Effects Of Genetic Drift Research Articles

Baker's law and the island syndromes in bryophytes

SummaryThe evolution of island syndromes has long served as a model to understand the mechanisms accounting for phenotypic differentiation. Combining literature data with actual observations, we determine whether typical syndromes such as the loss of dispersal power and the bias towards self‐compatibility (Baker's law) apply to vagile organisms, using bryophytes as a model.The life‐history traits (LHTs) observed in oceanic island floras were statistically different from those observed on continents, evidencing the evolution of island syndromes. In contrast,LHTs of continental and continental island floras were similar, pointing to differences in migration intensity between continents, continental islands and oceanic islands.The proportion of bisexual species was significantly higher on oceanic islands than on continents. A significant proportion of species that are unisexual or bisexual on continents shifted towards exclusive bisexuality on oceanic islands, suggesting thatBaker's law applies to bryophytes. The underlying mechanisms, however, probably differ fromin situselection for selfing.The proportion of species producing specialized asexual diaspores, which are assumed to play a role in short‐distance dispersal (SDD), was higher on oceanic islands than on continents. The proportion of species producing spores, which are involved in long‐distance dispersal (LDD), exhibited the reverse trend, suggesting a shift in the prevalent reproductive strategy to favourSDDon oceanic islands. Approximately 50% of the species, however, maintained the ability to produce sporophytes on oceanic islands, and the relative frequency of fertile shoots within collections of four model species was even higher on islands than on continents.Synthesis. Bryophytes exhibit typical island syndromes, indicating that migration rates between oceanic islands and continents are not sufficient to prevent the effects of genetic drift and contradicting the view that the sea does not impede migration in the group. Significant shifts in life‐history traits (LHTs) towards increased production of specialized asexual diaspores and decreased sporophyte production on oceanic islands indeed point to a global loss of long‐distance dispersal (LDD) ability. The maintenance of traits characteristic forLDDin a large number of species has, however, substantial consequences for our understanding of island plant evolution, and in particular, for our vision of islands as evolutionary dead ends.

Elucidation of the genetic differences in Trialeurodes vaporariorum populations under vegetable greenhouse conditions by using the allozyme approach

AbstractGenetic differentiation of Trialeurodes vaporariorum (Westwood 1856) populations was examined using biochemical and allozyme analysis. For biochemical analysis, general esterase and glutathion‐S‐transferase were tested. Allozyme genetic variability in 11 populations of T. vaporariorum was investigated using five loci from four enzyme systems. Although there are large variations between populations, T. vaporariorum is grouped into two populations with geographic barriers, based on Nei's genetic distance in the Baekdudaegan Mountains. Within these two groups, low migration and linkage disequilibrium reveal that populations tend to be influenced by gene drift rather than uniform selection pressures. The effect of genetic drift is greater than the effect of uniform selection by insecticides or host plant resistance, which is suggested by the FST estimates in this study. Based on this basic research, more effective whitefly control programs could be built in the future.

Playing with heart and soul…and genomes: sports implications and applications of personal genomics

Whether the integration of genetic/omic technologies in sports contexts will facilitate player success, promote player safety, or spur genetic discrimination depends largely upon the game rules established by those currently designing genomic sports medicine programs. The integration has already begun, but there is not yet a playbook for best practices. Thus far discussions have focused largely on whether the integration would occur and how to prevent the integration from occurring, rather than how it could occur in such a way that maximizes benefits, minimizes risks, and avoids the exacerbation of racial disparities. Previous empirical research has identified members of the personal genomics industry offering sports-related DNA tests, and previous legal research has explored the impact of collective bargaining in professional sports as it relates to the employment protections of the Genetic Information Nondiscrimination Act (GINA). Building upon that research and upon participant observations with specific sports-related DNA tests purchased from four direct-to-consumer companies in 2011 and broader personal genomics (PGx) services, this anthropological, legal, and ethical (ALE) discussion highlights fundamental issues that must be addressed by those developing personal genomic sports medicine programs, either independently or through collaborations with commercial providers. For example, the vulnerability of student-athletes creates a number of issues that require careful, deliberate consideration. More broadly, however, this ALE discussion highlights potential sports-related implications (that ultimately might mitigate or, conversely, exacerbate racial disparities among athletes) of whole exome/genome sequencing conducted by biomedical researchers and clinicians for non-sports purposes. For example, the possibility that exome/genome sequencing of individuals who are considered to be non-patients, asymptomatic, normal, etc. will reveal the presence of variants of unknown significance in any one of the genes associated with hypertrophic cardiomyopathy (HCM), long QT syndrome (LQTS), Marfan’s syndrome, and other conditions is not inconsequential, and how this information is reported, interpreted, and used may ultimately prevent the individual from participation in competitive sports. Due to the distribution of genetic diversity that reflects our evolutionary and demographic history (including the discernible effects of restricted gene flow and genetic drift associated with cultural constructs of race) and in recognition of previous policies for “leveling” the playing field in competitive sports based on “natural” athletic abilities, preliminary recommendations are provided to discourage genetic segregation of sports and to develop best practice guidelines for genomic sports medicine programs that will facilitate player success, promote player safety, and avoid genetic discrimination within and beyond the program.

Reevaluating a model of gender-biased gene flow among Sub-Saharan Hunter-gatherers and farmers.

In a previous study, we proposed a model for genetic admixture between African hunter-gatherers and food producers, in which we integrated demographic and genetic aspects together with ethnographic knowledge (Destro-Bisol et al. 2004b). In that study it was possible to test the model only using genetic information from widely dispersed and genetically heterogeneous populations. Here we reevaluate the congruence between the model and patterns of genetic variation using an anthropologically and geographically more homogeneous data set that includes Pygmies and farmers from Cameroon, Congo, and the Central African Republic. As implied by the model, the ratios of mtDNA to Y chromosome Nm estimates (effective population size, N, times the migration rate, m; 0.154 in Pygmies and 6.759 in farmers), support an asymmetric gene flow, with a higher Bantu-to-Pygmy gene flow for paternal than for maternal lineages, and vice versa for farmers. Analyses of intra- and interpopulation genetic variation further support the above observation, showing a prevailing effect of genetic drift on maternal lineages and gene flow on paternal lineages among Pygmies, and an opposite pattern among farmers. We also detected differences between patterns for classical and molecular measures of Y chromosome intrapopulation variation, which likely represent signatures of the introgression of Bantu lineages into the gene pool of Pygmy populations. On the whole, our results seem to reflect differences in the demographic history and the degree of patrilocality and polygyny between the two population groups, thus providing further support to our microevolutionary model in an anthropologically coherent framework.

Reevaluating a Model of Gender-Biased Gene Flow among Sub-Saharan Hunter-Gatherers and Farmers

In a previous study, we proposed a model for genetic admixture between African hunter-gatherers and food producers, in which we integrated demographic and genetic aspects together with ethnographic knowledge (). In that study it was possible to test the model only using genetic information from widely dispersed and genetically heterogeneous populations. Here we reevaluate the congruence between the model and patterns of genetic variation using an anthropologically and geographically more homogeneous data set that includes Pygmies and farmers from Cameroon, Congo, and the Central African Republic. As implied by the model, the ratios of mtDNA to Y chromosome Nm estimates (effective population size, N, times the migration rate, m; 0.154 in Pygmies and 6.759 in farmers), support an asymmetric gene flow, with a higher Bantu-to-Pygmy gene flow for paternal than for maternal lineages, and vice versa for farmers. Analyses of intra- and interpopulation genetic variation further support the above observation, showing a prevailing effect of genetic drift on maternal lineages and gene flow on paternal lineages among Pygmies, and an opposite pattern among farmers. We also detected differences between patterns for classical and molecular measures of Y chromosome intrapopulation variation, which likely represent signatures of the introgression of Bantu lineages into the gene pool of Pygmy populations. On the whole, our results seem to reflect differences in the demographic history and the degree of patrilocality and polygyny between the two population groups, thus providing further support to our microevolutionary model in an anthropologically coherent framework.

Genetic connectivity and diversity in inselberg populations of Acacia woodmaniorum, a rare endemic of the Yilgarn Craton banded iron formations

Historically rare plant species with disjunct population distributions and small population sizes might be expected to show significant genetic structure and low levels of genetic diversity because of the effects of inbreeding and genetic drift. Across the globe, terrestrial inselbergs are habitat for rich, often rare and endemic flora and are valuable systems for investigating evolutionary processes that shape patterns of genetic structure and levels of genetic diversity at the landscape scale. We assessed genetic structure and levels of genetic diversity across the range of the historically rare inselberg endemic Acacia woodmaniorum. Phylogeographic and genetic structure indicates that connectivity is not sufficient to produce a panmictic population across the limited geographic range of the species. However, historical levels of gene flow are sufficient to maintain a high degree of adaptive connectivity across the landscape. Genetic diversity indicates gene flow is sufficient to largely counteract any negative genetic effects of inbreeding and random genetic drift in even the most disjunct or smallest populations. Phylogeographic and genetic structure, a signal of isolation by distance and a lack of evidence of recent genetic bottlenecks suggest long-term stability of contemporary population distributions and population sizes. There is some evidence that genetic connectivity among disjunct outcrops may be facilitated by the occasional long distance dispersal of Acacia polyads carried by insect pollinators moved by prevailing winds.

Distance, dams and drift: what structures populations of an endangered, benthic stream fish?

Summary Spatial population structure plays an important role in species persistence, evolution and conservation. Benthic stream fishes are diverse and frequently imperilled, yet the determinants and spatial scaling of their population structure are understudied. We investigated the range‐wide population genetic structure of Roanoke logperch (Percina rex), an endangered, benthic stream fish of the eastern United States. Fish were sampled from 35 sites and analysed at 11 microsatellite DNA loci. Clustering models were used to sort individuals into genetically cohesive groups and thereby estimate the spatial scaling of population structure. We then used Bayesian generalized linear mixed models (BGLMMs) to test alternative hypotheses about the environmental factors most responsible for generating structure, as measured by the differentiation statistic FST. Clustering models delineated seven discrete populations, whose boundaries coincided with agents of fragmentation, including hydroelectric dams and tailwaters. In the absence of hydrological barriers, gene flow was extensive throughout catchments, whereas there was no evidence for contemporary dispersal between catchments across barriers. In the best‐supported BGLMM, FST was positively related to the spatial distance and degree of hydrological alteration between sites and negatively related to genetic diversity within sites. Whereas the effect of tailwaters was equivocal, dams strongly influenced differentiation: the effect of a dam on FST was comparable to that of a between‐site distance of over 1200 km of unimpounded river. Overall, the effect of distance‐mediated dispersal was negligible compared to the combined effects of fragmentation and genetic drift. The contemporary population structure of P. rex comprises a few geographically extensive ‘islands’ that are fragmented by hydroelectric projects. This information clarifies the importance of a catchment‐scale perspective on conserving the species and suggests that its recovery may require genetic and/or demographic reconnection of presently isolated populations.

Conservation genetics and the persistence and translocation of small populations: bighorn sheep populations as examples

Understanding and evaluating the factors that influence the persistence of small populations and establishment of new populations are basic goals of conservation biology. Genetic effects due to genetic drift and inbreeding can have important impacts on the success of new populations. Many bighorn sheep populations in western North America have had low numbers and many have gone extinct. Here, the possible effects of genetic drift and inbreeding are evaluated in three populations of desert bighorn sheep initiated in the 1970s from translocations. One of these has no molecular genetic data but has substantial demographic data (Aravaipa Canyon), one has both extensive demographic data and some molecular genetic data (Red Rock), and one has limited demographic data and some molecular genetic data (Tiburon Island). Overall, either from theoretical pedigree analysis and population genetic estimates from demographic history (Aravaipa, Tiburon) or from molecular data (Red Rock, Tiburon), it appears that the levels of genetic drift and inbreeding are substantial in all of these populations. This impact was larger when higher variance in male reproductive success was assumed. In other words, it appears that genetic factors are and will be important in the establishment and persistence of these populations. These examples in long-term monitored bighorn sheep populations are relevant to many endangered species in similar situations where demographic data are available but there is little or no historical molecular genetic data.

Gene flow and demographic history of leopards (Panthera pardus) in the central Indian highlands.

Gene flow is a critical ecological process that must be maintained in order to counteract the detrimental effects of genetic drift in subdivided populations, with conservation benefits ranging from promoting the persistence of small populations to spreading adaptive traits in changing environments. We evaluated historical and contemporary gene flow and effective population sizes of leopards in a landscape in central India using noninvasive sampling. Despite the dramatic changes in land-use patterns in this landscape through recent times, we did not detect any signs that the leopard populations have been through a genetic bottleneck, and they appear to have maintained migration–drift equilibrium. We found that historical levels of gene flow (mean mh = 0.07) were significantly higher than contemporary levels (mean mc = 0.03), and populations with large effective population sizes (Satpura and Kanha Tiger Reserves) are the larger exporters of migrants at both timescales. The greatest decline in historical versus contemporary gene flow is between pairs of reserves that are currently not connected by forest corridors (i.e., Melghat-Pench mh − mc = 0.063; and Kanha-Satpura mh − mc = 0.054). We attribute this reduction in gene flow to accelerated fragmentation and habitat alteration in the landscape over the past few centuries, and suggest protection of forest corridors to maintain gene flow in this landscape.

GENETIC DRIFT AND COLLECTIVE DISPERSAL CAN RESULT IN CHAOTIC GENETIC PATCHINESS

Chaotic genetic patchiness denotes unexpected patterns of genetic differentiation that are observed at a fine scale and are not stable in time. These patterns have been described in marine species with free-living larvae, but are unexpected because they occur at a scale below the dispersal range of pelagic larvae. At the scale where most larvae are immigrants, theory predicts spatially homogeneous, temporally stable genetic variation. Empirical studies have suggested that genetic drift interacts with complex dispersal patterns to create chaotic genetic patchiness. Here we use a co-ancestry model and individual-based simulations to test this idea. We found that chaotic genetic patterns (qualified by global FST and spatio-temporal variation in FST's between pairs of samples) arise from the combined effects of (1) genetic drift created by the small local effective population sizes of the sessile phase and variance in contribution among breeding groups and (2) collective dispersal of related individuals in the larval phase. Simulations show that patchiness levels qualitatively comparable to empirical results can be produced by a combination of strong variance in reproductive success and mild collective dispersal. These results call for empirical studies of the effective number of breeders producing larval cohorts, and population genetics at the larval stage.

Population genetics of Lymnaea stagnalis experimentally exposed to cocktails of pesticides

Freshwater invertebrates may be regularly exposed to pesticides in agricultural landscapes, as water bodies such as ditches and ponds are the final recipient of many chemicals, through various transfer pathways. Local evolutionary impacts may hence be expected on populations, especially for species with a completely aquatic life cycle. We tested the hypothesis that exposure to combinations of pesticides used in crop protection programmes could increase the effect of random genetic drift in a non-target species, via demographic impacts. To do so, experimental populations of the freshwater snail Lymnaea stagnalis were created from a common genetic pool and exposed for three successive generations to treatments corresponding to two different crop protection plans (conventional and low pesticide input). Population genetic parameters were estimated in each generation on the basis of ten polymorphic microsatellite loci. Effects consistent with increased random genetic drift were observed for one sampling campaign performed in the third generation, i.e., decreased genetic variability and increased population differentiation in the group of populations exposed to the treatment programme whose demographic impact was the most effective on L. stagnalis. Otherwise, no clear pattern emerged and even opposed effects could be observed. All populations were found significantly inbred, mostly due to biparental inbreeding. Conversely, selfing was generally not significant, and did not express preferentially under high pesticide pressure. We conclude from this study that population genetics should be used very cautiously in the context of ecological risk assessment, especially when applied to natural populations.

Effects of Genetic Drift and Gene Flow on the Selective Maintenance of Genetic Variation

Explanations for the genetic variation ubiquitous in natural populations are often classified by the population-genetic processes they emphasize: natural selection or mutation and genetic drift. Here we investigate models that incorporate all three processes in a spatially structured population, using what we call a construction approach, simulating finite populations under selection that are bombarded with a steady stream of novel mutations. As expected, the amount of genetic variation compared to previous models that ignored the stochastic effects of drift was reduced, especially for smaller populations and when spatial structure was most profound. By contrast, however, for higher levels of gene flow and larger population sizes, the amount of genetic variation found after many generations was greater than that in simulations without drift. This increased amount of genetic variation is due to the introduction of slightly deleterious alleles by genetic drift and this process is more efficient when migration load is higher. The incorporation of genetic drift also selects for fitness sets that exhibit allele-frequency equilibria with larger domains of attraction: they are "more stable." Moreover, the finiteness of populations strongly influences levels of local adaptation, selection strength, and the proportion of allele-frequency vectors that can be distinguished from the neutral expectation.

Basal metabolic rate can evolve independently of morphological and behavioural traits

Quantitative genetic analyses of basal metabolic rate (BMR) can inform us about the evolvability of the trait by providing estimates of heritability, and also of genetic correlations with other traits that may constrain the ability of BMR to respond to selection. Here, we studied a captive population of zebra finches (Taeniopygia guttata) in which selection lines for male courtship rate have been established. We measure BMR in these lines to see whether selection on male sexual activity would change BMR as a potentially correlated trait. We find that the genetic correlation between courtship rate and BMR is practically zero, indicating that the two traits can evolve independently of each other. Interestingly, we find that the heritability of BMR in our population (h(2)=0.45) is markedly higher than was previously reported for a captive zebra finch population from Norway. A comparison of the two studies shows that additive genetic variance in BMR has been largely depleted in the Norwegian population, especially the genetic variance in BMR that is independent of body mass. In our population, the slope of BMR increase with body mass differs not only between the sexes but also between the six selection lines, which we tentatively attribute to genetic drift and/or founder effects being strong in small populations. Our study therefore highlights two things. First, the evolvability of BMR may be less constrained by genetic correlations and lack of independent genetic variation than previously described. Second, genetic drift in small populations can rapidly lead to different evolvabilities across populations.

Effects of harvesting of increasing intensities on genetic diversity and population structure of white spruce.

Forest harvesting of increasing intensities is expected to have intensifying impacts on the genetic diversity and population structure of postharvest naturally regenerated stands by affecting the magnitude of evolutionary processes, such as genetic drift, gene flow, mating system, and selection. We have tested this hypothesis for the first time by employing widely distributed boreal white spruce (Picea glauca) as a model and controlled, replicated experimental harvesting and regeneration experiment at the EMEND project site (http://www.emendproject.org). We used two approaches. First, genetic diversity and population structure of postharvest natural regeneration after five harvesting treatments (green tree retention of 75%, 50%, 20%, and 10%, and clearcut) were assessed and compared with those of the unharvested control (pristine preharvest old‐growth) in two replicates each of conifer‐dominated (CD) and mixed‐wood (MW) forest, using 10 (six EST (expressed sequence tag) and four genomic) microsatellite markers. Second, genetic diversity and population structure of preharvest old‐growth were compared with those of postharvest natural regeneration after five harvesting treatments in the same treatment blocks in one replicate each of CD and MW forests. Contrary to our expectations, genetic diversity, inbreeding levels, and population genetic structure were similar between unharvested control or preharvest old‐growth and postharvest natural regeneration after five harvesting treatments, with clearcut showing no negative genetic impacts. The potential effects of genetic drift and inbreeding resulting from harvesting bottlenecks were counterbalanced by predominantly outcrossing mating system and high gene flow from the residual and/or surrounding white spruce. CD and MW forests responded similarly to harvesting of increasing intensities. Simulated data for 10, 50, and 100 microsatellite markers showed the same results as obtained empirically from 10 microsatellite markers. Similar patterns of genetic diversity and population structure were observed for EST and genomic microsatellites. In conclusion, harvesting of increasing intensities did not show any significant negative impact on genetic diversity, population structure, and evolutionary potential of white spruce in CD and MW forests. Our first of its kind of study addresses the broad central forest management question how forest harvesting and regeneration practices can best maintain genetic biodiversity and ecosystem integrity.

Worldwide population distribution of the common LCE3C-LCE3B deletion associated with psoriasis and other autoimmune disorders

BackgroundThere is increasing evidence of the importance of copy number variants (CNV) in genetic diversity among individuals and populations, as well as in some common genetic diseases. We previously characterized a common 32-kb insertion/deletion variant of the PSORS4 locus at chromosome 1q21 that harbours the LCE3C and LCE3B genes. This variant allele (LCE3C_LCE3B-del) is common in patients with psoriasis and other autoimmune disorders from certain ethnic groups.ResultsUsing array-CGH (Agilent 244 K) in samples from the HapMap and Human Genome Diversity Panel (HGDP) collections, we identified 54 regions showing population differences in comparison to Africans. We provided here a comprehensive population-genetic analysis of one of these regions, which involves the 32-kb deletion of the PSORS4 locus. By a PCR-based genotyping assay we characterised the profiles of the LCE3C_LCE3B-del and the linkage disequilibrium (LD) pattern between the variant allele and the tag SNP rs4112788. Our results show that most populations tend to have a higher frequency of the deleted allele than Sub-Saharan Africans. Furthermore, we found strong LD between rs4112788G and LCE3C_LCE3B-del in most non-African populations (r2 >0.8), in contrast to the low concordance between loci (r2 <0.3) in the African populations.ConclusionsThese results are another example of population variability in terms of biomedical interesting CNV. The frequency distribution of the LCE3C_LCE3B-del allele and the LD pattern across populations suggest that the differences between ethnic groups might not be due to natural selection, but the consequence of genetic drift caused by the strong bottleneck that occurred during “out of Africa” expansion.

Conservation genetics of an endemic from the Mediterranean Basin: high genetic differentiation but no genetic diversity loss from the last populations of the Sicilian Grape Hyacinth Leopoldia gussonei

The Mediterranean Basin is a biodiversity hotspot, housing (11.000 narrowly endemic plant species, many of which are declining due to mass tourism and agricultural intensification. To investigate the genetic resource impacts of ongoing habitat loss and degradation, we characterized the genetic variation in the last known populations of Leopoldia gussonei, a self-compatible endangered Sicilian Grape Hyacinth numbering less than 3,000 remaining individuals, using AFLP. Results dem- onstrated significant genome-wide genetic differentiation among all extant populations (UST = 0.05-0.56), and genetic clustering according to geographic location. Gene diversity was fairly constant across population (mean HE = 0.13) and was neither affected by current population size nor by spatial isolation. Vegetation analysis showed the presence of known invasive weeds in a quarter of the populations, but we found no relation between genetic diversity and plant community composition. The marked genetic differences among populations and the profusion of rare and private alleles indicate that any further population loss will lead to significant losses of genetic diversity. Conservation efforts should therefore focus on the preser- vation of all sites where L. gussonei still occurs, yet the deliberate introduction of diverse material into the smallest populations seems unneeded as clonality likely mitigated genetic drift effects thus far. More generally, our findings support the view that endemic plant species with a narrow ecological amplitude, as many specialists in Mediterranean coastal ecosystems, are highly genetically differentiated and that conservation of their genetic diversity requires preservation of most, if not all of their extant populations.

Development of genetic diversity, differentiation and structure over 500 years in four ponderosa pine populations

Population history plays an important role in shaping contemporary levels of genetic variation and geographic structure. This is especially true in small, isolated range-margin populations, where effects of inbreeding, genetic drift and gene flow may be more pronounced than in large continuous populations. Effects of landscape fragmentation and isolation distance may have implications for persistence of range-margin populations if they are demographic sinks. We studied four small, disjunct populations of ponderosa pine over a 500-year period. We coupled demographic data obtained through dendroecological methods with microsatellite data to discern how and when contemporary levels of allelic diversity, among and within-population levels of differentiation, and geographic structure, arose. Alleles accumulated rapidly following initial colonization, demonstrating proportionally high levels of gene flow into the populations. At population sizes of approximately 100 individuals, allele accumulation saturated. Levels of genetic differentiation among populations (F(ST) and Jost's D(est)) and diversity within populations (F(IS)) remained stable through time. There was no evidence of geographic genetic structure at any time in the populations' history. Proportionally, high gene flow in the early stages of population growth resulted in rapid accumulation of alleles and quickly created relatively homogenous genetic patterns among populations. Our study demonstrates that contemporary levels of genetic diversity were formed quickly and early in population development. How contemporary genetic diversity accumulates over time is a key facet of understanding population growth and development. This is especially relevant given the extent and speed at which species ranges are predicted to shift in the coming century.

Fine-Scale Population Structure of Blue Whale Wintering Aggregations in the Gulf of California

Population differentiation in environments without well-defined geographical barriers represents a challenge for wildlife management. Based on a comprehensive database of individual sighting records (1988–2009) of blue whales from the winter/calving Gulf of California, we assessed the fine-scale genetic and spatial structure of the population using individual-based approaches. Skin samples of 187 individuals were analyzed for nine microsatellite loci. A single population with no divergence among years and months and no isolation by distance (Rxy = 0.1–0.001, p>0.05) were found. We ran two Bayesian clustering methods using Structure and Geneland softwares in two different ways: 1) a general analysis including all individuals in which a single cluster was identified with both softwares; 2) a specific analysis of females only in which two main clusters (Loreto Bay and northern areas, and San Jose-La Paz Bay area) were revealed by Geneland program. This study provides information indicating that blue whales wintering in the Gulf of California are part of a single population unit and showed a fine-scale structure among females, possibly associated with their high site fidelity, particularly when attending calves. It is likely that the loss of genetic variation is minimized by male mediated gene flow, which may reduce the genetic drift effect. Opportunities for kin selection may also influence calf survival and, in consequence, have a positive impact on population demography in this small and endangered population.

Forensic parameters for 15 STRs in eight Amerindian populations from the north and west of Mexico

Allele frequency distributions for 15 STR loci (AmpFlSTR Identifiler kit) were estimated in 825 volunteers of the following eight Mexican-Amerindian populations from two geographical regions: (1) North: Tarahumara (204), Mayo (45), Seri (28), and Guarijío (17); (2) Northwest: Tepehuano (123), Mexicanero (84), Cora (85), and Huichol (239). Genotype frequency distribution was in agreement with Hardy-Weinberg expectations for all 15 STRs, excepting for two loci (D13S317 and FGA) in the Huichol population. The power of discrimination and power of exclusion values were both larger than 0.99999. These STR databases will support the correct interpreting of DNA profiles in paternity testing and forensic cases in Mexican-Amerindian groups from these regions, until know poorly studied. Genetic distances and pairwise comparisons were estimated between populations. A significant genetic differentiation was observed between these Mexican-Amerindian groups (F(ST)=3.43%; p=0.0000) that was 10 times larger than the observed between Mestizos (F(ST)=0.34%), which represent most of the Mexican population (~90%). This result was in agreement with the incapability to cluster these Native American populations by geographic criteria. Pre-Colombian descriptions of Aridoamerica, including the North region of Mexico, suggest genetic drift effects to explain this noticeable population differentiation of Mexican-Amerindian groups.

Structure analysis of the La Guajira-Colombia population: A genetic, demographic and genealogical overview

Background: This study examined whether cultural factors, as compared to geographical distance, have produced a population sub-structure among different groups from the La Guajira population (Amerindian Wayúu and other resident groups) that co-exist within the same region.Aims: The aims of this study were to analyse this population to discover whether cultural barriers result in the sub-structure, to evaluate whether there is a genetic drift effect and to describe migration dynamics using a genetic, genealogical and demographic approach.Subjects: This study examined a sample of 290 individuals who were grouped based on a genealogical criterion to distinguish between native individuals and migrants.Materials and methods: Using demographic information, the age and gender structure of the population and genetic drift estimators were analysed. Using 15 autosomal microsatellites, heterozygosity, Hardy-Weinberg equilibrium (HWE), inbreeding, sub-structure, recent migration rate and genetic relationships were also evaluated using a Principal Component analysis (PCA) using reference populations.Results: La Guajira is a young population that is growing and exposed to a moderate effect of genetic drift (Neme 11.903). The Wayúu are highly diverse (Ho 0.727) and different from other groups, with the exception of Wayúu-Guajiro. This trend was also observed in other Amerindian populations.Conclusion: This study found a high level of admixture and gene flow within the Wayúu population despite cultural differences. Thus, although the Wayúu population differs from other population groups, it is not an isolated population.