Latitudinal allozymic variability in natural populations ofZaprionus indianus from India

Twelve natural populations ofZ. indianus from India, collected along lines of latitude, were analyzed electrophoretically and the geographical pattern of variation was compared at 15 allozyme loci. Except forMdh-2, all the loci revealed extensive polymorphism. The allele frequency variation revealed a statistically significant correlation as well as regression coefficients with the latitude. The populations revealed extensive clinal variation at all the polymorphic loci, which depicted moderate to higherF _ST values. Thus, the observed genetic divergence in colonizing populations ofZ. indianus shows the role of natural selection that varies spatially along the north-south axis of the Indian subcontinent.Financial assistance from UGC, New Delhi, is gratefully acknowledged.     

Variation at the Est3 locus and adaptability to organophosphorous compounds in Zaprionus indianus populations

Carboxylesterases are enzymes often associated with insect resistance to insecticides. The Est3 locus of Zaprionus indianus Gupta (Diptera: Drosophilidae) harbors four alleles that encode carboxylesterases with potentially detoxifying roles. In this study, we propose a model of resistance to insecticides in Z. indianus based on the adaptability of the Est3 locus inferred from the spread of its alleles over 27 generations in experimental populations, and their frequencies in field populations, which were either exposed or unexposed to the organophosphorous insecticide malathion. The increase in the frequency of this allele in experimental populations, and its high prevalence in field populations exposed to organophosphorous insecticides suggest that natural selection favors individuals with the Est3-3 allele. The low frequency of this allele in unexposed field populations, and the low productivity of Est3-3 homozygotes indicate that an adaptive cost is associated with this allele. The existence of a marker locus for insecticide resistance in Z. indianus makes it possible to use this species as a bioindicator for monitoring the excessive use of organophosphorous products and the emergence of resistance, and to devise strategies for the management of agricultural pests.     

Homology of polytene elements between Drosophila and Zaprionus determined by in situ hybridization in Zaprionus indianus

The drosophilid Zaprionus indianus due to its economical importance as an insect pest in Brazil deserves more investigation into its genetics. Its mitotic karyotype and a line-drawing map of its polytene chromosomes are already available. This paper presents a photomap of Z. indianus polytene chromosomes, which was used as the reference map for identification of sections marked by in situ hybridization with gene probes. Hybridization signals for Hsp70 and Hsr-omega were detected, respectively, in sections 34B and 32C of chromosome V of Z. indianus, which indicates its homology to the chromosomal arm 3R of Drosophila melanogaster and, therefore, to Muller's element E. The main signal for Hsp83 gene probe hybridization was in section 17C of Z. indianus chromosome III, suggesting its homology to arm 3L of D. melanogaster and to element D of Muller. The Ubi probe hybridized in sections 10C of chromosome II and 17A of chromosome III. Probably the 17A is the polyubiquitin locus, with homology to arm 3L of D. melanogaster and to the mullerian D element, as suggested also by Hsp83 gene location. The Br-C gene was mapped in section 1D, near the tip of the X chromosome, indicating its homology to the X chromosome of D. melanogaster and to mullerian element A. The Dpp gene probe hybridized mainly in the section 32A of chromosome V and, at lower frequencies to other sections, although no signal was observed as expected in the correspondent mullerian B element. This result led to the suggestion of a rearrangement including the Dpp locus in Z. indianus, the secondary signals possibly pointing to related genes of the TGF-beta family. In conclusion, the results indicate that chromosomes X, III, V of Z. indianus are respectively correspondents to elements A, D, and E of Muller. At least chromosome V of Z. indianus seems to share synteny with the 3R arm of D. melanogaster, as indicated by the relative positions of Hsp70 and Hsr-omega, although the Dpp gene indicates a disruption of synteny in its distal region.     

Allozyme variability in an invasive drosophilid,Zaprionus indianus (Diptera: Drosophilidae): comparison of a recently introduced Brazilian population with Old World populations

Colonizing species often go through genetic bottlenecks when new territories are invaded. The South American continent has been recently colonized by a generalist African drosophilid, Zaprionus indianus, which has become an agricultural pest in Brazil in the last five years. In this paper we used allozyme electrophoresis to estimate levels of genetic differentiation of Z. indianus collected from sites 4 300 km apart in Brazil. We also compared the level of polymorphism of the Brazilian populations with that found in laboratory strains from Africa and Asia, to verify if a significant decrease in gene variability has taken place during the invasion process. The populations were polymorphic for three out of the 11 loci investigated. Genetic distances and F_ST indices among Brazilian populations were small and generally non significant, suggesting a colonization from one single propagule followed by a rapid demographic expansion. Ancestral and old populations from Africa and Asia were slightly more heterozygous than those from Brazil. Compared to other drosophilids, Z. indianus appears to be characterized by a low proportion (25%) of polymorphic loci. We suggest that the propagule introduced to Brazil had a sufficient size to carry almost all the polymorphism from the (unknown) origin population, although not the precise allelic frequencies.     

Population genetics and recent colonization history of the invasive drosophilid Zaprionus indianus in Mexico and Central America

Zaprionus indianus, also known as the African fig fly, is an invasive pest of a variety of commercial and native fruit. The species was first reported in Brazil in 1999, but has established itself in much of the New World within the last 10–15 years. We used nucleotide sequences from a segment of the mitochondrial cytochrome c oxidase subunit I (COI) gene to examine haplotype relationships, population structure, and infer the colonization history of Z. indianus in Mexico and Panama. Construction of a haplotype network showed that six COI haplotypes, obtained from flies collected at six localities in Mexico and one in Panama, clustered into three distinct clades. Clade composition was generally consistent in flies from Panama to northwestern Mexico, and analysis of molecular variance indicated no significant structure among populations. Three of the six haplotypes from Mexico and Panama were identical to previously reported haplotypes from Brazil. None of the six haplotypes, however, were shared with previously reported haplotypes from potential source populations in the Old World. The results of our genetic analysis suggest that the invasion of Z. indianus into Central America and Mexico most probably includes a northward migration of individuals from Brazil, with the possibility of at least one additional introduction of Z. indianus to the New World. Additional sequence data from potential source populations in the Old World will be required to confidently determine the number of introductions of Z. indianus into the New World, and to identify the geographic source.     

Spermatogenesis of Zaprionus indianus and Zaprionus sepsoides (Diptera,Drosophilidae): Cytochemical,structural and ultrastructural characterization

Zaprionus indianus is a drosophilid native to the Afrotropical region that has colonized South America and exhibits a wide geographical distribution. In contrast, Z. sepsoides is restricted to certain African regions. The two species differ in the size of their testes, which are larger in Z. indianus than in Z. sepsoides. To better understand the biology and the degree of differentiation of these species, the current study evaluated spermatogenesis in males of different ages by conventional staining techniques and ultrastructural analysis. Spermatogenesis and the ultrastructure of spermatozoa were similar in the two species, and the diploid number was confirmed to be 2n = 12. A greater number of spermatozoa were observed in young Z. indianus (1–3 days old) compared to Z. sepsoides males, which showed a higher frequency of cells at the early stages of spermatogenesis. The head of the sperm was strongly marked by silver staining, lacto-acetic orcein and the Feulgen reaction; the P.A.S. reaction revealed glycogen granules in the testes of both species. Both species presented similar arrangement of microtubules (9+9+2), two mitochondrial derivatives of different size and 64 spermatozoa per bundle. Such similarity within the genus Zaprionus with other species of Drosophila, indicates that these structures are conserved in the family Drosophilidae. The differences observed the number and frequency of sperm cells in the early stages of spermatogenesis, between the young males of Z. indianus and Z. sepsoides, are features that may interfere with reproductive success and be related to the invasive potential of Z. indianus.     

Scenario of the spread of the invasive species Zaprionus indianus Gupta, 1970 (Diptera, Drosophilidae) in Brazil

Zaprionus indianus was first recorded in Brazil in 1999 and rapidly spread throughout the country. We have obtained data on esterase loci polymorphisms (Est2 and Est3), and analyzed them, using Landscape Shape Interpolation and the Monmonier Maximum Difference Algorithm to discover how regional invasion occurred. Hence, it was apparent that Z. indianus, after first arriving in São Paulo state, spread throughout the country, probably together with the transportation of commercial fruits by way of the two main Brazilian freeways, BR 153, to the south and the surrounding countryside, and the BR 116 along the coast and throughout the north-east.     

Quantitative trait locus mapping in natural populations: progress, caveats and future directions

Over the last 15 years quantitative trait locus (QTL) mapping has become a popular method for understanding the genetic basis of continuous variation in a variety of systems. For example, the technique is now an integral tool in medical genetics, livestock production, plant breeding and population genetics of model organisms. Ten years ago, it was suggested that the method could be used to understand continuous variation in natural populations. In this review I: (i) clarify what is meant by natural population in the QTL context, (ii) discuss whether evolutionary biologists have successfully mapped QTL in natural populations, (iii) highlight some of the questions that have been addressed by QTL mapping in natural populations, (iv) describe how QTL mapping can be conducted in unmanipulated natural populations, (v) highlight some of the limitations of QTL mapping and (vi) try to predict some future directions for QTL mapping in natural populations.     

Quantitative genetic analysis of natural populations

Quantitative genetic studies in natural populations have been rare because they require large breeding programmes or known pedigrees. The relatedness that has been estimated from molecular markers can now be used to substitute for breeding, allowing studies of previously inaccessible species. Many behavioural ecologists have a sufficient number of markers and study species with characteristics that are amenable to this approach. It is now time to combine studies of selection with studies of genetic variation for a more complete understanding of behavioural evolution.     

Drosophila suzukii in Michigan vineyards,and the first report of Zaprionus indianus from this region

Drosophila suzukii is a new invasive pest that in recent years has become established in the Great Lakes region of the United States. Understanding the level of infestation in potentially susceptible crops is an important first step for planning appropriate management responses. This study was conducted in 2010–2012 to determine the infestation potential of this pest in native Vitis labrusca, French hybrid and V. vinifera grape cultivars grown in Michigan vineyards. Drosophila suzukii adults were reared out of collected grape samples in all 3 years, comprising a low proportion of all emerged drosophilids in each of the years. This trend was also found in vacuum sampling, conducted in 2011, with the majority of flies collected being non‐D. suzukii drosophilids. Another recently introduced invasive fly species, Zaprionus indianus, was also reared out of grape samples collected in 2012. While the results of this study indicate no immediate threats to commercial grape production from D. suzukii, further research is needed to elucidate possible secondary effects that this species may have on vineyards, such as the introduction of diseases to the fruit.     

Contrasting levels of genotype by environment interaction for life history and morphological traits in invasive populations of Zaprionus indianus (Diptera: Drosophilidae)

It has been demonstrated that phenotypic plasticity and genotype by environment interaction are important for coping with new and heterogeneous environments during invasions. Zaprionus indianus Gupta (Diptera: Drosophilidae) is an Afrotropical invasive fly species introduced to the South American continent in 1999. This species is generalist and polyphagous, since it develops and feeds in several different fruit species. These characteristics of Z. indianus suggest that phenotypic plasticity and genotype by environment interaction may be important in this species invasion process. In this sense, our aim was to investigate the role of genetic variation for phenotypic plasticity (genotype by environment interaction) in Z. indianus invasion of the South American continent. Specifically, we quantified quantitative genetic variation and genotype by environment interactions of morphological and life history traits in different developmental environments, that is, host fruits. This was done in different populations in the invasive range of Z. indianus in Argentina. Results showed that Z. indianus populations have considerable amounts of quantitative genetic variation. Also, genotype by environment interactions was detected for the different traits analyzed in response to the different developmental environments. Interestingly, the amounts and patterns of these parameters differed between populations. We interpreted these results as the existence of differences in evolutionary potential between populations that have an important role in the short‐ and long‐term success of the Z. indianus invasion process.     

Characterization of mitochondrial control region, two intergenic spacers and tRNAs of Zaprionus indianus (Diptera: Drosophilidae)

Total synaptonemal complex (SC) lengths were estimated from Oreochromis aureus Steindachner (which has a WZ/ZZ sex determination system), O. mossambicus Peters and O. niloticus L. (both of which have XX/XY sex determination systems). The total SC length in oocytes was greater than that in spermatocytes in all three species (194 ± 30 μm and 134 ± 13 μm, 187 ± 22 μm and 127 ± 17 μm, 193 ± 37 μm and 144 ± 19 μm, respectively). These sex-specific differences did not appear to be influenced by the type of sex determination system (the female/male total SC length ratio was 1.45 in O. aureus, 1.47 in O. mossambicus and 1.34 in O. niloticus) and do not correlate with the lack of any overall sex-specific length differences in the current Oreochromis linkage map. Although based on data from relatively few species, there appears to be no consistent relationship between sex-specific SC lengths and linkage map lengths in fish. Neomale (hormonally masculinized genetic female) O. aureus and O. mossambicus had total SC lengths of 138 ± 13 μm and 146 ± 13 μm respectively, more similar to normal males than to normal females. These findings agree with data from other vertebrate species that suggest that phenotypic sex, rather than genotype, determines traits such as total SC length, chiasmata position and recombination pattern, at least for the autosomes.     

The genetics of a putative social trait in natural populations of yeast

The sharing of secreted invertase by yeast cells is a well‐established laboratory model for cooperation, but the only evidence that such cooperation occurs in nature is that the SUC loci, which encode invertase, vary in number and functionality. Genotypes that do not produce invertase can act as ‘cheats’ in laboratory experiments, growing on the glucose that is released when invertase producers, or ‘cooperators’, digest sucrose. However, genetic variation for invertase production might instead be explained by adaptation of different populations to different local availabilities of sucrose, the substrate for invertase. Here we find that 110 wild yeast strains isolated from natural habitats, and all contained a single SUC locus and produced invertase; none were ‘cheats’. The only genetic variants we found were three strains isolated instead from sucrose‐rich nectar, which produced higher levels of invertase from three additional SUC loci at their subtelomeres. We argue that the pattern of SUC gene variation is better explained by local adaptation than by social conflict.     

Bud set in poplar--genetic dissection of a complex trait in natural and hybrid populations

? The seasonal timing of growth events is crucial to tree distribution and conservation. The seasonal growth cycle is strongly adapted to the local climate that is changing because of global warming. We studied bud set as one cornerstone of the seasonal growth cycle in an integrative approach. ? Bud set was dissected at the phenotypic level into several components, and phenotypic components with most genetic variation were identified. While phenotypic variation resided in the timing of growth cessation, and even so more in the duration from growth cessation to bud set, the timing of growth cessation had a stronger genetic component in both natural and hybrid populations. ? Quantitative trait loci (QTL) were identified for the most discriminative phenotypic bud-set components across four poplar pedigrees. The QTL from different pedigrees were recurrently detected in six regions of the poplar genome. ? These regions of 1.83-4.25 Mbp in size, containing between 202 and 394 genes, form the basis for further molecular-genetic dissection of bud set.     

Inferring linkage disequilibrium between a polymorphic marker locus and a trait locus in natural populations

Three approaches are proposed in this study for detecting or estimating linkage disequilibrium between a polymorphic marker locus and a locus affecting quantitative genetic variation using the sample from random mating populations. It is shown that the disequilibrium over a wide range of circumstances may be detected with a power of 80% by using phenotypic records and marker genotypes of a few hundred individuals. Comparison of ANOVA and regression methods in this article to the transmission disequilibrium test (TDT) shows that, given the genetic variance explained by the trait locus, the power of TDT depends on the trait allele frequency, whereas the power of ANOVA and regression analyses is relatively independent from the allelic frequency. The TDT method is more powerful when the trait allele frequency is low, but much less powerful when it is high. The likelihood analysis provides reliable estimation of the model parameters when the QTL variance is at least 10% of the phenotypic variance and the sample size of a few hundred is used. Potential use of these estimates in mapping the trait locus is also discussed.     

Cytogenetics of Zaprionus indianus Gupta (Diptera: Drosophilidae): Nucleolar organizer regions,mitotic and polytene chromosomes and inversion polymorphism

Zaprionus indianus, a member of the family Drosophilidae, is one of the commonest and most widespread species in India. It exploits a variety of fermenting fruits in nature. The nucleolar organizer regions (NORs), mitotic and polytene chromosomes were studied. A standard map of the polytene chromosomes has been constructed in order to locate break-points precisely for naturally occurring chromosomal rearrangements. Analysis of population samples of this species from four different geographical areas has revealed the presence of a single paracentric inversion in the second chromosome. Our quantitative data on the above inversion have confirmed the excess of inversion heterozygotes in nature.     

Variability of Wing Size and Shape in Three Populations of a Recent Brazilian Invader, Zaprionus indianus (Diptera: Drosophilidae), from Different Habitats

Zaprionus indianus (Diptera: Drosophilidae) is an African species that was introduced in Brazil near the end of the 1990’s decade. To evaluate the adaptive potential of morphological traits in natural populations of this recently introduced species, we have investigated wing size and shape variation at Rio de Janeiro populations only two years after the first record of Z. indianus in Brazil. Significant genetic differences among populations from three distinct ecological habitats were detected. The heritability and evolvability estimates show that, even with the population bottleneck that should have occurred during the invasion event, an appreciable amount of additive genetic variation for wing size and shape was retained. Our results also indicated a greater influence of environmental variation on wing size than on wing shape. The importance of quantitative genetic variability and plasticity in the successful establishment and dispersal of Z. indianus in the Brazilian territory is then discussed.     

Quantitative trait loci for production traits in pigs: a combined analysis of two Meishan x Large White populations

Combined analysis of data from two or more resource populations can improve the power and accuracy of QTL mapping and allow some cross-validation of results. In this study, we performed a genome-wide scan using combined data from two F(2) populations derived from a cross between Large White and Chinese Meishan pigs. A total of 739 pigs were included in the analysis. In total 187 markers were genotyped in the two populations, including 115 markers genotyped in both populations, and these markers covered 2282 cM of the pig genome with an average of 13.58 cM between markers. Seven traits (teat number, birth weight, weaning weight, test-end weight, fat depth at shoulder, fat depth at mid back and fat depth at loin) were analysed for both individual populations and the combined population. There were 9 (2, 10), 1 (4, 4) and 14 (5, 18) QTL that achieved 1% genome-wide, 5% genome-wide and suggestive significance levels respectively in population 1 (population 2, combined population). Additive effects of QTL detected in the two populations at all significance levels were largely consistent suggesting that the QTL represent real genetic effects, but this was not the case for dominance or imprinting effects. There were also a number of significant interactions between detected QTL effects and population.