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PubMed1986

Hierarchical selection theory and sex ratios. I. General solutions for structured populations.

Models of sex-ratio evolution in structured populations are derived with G.R. Price's covariance form for the hierarchical analysis of natural selection (1970, Nature 227, 520-521). Previous work on competition among related males for mates (local mate competition), competition among related females for a limiting resource (local resource competition), inbreeding, group selection, and asymmetry of genetic inheritance between males and females, are subsumed under a general formulation for sex-ratio biases in structured populations. I found that the evolutionarily stable strategy sex ratio (males:females) for diploids is 1 - rho m:1 - rho f, where rho m is the regression coefficient of relatedness of the controlling genotypes on males competing for mates, rho f is the regression of controlling genotypes on females that compete for a fixed, limiting resource, and there is no inbreeding. For inbreeding and no competition among females, the evolutionarily stable strategy is 1 - rho m:1 + rho mf, where rho mf is the regression of controlling genotypes on females' mates.

Animals↗
PubMed2000

Genetic structure through surnames in Campobasso Province, Italy.

The population of Campobasso Province shows a level of inbreeding that is distinct from most Italian rural populations, regardless of their geographic location (Fr=0.0040; Fn=0.0102; Ft=0.0142). The genetic structure of the Italian-Greek communities of Lecce and Reggio Calabria Provinces does not appear to be affected by ethnicity. The level of inbreeding in Italian-Greeks of Reggio Calabria Province is similar to other Italians of Campobasso Province (Fr=0.0041; Fn=0.0127; Ft=0.0168). The Italian-Greeks of Lecce Province show random mating, and their inbreeding is in fact very low (Fr=0.0038; Fn=0.0024; Ft=0.0062).

Consanguinity↗
PubMed1997

Marital structure of the Italian community of Boston, Massachusetts, 1880-1920.

The marital structure of Italians living in Boston, Massachusetts, in the period 1880-1920 was studied in order to explore the integration process in the urban context. The study analyses endogamy and inbreeding, using data on 15,579 marriages from the parish books of the three Italian parishes of Boston. Endogamic rates are very high and increased in time, ranging from 93.9% to 97.3%. This correlated with the growth of the Italian community and the decline of the biased sex ratio. One parish, Our Lady of Pompeii in the South End, displays lower endogamic rates because of the reduced and scattered population attending it. The rate of consanguineous (2.33%) and isonymous (6.38%) marriages, and the coefficients of inbreeding, alpha (0.98 x 10(-3)) and Ft (0.0159), are similar to those of north Italian populations, and lower than those for south and insular Italy. The parish of Our Lady of Pompeii shows consistently higher values than the other two parishes. Marriages between first and second cousins are the main cause of the above values in each parish. Consanguineous marriages and inbreeding increased over time, from the 1890s, and this is in general agreement, although slightly delayed, with the Italian trend.

Acculturation↗
PubMed1998

Sib mating designs for mapping quantitative trait loci.

The power to separate the variance of a quantitative trait locus (QTL) from the polygenic variance is determined by the variability of genes identical by descent (IBD) at the QTL. This variability may increase with inbreeding. Selfing, the most extreme form of inbreeding, increases the variability of the IBD value shared by siblings, and thus has a higher efficiency for QTL mapping than random mating. In self-incompatible organisms, sib mating is the closest form of inbreeding. Similar to selfing, sib mating may also increase the power of QTL detection relative to random mating. In this study, we develop an IBD-based method under sib mating designs for QTL mapping. The efficiency of sib mating is then compared with random mating. Monte Carlo simulations show that sib mating designs notably increase the power for QTL detection. When power is intermediate, the power to detect a QTL using full-sib mating is, on average, 7% higher than under random mating. In addition, the IBD-based method proposed in this paper can be used to combine data from multiple families. As a result, the estimated QTL parameters can be applied to a wide statistical inference space relating to the entire reference population.

Animals↗
PubMed1998

One step beyond lethal equivalents: characterization of deleterious loci in the rapid cycling Brassica rapa L. base population.

The total number of lethal equivalents as defined by Morton, Crow and Muller (1956) is a function of three parameters: M, the number of loci at which deleterious mutations can occur, q, the frequency of the deleterious alleles at each locus, and s, their selective value. A new approach based on multi-generation inbreeding data is outlined and used to infer these three parameters as well as the dominance coefficient, h, in a self-incompatible species, Brassica rapa L. Germination and flowering data from thirty bud-selfed lines of fast-cycling B.rapa were assessed over three generations. Germination and flowering were significantly postponed by inbreeding but germination and flowering success were not so strongly decreased. Estimates of the average s values were obtained but it was not possible to get separate estimates of M and q. For both characters, the average dominance coefficient was particularly low. The number of lethal equivalents at the zygotic level was around two for germination and three for flowering, which, owing to the self-incompatibility of B.rapa, is an unexpectedly low value. These results may be explained by past biparental inbreeding which in turn may have increased self-compatibility thus allowing the purging of more deleterious alleles than under strict self-incompatibility.

Journal Article↗
PubMed2002

Extensions of models for the estimation of mating systems using n independent loci.

Inferences about plant mating systems increasingly use highly informative genetic markers, and investigate finer facets of the mating system. Here, four extensions of models for the estimation mating systems are described. (1) Multiallelic probabilities for the mixed selfing-random mating model are given; these are especially suitable for microsatellites; a generalized Kronecker operator is basis of this formula. (2) Multilocus probabilities for the "correlated-matings model" are given; interestingly, comparisons between single- vs multilocus estimates of correlated-paternity can provide a new measure of population substructure. (3) A measure of biparental inbreeding, the "correlation of selfing among loci", is shown to approximate the fraction of selfing due to uniparental (as opposed to biparental) inbreeding; also joint estimation of 1- 2- and 3-locus selfing rates allow separation, under a simple model, of the frequency vs the magnitude of biparental inbreeding. (4) Method-of-moments estimators for individual outcrossing rates are given. Formulae are given for both gymnosperms and angiosperms, and the computer program "MLTR" implements these methods.

Alleles↗
PubMed2005

Mating system, sex ratio, and persistence of females in the gynodioecious shrub Daphne laureola L. (Thymelaeaceae).

Although in gynodioecious populations male steriles require a fecundity advantage to compensate for their gametic disadvantage, southern Spanish populations of the long-lived shrub Daphne laureola do not show any fecundity advantage over hermaphrodites in terms of seed production and early seedling establishment. By using allozyme markers, we assess the mating system of this species in five populations differing in sex ratio, and infer levels of inbreeding depression over the whole life cycle by comparing the inbreeding coefficients at the seed and adult plant stages. Extremely low outcrossing rates (0.001<t<0.125) were consistently found for hermaphrodites in all populations, whereas, as expected, female progeny were entirely outcrossed. In most populations, offspring were much more inbred than their parents, and heterozygosity of adults was greater than expected from outcrossing rate estimates, with very few selfed progeny appearing to reproduce in the field. The combination of extensive selfing in hermaphrodites and a strong inbreeding depression expressed late in the life cycle (and thus, only estimable by indirect measures based on genetic markers) may explain the persistence and high frequency of D. laureola females in southern Spanish populations.

Biological Evolution↗
PubMed2006

Single-locus sex determination in the parasitoid wasp Cotesia glomerata (Hymenoptera: Braconidae).

The parasitoid Cotesia glomerata usually produces female-biased sex ratios in the field, which are presumably caused by inbreeding and local mate competition (LMC); yet, sibling mating increases the production of males, leading to the male-biased sex ratio of broods in the laboratory. Previous studies have suggested that the sex allocation strategy of C. glomerata is based on both partial LMC in males and inbreeding avoidance in females. The current study investigated the presence of single-locus complementary sex determination (sl-CSD) as a sex-determining mechanism in this species through inbreeding experiment, cytological examination and microsatellite analysis. Cytological examination detected diploid males in nine of 17 single pairs of sibling mating, thus in agreement with the proportion of matched matings predicted by the sl-CSD model. Sex ratio shifts in these matched sibling matings were consistent with the sl-CSD model with less viable diploid males. The haploid males have a single set of maternal chromosomes (n = 10), whereas diploid males possess a double set of chromosomes (2n = 20). Microsatellite analyses confirmed that diploid males produced from the matched matings inherited segregating genetic materials from both parents. Thus, this study provides the first solid evidence for the presence of sl-CSD as a sex-determining mechanism in the braconid genus Cotesia.

Animals↗
PubMed1999

History can be more important than 'pollination syndrome' in determining the genetic structure of plant populations: the case of aconitum lycoctonum (Ranunculaceae)

The Aconitum lycoctonum complex is a widespread yellow-flowered group of species found in central and southern Europe. Because of extreme morphological variability, the systematics of this group is confusing, and hybridizations among taxa are often hypothesized. To determine whether hybridization, realized mating system within populations or colonization from different Pleistocene refugia might explain some of the morphological variation, the genetic structure of 19 populations from central and southern Europe was studied using starch gel electrophoresis and 10 enzyme loci, of which eight were polymorphic. A pattern typical of an outcrossing species was expected because A. lycoctonum flowers are adapted to pollination by long-tongued bumblebees. However, heterozygosity was very low (between 0.031 and 0.150), which is atypical of either widespread or outcrossing species. The inbreeding coefficient, FIS, also suggested inbreeding in more than half the populations. Analysis of molecular variance showed that 31% of the genetic variation is found among populations, again suggesting inbreeding. A neighbour-joining tree based on Reynolds's genetic distance showed a clear separation between the central/eastern European populations and the samples from the Iberian peninsula and Alpes Maritimes. These data are consistent with the hypothesized refugia and the phylogeographical histories of several European forest trees. The genetic identity of all populations was very high, suggesting that all investigated populations belong to the same species despite high morphological variability. Hybridization was not supported by the data.

Journal Article↗
PubMed2001

Islands on the plains: metapopulation dynamics and female biased dispersal in hyraxes (Hyracoidea) in the Serengeti National Park.

Two species of hyrax, Heterohyrax brucei and Procavia johnstoni, inhabit rock outcrops, or kopjes, in the Serengeti National Park, Tanzania. Such distinct 'island' habitats provide an excellent model to investigate natural metapopulation dynamics with distinct small populations with extinction and colonization events, as well as migration between populations. Allele frequencies, genetic variability and genetic distances between populations were calculated based on DNA microsatellite markers. The genetic diversity in both species of hyrax, especially P. johnstoni, was surprisingly low: allelic diversity ranged from 2 to 7 alleles per locus. This may have been induced by colonization by a small number of individuals from single source populations. F-statistics, assignment tests and calculations of pairwise relatedness all indicated female-biased dispersal in H. brucei but not P. johnstoni. Values of FIS in P. johnstoni showed an excess of homozygotes indicative of high rates of inbreeding; evidence for inbreeding could not be detected in H. brucei. Although female dispersal patterns in H. brucei seem to prevent inbreeding and consequently reduce risk of local extinction, this seems not to be the case in P. johnstoni.

Animals↗
PubMed1998

Dispersal, philopatry, and genetic relatedness in a social carnivore: comparing males and females.

A balance must be maintained between the proportion of individuals dispersing and the proportion remaining philopatric such that inbreeding and resource competition are minimized. Yet the relative importance of dispersal and philopatric behaviour is uncertain, especially for species with complex social systems. We examine the influence of dispersal on genetic relationships of a white-nosed coati (Nasua narica: Procyonidae) population from Panama. Field studies of the coati indicate a social system in which all females are highly philopatric and live in bands while all adult males become solitary at maturity, but do not disperse from the home range of their natal band. Based on analyses of multilocus DNA fingerprints, we confirm that female philopatry is the rule, long-distance dispersal is rare, and that relatedness between most bands is low. However, some new bands result from fission events and these bands retain relatively high relatedness to one another for several years. Adult males inhabiting the home range of a band are closely related to band members. In contrast, males and band members whose ranges do not overlap are unrelated or only slightly related. Adult males are also more closely related to other males whose home ranges they overlap extensively than to males whose home ranges they overlap only slightly. These results indicate that males initially disperse from their natal bands to reduce resource competition and not to avoid inbreeding. Inbreeding avoidance, if it occurs, results from more extensive range movements by males during the mating season.

Animals↗
PubMed2001

Population structure in the endangered Mauna Loa silversword, Argyroxiphium kauense (Asteraceae), and its bearing on reintroduction.

Reintroduction of populations of endangered species is a challenging task, involving a number of environmental, demographic and genetic factors. Genetic parameters of interest include historical patterns of genetic structure and gene flow. Care must be taken during reintroduction to balance the contrasting risks of inbreeding and outbreeding depression. The Mauna Loa silversword, Argyroxiphium kauense, has experienced a severe decline in population size and distribution in the recent past. Currently, three populations with a total of fewer than 1000 individuals remain. We measured genetic variation within and among the remnant populations using seven microsatellite loci. We found significant genetic variation remaining within all populations, probably related to the recent nature of the population impact, the longevity of the plants, and their apparent self-incompatibility. We also found significant genetic differentiation among the populations, reinforcing previous observations of ecological and morphological differentiation. With respect to reintroduction, the results suggest that, in the absence of additional data to the contrary, inbreeding depression may not be a substantial risk as long as propagules for the founding of new populations are adequately sampled from within each source population before additional inbreeding takes place. The results further suggest that if mixing of propagules from different source populations is not required to increase within-population genetic variation in the reintroduced populations, it may best be avoided.

Asteraceae↗
PubMed2002

A Bayesian approach to inferring population structure from dominant markers.

Molecular markers derived from polymerase chain reaction (PCR) amplification of genomic DNA are an important part of the toolkit of evolutionary geneticists. Random amplified polymorphic DNA markers (RAPDs), amplified fragment length polymorphisms (AFLPs) and intersimple sequence repeat (ISSR) polymorphisms allow analysis of species for which previous DNA sequence information is lacking, but dominance makes it impossible to apply standard techniques to calculate F-statistics. We describe a Bayesian method that allows direct estimates of FST from dominant markers. In contrast to existing alternatives, we do not assume previous knowledge of the degree of within-population inbreeding. In particular, we do not assume that genotypes within populations are in Hardy-Weinberg proportions. Our estimate of FST incorporates uncertainty about the magnitude of within-population inbreeding. Simulations show that samples from even a relatively small number of loci and populations produce reliable estimates of FST. Moreover, some information about the degree of within-population inbreeding (FIS) is available from data sets with a large number of loci and populations. We illustrate the method with a reanalysis of RAPD data from 14 populations of a North American orchid, Platanthera leucophaea.

Bayes Theorem↗
PubMed2003

Gene dispersal and outbreeding in a philopatric mammal.

Extensive mark-recapture data from banner-tailed kangaroo rats, Dipodomys spectabilis, have shown that both males and females are highly philopatric and suggest the possibility of close inbreeding. However, indirect analyses based on genetic structure appear to contradict direct observations, suggesting longer dispersal distances. Using microsatellite genotypes from most members of a banner-tailed kangaroo rat population during five successive breeding seasons, we ask how relatedness is influenced by dispersal and how it in turn influences mating patterns. The data confirm that, because of philopatry, neighbours are often close relatives. However, patterns of parentage also show that the average distance between mates is large relative to natal dispersal distances and larger than the average distance between nearest opposite-sexed neighbours. Females' mates were often not their nearest male neighbour and many were less related than the nearest male neighbour. We detected multiple paternity in some females' litters; both sexes produce offspring with multiple mates within and between breeding seasons. At the population level, heterozygosities were high and estimates of F were low, indicating that levels of inbreeding were low. Using individual inbreeding coefficients of all juveniles to estimate their parents' relatedness, we found that parental relatedness was significantly lower than relatedness between nearest opposite-sexed adult neighbours. Thus in philopatric populations, long breeding forays can cause genes to move further than individuals disperse, and polyandry may serve to reduce relatedness between mates.

Animals↗
PubMed2003

Conservation genetics of the wood ant, Formica lugubris, in a fragmented landscape.

Various intrinsic factors connected to the special features of sociality influence the persistence of social insect populations, including low effective population size, reduced amount of genetic variation easily leading to inbreeding depression, and spatially structured populations. In this work, we studied an isolated, small and fragmented population system of the red wood ant Formica lugubris, and evaluated the impact of social and genetic population structure on the persistence and conservation of the populations. The effective population size was large in our study population because all nests were polygynous. As a result, and despite the apparent isolation, the amount of nuclear genetic variability was similar to that in a nonisolated population system. Lack of inbreeding, as well as a high level of variability, indirectly suggests that this population does not suffer from inbreeding depression. The spatial distribution of genetic variation between local populations suggests intensive, but strongly male-biased, nuclear gene flow. Thus, the persistence of this population system does not seem to be threatened by any immediate social or genetic factor, but colonization of new habitat patches may be difficult because of restricted female dispersal.

Animals↗
PubMed2006

Fine-scale spatial genetic structure of the distylous Primula veris in fragmented habitats.

In Flanders (northern Belgium), the distylous self-incompatible perennial herb Primula veris is common, but mainly occurs in fragmented habitats. Distyly, which favours disassortative mating, is characterized in P. veris by two genetically determined floral morph types (pin or thrum). Using 18 polymorphic loci, we investigated fine-scale spatial genetic structure (SGS) and spatial distribution of the morphs within four populations from two regions that differ in degree of habitat fragmentation. We studied the contributions made by sexual reproduction and clonal propagation and compared the SGS patterns between pin and thrum morph types. Clonal growth was very restricted to a few individuals and to short distances. One population showed a non-random spatial distribution of the morphs. Pin and thrum individuals differed in SGS patterns at a small scale, suggesting intrapin biparental inbreeding, also related to high plant densities. This may be explained by partial self-compatibility of the pin morph combined with restricted seed dispersal and pollinator behaviour. There is an indication of more pronounced SGS when populations occur in highly fragmented habitats. From our findings, we may hypothesize disruption of the gene flow processes if these large populations evolve into patchworks of small remnants, but also a possible risk for long-term population survival if higher intrapin biparental inbreeding leads to inbreeding depression. Our study emphasizes the need for investigating the interactions between the heterostylous breeding system, population demographic and genetic structure for understanding population dynamics in fragmented habitats and for developing sustainable conservation strategies.

Breeding↗
PubMedDate not supplied

Evolution of consanguinity in the Bishopric of Lugo (Spain) from 1900 to 1979.

BACKGROUND: The levels of consanguinity in human populations are known to be influenced by demographic and geographical factors, and by socio-cultural customs that govern spouse choice. Within the general model applicable to the populations of Western Europe, Galicia (north-west Spain) is a region that is especially interesting, due to its geographical and historical peculiarities that could have conditioned its behaviour pattern with respect to consanguinity. PRIMARY OBJECTIVE: The object of this paper is to analyse the evolution of the consanguinity structure levels in the rural population of the Bishopric of Lugo (Galicia) during the period 1900-1979. SUBJECTS AND METHODS: The study covers a total of 752 parishes included in 52 municipalities of the rural area of the Bishopric of Lugo. Of a total of 117,583 marriages in the period studied, 6701 were between biologically related individuals up to the level of second cousins. The percentage of the different types of consanguineous marriages, the consanguinity rates, and the average coefficient of inbreeding of the population was calculated. Also, for the analysis of the temporal variation of consanguinity, version 3.01 of Jandel Scientific's Table Curve program was used. MAIN OUTCOMES AND RESULTS: The consanguinity rate for the whole of the period is 5.70% and the average coefficient of inbreeding is 2.2477 x 10(-3), values which fall within the observed range for Spanish populations. As for the consanguinity structure, the most frequent types of consanguineous marriages are between second cousins (2.65% of all marriages), but the high proportion of marriages between uncles/nieces or aunts/nephews (0.16%) and first cousins (2.12%) with regard to the total number of marriages should be emphasized. The average value of the M22/M33 ratio is 0.80, and throughout the study period it was above the 0.25 expected in conditions of panmixia. Regarding the evolution of the average coefficient of inbreeding, its annual values fit a polynomial regression curve with one ascending and one descending branch and an inflection point in the year 1919. CONCLUSIONS: As in other rural areas of Galicia, the structure of consanguinity in the Bishopric of Lugo is characterized by the high proportion of marriages between uncles/nieces or aunts/nephews and first cousins, a phenomenon which appears to be generalized in the rural populations of northern Spain. It is suggested that the high proportion of uncle/niece marriages that have been found in the population studied are very probably due to the important migratory phenomenon which took place in this region at the end of the 19th century and in the first third of the 20th century.

Consanguinity↗
PubMedDate not supplied

Polymorphism and genetic evolution in an isolate in the Antilles: Saint-Barthélémy.

St Barthélémy, a small island near Guadaloupe, has been isolated since the eighteenth century. The population is made up of two geographical isolates, genetically separated. In each, the inbreeding level is increasing on account of random genetic drift, which is reinforced by village endogamy, equivalent to a kind of spouse selection. Consanguinity between spouses has been analysed to give an estimate of the contributions of random genetic drift and spouse choice to total inbreeding. A second estimate to inbreeding can be obtained from the variation in observed gene frequencies. The two estimates obtained are of the same order, 0.6-1.0%, and are comparable with those still observed in isolated villages of the French Pyrenees.

Alleles↗