Morphological, genetic, and chromosomal variation at a small spatial scale within a mosaic hybrid zone of the grasshopper Dichroplus pratensis Bruner (Acrididae)

Hybrid zones are regions where genetically different populations meet and mate, resulting in offspring of mixed characteristics. In organisms with limited dispersal, such as melanopline grasshoppers, hybrid zones can occur at small spatial scales (i.e., <500 m). We assessed levels of morphological, chromosomal, and molecular variability in adult males of the grasshopper Dichroplus pratensis Bruner (N = 137 males, 188 females) collected at 12 sites within a mosaic hybrid zone in a heterogeneous environment in Sierra de la Ventana, Argentina. In this hybrid zone, 2 Robertsonian chromosomal races, polymorphic for different centric fusions, meet (the "Northern race" at low altitudes and the "Southern race" at higher altitudes), forming hybrids that show monobrachial homologies during meiosis. High morphometric variation in 6 traits was revealed among grasshoppers of both sexes, with male body size positively and significantly correlated with increasing altitude. Frequency of Robertsonian fusions characteristic of the Southern race increased significantly with altitude. Moreover, fusion frequencies covaried between samples. Considerable genetic variation was revealed by random amplification of polymorphic DNA markers, with heterozygosity ranging from 0.3477 to 0.3745. Insects from low-altitude and high-altitude populations showed significant genetic differentiation, as indicated by F(ST) values. The proposed model for D. pratensis, involving the generation and maintenance by chromosomal fusions, of gene complexes adaptive in different environments, could explain the observed clinal patterns within the contact zone.     

Studies of mitochondrial DNA,allozyme and morphometric variation in a house mouse hybrid zone

An unusual chromosomal hybrid zone of the house mouse, Mus musculus domesticus, exists in Upper Valtellina, Northern Italy, consisting of four Robertsonian (Rb) races and the standard (all-acrocentric, or 2n = 40) race, all hybridizing freely within 10 km2. The hybrid zone in Valtellina provides an excellent opportunity to study the role of Rb fusions in reproductive isolation and speciation. This hybrid zone has already been well studied for the distribution of Rb fusions and the fertility of hybrids, but in order to understand the dynamics of the zone, a basic understanding of the origin and genetic similarity of the chromosomal races is necessary. This paper presents the results of three different methods of measuring genetic differentiation: multivariate analysis of morphological traits and analyses of allozyme variation and mitochondrial DNA sequences. The standard race is clearly distinguishable from the three Rb races by all three methods, but the Rb races are not distinguishable from one another. This provides strong evidence for our previous suggestions that the well-established Rb races in Valtellina are closely related, and that the standard race was introduced into the valley more recently from a distant source. The fact that the Rb races are indistinguishable is also consistent with our hypothesis that a within-village speciation event involving two of the races (Hauffe & Searle, 1992) was a recent occurrence. The low level of allozyme heterozygosity among the Rb races suggests that these populations are the products of at least one bottleneck. The present article substantially extends earlier studies and provides the first detailed morphological and molecular analysis of this complex hybrid zone.     

Genetic races associated with the genera and sections of host species in the holoparasitic plant Cytinus (Cytinaceae) in the Western Mediterranean basin

* Speciation via race formation is an important evolutionary process in parasites, producing changes that favour their development on particular host species. Here, the holoparasitic plant Cytinus, which has diverse host species in the family Cistaceae, has been used to study the occurrence of such races. * Amplified fragment length polymorphism (AFLP) analyses were performed on 174 individuals of 22 populations parasitizing 10 Cistaceae species in the Western Mediterranean basin. * Neighbour-joining, multivariate ordination analyses, and individual-based Bayesian analyses, clustered Cytinus populations into five well-characterized genetic races that, overall, agreed with the taxonomic sections of their hosts. In the AMOVA, among-races differences accounted for almost 50% of the genetic variation. The isolation-by-distance model was not supported by a Mantel test among Cytinus populations (r = 0.012; P = 0.456). All races showed low within-population genetic diversity, probably as a result of restricted pollen flow aggravated by flowering asynchrony, restricted seed dispersion, or stochastic processes. * The genetic differentiation among the five races of Cytinus is congruent with the view that these races are well-characterized lineages that have evolved independently as a result of selective pressures imposed by their hosts. This pattern, with genetically distinctive groups associated with the infrageneric sections of the host species, has not been reported previously for parasitic angiosperms.     

Genetics and the origin of human races

In the last decades, the concept of human races was considered scientifically unfounded as it was not confirmed by genetic evidence. None of the racial classifications, which strongly differ in the number of races and their composition, reflects actual genetic similarity and genealogy of human populations inferred from variability of classical markers and DNA regions. Moreover, intercontinental ("interracial") variability was shown to be far lower than that within populations: the former constitutes 7 to 10% and the latter, about 85% of the total genetic variation. It is believed that the low level of differentiation of regional population groups contradicts their race status and suggests a recent origin of humans from one ancestral population. The results of studies of various genetic systems are in agreement with last conclusion rejecting the hypothesis of regional continuity. According to this hypothesis, the populations of continents regarded as large races have developed during long evolution from local types of archaic humans, in particular, Neanderthals. Phenotypic similarity of different, sometimes unrelated, populations united into one "race" is explained by strong selection since race-diagnostic traits characterize body surface and thus are directly subjected to the influence of environmental (primarily climatic) factors. It has been recently established that variability of the most important of these traits, body and hair pigmentation, is largely controlled by one locus (MC1R), which accounts for its high evolutionary lability. Other traits used for race identification are also likely to be labile and controlled by major genes. However, the fact that the currently existing race classifications are groundless does not mean that such classifications are impossible in principle. Commonly used argumentation (races do not exist because populations are not genetically separated) does not hold water. A polytypic species is characterized by genetic continuity of allopatric populations rather than the presence of narrow genetic boundaries between them. Borderlines between races are usually conventional and arbitrary. As to intergroup variation in humans, it is indeed low but comparable with that in some other species. There are no obstacles to the development of genetic systematics of human races.     

Electrophoretic analysis of a chromosomal hybrid zone in the grasshopper Podisma pedestris

We have made an extensive allozyme survey of 21 enzyme and protein loci in populations of the alpine grasshopper Podisma pedestris. This species occurs in two races, differing by a chromosomal fusion which separates the ancestral XO/XX race from a derived neo-XY race. These races also differ in DNA content, and hybrids between them have reduced viability. Electrophoresis reveals that the amount of genetic differentiation between these races is no greater than the variation among populations within each race. Both larger-scale surveys and a detailed survey of an area where the races hybridize, show that the chromosomal change is not correlated with gene frequency changes at any of the 21 loci studied. These findings are consistent with recently developed theory concerning the strength of the barrier to gene flow posed by a hybrid zone with characteristics such as those measured experimentally in Podisma. It is argued that hybrid zones in other species which involve allozymic differences do so because of stronger selection against hybrids rather than through mating isolation.     

mtDNA perspective of chromosomal diversification and hybridization in Peters' tent-making bat (Uroderma bilobatum: Phyllostomidae)

We compared sequence variation in the complete mitochondrial cytochrome-b gene with chromosomal and geographical variation for specimens of Peters' tent-making bat (Uroderma bilobatum). Three different chromosomal races have been described in this species: a 2n = 42 race from South America east of the Andes, a 2n = 44 from NW Central America and 2n = 38 from the rest of Central America and NW South America. The deepest nodes in the tree were found within the South American race (42 race), which is consistent with a longer history of this race. Average distance among races ranged from 2.5 to 2.9%, with the highest amount of intraracial variation found within the 2n = 42 race (1.7%), intermediate values within the 2n = 38 race (0.9%) and lowest within the 2n = 44 race (0.5%). Variation among chromosomal races accounted for over 55% of molecular variance, whereas variation among populations within races accounted for 6%. The 2n = 38 and 2n = 44 races hybridize in the coastal lowlands of Honduras, near the Gulf of Fonseca. Introgression between these two races is low (two introgressed individuals in 45 examined). Clinal variation across the hybrid zone for the cytochrome-b of U. bilobatum, is similar to clinal variation reported for chromosomes and isozymes of this species. Mismatch distribution analyses suggests that geographical isolation and karyological changes have interplayed in a synergistic fashion. Fixation of the alternative chromosomal rearrangements in geographical isolation and secondary contact is the most likely mechanism accounting for the hybrid zone between the 2n = 38 and 2n = 44 races. If a molecular clock is assumed, with rates ranging from 2.3 to 5.0% per million years, then isolation between these races occurred within the last million years, implying a relatively recent origin of the extant diversity in Uroderma bilobatum. None the less, the three chromosomal races probably represent three different biological species.     

Host-associated genetic differentiation in the goldenrod elliptical-gall moth,Gnorimoschema gallaesolidaginis (Lepidoptera: Gelechiidae)

Careful study of apparently generalist phytophagous insects often reveals that they instead represent complexes of genetically differentiated host races or cryptic species. The goldenrod elliptical-gall moth, Gnorimoschema gallaesolidaginis, attacks two goldenrods in the Solidago canadensis complex: S. altissima and S. gigantea (Asteraceae). We tested for host-associated genetic differentiation in G. gallaesolidaginis via analysis of variation at 12 allozyme loci among larvae collected at six sites in Iowa, Minnesota, and Nebraska. Gnorimoschema gallaesolidaginis from each host are highly polymorphic (3.6-4.7 alleles/locus and expected heterozygosity 0.28-0.38 within site-host combinations). Although there were no fixed differences between larvae from S. altissima and S. gigantea at any site, these represent well differentiated host forms, with 11 of 12 loci showing significantly different allele frequencies between host-associated collections at one or more sites. Host plant has a larger effect on genetic structure among populations than does location (Wright's FST = 0.16 between host forms vs. F(ST) = 0.061 and 0.026 among altissima and gigantea populations, respectively). The estimated F(ST) between host forms suggests that the historical effective rate of gene flow has been low (N(e)m approximately 1.3). Consistent with this historical estimate is the absence of detectable recombinant (hybrid and introgressant between host form) individuals in contemporary populations (none of 431 genotyped individuals). Upper 95% confidence limits for the frequency of recombinant individuals range from 5% to 9%. Host association is tight, but imperfect, with only one likely example of a host mismatch (a larva galling the wrong host species). Our inferences about hybridization and host association are based on new maximum-likelihood methods for estimating frequencies of genealogical classes (in this case, two parental classes, F1 and F2 hybrids, and backcrosses) in a population and for assigning individuals to genealogical classes. We describe these new methods in the context of their application to genetic structure in G. gallaesolidaginis. Population phenograms are consistent with the origin of the host forms (at least in the midwestern United States) via a single host shift: altissima and gigantea moth populations form distinct lineages with 100% bootstrap support. Genetic structure in Gnorimoschema is of particular interest because another gallmaking insect attacking the same pair of hosts, the tephritid fly Eurosta solidaginis, includes a pair of host races with partial reproductive isolation. Gnorimoschema gallaesolidaginis and E. solidaginis therefore represent the first reported case of parallel host-associated differentiation, that is, differentiation by evolutionarily independent insect lineages across the same pair of host plants.     

Genetics and the Origin of Human “Races”

In the last decades, the concept of human races was considered scientifically unfounded as it was not confirmed by genetic evidence. None of the racial classifications, which strongly differ in the number of races and their composition, reflects actual genetic similarity and genealogy of human populations inferred from variability of classical markers and DNA regions. Moreover, intercontinental (interracial) variability was shown to be far lower than that within populations: the former constitutes 7 to 10% of the total genetic variation and the latter about 85% of it. It is believed that the low level of differentiation of regional population groups contradicts their race status and suggests a recent origin of humans from one ancestral population. The results of studies of various genetic systems are in agreement with the latter conclusion rejecting the hypothesis of regional continuity. According to this hypothesis, the populations of continents regarded as large races have developed during long evolution from local types of archaic humans, in particular, Neanderthals. Phenotypic similarity of different, sometimes unrelated, populations united into one race is explained by strong selection since race-diagnostic traits characterize body surface and thus are directly subjected to the influence of environmental (primarily climatic) factors. It has been recently established that variability of the most important of these traits, body and hair pigmentation, is largely controlled by one locus (MC1R), which accounts for its high evolutionary lability. Other traits used for race identification are also likely to be labile and controlled by major genes. However, the fact that the currently existing race classifications are groundless does not mean that such classifications are impossible in principle. Commonly used argumentation (races do not exist because populations are not genetically separated) does not hold water. A polytypic species is characterized by genetic continuity of allopatric populations rather than the presence of narrow genetic boundaries between them. Borderlines between races are usually conventional and arbitrary. As to intergroup variation in humans, it is indeed low but comparable with that in a number of other species. There are no obstacles to the development of genetic systematics of human races.     

Apportionment of global human genetic diversity based on craniometrics and skin color

A number of analyses of classical genetic markers and DNA polymorphisms have shown that the majority of human genetic diversity exists within local populations (approximately 85%), with much less among local populations (approximately 5%) or between major geographic regions or "races" (approximately 10%). Previous analysis of craniometric variation (Relethford [1994] Am J Phys Anthropol 95:53-62) found that between 11-14% of global diversity exists among geographic regions, with the remaining diversity existing within regions. The methods used in this earlier paper are extended to a hierarchical partitioning of genetic diversity in quantitative traits, allowing for assessment of diversity among regions, among local populations within regions, and within local populations. These methods are applied to global data on craniometric variation (57 traits) and skin color. Multivariate analysis of craniometric variation shows results similar to those obtained from genetic markers and DNA polymorphisms: roughly 13% of the total diversity is among regions, 6% among local populations within regions, and 81% within local populations. This distribution is concordant with neutral genetic markers. Skin color shows the opposite pattern, with 88% of total variation among regions, 3% among local populations within regions, and 9% within local populations, a pattern shaped by natural selection. The apportionment of genetic diversity in skin color is atypical, and cannot be used for purposes of classification. If racial groups are based on skin color, it appears unlikely that other genetic and quantitative traits will show the same patterns of variation.     

Hybridization of Races of Heterodera glycines

Progeny from single females of four known races of Heterodera glycines Ichinohe were used to establish relatively uniform populations. Single females from these populations were mated with males of other races in all possible combinations to study compatibility and inheritance patterns. When race 1 or 3 was crossed with either race 2 or 4, there was a significant reduction in number of females and a greater number of eggless females than in crosses of races 1 × 3 and 2 × 4. More females matured and fewer were eggless when matings were of the same race. Parasitic capabilities of races 2 and 4 were dominant or partially dominant over those of races 1 and 3, based on parasitism of F₁ hybrids. Segregation patterns were generally similar for reciprocal crosses between races. There appeared to be either one or two major genes segregating for parasitism of ''Pickett'' soybean in the different crosses. A hybrid isolate (race 3 × 4) that differed in parasitic capability from the four known races produced as many females on the resistant soybean genotype, PI 90,763, as on the susceptible Lee cultivar. Those data indicate that isolates of H. glycines with a different parasitic capability may develop from gene recombination.     

A microsatellite study in the Łęgucki Młyn/Popielno hybrid zone reveals no genetic differentiation between two chromosome races of the common shrew (Sorex araneus)

This study investigated a chromosome hybrid zone between two chromosomal races of the common shrew (Sorex araneus). Gene flow and genetic structure of the hybrid zone, located in the northeast of Poland, were studied using seven polymorphic autosomal microsatellite loci (L9, L14, L33, L45, L67, L68, L97) and a Y-linked microsatellite locus (L8Y). Seventy-five animals (46 of the ??gucki M?yn race and 29 of the Popielno race) from nine different localities were examined and the data were analyzed using hierarchical AMOVA and F-statistic. The studied microsatellite loci and races (divided into nine geographical populations) were characterized by observed heterozygosity (H(O)), expected heterozygosities within (H(S)), and between (H(T)) populations, inbreeding coefficient (F(IS)), fixation index (F(ST)), and average allelic richness (A). We found that genetic structuring within and between the two chromosome races were weak and non-significant. This finding and unconstrained gene flow between the races indicates a high level of migration within the ??gucki M?yn/Popielno hybrid zone, suggesting that evolutionarily important genetic structuring does not occur in interracial zones where races which are not genetically distinct come into contact.     

Impact of patient-doctor race concordance on rates of weight-related counseling in visits by black and white obese individuals

The objective of this study was to assess the impact of patient-provider race concordance on weight-related counseling among visits by obese patients. We hypothesized that race concordance would be positively associated with weight-related counseling. We used clinical encounter data obtained from the 2005-2007 National Ambulatory Medical Care Surveys (NAMCS). The sample size included 2,231 visits of black and white obese individuals (ages 20 and older) to their black and white physicians from the specialties of general/family practice and general internal medicine. Three outcome measures of weight-related counseling were explored: weight reduction, diet/nutrition, and exercise. Logistic regression was used to model the outcome variables of interest. Wald tests were used to statistically compare whether physicians of each race provided counseling at different rates for obese patients of different races. We did not observe a positive association between patient-physician race concordance and weight-related counseling. We found that visits by black obese patients to white doctors had a lower odds of exercise counseling as compared to visits by white obese patients to white doctors (odds ratio (OR) = 0.54; 95% confidence interval (CI): 0.31, 0.95), and visits by black obese patients to black physicians had lower odds of receiving weight-reduction counseling than visits among white obese patients seeing black physicians (OR = 0.34; 95% CI: 0.13, 0.90). Black obese patients receive less exercise counseling than white obese patients in visits to white physicians and may be less likely than white obese patients to receive weight-reduction counseling in visits to black physicians.     

Behavioural discrimination among chromosomal races of the house mouse (Mus musculus domesticus)

This work is concerned with the extent of behavioural discrimination between three chromosomal races of the house mouse (the standard 40-chromosome race and a 32- and 36-chromosome races) found in the vicinity of a hybrid zone in northern Scotland. Mice were investigated for several elements of their social behaviour. Within-population dyadic encounters did not show consistent behavioural differences attributable to karyotype among five populations (two standard race, two 36-chromosome race, one 32-chromosome race). Between-population dyadic encounters revealed significant differences between three populations. The standard population examined appeared to be the most “open” to foreigners, the 32-chromosome population the most “closed” while the 36-chromosome mice displayed an intermediate response. Differences in behaviour displayed during between-population as compared to within-population dyadic encounters revealed the occurrence of behavioural discrimination between populations. The implication of these results on the dynamics of the hybrid zone are discussed.     

Is chromosomal speciation occurring in house mice in Tunisia?

Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the 40-acrocentric standard karyotype and the other by a Robertsonian race (2re = 22) homozygous for nine centric fusions (Rb). A comparative summary on allozyme divergence, geographical distribution and level of reproductive isolation in the Tunisian and European Rb races is presented, to which new data on mitochondrial DNA and morphological divergence are added. The Tunisian 22Rb race revealed unique features not matched by the European chromosomal races, such as a decrease in allozymic variability, a higher level of genetic and morphological differentiation and a mosaic geographical distribution. The mtDNA analysis argued in favour of a local origin of the chromosomal divergence suggesting that the higher level of differentiation between the Tunisian races resulted from the older age of the 22Rb race and/or from a severe botdeneck. The decrease in fertility of chromosomal hybrids between the Tunisian races was compatible with the limited genetic introgression between diem. Furthermore, data on the restricted distribution of hybrid populations suggested that premating reproductive barriers may be evolving. The Tunisian 22Rb race is thus an appropriate model to investigate a chromosomally-mediated speciation event.     

Translocations maintain genetic diversity and increase connectivity in sea otters,Enhydra lutris

Sea otters, Enhydra lutris, were once abundant along the nearshore areas of the North Pacific. The international maritime fur trade that ended in 1911 left 13 small remnant populations with low genetic diversity. Subsequent translocations into previously occupied habitat resulted in several reintroduced populations along the coast of North America. We sampled sea otters between 2008 and 2011 throughout much of their current range and used 19 nuclear microsatellite markers to evaluate genetic diversity, population structure, and connectivity between remnant and reintroduced populations. Average genetic diversity within populations was similar: observed heterozygosity 0.55 and 0.53, expected heterozygosity 0.56 and 0.52, unbiased expected heterozygosity 0.57 and 0.52, for reintroduced and remnant populations, respectively. Sea otter population structure was greatest between the Northern and Southern sea otters with further structuring in Northern sea otters into Western, Central, and Southeast populations (including the reintroduced populations). Migrant analyses suggest the successful reintroductions and growth of remnant groups have enhanced connectivity and gene flow between populations throughout many of the sampled Northern populations. We recommend that future management actions for the Southern sea otter focus on future reintroductions to fill the gap between the California and Washington populations ultimately restoring gene flow to the isolated California population.     

Variants of endothelin-1 and its receptors in atopic asthma.

Endothelin-1 (ET-1) is a 21 amino acid peptide released from several types of bronchial cells. It operates through two types of receptors, type A(ET-RA) and type B(ET-RB) and has various activities in the pathophysiology of atopic asthma. These genes are localised on different chromosomes where genome-wide searches have identified linkage for atopic asthma, thus supporting the candidacy of ET-1 and its receptors for atopic asthma. A genetic association study was performed with variants of these three genes in both British (n = 300) and Japanese populations (n = 200). No significant association was found between variants of EDN1 and EDNRB genes, and atopic asthma in either population. However, variants of EDNRA gene showed a marginal association with atopy [odds = 0.39(95% CI: 0.17-0.89), p = 0.022, Pc = 0.066], especially with antigen specific IgE levels [odds = 0.31 (95% CI: 0.20-0.77), p = 0.006, Pc = 0.018] in the British population. These findings suggest that EDNRA is a major candidate locus for atopy on chromosome 4.     

Genetic and karyotypic structure in the shrews of the Sorex araneus group: are they independent?

The species of the common shrew (Sorex araneus) group are morphologically very similar but exhibit high levels of karyotypic variation. Here we used genetic variation at 10 microsatellite markers in a data set of 212 individuals mostly sampled in the western Alps and composed of five karyotypic taxa (Sorex coronatus, Sorex antinorii and the S. araneus chromosome races Cordon, Bretolet and Vaud) to investigate the concordance between genetic and karyotypic structure. Bayesian analysis confirmed the taxonomic status of the three sampled species since individuals consistently grouped according to their taxonomical status. However, introgression can still be detected between S. antinorii and the race Cordon of S. araneus. This observation is consistent with the expected low karyotypic complexity of hybrids between these two taxa. Geographically based cryptic substructure was discovered within S. antinorii, a pattern consistent with the different postglaciation recolonization routes of this species. Additionally, we detected two genetic groups within S. araneus notwithstanding the presence of three chromosome races. This pattern can be explained by the probable hybrid status of the Bretolet race but also suggests a relatively low impact of chromosomal differences on genetic structure compared to historical factors. Finally, we propose that the current data set (available at http://www.unil.ch/dee/page7010_en.html#1) could be used as a reference by those wanting to identify Sorex individuals sampled in the western Alps.     

RFLP diversity and relationships among traditional European maize populations

Given the large extent of hybrid cultivation, the importance of conserving the diversity of crop genetic resources has given birth to numerous collections of old races. In the present paper, we conduct a molecular characterisation of a large collection of 488 European maize populations using the bulk RFLP analysis. The analysis of 23 RFLP loci showed a high allelic richness of 11.5 alleles per locus. Populations from eastern Europe (Poland, Austria, Germany, etc.) showed the lowest genetic diversity, a lower number of unique alleles and a higher percentage of fixed loci than populations from southern Europe. In fact, genetic diversity appeared higher in Southern regions where the first maize populations are thought to have been introduced. Molecular classification based on Rogers' distance (i.e. alleles frequencies) allowed us to distinguish three main clusters which were highly consistent with geographic origins. A Northeastern cluster grouped together early or intermediate populations from Northeastern countries and the Balkans, a southeastern cluster joined late and partially dent populations from Greece and Italy, and, a southwestern cluster was made up of early flint populations from northern Spain, Portugal and the Pyrenees. A correlation between allelic frequencies at some loci and latitude and/or longitude was observed. Such tendencies may reflect the direction of gene flow between different races of maize: for instance, North American (Northern flint) and Caribbean populations were introduced, respectively, to northern and southern Europe, in the past.