow for recovery in areas of low aboveground abundance through soil manipulation.     

Phenotypic consequences of nonrandom migration in the Jirels of Nepal

The phenotypic structure of human populations is shaped by a number of factors such as population size and marital migration. This paper examines the impact of migration on the between-village phenotypic differentiation of the Jirels, a tribal group of eastern Nepal. Data on stature and five cranial measurements for 526 individuals (males and females) are utilized to illustrate the patterns of phenotypic variation. A permutation method is used to generate the phenotypic consequences of random migration constrained to observed levels of movement. The results suggest that Jirel migration is nonrandom and that it produces higher levels of phenotypic differentiation than would result from a random migration process.     

A continuous migration model with stable demography

A probability model of a population undergoing migration, mutation, and mating in a geographic continuum R is constructed, and an integrodifferential equation is derived for the probability of genetic identity. The equation is solved in one case, and asymptotic analysis done in others. Individuals at x, y R in the model mate with probability V(x, y) dt in any time interval (t, t + dt). In two dimensions, if V(x,y) = V(x–y) where V(x) V(x/)/ ² approaches a delta function, the equilibrium probability of identity vanishes as 0. The asymptotic rate at which this occurs is discussed for mutation rates u u _o > 0 and for Cu , > 0, and u 0.Partially supported by NSF grant MCS79-03472Research was partially supported by Task Agreement No. DE-AT06-76EV71005 under Contract No. DE-AM06-76RL02225 between the U.S. Dept. Energy and the University of Washington     

Population structure and survival in a solitary wasp (Microbembex cubana: Hymenoptera,Sphecidae, Nyssoninae)

Summary This paper documents population structure in a solitary wasp, Microbembex cubana (Hymenoptera, Sphecidae, Nyssoninae), on a small (15 km²) Bahamian island. A relatively isolated portion of this population was studied April–June 1985. The population comprised small aggregations of territorial males and nesting females. Individuals of both sexes were with rare exceptions faithful to a home aggregation during their one- to two-month adult lifespans, conducting all reproductive activities there. Individuals from different aggregations, however, mixed daily during these activities: feeding on nectar, hunting for provisions and retiring to clustered sleeping burrows. Significant variation occurred among the nine breeding aggregations in size, density, sex-ratio (which was on average 2:1 in favor of males) and survival (which was 0.93–0.99 per individual/per day and which was not higher for females than for males). Aggregations retained the same characteristics for longer than the life expectancies of individuals in them.Factors affecting reproductive success and survivorship in M. cubana are complex: they are apparently only partially overlapping between males and females and subject to spatial variation. Patterns in the data suggest several hypotheses about how behavior, morphology and habitat interact to shape population processes. I propose that aggregations arise and are characterized by considerable behavioral inertia because individual M. cubana use conspecifics as sources of information on resource quality. Because M. cubana occurs in secondary habitats, individuals retain flexibility in responding to better opportunities for reproduction, but this population exhibits more viscosity than reported for other ground-nesting solitary Hymenoptera.     

The coalescent in two colonies with symmetric migration

Kingman's coalescent process is extended to two colonies with symmetric migration. The mean waiting time until a sample of genes taken from two colonies coalesces to a common ancestor is obtained. The final step in the waiting time before the process is absorbed at 1 is observed to have an intriguing behaviour. The distribution of this final waiting time converges to the known distribution of the corresponding waiting time in the case of a single population as the migration rate tends to zero. The mean, however, does not converge. The waiting time until a sample has two common ancestors is modeled as a function of the migration rate. Finally bounds for the expected waiting time for the two colonies to have j > 1 ancestors are derived.     

Marital and migration structure and inbreeding in the Adyg population]

Endogamy and gametic indices for both Russian and Adyg populations living in the Adyg autonomous region of Krasnodar district were determined on different levels of territorial units: village, rural, community (a group of villagers) and rural region. Inbreeding coefficient was estimated for Adyg population and its structure analysed: a random component contributes mostly to the inbreeding coefficient (Fst = 0.00991), non-random component of the inbreeding coefficient being Fis = 0.010009, which testifies to negative marital assortativity among Adygs. Local inbreeding "a" and decline in the inbreeding "phi" coefficient at a distance from 0 to 500 km were calculated using the Malecot's formula: the coefficient "a" was found to be 0.00397, which is in good accordance with the Fst.