Inbreeding avoidance in an isolated indigenous Zapotec community in the valley of Oaxaca, southern Mexico

We analyzed inbreeding using surname isonymy in an indigenous genetic isolate. The subjects were residents of a rural Zapotec-speaking community in the valley of Oaxaca, southern Mexico. The community can be classified as a genetic isolate with an average gene flow of < or = 3% per generation. Surnames were collected for individuals in each household in pedigree form using the culturally traditional patronym-matronym naming. Estimation of inbreeding from surname isonymy is facilitated by the traditional patronym-matronym name assignment among indigenous Mexican populations. A total of 2,149 individuals had valid surname patronym-matronym pairings, including 484 deceased ancestors. Surname isonymy analysis methods were used to estimate total inbreeding and to segregate it into random and nonrandom components. The surname isonymy coefficient computed from 119 isonymous surname pairings (119/2,149) was 0.0554. The estimated inbreeding coefficient from surname isonymy was 0.0138 (0.0554/4). The random and nonrandom components of inbreeding were F(r) = 0.0221 and F(n) = -0.0091, respectively. The results suggest that consanguinity is culturally avoided. Nonrandom inbreeding decreased total inbreeding by about 41%. Total estimated inbreeding by surname isonymy was 0.0138, which is similar to inbreeding estimated from a sample of pedigrees, 0.01. Socially prescribed inbreeding avoidance substantially lowered total F through negative nonrandom inbreeding. Even in the situation of genetic isolation and small effective population size (N(e)), estimated inbreeding is lower than may have otherwise occurred if inbreeding were only random. However, among the poorest individuals, socially prescribed jural rules for inbreeding avoidance failed to operate. Thus the preponderance of inbreeding appears to occur among the poor, economically disadvantaged in the community.     

Heterozygosity and craniofacial dimensions of Zapotec school children from a subsistence community in the valley of Oaxaca, southern Mexico

Gene flow is associated with differences in craniofacial and postcranial dimensions among indigenous populations of southern Mexico. This study compares four craniofacial dimensions in 322 children from families which have an average inbreeding coefficient of 0.01 and 36 children from families which have an inbreeding coefficient of zero (more heterozygous) in a Zapotec speaking community. In addition, two indices were computed. With sex and chronological age constant, there is a statistically significant difference between more and less heterozygous children in bizygomatic diameter. Differences in biparietal diameter and fronto-occipital length reflect the same tendency. The differences probably reflect more an effect of heterozygosity on these dimensions than facial dissimilarity of the populations from which the new genetic materials were drawn because gene flow was from related groups of Indians (e.g., Mixtec) in southern Mexico. Hence, midface growth and overall normal size appear to be affected by fluctuation in level of heterozygosity.     

Epidemiologic transition in an isolated indigenous community in the Valley of Oaxaca, Mexico

The objective of the present study is to analyze age-specific mortality in a rural indigenous community in the throes of a secular increase in size in the Valley of Oaxaca, southern Mexico, over 30 years, 1970-1999. Variation in mortality by age group was analyzed over time for evidence of an epidemiological transition. The seasonal rain pattern in the Valley of Oaxaca (83% from May through September) was evaluated for its relationship with mortality in wet and dry months. Mortality and causes of death changed markedly over the 30-year interval. Infant and preschool mortality, overall mortality, and causes of death changed from the 1970s through the 1990s. Prereproductive deaths (<15 years) predominated in the 1970s and were largely due to gastrointestinal and respiratory diseases, with periodic outbreaks of measles. Deaths of adults 65+ years predominated in the 1990s and were largely due to degenerative diseases usually associated with aging. The marked changes in age and causes of death over the three decades (epidemiologic transition from Stage I to Stage II) occurred concurrently with significant secular increases in body size in children, adolescents, and young adults, highlighting improved health and nutritional conditions in the community which is in early Stage II of the demographic transition. The demographic transition to Stage II is a leading indicator (15-25 years lag) for the onset of the secular trend, while the epidemiologic transition to Stage II is a predictor that the secular increase is in process in the study community.     

Genetic drift and natural selection in an isolated Zapotec-speaking community in the Valley of Oaxaca, southern Mexico

Genetic drift and natural selection were analyzed in a genetically isolated Zapotec-speaking community in the Valley of Oaxaca, southern Mexico. Moderately intense genetic drift and selection potentials were found. Potential for drift was related to (1) the small effective size of the population, and (2) the exceptionally low number of migrants into the population. Potential for selection was due to (1) an unusually high variance in fertility, and (2) a high contribution of prereproductive mortality. Significant potential for genetic evolution was found due to genetic drift and natural selection.     

Genetic and environmental effects on growth of children from a subsistence agricultural community in southern Mexico

Sibling correlations for size attained in height, weight, sitting height, estimated leg length, the triceps skinfold, arm circumference, and estimated midarm muscle circumference were compared in 6- through 13-year-old schoolchildren grouped by household socioeconomic status. The children were residents of a Zapotec-speaking, subsistence agricultural community in the Valley of Oaxaca in southern Mexico. Sibling pairs were classified as being from high and low socioeconomic status (SES) households, and sibling correlations were computed within each SES group controlling for environmental effects derived from a factor analysis of information on household demography and land and livestock holdings. Like-sex siblings from lower SES households have significantly different correlations in four instances. Correlations are higher for leg length in lower SES brothers and higher for sitting height and weight in lower SES sisters, while the correlation for sitting height is higher in upper SES brothers. The sibling correlation results are not entirely consistent with observations on growth status by SES, particularly if the power and similarity of a common environment is the only cause of higher sibling correlations. Reduced body size under poorer socioeconomic and presumably nutritional circumstances is apparent, but it is not possible in this analysis to distinguish whether genotypic (developmental) plasticity or genetic adaptation, or both, are involved.     

Socioeconomic variation in estimated growth velocity of schoolchildren from a rural, subsistence agricultural community in southern Mexico

Socioeconomic variation in estimated growth velocities (annual growth increments) of several anthropometric dimensions was considered in schoolchildren from a rural, subsistence agricultural community in the Valley of Oaxaca in southern Mexico. The children (114 males, 99 females), 6-13 years of age, were measured twice, approximately one year apart. Annual growth increments were computed by subtracting measurements taken in the fall of 1978 from those taken in the fall of 1979. Information on household land holdings and appliances and parental occupation was used to compute an index of socioeconomic status (SES). Analysis of annual increments among upper SES (65 males, 45 females) and lower (49 males, 54 females) children indicated negligible differences. The results suggest that growth deficits evident in the children at school age occurred in infancy and early childhood so that there was little, if any, SES variation in growth rate at the school ages.     

Growth of rural and urban children in the valley of Oaxaca,Mexico

Weight, stature, arm circumference, and the triceps skinfold were measured in 1,410 school children, 6 through 14 years of age, from two urban colonias in the city of Oaxaca de Juarez (n = 479), and from two rural Ladino (n = 467) and two rural Zapotec (n = 464) communities in the Valley of Oaxaca in southern Mexico. Children from rural Ladino communities and urban colonias are significantly taller, heavier, and more muscular than children in rural Zapotec communities. The differences between rural Ladino and urban colonia children favor the former, particularly for weight and stature. These observations thus suggest (1) that children in the rural, indigenous communities in the Valley of Oaxaca are relatively undernourished compared to children in Ladinoized and urban communities, and (2) that rural-to-urban migration does not necessarily result in improved growth status.     

Enzyme heterozygosity and growth of rainbow trout reared at two rations

The relationship between heterozygosity at nine enzyme loci and both size and growth in rainbow trout ( Salmo gairdneri ) reared at either low (LRT) or high (HRT) ration for 84 days is reported. The experimental fish were progeny produced from a pooled mating of 25 female and 25 male rainbow trout captured in spawning condition at the Ganaraska River, Ontario. There is a significant negative regression between the number of heterozygous loci per fish and size (fork length and weight) among fish at the beginning of the experiment. Heterozygotes at two loci, Sod and Mdh3,4 , were significantly smaller than homozygotes. A significant negative regression between multilocus heterozygosity and size was detectable among the fish reared at HRT for 84 days but not at LRT. Ration appeared to affect the strength of the association between heterozygosity and growth because at HRT homozygotes at the majority of loci grew faster than heterozygotes, but the reverse was true at LRT.     

Health and agricultural intensification in the prehistoric Valley of Oaxaca, Mexico

The effects of agricultural intensification on health are examined in prehistoric populations of the Valley of Oaxaca, Mexico. Agriculture was practiced in the Valley of Oaxaca by the beginning of the Early Formative period (ca. 1400 B.C.), and had intensified by the Late Formative (ca. 500 B.C.). Skeletal remains from 14 archaeological sites in the Valley are pooled by temporal affiliation into a nonintensive agriculture group (1400-500 B.C.) and an intensive agriculture group (500 B.C.-1400 A.D.). The health effects of agricultural intensification are assessed by comparing the frequency of periosteal reactions, cribra orbitalia, and enamel hypoplasia between the intensive and nonintensive agricultural groups. Overall, no significant differences (alpha = 0.05) are found between the nonintensive and intensive groups. Power analyses of the chi-square tests indicate that the tests have a high probability of rejecting a false null hypothesis. The intensification of agriculture does not appear to have had a deleterious effect on the health of the prehistoric population of the Valley. The differences between this study and previous studies of health and agricultural development may be explained by differences between the processes of intensification and development or by differences between primary and secondary centers of agricultural development.     

Socioeconomic variation in the growth status of children in a subsistence agricultural community

Socioeconomic variation in the growth status of 293 children, 6 through 13 years of age, from a rural subsistence agricultural community in southern Mexico was considered. Socioeconomic status was based on an index developed from landholdings, household goods, and occupation, and households were classified as high and low status. Growth measurements included weight, stature, sitting height, estimated leg length, arm and estimated arm muscle circumferences, triceps skinfold, and right gripping strength. The growth status of boys showed a clear socioeconomic differential, while that of girls did not. The results are consistent with the generalization that males are more influenced by environmental stresses than females, including, of course, the favorable stress of improved socioeconomic circumstances, even within seemingly single-class rural communities.     

Analysis of the relationship between allozyme heterozygosity and fitness in the rare Gentiana pneumonanthe L.

Especially for rare species occurring in small populations, which are prone to loss of genetic variation and inbreeding, detailed knowledge of the relationship between heterozygosity and fitness is generally lacking. After reporting on allozyme variation and fitness in relation to population size in the rare plant Gentiana pneumonanthe, we present a more detailed analysis of the association between heterozygosity and individual fitness. The aim of this study was to test whether increased fitness of more heterozygous individuals is explained best by the ‘inbreeding’ hypothesis or by the ‘overdominance’ hypothesis. Individual fitness was measured during 8 months of growth in the greenhouse as the performance for six life-history parameters. PCA reduced these parameters to four main Fitness Components. Individual heterozygosity was scored for seven polymorphic allozyme loci. For some of these loci (e.g. Aat3, Pgm1 and 6Pgdh2) heterozygotes showed a significantly higher relative fitness than homozygotes. To test the inbreeding model, regression analyses were performed between each Fitness Component and the number of heterozygous loci per individual. Multiple regressions with the adaptive distance of five loci as independent variables were used to test the overdominance model. Only the inbreeding model was a statistically significant explanation for the relationship between heterozygosity and fitness in G. pneumonanthe. The number of heterozygous loci was significantly negatively correlated with the coefficients of variation of three of the six initially measured fitness parameters. This suggests a lower developmental stability among more homozygous plants and may explain the higher phenotypic variation in small populations of the species observed earlier. The importance of the results for conservation biology is discussed.     

The effects of heterozygosity at the af,st and tl loci in peas

Summary Eight near-isogenic lines of pea representing all the homozygous combinations of three genes af, st and tl, which modify leaf shape and size, were crossed in all possible ways excepting reciprocals. An analysis of the resulting 36 families has shown that homozygous mutant alleles at the tl locus acting with homozygous mutant alleles at the af and st loci increase both seed weight and plant haulm weight. The mutant alleles at the af and st loci seem, when homozygous, to have little effect by themselves upon seed weight but they do increase or decrease haulm weight, respectively. There is clear evidence of heterotic effects resulting from heterozygosity at each one of the three loci which modify seed weight, haulm weight and basal branching. The implications of such heterotic effects in pea breeding programmes are discussed.     

The genetic signature of rapid range expansions: How dispersal,growth and invasion speed impact heterozygosity and allele surfing

As researchers collect spatiotemporal population and genetic data in tandem, models that connect demography and dispersal to genetics are increasingly relevant. The dominant spatiotemporal model of invasion genetics is the stepping-stone model which represents a gradual range expansion in which individuals jump to uncolonized locations one step at a time. However, many range expansions occur quickly as individuals disperse far from currently colonized regions. For these types of expansion, stepping-stone models are inappropriate. To more accurately reflect wider dispersal in many organisms, we created kernel-based models of invasion genetics based on integrodifference equations. Classic theory relating to integrodifference equations suggests that the speed of range expansions is a function of population growth and dispersal. In our simulations, populations that expanded at the same speed but with spread rates driven by dispersal retained more heterozygosity along axes of expansion than range expansions with rates of spread that were driven primarily by population growth. To investigate surfing we introduced mutant alleles in wave fronts of simulated range expansions. In our models based on random mating, surfing alleles remained at relatively low frequencies and surfed less often compared to previous results based on stepping-stone simulations with asexual reproduction.     

Autotrophic growth of nitrifying community in an agricultural soil

The two-step nitrification process is an integral part of the global nitrogen cycle, and it is accomplished by distinctly different nitrifiers. By combining DNA-based stable isotope probing (SIP) and high-throughput pyrosequencing, we present the molecular evidence for autotrophic growth of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB) in agricultural soil upon ammonium fertilization. Time-course incubation of SIP microcosms indicated that the amoA genes of AOB was increasingly labeled by ¹³CO₂ after incubation for 3, 7 and 28 days during active nitrification, whereas labeling of the AOA amoA gene was detected to a much lesser extent only after a 28-day incubation. Phylogenetic analysis of the ¹³C-labeled amoA and 16S rRNA genes revealed that the Nitrosospira cluster 3-like sequences dominate the active AOB community and that active AOA is affiliated with the moderately thermophilic Nitrososphaera gargensis from a hot spring. The higher relative frequency of Nitrospira-like NOB in the ¹³C-labeled DNA suggests that it may be more actively involved in nitrite oxidation than Nitrobacter-like NOB. Furthermore, the acetylene inhibition technique showed that ¹³CO₂ assimilation by AOB, AOA and NOB occurs only when ammonia oxidation is not blocked, which provides strong hints for the chemolithoautotrophy of nitrifying community in complex soil environments. These results show that the microbial community of AOB and NOB dominates the nitrification process in the agricultural soil tested.     

Genetic structure and heterozygosity in the kuru region,Eastern Highlands of New Guinea

Genetic structure of 20 of the 37 linguistic groups in the Eastern Highlands of New Guinea including the kuru region is analyzed using information on blood groups and serum protein polymorphisms. The average individual is heterozygous at 28.6% of loci and the average number of alleles per locus is 1.234. Coefficients of kinship for linguistic groups range from 0.005 for the sweet potato cultivating North Fore to 0.075 for the isolated Pawaians whose dietary staple is sago and who depend more on hunting and gathering. As one selects linguistic groups with smaller and smaller population size and increasing isolation, one finds that kinship coefficients rise as much as tenfold, but there is no concomitant loss of heterozygosity or trend toward fixation of alleles. Genetic relationships established by genetic distance trees and by principal components analysis are comparable and are consistent with other anthropological observations.     

Growth of rural and urban children in the Valley of Oaxaca,Mexico

Weight, stature, arm circumference, and the triceps skinfold were measured in 1,410 school children, 6 through 14 years of age, from two urban colonias in the city of Oaxaca de Juarez (n = 479), and from two rural Ladino (n = 467) and two rural Zapotec (n = 464) communities in the Valley of Oaxaca in southern Mexico. Children from rural Ladino communities and urban colonias are significantly taller, heavier, and more muscular than children in rural Zapotec communities. The differences between rural Ladino and urban colonia children favor the former, particularly for weight and stature. These observations thus suggest (1) that children in the rural, indigenous communities in the Valley of Oaxaca are relatively undernourished compared to children in Ladinoized and urban communities, and (2) that rural-to-urban migration does not necessarily result in improved growth status.     

Helpful grandmothers in rural Ethiopia: A study of the effect of kin on child survival and growth

Kin selection and parental investment theories state that, in highly social species, such as humans, individuals can increase their inclusive fitness by extending support to their relatives. Here, we document patterns of kin support in a rural Ethiopian community, where postmarital residence practices provide differential access to relatives. Using demographic, anthropometric, and behavioral data collected from four villages we are able to (a) identify the effects of the presence of kin on child mortality and growth patterns and (b) provide detailed information on the role of relatives within the household.

Mortality analyses indicate that grandmothers had a positive effect on child survival. Anthropometric data reveal that maternal grandmothers had a particularly beneficial effect on child height, but paternal grandmothers less so. Time allocation data suggest that grandmothers continued to visit their daughters' households, irrespective of postmarital residence, where they relieved their daughters of heavy domestic tasks rather than helping with direct grandchild care. Matrilocal postmarital residence was associated with improved child survival, although children in matrilocal households were actually smaller. This may be due to wealth effects, increased competition between siblings, or higher survival of smaller infants in matrilocal households.     

Mazahua ethnobotany and subsistence in the monarch butterfly biosphere reserve, Mexico

This is the first report on Mazahua knowledge and classification of plants and mushrooms and the roles of these resources in the local economy in the Monarch Butterfly Biosphere Reserve, Mexico. A total of 213 useful plant species and 31 species of edible mushrooms were recorded. Fruits ofPrunus serotina, Rubus liebmanii, andCrataegus mexicana were the main wild fruit gathered by people (7.47, 4.40, and 1.82 tons of fruits per year, respectively), whereas their availability in the territory of the village was approximately 302.6, 6.0, and 34.188 tons.Brassica campestris, Rorippa nasturtium-aquaticum, Chenopodium berlandieri, and Amaranthus hybridus were the principal non-cultivated greens consumed by people (4.3, 0.5, 0.7, and 0.9 tons per year, while 23.6, 3.78, traces, and 46.0 tons, respectively, were available). Extraction of medicinal plants is low but gathering ofTernstroemia spp. flowers endangers local populations of these plants. All households of the village used fuelwood (1,767.2 tons per year), mainly of pine and oak species. Strategies for sustainable use of these resources are discussed