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Litter size is an important reproductive trait as it makes a major contribution to fitness. Generally, traits closely related to fitness show low heritability perhaps because of the corrosive effects of directional natural selection on the additive genetic variance. Nonetheless, low heritability does not imply, necessarily, a complete absence of genetic variation because genetic interactions (epistasis and dominance) contribute to variation in traits displaying strong heterosis in crosses, such as litter size. In our study, we investigated the genetic architecture of litter size in 166 females from an F2 intercross of the SM/J and LG/J inbred mouse strains. Litter size had a low heritability (h2 = 12%) and a low repeatability (r = 33%). Using interval‐mapping methods, we located two quantitative trait loci (QTL) affecting litter size at locations D7Mit21 + 0 cM and D12Mit6 + 8 cM, on chromosomes 7 and 12 respectively. These QTL accounted for 12.6% of the variance in litter size. In a two‐way genome‐wide epistasis scan we found eight QTL interacting epistatically involving chromosomes 2, 4, 5, 11, 14, 15 and 18. Taken together, the QTL and their interactions explain nearly 49% (39.5% adjusted multiple r2) of the phenotypic variation for litter size in this cross, an increase of 36% over the direct effects of the QTL. This indicates the importance of epistasis as a component of the genetic architecture of litter size and fitness in our intercross population.

A new set of LGXSM recombinant inbred (RI) strains is presented. The RI strain panel consists of 18 remaining strains of the original 55 founding strains. Strain characterization is based on 506 polymorphic microsatellites and 4,289 single nucleotide polymorphisms (SNPs) distributed across the genome. Average microsatellite inter-marker distance is 4.80+/-4.84 Mb or 2.91+/-3.21 F(2) cM. SNPs are more densely spaced at 0.57+/-1.27 Mb. Ninety-five percent of all microsatellite inter-marker intervals are separated by less than 15.00 Mb or 8.50 F(2) cM, while 95% of the SNPs are less than 0.95 Mb apart. Strains show expected low levels of nonsyntenic association among loci and complete genomic independence. During inbreeding, the RI strains went through strong natural selection on the agouti locus on Chromosome 2, especially when the epistatically interacting tyrosinase locus on Chromosome 7 carried the wild-type allele. The LG/J and SM/J strains differ in a large number of biomedically important traits, and they and their inter-cross progeny have been used in multiple mapping studies. The LGxSM RI strain panel provides a powerful new resource for mapping the genetic bases of complex traits and should prove to be of great biomedical utility in modeling complex human diseases such as obesity and diabetes.

The West Indian fruit fly, Anastrepha obliqua, is an important agricultural pest in the New World. The use of pesticide-free methods to control invasive species such as this reinforces the search for genes potentially useful in their genetic control. Therefore, the study of chemosensory proteins involved with a range of responses to the chemical environment will help not only on the understanding of the species biology but may also help the development of environmentally friendly pest control strategies. Here we analyzed the expression patterns of three OBP genes, Obp19d_2, Obp56a and Obp99c, across different phases of A. obliqua development by qPCR. In order to do so, we tested eight and identified three reference genes for data normalization, rpl17, rpl18 and ef1a, which displayed stability for the conditions here tested. All OBPs showed differential expression on adults and some differential expression among adult stages. Obp99c had an almost exclusive expression in males and Obp56a showed high expression in virgin females. Thereby, our results provide relevant data not only for other gene expression studies in this species, as well as for the search of candidate genes that may help in the development of new pest control strategies.

Conflict is thought to play a critical role in the evolution of social interactions by promoting diversity or driving accelerated evolution. However, despite our sophisticated understanding of how conflict shapes social traits, we have limited knowledge of how it impacts molecular evolution across the underlying social genes. Here we address this problem by analyzing the genome-wide impact of social interactions using genome sequences from 67 Dictyostelium discoideum strains. We find that social genes tend to exhibit enhanced polymorphism and accelerated evolution. However, these patterns are not consistent with conflict driven processes, but instead reflect relaxed purifying selection. This pattern is most likely explained by the conditional nature of social interactions, whereby selection on genes expressed only in social interactions is diluted by generations of inactivity. This dilution of selection by inactivity enhances the role of drift, leading to increased polymorphism and accelerated evolution, which we call the Red King process.

BackgroundOdorant-binding proteins (OBPs) are of great importance for survival and reproduction since they participate in initial steps of the olfactory signal transduction cascade, solubilizing and transporting chemical signals to the olfactory receptors. A comparative analysis of OBPs between closely related species may help explain how these genes evolve and are maintained under natural selection and how differences in these proteins can affect olfactory responses. We studied OBP genes in the closely related species Anastrepha fraterculus and A. obliqua, which have different host preferences, using data from RNA-seq cDNA libraries of head and reproductive tissues from male and female adults, aiming to understand the speciation process occurred between them.ResultsWe identified 23 different OBP sequences from Anastrepha fraterculus and 24 from A. obliqua, which correspond to 20 Drosophila melanogaster OBP genes. Phylogenetic analysis separated Anastrepha OBPs sequences in four branches that represent four subfamilies: classic, minus-C, plus-C and dimer. Both species showed five plus-C members, which is the biggest number found in tephritids until now. We found evidence of positive selection in four genes and at least one duplication event that preceded the speciation of these two species. Inferences on tertiary structures of putative proteins from these genes revealed that at least one positively selected change involves the binding cavity (the odorant binding region) in the plus-C OBP50a.Conclusions A. fraterculus and A. obliqua have a bigger OBP repertoire than the other tephritids studied, though the total number of Anastrepha OBPs may be larger, since we studied only a limited number of tissues. The contrast of these closely related species reveals that there are several amino acid changes between the homologous genes, which might be related to their host preferences. The plus-C OBP that has one amino acid under positive selection located in the binding cavity may be under a selection pressure to recognize and bind a new odorant. The other positively selected sites found may be involved in important structural and functional changes, especially ones in which site-specific changes would radically change amino acid properties.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0775-0) contains supplementary material, which is available to authorized users.

The Argentinean Chaco region has been considered the center of origin of Drosophila buzzatii in South America because it contains most of the chromosomal polymorphism detected in natural populations. Two hypotheses have been put forward to explain the distribution of D. buzzatii in Brazil, one proposing that it has only recently passively colonized Brazil via human dispersal and the other suggesting that D. buzzatii has actively migrated to Brazil some time ago. Data from chromosomal inversions support recent colonization, whereas data from allozymes and mtDNA variation indicate that D. buzzatii has been in Brazil longer, favoring an active dispersal hypothesis. In our present work we analyzed data on 56 South American flies, mostly from Brazil, sequenced for the 5' end of the mtDNA COI gene. The combined use of many neutrality tests and phylogeographic methods (e.g. nested clade analysis) indicated high gene flow throughout most of the range of D. buzzatii, although significant population structure was still detected. The high nucleotide diversity in the Northeast region of Brazil and the results from the nested clade analysis suggest that D. buzzatii has been in Brazil longer than proposed by the passive dispersal hypothesis. Our data indicate that D. buzzatii has been distributed throughout Brazil and Argentina since the Quaternary, though more data from different localities and markers need to be gathered to determine how the occupation of South America by D. buzzatii has occurred.