Marked Genetic Divergence Research Articles

Dispersal of the Ponto-Caspian amphipod Echinogammarus ischnus: invasion waves from the Pleistocene to the present.

The geographical range of the amphipod crustacean Echinogammarus ischnus has expanded over the past century from the Ponto-Caspian region to Western Europe, the Baltic Sea, and the Great Lakes of North America. The present study explores the phylogeographic patterns of this amphipod across its current distribution, based on an examination of nucleotide diversity in the mitochondrial cytochrome c oxidase subunit I (COI) gene. Marked genetic divergence exists among populations of E. ischnus from the Black and Caspian Seas, as well as those from the drainage system of the Black Sea. This divergence suggests the prolonged geographic isolation of these native populations, reflecting the limited dispersal capability of E. ischnus. By contrast, invading populations are characterized by a lack of genetic variation; a single mitochondrial genotype of Black Sea origin has colonized sites from the Rhine River to North America. The dispersal pattern in E. ischnus is very similar to that in the Ponto-Caspian cladoceran Cercopagis pengoi. Despite their contrasting life history strategies, these invading species followed the same route of invasion from the northern Black Sea to the Baltic Sea region, and subsequently to North America.

Sibling species in interstitial flatworms: a case study using Monocelis lineata (Proseriata: Monocelididae)

The genetic relationships between morphologically indistinguishable marine and brackish-water populations of Monocelis lineata (O.F. Muller, 1774) (Proseriata: Monocelididae) were analysed by means of allozyme electrophoresis. Fifteen samples of M. lineata (13 from the Mediterranean and two from the Atlantic) from coastal marine and brackish-water habitats were examined for variation at 18 loci. Eleven loci were polymorphic in at least one population of M. lineata. Low levels of within-population genetic variability were found, with average observed and expected heterozygosity values ranging from Ho=0.015±0.015 to 0.113±0.044, and from He=0.028±0.028 to 0.138±0.054, respectively. The occurrence of a number of private alleles indicated a marked genetic divergence among populations of M. lineata, with Rogers’ genetic distances ranging from DR=0.003 to 0.676 and a highly significant FST value (0.918±0.012, P<0.001). UPGMA (unweighted pair-group method using arithmetic average) cluster analysis and multidimensional scaling showed a clear genetic divergence between marine and brackish-water populations. Moreover, Atlantic and Mediterranean populations were sharply separated. Our results suggest that M. lineata is a complex of sibling species.

Diversity among rhizobiophages from rhizospheres of legumes inhabiting three ecogeographical regions of India

Diversity in rhizobiophages from rhizosphere soils of different legumes inhabiting eight localities in the Delhi, Jaisalmer Plateau and Great Nicobar ecogeographical regions of India was assessed using 14 rhizobial indicator strains that nodulate three species of Sesbania ( S. sesban, S. aegyptica and S. rostrata). Phage activity was detected in 47% of the soil samples tested. Most of the positive responses were observed in soils of localities inhabited by host legumes of indicator bacterial strains and their close relatives. The results suggest that rhizobiophages are maintained in the vicinity of their target host populations and are spread through the man-made introduction of host legumes and their rhizobia. Diversity among phage isolates was assessed by studying the plaque traits on their indicator bacterial strains, and variation in morphology using transmission electron microscopy. Except for plaque size, the variation in the plaque traits was rather narrow. Based on the variability pattern, the 64 phages were grouped into 11 plaque types. In contrast to plaque characteristics, the diversity in morphological characters was high and phage isolates differ from the rhizobiophages reported from Indian soils; the Indian phages of Azorhizobium caulinodans strain ORS571 are different from the Senegal isolates. Based on the morphological diversity, the phages are grouped into Bradley's basic four phage groups (A1, B1, B2 and C1) and three families, Myoviridae, Siphoviridae and Podoviridae. This pattern of grouping is reflected in cluster formation based on the variability in plaque and morphological characters. The host range of the phage isolates is rather narrow and restricted to their indicator strains and their close relatives due to marked genetic divergence among rhizobia due to legume host specialization and ecological conditions. The phages can be used for typifying closely related stem-nodulating rhizobia and other rhizobia, which are promiscuous within sesbanias.

Total iron binding capacity and transferrin concentration in the assessment of iron status.

Transferrin concentration and total iron binding capacity (TIBC) are currently used to assess iron status. Although correlation between TIBC and transferrin is generally considered as good, conversion factors between the two analytes found in literature show large differences. Although the price per test is lower for TIBC, there are a number of analytical advantages of serum transferrin. Due to binding of iron to other plasma proteins (mainly albumin), TIBC methods generally overestimate the iron binding capacity of transferrin. Moreover, no generic reference values are available for TIBC. In contrast to TIBC, internationally accepted interim reference ranges are available for serum transferrin. The introduction of the international CRM 470 protein standard material has lead to a significant reduction in interlaboratory variation for transferring measurements. In view of these observations, determination of transferrin concentration, rather than TIBC, is recommended. However, in non-European populations characterized by a marked genetic variation in transferrin (TF BC and TF CD variants), in certain cases, immunochemical determination of transferrin may lead to errors. In these populations, TIBC measurements may be preferred.

An invasion history for Cercopagis pengoi based on mitochondrial gene sequences

The predatory cladoceran Cercopagis pengoi has extended its range over the past decade from the Ponto‐Caspian basin into the Baltic Sea and the Laurentian Great Lakes. This study employs mitochondrial DNA (mtDNA) sequence analysis to elucidate the invasion corridors exploited during this range expansion. The Caspian and Black Sea populations of C. pengoi exhibit marked genetic divergence, enabling their discrimination as potential sources of the Baltic and Great Lakes populations. The limited mtDNA haplotype diversity detected in the Baltic populations suggests they were founded by a small number of colonists from the Black Sea. The colonization of North America was apparently a result of the transfer of animals from the Baltic Sea in ballast water.

Análise dialélica para avaliação de híbridos interpopulacionais de cajueiro

Os objetivos deste trabalho foram obter informações dos componentes de médias de populações de cajueiro (Anacardium occidentale L.), por meio de análise dialélica parcial, e verificar o potencial per se de dois grupos distintos de parentais: um, constituído por clones comerciais de cajueiro-anão-precoce (CCP06, CCP76, CCP09 e CCP1001), e o outro, por matrizes de cajueiro comum (CP07, CP12, CP77, CP96 e BTON), e a heterose em suas respectivas combinações híbridas. Utilizou-se o delineamento experimental de blocos casualizados, com quatro repetições. Os caracteres avaliados foram altura da planta, diâmetro da copa, número da castanhas por planta, produtividade de castanhas, peso médio da castanha, peso médio da amêndoa e relação peso da amêndoa/peso da castanha. Constatou-se que os efeitos de parentais e heterose são importantes componentes das médias das populações em estudo, em relação a todos os caracteres. Entre os componentes heteróticos, a heterose média apresentou-se como o mais expressivo, indicando presença de dominância e considerável divergência genética entre os dois grupos. Apenas em relação aos caracteres número de castanhas e produtividade a capacidade específica de combinação foi significativa. As combinações híbridas CCP76 x CP07, CCP09 x BTON e CCP09 x CP77 são as mais promissoras, sendo indicadas para formação de populações-base para programas de melhoramento do cajueiro.

Is Syllis gracilis (Polychaeta: Syllidae) a species complex? An allozyme perspective

The genetic relationships between morphologically indistinguishable marine and brackish populations of Syllis gracilis Grube, 1840 (Polychaeta: Syllidae) were studied by means of allozyme electrophoresis. Samples of S. gracilis from marine coastal and brackish-water habitats were examined for variation at 13 presumptive loci. In addition, a sample of the closely related species S. prolifera (Krohn, 1852) was analysed. Five loci were multiallelic in at least one population of S. gracilis and eight loci in S. prolifera. Low to moderate levels of within-population genetic variability were found, with average expected heterozygosity values ranging from H = 0.068 (±0.043 SE) to 0.187 (±0.069 SE) in the populations of S. gracilis; higher values were found in S. prolifera (H = 0.325 ± 0.076). The presence of various private alleles indicated a marked genetic divergence among populations of S. gracilis, with Nei's genetic distances ranging from D = 0.000 to 0.833 and a highly significant FST value. Furthermore, evidence for strong genetic heterogeneity between two sympatric marine populations was found. UPGMA cluster analysis and multidimensional scaling pointed out a clear genetic divergence between brackish and marine populations. At least two genetically divergent entities occurred in marine and brackish habitats. This could be due to local adaptation of individuals coming from marine populations to brackish habitats, but more presumably to the occurrence of a species complex within S. gracilis.

Quantitative genetic evidence that the timing of vegetative phase change in Eucalyptus globulus ssp. globulus is an adaptive trait

Quantitative genetic analysis of six field trials suggests a complex pattern of adaptive significance for the timing of the abrupt change in leaf form in Eucalyptus globulus Labill. spp. globulus. Data from one small trial demonstrated a genetic basis to a steep local cline in habit, in the size of plants flowering and in the height of the change in foliage type. Thus, slow growth, early phase change and precocious flowering appear to be maintained in exposed coastal environments by current selection. This contrasts with results from five large trials that contained open-pollinated progeny from across the whole geographic range of this taxon. On this broad scale, early phase change appears to promote growth, a fitness surrogate, in two trials but not the others, implying differential selection for the timing of phase change. In these cases, early phase change may have been favoured in warm, wet environments by reducing damage by leaf fungi. There was marked genetic variation in the timing of vegetative phase change among broad regions, consistent with either adaptation to broad-scale environmental variation or historical differentiation.

Genetic divergence in natural populations of the Mediterranean brackish-water killifish Aphanius fasciatus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 179:155-162 (1999) - doi:10.3354/meps179155 Genetic divergence in natural populations of the Mediterranean brackish-water killifish Aphanius fasciatus Ferruccio Maltagliati* Dipartimento di Scienze dell'Uomo e dell'Ambiente, Università di Pisa, Via Volta 6, I-56126 Pisa, Italy *E-mail: maltagli@discat.unipi.it ABSTRACT: Samples of the brackish-water cyprinodontid fish Aphanius fasciatus from 11 Mediterranean coastal brackish-water habitats were examined for variation at 43 allozyme loci. Sixteen loci were polymorphic in at least 1 population. Estimates of genetic variability revealed low levels of polymorphism, with mean effective number of alleles per locus ranging from 1.02 (SE 0.01) to 1.10 (SE 0.04) and average expected heterozygosity values from 0.013 (SE 0.007) to 0.062 (SE 0.022). The mean Weir & Cockerham f = 0.060 (SE 0.019) confirmed the general concordance with Hardy-Weinberg equilibrium within populations assessed by exact tests. The presence of various private alleles and the mean value of the coancestry coefficient, q = 0.507 (SE 0.078), indicated a marked genetic divergence among populations. Nei's genetic distance values were characteristic of populations within species, ranging from 0.001 (SE 0.000) to 0.098 (SE 0.044). Genetic affinities obtained by UPGMA cluster analysis were consistent with the geographical distribution of populations. The high degree of genetic divergence among A. fasciatus populations corresponds to the naturally fragmented distribution of the species and to restricted gene flow between populations, due to the limited dispersal potential of the species. Furthermore, genetic and geographical distances between populations are consistent with the prediction that the species is genetically structured by isolation by distance. KEY WORDS: Isolation by distance · Genetic structure · Heterozygosity · Life history traits · Cyprino-dontidae · Allozymes · Mediterranean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 179. Publication date: April 15, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Genetic subdivision and morphological variation in a freshwater snail species complex formerly referred to as Viviparus georgianus (Lea)

Genetic and morphological variation was studied in a brooding (ovoviviparous) and morphologically variable freshwater snail [ Viviparus georgianus (Lea)] species complex in southern Georgia and Florida. Eleven populations were clustered into three genetically isolated, allopatric groups characterized by 7 to 14 diagnostic loci out of the 38 loci examined. These allopatric groups were identified as V. georgianus (in eastern and southern Florida), V. limi (in the Ochlockonee River) and V. goodrichi (in the Florida panhandle). Nei's standard genetic distances between the species were large (0.23-0.52) compared to intraspecific distances (0.00-0.06). Hierarchical F-statistics for differentiation among sites within drainage systems (F SD) for V. goodrichi and V. georgianus were large (0.519 and 0.387, respectively). The F DT values (differentiation among drainage systems within the total area sampled) were negative or close to zero, so most of the intraspecific genetic differentiation was due to differences among populations within drianage systems, rather than to differences among systems. Canonical discriminant analysis of nine shell morphological measurements separated all three species with little overlap. Principal components analysis of the shell morphology revealed intraspecific variation among sites possibly due to environmental effects. This study demonstrates the marked genetic and morphological variation among and within drainage systems in freshwater prosobranchs.

Genetic subdivision and morphological variation in a freshwater snail species complex formerly referred to as Viviparus georgianus (Lea)

Genetic and morphological variation was studied in a brooding (ovoviviparous) and morphologically variable freshwater snail [Viviparus georgianus (Lea)] species complex in southern Georgia and Florida. Eleven populations were clustered into three genetically isolated, allopatric groups characterized by 7 to 14 diagnostic loci out of the 38 loci examined. These allopatric groups were identified as V. georgianus (in eastern and southern Florida), V. limi (in the Ochlockonee River) and V. goodrichi (in the Florida panhandle). Nei's standard genetic distances between the species were large (0.23-0.52) compared to intraspecific distances (0.00-0.06). Hierarchical F-statistics for differentiation among sites within drainage systems (FSD) for V. goodrichi and V. georgianus were large (0.519 and 0.387, respectively). The FDT values (differentiation among drainage systems within the total area sampled) were negative or close to zero, so most of the intraspecific genetic differentiation was due to differences among populations within drianage systems, rather than to differences among systems. Canonical discriminant analysis of nine shell morphological measurements separated all three species with little overlap. Principal components analysis of the shell morphology revealed intraspecific variation among sites possibly due to environmental effects. This study demonstrates the marked genetic and morphological variation among and within drainage systems in freshwater prosobranchs.

Genetic diversity and population differentiation of the shortfin squid Illex argentinus in the south-west Atlantic

Sixteen samples (588 individuals) of the Argentine shortfin squid Illex argentinus were collected by commercial vessels from Falkland and surrounding waters (42°06–51°17S) between February and May 1990 and subjected to starch gel electrophoresis. Levels of electrophoretically detectable generic variability and the extent of population differentiation were determined from allele frequencies at 25 enzyme-coding loci. Low levels of genetic variability were detected, with the overall proportion of polymorphic loci, P = 0.28, mean heterozygosities per locus, H 1 = 0.011, and the average effective number of alleles, N c = 1.23. Marked population differentiation was indicated by significant differences in allele frequency among samples, and unbalanced genotypic distributions with heterozygote deficits at most loci. Nei's mean genetic distances ( D) and identities ( I) ranged from 0.000 to 0.130 and 1.000 to 0.878, respectively, underlining the marked genetic divergence detected. Some evidence of microgeographic differentiation (between replicates within sites) was observed. Individuals collected from northerly limits of the sampled area (42: 06 S, 58:09 W) were most genetically distinct ( I = 0.878−0.904), suggesting the existence of a hitherto unrecognised subspecies or species of Illex. Emphasis is placed on the need to delimit putative stock boundaries, and develop appropriate population models to ensure conservation of genetic resources.

Marked genetic divergence revealed by allozymes among populations of the guppy Poecilia reticulata (Poeciliidae), in Trinidad

Populations of the guppy Poecilia reticulata from six locations in N. Trinidad were examined by starch gel electrophoresis to estimate their degree of genetic divergence. Variability at seven enzyme-coding loci demonstrated that populations differed markedly in allele frequencies with some allelic substitution between sites (for 23 loci, Nei's mean genetic identity, Ī ranged from 0.869–1.00; the coefficient of gene differentiation, GST= 0.086; and the absolute differentiation between populations, Dm= 0.044). There was a good correspondence between degree of physical isolation and extent of genetic differentiation, as exemplified by the partitioning of gene diversity (Nei's gene diversity analysis = 66% between river basins; 32% within river basins; 2% within rivers), though there was considerable variability in the contribution of individual loci. Most populations were in Hardy-Weinberg equilibrium, and any significant deviations were due exclusively to heterozygote deficiencies. The patterns of population differentiation are discussed in relation to probable past geological and historical events, and present-day evolutionary forces. Notable among these are previous continental land connections, periodic immigration from N.E. South America, and post-colonization events including differential predation, sexual selection, apparent restricted vagility and small effective population sizes.

Genetic Influences on the Timing of Puberty in Mice1

Genetic influences on the timing of three pubertal events--vaginal opening, first vaginal cornification, and onset of cyclicity--were studied in C57BL/6J, DBA/2J, and C3H/HeJ mice and in two F1 hybrid strains (B6D2F1 and B6C3HF1). Marked genotypic differences were found. Among inbred strains, differences in the onset of vaginal opening and first vaginal cornification (C3H less than DBA less than C57) did not parallel those for the onset of cyclicity (C3H much greater than DBA = C57). Compared to parental strains, F1 hybrid strains were intermediate for times of vaginal opening and first vaginal cornification, consistent with the model in which the genetic effects on the timing of these events are additive. By contrast, onset of cyclicity occurred significantly earlier in the F1 hybrids than in their parent strains, indicating heterosis for one or more genes specifying this event. Body weights also differed among the genotypes from weaning onward, but these differences were only partially correlated with the differences in the timing of the pubertal events. Thus, genetic influences other than those affecting body weight contribute to the differential timing of pubertal events in these mouse strains. These results reveal marked genetic variation in the timing of puberty, and indicate that the set of genes specifying the timing of vaginal opening and first vaginal cornification differs from those specifying the onset of cyclicity.

Species and strain differences in urinary protein excretion.

The physiological excretion of urinary protein is subject to great variation influenced not only by environmental and hormonal factors but also by genetics. The present study demonstrates that there is not only variation in respect to the excretion of plasma proteins but also of other types of proteins which are specific urinary proteins. There is a close relation between body weight and total protein excretion. However, male rats and mice do not fit the allometric line calculated for the other species studied. This is of special importance since these two species are often used in kidney research. The reason for this divergence in total protein is the excretion of sex-dependent low molecular weight proteins. The excretion of albumin, which is a marker of glomerular permeability and tubular reabsorption as well, shows a marked genetic variation between different rat strains. The data presented in this study demonstrate the general admissibility of transferring data from one species to the other but also the limitations in respect especially to the sex-dependent proteins which are excreted by some species.

Genetic variation in cytochrome P-450 and xenobiotic metabolism in Drosophila melanogaster

A marked genetic variation in the capacity to perform xenobiotic metabolism was observed in microsomal fractions from the seven Drosophila strains studied. A 1,5 to 2-fold variation was found in the content of cytochrome P-450 and in the NADPH-cytochrome c reductase activity. The two insecticide-resistant strains Hikone R and Oregon R differed markedly when compared to sensitive strains by having a 3 to 17-fold higher p-nitroanisole (PNA) demethylase activity and biphenyl-3-hydroxylase activity. SDS-polyacrylamide gel electrophoresis of the microsomes also revealed an increased content of a protein band with an apparent mol. wt of 54,000 in the resistant strains. The 4-hydroxylation of biphenyl was also 2–7-fold higher in the Oregon R strain, and the band with a mol. wt of 56,000 had a higher protein content compared to the other strains. The biphenyl-4-hydroxylation was several-fold lower in the strain Berlin K. 2-OH-biphenyl was formed only in trace amounts by all strains. 7-Ethoxycoumarin (EC) deethylase activity and benzo(a)pyrene (BP) monooxygenase activity was 2–6-fold lower in the Hikone R strain. An increased amount of the protein with a mol. wt of 58,000 was noted in the Canton S strain. No concomitant increase in any enzyme activity was observed. A genetic variation between the strains was observed after phenobarbital (PB) treatment in the content of cytochrome P-450 and in the various enzyme activities, varying from non-responsiveness to a 4- to 5-fold increase. Aroclor 1254 (PCB) was less efficient in enhancing the activities. It caused maximally a 3-fold increase, had often no effect and in some cases even decreased the metabolism. β-naphthoflavone (BNF) caused only marginal increases in the activities in most strains. The only significant effects were an increased formation of 3-OH-biphenyl in Berlin K and an enhanced NADPH-cytochrome c reductase activity in Lausanne-S. In conclusion, the variations observed in this study provide a basis for further studies on the genetic regulation of the cytochrome P-450 system in Drosophila. Furthermore, similarities in the regulation when compared to mammals indicate that studies on this genetically well characterized organism might contribute to the general understanding of the genetics of xenobiotic metabolism.

Genetic control of lipid transport in mice. I. Structural properties and polymorphisms of plasma lipoproteins.

To examine genetic factors involved in mammalian lipid transport, we present a detailed analysis of the plasma lipoproteins of the mouse and a survey of these lipoproteins among different inbred strains for genetic variations. Plasma lipoproteins were separated by differential ultracentrifugation into three density fractions: with densities less than 1.006 g/ml, between 1.006 and 1.063 g/ml, and between 1.063 and 1.21 g/ml. On agarose gels, the d less than 1.006 g/ml fraction migrated as a single major band with pre-beta mobility and appeared to correspond to human very low density lipoproteins based on its lipid and protein composition. The intermediate density class was heterogeneous, containing particles with beta and alpha mobilities on agarose gels. The 1.063-1.21 g/ml density fraction exhibited a single alpha-migrating band on agarose gels, characteristic of high density lipoprotein in other mammalian plasma. Marked genetic variation was seen for lipoprotein mobilities among different inbred strains. In Swiss random bred mice, most of the apoprotein was in high density lipoprotein (104 mg/dl of plasma). Lower protein concentrations of 8.5 and 6.2 mg/dl were found in the d = 1.006-1.063 g/ml class and in the very low density lipoprotein, respectively. Proteins thought to be homologous to human apolipoproteins A-I, A-II, B, and E were identified on the basis of their distributions among the lipoprotein fractions, their molecular weights and isoelectric points and, for A-I, B, and E, by their cross-reactivities with antibodies prepared against purified rat apolipoproteins. Considerable structural and quantitative variations also exist among these apolipoproteins isolated from different inbred mouse strains. Our results provide a basis for the use of the mouse as a model system for the study of the genetic control of lipid transport.

Immune memory to a nonmitogenic, thymic independent antigen in mice: variation among inbred strains and possible relationship to oncogenesis.

Immune memory to DNP-Ficoll, a nonmitogenic, thymic-independent (TI-2) antigen, was demonstrated in several inbred strains of mice. Direct and indirect splenic plaque-forming cell responses were measured in mice given a secondary challenge with DNP-Ficoll and in appropriate control mice. Strong IgM memory, but no IgG memory, was observed in SJL/J, AKR/J, and C58/J mice. C57L/J mice gave both a strong IgM memory response and a relatively strong IgG memory response to DNP-Ficoll. C57BL/6N, C57BR/cdJ, and A/HeJ mice were unable to mount significant IgM or IgG memory responses to this antigen under an identical immunization schedule. These results are indicative of marked genetic variation in mice in the capacity for B memory cell expression. They also identify a provocative but unexplained association between positive IgM memory responses to DNP-Ficoll in SJL/J, AKR/J, and C58/J mice and a propensity to develop lymphoreticular neoplasia. This association is observed when there is no clear evidence for IgG memory.

THE IMPACT OF RANDOM AND LINEAL FISSION ON THE GENETIC DIVERGENCE OF SMALL HUMAN GROUPS: A CASE STUDY AMONG THE YANOMAMA

ABSTRACT Most of the genetic divergence that currently separates populations of Homo sapiens must have arisen during that long period when the local village (or band) was the basic unit of biological evolution. Studies of tribally intact Amerindian groups exhibiting such small-group organization have demonstrated marked genetic divergence between nearby villages. Some of this genetic radiation can be attributed to the effects of random genetic drift over time within these small demes. Some of it, however, might be better ascribed to the consequences of nonrandom genetic assortment at the time of village fission, a recurring event for such groups. Even random genetic assortment at the time of fission would lead to some genetic divergence, due to the finite size of the parent gene pool. We term the genetic consequences of random assortment the random fission effect. Routinely, village fission occurs along family lines, leading to even greater genetic divergence between the daughter villages. We use the term lineal fission effect to describe the genetic consequences of nonrandom assortment and contrast these results with those derived from random assortment.——A formal treatment of random and lineal fission effects is developed, first for the single-locus case, then for the multiple-locus extension. Using this formulation, three Yanomama fission events were examined. Fission in the Yanomama often involves a great deal of mutual hostility between the two factions, so that subsequent gene flow between the two daughter villages is minimal. The first two examples are typical of the Yanomama behavior norm, and are accompanied by a minimum of subsequent gene flow between the daughter villages. In these two cases, the observed divergence values are very large and are also very unlikely under random fission. The lineal fission effect is pronounced. The net impact of lineal fission is to reduce the effective size of the village at the time of fission by a factor of four, relative to expectation from random fission. The third example, however, involved an unusually amicable split of a village, followed by free genetic exchange between the fission products. This "friendly fission" yields an observed divergence value not much in excess of the expectation from random fission.—The long-term consequences of such fission bottlenecks in effective population size are discussed for both intra- and inter-tribal genetic diversity. It appears that the rate of genetic divergence for tribal and subtribal groups may have been somewhat greater than would be expected from classical drift arguments.