Heredity

Pleiotropy and eye degeneration in cavefish.

Publication Date: 2010 Feb 24 PMID: 20179737
Authors: Jeffery, W. R.
Journal: Heredity

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Environmental epigenetics.

Publication Date: 2010 Feb 24 PMID: 20179736
Authors: Bollati, V. - Baccarelli, A.
Journal: Heredity

Epigenetics investigates heritable changes in gene expression that occur without changes in DNA sequence. Several epigenetic mechanisms, including DNA methylation and histone modifications, can change genome function under exogenous influence. We review current evidence indicating that epigenetic alterations mediate effects caused by exposure to environmental toxicants. Results obtained from animal models indicate that in utero or early-life environmental exposures produce effects that can be inherited transgenerationally and are accompanied by epigenetic alterations. The search for human equivalents of the epigenetic mechanisms identified in animal models is under way. Recent investigations have identified a number of environmental toxicants that cause altered methylation of human repetitive elements or genes. Some exposures can alter epigenetic states and the same and/or similar epigenetic alterations can be found in patients with the disease of concern. On the basis of current evidence, we propose possible models for the interplay between environmental exposures and the human epigenome. Several investigations have examined the relationship between exposure to environmental chemicals and epigenetics, and have identified toxicants that modify epigenetic states. Whether environmental exposures have transgenerational epigenetic effects in humans remains to be elucidated. In spite of the current limitations, available evidence supports the concept that epigenetics holds substantial potential for furthering our understanding of the molecular mechanisms of environmental toxicants, as well as for predicting health-related risks due to conditions of environmental exposure and individual susceptibility.Heredity advance online publication, 24 February 2010; doi:10.1038/hdy.2010.2.

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Artificial selection of the melanocortin receptor 1 gene in Chinese domestic pigs during domestication.

Publication Date: 2010 Feb 24 PMID: 20179735
Authors: Li, J. - Yang, H. - Li, J. R. - Li, H. P. - Ning, T. - Pan, X. R. - Shi, P. - Zhang, Y. P.
Journal: Heredity

Black coat colour is common in Chinese indigenous domestic pigs, but not among their wild ancestors, and it is thus presumed to be a 'domestication trait.' To determine whether artificial interference contributes to morphological diversification, we examined nucleotide variation from 157 Chinese domestic pigs and 40 wild boars in the melanocortin receptor 1 (MC1R) gene, which has a key role in the coat pigmentation of Sus scrofa. Compared with a pseudogene GPIP, our results showed that the joint effects of demography and selection have resulted in markedly low genetic diversity of MC1R in Chinese domestic pigs. Coalescent simulation and selection tests further suggest that the fixation of two non-synonymous substitutions associated with black colour is the result of artificial selection. In contrast, a much higher genetic diversity and only a single non-synonymous substitution were found among the wild boars, suggesting a strong functional constraint. Moreover, our conclusion is consistent with the preference for black colour in the ancient Chinese sacrificial culture. This case provides an interesting example of a molecular evaluation of artificial livestock selection and its associated cultural impact in ancient China.Heredity advance online publication, 24 February 2010; doi:10.1038/hdy.2009.191.

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Epigenetic regulatory mechanisms in vertebrate eye development and disease.

Publication Date: 2010 Feb 24 PMID: 20179734
Authors: Cvekl, A. - Mitton, K. P.
Journal: Heredity

Eukaryotic DNA is organized as a nucleoprotein polymer termed chromatin with nucleosomes serving as its repetitive architectural units. Cellular differentiation is a dynamic process driven by activation and repression of specific sets of genes, partitioning the genome into transcriptionally active and inactive chromatin domains. Chromatin architecture at individual genes/loci may remain stable through cell divisions, from a single mother cell to its progeny during mitosis, and represents an example of epigenetic phenomena. Epigenetics refers to heritable changes caused by mechanisms distinct from the primary DNA sequence. Recent studies have shown a number of links between chromatin structure, gene expression, extracellular signaling, and cellular differentiation during eye development. This review summarizes recent advances in this field, and the relationship between sequence-specific DNA-binding transcription factors and their roles in recruitment of chromatin remodeling enzymes. In addition, lens and retinal differentiation is accompanied by specific changes in the nucleolar organization, expression of non-coding RNAs, and DNA methylation. Epigenetic regulatory mechanisms in ocular tissues represent exciting areas of research that have opened new avenues for understanding normal eye development, inherited eye diseases and eye diseases related to aging and the environment.Heredity advance online publication, 24 February 2010; doi:10.1038/hdy.2010.16.

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Genetic differentiation of eastern wolves in Algonquin Park despite bridging gene flow between coyotes and grey wolves.

Publication Date: 2010 Feb 17 PMID: 20160760
Authors: Rutledge, L. Y. - Garroway, C. J. - Loveless, K. M. - Patterson, B. R.
Journal: Heredity

Distinguishing genetically differentiated populations within hybrid zones and determining the mechanisms by which introgression occurs are crucial for setting effective conservation policy. Extensive hybridization among grey wolves (Canis lupus), eastern wolves (C. lycaon) and coyotes (C. latrans) in eastern North America has blurred species distinctions, creating a Canis hybrid swarm. Using complementary genetic markers, we tested the hypotheses that eastern wolves have acted as a conduit of sex-biased gene flow between grey wolves and coyotes, and that eastern wolves in Algonquin Provincial Park (APP) have differentiated following a history of introgression. Mitochondrial, Y chromosome and autosomal microsatellite genetic data provided genotypes for 217 canids from three geographic regions in Ontario, Canada: northeastern Ontario, APP and southern Ontario. Coyote mitochondrial DNA (mtDNA) haplotypes were common across regions but coyote-specific Y chromosome haplotypes were absent; grey wolf mtDNA was absent from southern regions, whereas grey wolf Y chromosome haplotypes were present in all three regions. Genetic structuring analyses revealed three distinct clusters within a genetic cline, suggesting some gene flow among species. In APP, however, 78.4% of all breeders and 11 of 15 known breeding pairs had assignment probability of Q>/=0.8 to the Algonquin cluster, and the proportion of eastern wolf Y chromosome haplotypes in APP breeding males was higher than expected from random mating within the park (P<0.02). The data indicate that Algonquin wolves remain genetically distinct despite providing a sex-biased genetic bridge between coyotes and grey wolves. We speculate that ongoing hybridization within the park is limited by pre-mating reproductive barriers.Heredity advance online publication, 17 February 2010; doi:10.1038/hdy.2010.6.

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The B in 'BDM.' William Bateson did not advocate a genic speciation theory.

Publication Date: 2010 Feb 17 PMID: 20160759
Authors: Forsdyke, D. R.
Journal: Heredity

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Population structure and historical biogeography of European Arabidopsis lyrata.

Publication Date: 2010 Feb 17 PMID: 20160758
Authors: Ansell, S. W. - Stenoien, H. K. - Grundmann, M. - Schneider, H. - Hemp, A. - Bauer, N. - Russell, S. J. - Vogel, J. C.
Journal: Heredity

Understanding the natural history of model organisms is important for the effective use of their genomic resourses. Arabidopsis lyrata has emerged as a useful plant for studying ecological and evolutionary genetics, based on its extensive natural variation, sequenced genome and close relationship to A. thaliana. We studied genetic diversity across the entire range of European Arabidopsis lyrata ssp. petraea, in order to explore how population history has influenced population structure. We sampled multiple populations from each region, using nuclear and chloroplast genome markers, and combined population genetic and phylogeographic approaches. Within-population diversity is substantial for nuclear allozyme markers (mean P=0.610, A(e)=1.580, H(e)=0.277) and significantly partitioned among populations (F(ST)=0.271). The Northern populations have modestly increased inbreeding (F(IS)=0.163 verses F(IS)=0.093), but retain comparable diversity to central European populations. Bottlenecks are common among central and northern Europe populations, indicating recent demographic history as a dominant factor in structuring the European diversity. Although the genetic structure was detected at all geographic scales, two clear differentiated units covering northern and central European areas (F(CT) =0.155) were identified by Bayesian analysis and supported by regional pairwise F(CT) calculations. A highly similar geographic pattern was observed from the distribution of chloroplast haplotypes, with the dominant northern haplotypes absent from central Europe. We conclude A. l. petraea's cold-tolerance and preference for disturbed habitats enabled glacial survival between the alpine and Nordic glaciers in central Europe and an additional cryptic refugium. While German populations are probable peri-glacial leftovers, Eastern Austrian populations have diversity patterns possibly compatible with longer-term survival.Heredity advance online publication, 17 February 2010; doi:10.1038/hdy.2010.10.

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Gene copy number evolution during tetraploid cotton radiation.

Publication Date: 2010 Feb 17 PMID: 20160757
Authors: Rong, J. - Feltus, F. A. - Liu, L. - Lin, L. - Paterson, A. H.
Journal: Heredity

After polyploid formation, retention or loss of duplicated genes is not random. Genes with some functional domains are convergently restored to 'singleton' state after many independent genome duplications, and have been referred to as 'duplication-resistant' (DR) genes. To further explore the timeframe for their restoration to the singleton state, 27 cotton homologs of genes found to be 'DR' in Arabidopsis were selected based on diagnostic Pfam domains. Their copy numbers were studied using southern hybridization and sequence analysis in five tetraploid species and their ancestral A and D genome diploids. DR genes had significantly lower copy number than gene families hybridizing to randomly selected cotton ESTs. Three DR genes showed complete loss of D genome-derived homoeologs in some or all tetraploid species. Prior analysis has shown gene loss in polyploid cotton to be rare, and herein only one randomly selected gene showed loss of a homoeolog in only one of the five tetraploid species (Gossypium mustelinum). BAC sequencing confirmed two cases of gene loss in tetraploid cotton. Divergence among 5' sequences of DR genes amplified from G. arboreum, G. raimondii, and Gossypioides kirkii was correlated with gene copy number. These results show that genes containing Pfam domains associated with duplication resistance in Arabidopsis have also been preferentially restored to low copy number after a more recent polyploidization event in cotton. In tetraploid cotton, genes from the progenitor D genome seem to experience more gene copy number divergence than genes from the A genome. Together with D subgenome-biased alterations in gene expression, perhaps gene loss may contribute to the relatively larger portion of quantitative trait variation attributable to D than A subgenome chromosomes of tetraploid cotton.Heredity advance online publication, 17 February 2010; doi:10.1038/hdy.2009.192.

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Don't forget the ancestral polymorphisms.

Publication Date: 2010 Feb 17 PMID: 20160756
Authors: Charlesworth, D.
Journal: Heredity

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Nasonia: a jewel among wasps.

Publication Date: 2010 Mar PMID: 20160755
Authors: Godfray, H. C.
Journal: Heredity

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Expression quantitative trait loci analysis of genes in porcine muscle by quantitative real-time RT-PCR compared to microarray data.

Publication Date: 2010 Feb 10 PMID: 20145673
Authors: Ponsuksili, S. - Murani, E. - Phatsara, C. - Schwerin, M. - Schellander, K. - Wimmers, K.
Journal: Heredity

Genetic analysis of transcriptional profiling is a promising approach for identifying biological pathways and dissecting the genetics of complex traits. Here, we report on expression quantitative trait loci (eQTL) that were estimated from the quantitative real-time RT-PCR data of 276 F(2) animals and compared with eQTL identified using 74 microarrays. In total, 13 genes were selected that showed trait-dependent expression in microarray experiments and exhibited 21 eQTL. Real-time RT-PCR and microarray data revealed seven cis eQTL in total, of which one was only detected by real-time RT-PCR, one was only detected by microarray analysis, three were consistently found in overlapping intervals and two were in neighbouring intervals on the same chromosome; whereas no trans eQTL was confirmed. We demonstrate that cis regulation is a stable characteristic of individual transcripts. Consequently, a global microarray eQTL analysis of a limited number of samples can be used for exploring functional and regulatory gene networks and scanning for cis eQTL, whereas the subsequent analysis of a subset of likely cis-regulated genes by real-time RT-PCR in a larger number of samples is relevant to narrow down a QTL region by targeting these positional candidate genes. In fact, when modelling SNPs of six genes as fixed effects in the eQTL analysis, eQTL peaks were shifted downwards, experimentally confirming the impact of the respective polymorphic genes, although these SNPs were not located in the regulatory sequence and these shifts occur as a result of linkage disequilibrium in the F(2) population.Heredity advance online publication, 10 February 2010; doi:10.1038/hdy.2010.5.

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Bateman (1948): pioneer in the measurement of sexual selection.

Publication Date: 2010 Feb 10 PMID: 20145672
Authors: Wade, M. J. - Shuster, S. M.
Journal: Heredity

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Genetic basis of incidence and period length of circadian rhythm for locomotor activity in populations of a seed beetle.

Publication Date: 2010 Feb 10 PMID: 20145671
Authors: Harano, T. - Miyatake, T.
Journal: Heredity

Circadian rhythms are ubiquitous in a wide variety of organisms, although their genetic variation has been analyzed in only a few species. We found genetic differences in the circadian rhythm of adult locomotor activity among strains of the adzuki bean beetle, Callosobruchus chinensis, which differed in origin and have been maintained in isolation. All beetles in some strains clearly had free-running rhythms in constant darkness whereas most beetles in other strains were arrhythmic. The period of free-running rhythm varied from approximately 19 to 23 h between the strains. F(1) males from reciprocal crosses among strains with different periods of circadian rhythms had circadian periods that were intermediate between their parental strains. Segregation of the circadian rhythm appeared in the F(2) generation. These findings are consistent with the hypothesis that variation in the period length of circadian rhythm is explained by a major autosomal gene with additive effects and no dominance. This hypothesis was supported by the joint scaling test for the free-running period in the F(1) and F(2) generations. We discuss possible causes for genetic variation in circadian rhythm in the C. chinensis strains in terms of random factors and selection.Heredity advance online publication, 10 February 2010; doi:10.1038/hdy.2010.4.

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Heritable artificial sex chromosomes in medaka: a leap towards real-time observation of sex chromosome evolution.

Publication Date: 2010 Feb 10 PMID: 20145670
Authors: Lawson Handley, L. J.
Journal: Heredity

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Variation explained in mixed-model association mapping.

Publication Date: 2010 Feb 10 PMID: 20145669
Authors: Sun, G. - Zhu, C. - Kramer, M. H. - Yang, S. S. - Song, W. - Piepho, H. P. - Yu, J.
Journal: Heredity

Genomic mapping of complex traits across species demands integrating genetics and statistics. In particular, because it is easily interpreted, the R(2) statistic is commonly used in quantitative trait locus (QTL) mapping studies to measure the proportion of phenotypic variation explained by molecular markers. Mixed models with random polygenic effects have been used in complex trait dissection in different species. However, unlike fixed linear regression models, linear mixed models have no well-established R(2) statistic for assessing goodness-of-fit and prediction power. Our objectives were to assess the performance of several R(2)-like statistics for a linear mixed model in association mapping and to identify any such statistic that measures model-data agreement and provides an intuitive indication of QTL effect. Our results showed that the likelihood-ratio-based R(2) (R(LR)(2)) satisfies several critical requirements proposed for the R(2)-like statistic. As R(LR)(2) reduces to the regular R(2) for fixed models without random effects other than residual, it provides a general measure for the effect of QTL in mixed-model association mapping. Moreover, we found that R(LR)(2) can help explain the overlap between overall population structure modeled as fixed effects and relative kinship modeled though random effects. As both approaches are derived from molecular marker information and are not mutually exclusive, comparing R(LR)(2) values from different models provides a logical bridge between statistical analysis and underlying genetics of complex traits.Heredity advance online publication, 10 February 2010; doi:10.1038/hdy.2010.11.

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Mito-nuclear discordance in the degree of population differentiation in a marine goby.

Publication Date: 2010 Feb 10 PMID: 20145668
Authors: Larmuseau, M. H. - Raeymaekers, J. A. - Hellemans, B. - Van Houdt, J. K. - Volckaert, F. A.
Journal: Heredity

An increasing number of phylogeographic studies on marine species shows discordant patterns in the degree of population differentiation between nuclear and mitochondrial markers. To understand better which factors have the potential to cause these patterns of discordance in marine organisms, a population genetic study was realized on the sand goby Pomatoschistus minutus (Pallas 1770; Gobiidae, Teleostei). Sand gobies from eight European locations were genotyped at eight microsatellite markers. Microsatellites confirmed the global phylogeographical pattern of P. minutus observed with mitochondrial DNA (mtDNA) markers and nuclear allozyme markers. Three groups consistent with the mitochondrial lineages were defined (the Mediterranean, Iberian and North Atlantic groups) and indications of a recent founder event in the northern Baltic Sea were found. Nevertheless, differences in the degree of population differentiation between the nuclear and mitochondrial markers were large (global F(ST)-values for microsatellites=0.0121; for allozymes=0.00831; for mtDNA=0.4293). Selection, sex-biased dispersal, homoplasy and a high effective population size are generally accepted as explanations for this mitonuclear discrepancy in the degree of population differentiation. In this study, selection on mtDNA and microsatellites, male-biased dispersal and homoplasy on microsatellite markers are unlikely to be a main cause for this discrepancy. The most likely reason for the discordant pattern is a recent demographical expansion of the sand goby, resulting in high effective population sizes slowing down the differentiation of nuclear DNA.Heredity advance online publication, 10 February 2010; doi:10.1038/hdy.2010.9.

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Phylogeography of Nasonia vitripennis (Hymenoptera) indicates a mitochondrial-Wolbachia sweep in North America.

Publication Date: 2010 Mar PMID: 20087396
Authors: Raychoudhury, R. - Grillenberger, B. K. - Gadau, J. - Bijlsma, R. - van de Zande, L. - Werren, J. H. - Beukeboom, L. W.
Journal: Heredity

Here we report evidence of a mitochondrial-Wolbachia sweep in North American populations of the parasitoid wasp Nasonia vitripennis, a cosmopolitan species and emerging model organism for evolutionary and genetic studies. Analysis of the genetic variation of 89 N. vitripennis specimens from Europe and North America was performed using four types of genetic markers: a portion of the mitochondrial cytochrome oxidase I gene, nine polymorphic nuclear microsatellites, sequences from 11 single-copy nuclear markers and six Wolbachia genes. The results show that the European populations have a sevenfold higher mitochondrial sequence variation than North American populations, but similar levels of microsatellite and nuclear gene sequence variation. Variation in the North American mitochondria is extremely low (pi=0.31%), despite a highly elevated mutation rate (approximately 35-40 times higher than the nuclear genes) in the mitochondria of Nasonia. The data are indicative of a mitochondrial sweep in the North American population, possibly due to Wolbachia infections that are maternally co-inherited with the mitochondria. Owing to similar levels of nuclear variation, the data could not resolve whether N. vitripennis originated in the New or the Old World.

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Behavioral and spermatogenic hybrid male breakdown in Nasonia.

Publication Date: 2010 Mar PMID: 20087395
Authors: Clark, M. E. - O'Hara, F. P. - Chawla, A. - Werren, J. H.
Journal: Heredity

Several reproductive barriers exist within the Nasonia species complex, including allopatry, premating behavioral isolation, postzygotic inviability and Wolbachia-induced cytoplasmic incompatibility. Here we show that hybrid males suffer two additional reproductive disadvantages, an inability to properly court females and decreased sperm production. Hybrid behavioral sterility, characterized by a reduced ability of hybrids to perform necessary courtship behaviors, occurs in hybrids between two species of Nasonia. Hybrid males produced in crosses between N. vitripennis and N. giraulti courted females at a reduced frequency (23-69%), compared with wild-type N. vitripennis and N. giraulti males (>93%). Reduced courtship frequency was not a simple function of inactivity among hybrids. A strong effect of cytoplasmic (mitochondrial) background was also found in N. vitripennis and N. giraulti crosses; F2 hybrids with giraulti cytoplasm showing reduced ability at most stages of courtship. Hybrids produced between a younger species pair, N. giraulti and N. longicornis, were behaviorally fertile. All males possessed motile sperm, but sperm production is greatly reduced in hybrids between the older species pair, N. vitripennis and N. giraulti. This effect on hybrid males, lowered sperm counts rather than nonfunctional sperm, is different from most described cases of hybrid male sterility, and may represent an earlier stage of hybrid sperm breakdown. The results add to previous studies of F2 hybrid inviability and behavioral sterility, and indicate that Wolbachia-induced hybrid incompatibility has arisen early in species divergence, relative to behavioral sterility and spermatogenic infertility.

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Behavioral and genetic characteristics of a new species of Nasonia.

Publication Date: 2010 Mar PMID: 20087394
Authors: Raychoudhury, R. - Desjardins, C. A. - Buellesbach, J. - Loehlin, D. W. - Grillenberger, B. K. - Beukeboom, L. - Schmitt, T. - Werren, J. H.
Journal: Heredity

Nasonia (Hymenoptera: Pteromalidae) is a genus of parasitoid wasps, which is fast emerging as a model system for evolutionary, genetic, developmental and host-endosymbiont interaction studies. In this study, we report a new species, Nasonia oneida, distinguish its behavioral, genetic and morphological features, and characterize its pre-mating and post-mating isolation with the other Nasonia species. Phylogenetic analyses indicate that N. oneida is the sister species to Nasonia giraulti with its own uniquely distinct cuticular hydrocarbon profiles, behavioral characteristics and subtle morphological differences. An important characteristic of N. oneida is the strong mate discrimination shown by the females against all the other Nasonia species. A genetic analysis of this phenotype by interspecies hybridization indicates that this strong discriminating phenotype is recessive. A formal species description of N. oneida Raychoudhury & Desjardins is also provided.

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The genetic basis of interspecies host preference differences in the model parasitoid Nasonia.

Publication Date: 2010 Mar PMID: 20087393
Authors: Desjardins, C. A. - Perfectti, F. - Bartos, J. D. - Enders, L. S. - Werren, J. H.
Journal: Heredity

The genetic basis of host preference has been investigated in only a few species. It is relevant to important questions in evolutionary biology, including sympatric speciation, generalist versus specialist adaptation, and parasite-host co-evolution. Here we show that a major locus strongly influences host preference in Nasonia. Nasonia are parasitic wasps that utilize fly pupae; Nasonia vitripennis is a generalist that parasitizes a diverse set of hosts, whereas Nasonia giraulti specializes in Protocalliphora (bird blowflies). In laboratory choice experiments using Protocalliphora and Sarcophaga (flesh flies), N. vitripennis shows a preference for Sarcophaga, whereas N. giraulti shows a preference for Protocalliphora. Through a series of interspecies crosses, we have introgressed a major locus affecting host preference from N. giraulti into N. vitripennis. The N. giraulti allele is dominant and greatly increases preference for Protocalliphora pupae in the introgression line relative to the recessive N. vitripennis allele. Through the utilization of a Nasonia genotyping microarray, we have identified the introgressed region as 16 Mb of chromosome 4, although a more complete analysis is necessary to determine the exact genetic architecture of host preference in the genus. To our knowledge, this is the first introgression of the host preference of one parasitoid species into another, as well as one of the few cases of introgression of a behavioral gene between species.

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The cys-loop ligand-gated ion channel gene superfamily of the parasitoid wasp, Nasonia vitripennis.

Publication Date: 2010 Mar PMID: 20087392
Authors: Jones, A. K. - Bera, A. N. - Lees, K. - Sattelle, D. B.
Journal: Heredity

Members of the cys-loop ligand-gated ion channel (cysLGIC) superfamily mediate chemical neurotransmission and are studied extensively as potential targets of drugs used to treat neurological disorders, such as Alzheimer's disease. Insect cys-loop LGICs also have central roles in the nervous system and are targets of highly successful insecticides. Here, we describe the cysLGIC superfamily of the parasitoid wasp, Nasonia vitripennis, which is emerging as a highly useful model organism and is deployed as a biological control of insect pests. The wasp superfamily consists of 26 genes, which is the largest insect cysLGIC superfamily characterized, whereas Drosophila melanogaster, Apis mellifera and Tribolium castaneum have 23, 21 and 24, respectively. As with Apis, Drosophila and Tribolium, Nasonia possesses ion channels predicted to be gated by acetylcholine, gamma-amino butyric acid, glutamate and histamine, as well as orthologues of the Drosophila pH-sensitive chloride channel (pHCl), CG8916 and CG12344. Similar to other insects, wasp cysLGIC diversity is broadened by alternative splicing and RNA A-to-I editing, which may also serve to generate species-specific receptor isoforms. These findings on N. vitripennis enhance our understanding of cysLGIC functional genomics and provide a useful basis for the study of their function in the wasp model, as well as for the development of improved insecticides that spare a major beneficial insect species.

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Contrasting patterns of selective constraints in nuclear-encoded genes of the oxidative phosphorylation pathway in holometabolous insects and their possible role in hybrid breakdown in Nasonia.

Publication Date: 2010 Mar PMID: 20087391
Authors: Gibson, J. D. - Niehuis, O. - Verrelli, B. C. - Gadau, J.
Journal: Heredity

The principal energy generating system in animals is the oxidative phosphorylation (OXPHOS) pathway, which depends on the tight interaction of nuclear- and mitochondrial-encoded genes to function properly. Mitochondrial genes accumulate substitutions more quickly than nuclear genes, yet the impact of selection on mitochondrial genes is significantly reduced relative to nuclear genes because of the non-recombining nature of the mitochondrial genome and its predicted smaller effective population size. It has therefore been hypothesized that the nuclear-encoded genes of the OXPHOS pathway are under strong selective pressure to compensate for the accumulation of deleterious nucleotide substitutions in mitochondrial-encoded OXPHOS genes, a process known as compensatory co-adaptation. We evaluated this hypothesis by analyzing nuclear-encoded OXPHOS genes for signatures of positive selection as well as evolutionary constraints at amino acid sites. We considered OXPHOS genes of six holometabolous insects and their orthologs from three Nasonia parasitoid wasps, the hybrids of which suffer from an increased mortality rate caused by cytonuclear genic incompatibilities. Although nuclear OXPHOS genes are typically highly conserved, we found significant evidence for elevated amino acid divergence in 4 of the 59 studied nuclear-encoded OXPHOS genes. We also found that three of these four genes, as well as six other OXPHOS genes, contain amino acid substitutions between Nasonia species at evolutionarily constrained sites. It is possible that these genes account for the reported incompatibility in Nasonia hybrids and their characterization may lead to a better understanding of the role of positive selection in the genetics of speciation.

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Evolution of sex-specific wing shape at the widerwing locus in four species of Nasonia.

Publication Date: 2010 Mar PMID: 20087390
Authors: Loehlin, D. W. - Enders, L. S. - Werren, J. H.
Journal: Heredity

How do morphological differences between species evolve at the genetic level? This study investigates the genetic basis of recent divergence in male wing size between species of the model parasitoid wasp Nasonia. The forewings of flightless Nasonia vitripennis males are 2.3 times smaller than males of their flighted sister species N. giraulti. We describe a major genetic contributor to this difference: the sex-specific widerwing (wdw) locus, which we have backcrossed from N. giraulti into N. vitripennis and mapped to an 0.9 megabase region of chromosome 1. This introgression of wdw from large-winged N. giraulti into small-winged N. vitripennis increases male but not female forewing width by 30% through wing region-specific size changes. Indirect evidence suggests that cell number changes across the wing explain the majority of the wdw wing-size difference, whereas changes in cell size are important in the center of the wing. Introgressing the same locus from the other species in the genus, N. longicornis and N. oneida, into N. vitripennis produces intermediate and large male wing sizes. To our knowledge, this is the first study to introgress a morphological quantitative trait locus (QTL) from multiple species into a common genetic background. Epistatic interactions between wdw and other QTL are also identified by introgressing wdw from N. vitripennis into N. giraulti. The main findings are (1) the changes at wdw have sex- and region-specific effects and could, therefore, be regulatory, (2) the wdw locus seems to be a co-regulator of cell size and cell number, and (3) the wdw locus has evolved different wing width effects in three species.

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A comparison of recombination frequencies in intraspecific versus interspecific mapping populations of Nasonia.

Publication Date: 2010 Mar PMID: 20087389
Authors: Beukeboom, L. W. - Niehuis, O. - Pannebakker, B. A. - Koevoets, T. - Gibson, J. D. - Shuker, D. M. - van de Zande, L. - Gadau, J.
Journal: Heredity

We present the first intraspecific linkage map for Nasonia vitripennis based on molecular markers. The map consists of 36 new microsatellite markers, extracted from the Nasonia genome sequence, and spans 515 cM. The five inferred linkage groups correspond to the five chromosomes of Nasonia. Comparison of recombination frequencies of the marker intervals spread over the whole genome (N=33 marker intervals) between the intraspecific N. vitripennis map and an interspecific N. vitripennis x N. giraulti map revealed a slightly higher (1.8%) recombination frequency in the intraspecific cross. We further considered an N. vitripennis x N. longicornis map with 29 microsatellite markers spanning 430 cM. Recombination frequencies in the two interspecific crosses differed neither between reciprocal crosses nor between mapping populations of embryos and adults. No major chromosomal rearrangements were found for the analyzed genomic segments. The observed differential F(2) hybrid male mortality has no significant effect on the genome-wide recombination frequency in Nasonia. We conclude that interspecific crosses between the different Nasonia species, a hallmark of Nasonia genetics, are generally suitable for mapping quantitative and qualitative trait loci for species differences.

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An insect-endosymbiont conundrum.

Publication Date: 2010 Mar PMID: 19862011
Authors: Godfray, H. C.
Journal: Heredity

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Population dynamics and rapid spread of Cardinium, a bacterial endosymbiont causing cytoplasmic incompatibility in Encarsia pergandiella (Hymenoptera: Aphelinidae).

Publication Date: 2010 Mar PMID: 19812617
Authors: Harris, L. R. - Kelly, S. E. - Hunter, M. S. - Perlman, S. J.
Journal: Heredity

Cytoplasmic incompatibility (CI) is a common phenotype of maternally inherited bacterial symbionts of arthropods; in its simplest expression, uninfected females produce few or no viable progeny when mated to infected males. Infected females thus experience a reproductive advantage relative to that of uninfected females, with the potential for the symbiont to spread rapidly. CI population dynamics are predicted to depend primarily on the strength of incompatibility, the fitness cost of the infection and how faithfully symbionts are inherited. Although the bacterial symbiont lineage Wolbachia has been most identified with the CI phenotype, an unrelated bacterium, Cardinium may also cause CI. In the first examination of population dynamics of CI-inducing Cardinium, we used population cages of the parasitic wasp Encarsia pergandiella (Hymenoptera: Aphelinidae) with varying initial infection frequencies to test a model of invasion. Cardinium was found to spread rapidly in all populations, even in cases where the initial infection frequency was well below the predicted invasion threshold frequency. The discrepancy between the modeled and actual results is best explained by weaker CI than measured in the lab and a cryptic fitness benefit to the infection.

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