The attractiveness fragment—AFLP analysis of local adaptation and sexual selection in a caeliferan grasshopper, Chorthippus biguttulus

Screening and characterization of sex-specific DNA fragments in the freshwater fish matrinchã, Brycon amazonicus (Teleostei: Characiformes: Characidae)

The matrinchã Brycon amazonicus, a commercially important freshwater fish resource, has no heteromorphic sex chromosomes so far described. In the present study, we performed a screening of sex-associated DNA markers in this species, through the use of a random amplified polymorphic DNA (RAPD) assay and a genomic DNA restriction digestion analysis. DNA digestions evidenced no differences between sexes. Sixty-six random primers were used in pooled and individual DNA samples of males and females, and the analysis of the RAPD fingerprints revealed one female sex-associated band. Cloning and sequencing of this band led to the identification of two distinct DNA segments. While one of the isolated fragments showed a significant identity with a described protein gene (phosphatidylinositol glycan anchor biosynthesis, class W), the other fragment, composed of 535 bp, corresponds to a novel DNA marker. Further experiments were performed with this second DNA fragment in order to verify its sex-specificity. Data on dot blot hybridization, using total DNA of both sexes, confirmed its female-specificity in B. amazonicus. A primer set was designed based on its sequence data and used in PCR with DNA samples of this species, leading to diagnose the animals' sexes with a 100 % overall accuracy through a sequence characterized amplified region approach. No amplification results were found for two other species of the genus--B. orbignyanus and B. lundii. The obtained data can lead to the hypothesis that B. amazonicus may present heteromorphic sex chromosomes that should be in an early phase of differentiation.

Genomic scan as a tool for assessing the genetic component of phenotypic variance in wild populations

Methods for estimating quantitative trait heritability in wild populations have been developed in recent years which take advantage of the increased availability of genetic markers to reconstruct pedigrees or estimate relatedness between individuals, but their application to real-world data is not exempt from difficulties. This chapter describes a recent marker-based technique which, by adopting a genomic scan approach and focusing on the relationship between phenotypes and genotypes at the individual level, avoids the problems inherent to marker-based estimators of relatedness. This method allows the quantification of the genetic component of phenotypic variance ("degree of genetic determination" or "heritability in the broad sense") in wild populations and is applicable whenever phenotypic trait values and multilocus data for a large number of genetic markers (e.g., amplified fragment length polymorphisms, AFLPs) are simultaneously available for a sample of individuals from the same population. The method proceeds by first identifying those markers whose variation across individuals is significantly correlated with individual phenotypic differences ("adaptive loci"). The proportion of phenotypic variance in the sample that is statistically accounted for by individual differences in adaptive loci is then estimated by fitting a linear model to the data, with trait value as the dependent variable and scores of adaptive loci as independent ones. The method can be easily extended to accommodate quantitative or qualitative information on biologically relevant features of the environment experienced by each sampled individual, in which case estimates of the environmental and genotype × environment components of phenotypic variance can also be obtained.

Comparing geographical genetic differentiation between candidate and noncandidate loci for adaptation strengthens support for parallel ecological divergence in the marine snail Littorina saxatilis

The Galician sympatric ecotypes of Littorina saxatilis have been proposed as a model system for studying parallel ecological speciation. Such a model system makes a clear prediction: candidate loci (for divergent adaptation) should present a higher level of geographical differentiation than noncandidate (neutral) loci. We used 2356 amplified fragment length polymorphisms (AFLPs) and four microsatellite loci to identify candidate loci for ecological adaptation using the F(ST) outlier method. Three per cent of the studied AFLP loci were identified as candidate loci associated with adaptation, after multitest adjustments, thus contributing to ecotype differentiation (candidate loci were not detected within ecotypes). Candidate and noncandidate loci were analysed separately at four different F(ST) partitions: differences between ecotypes (overall and local), differences between localities and micro-geographical differences within ecotypes. The magnitude of F(ST) differed between candidate and noncandidate loci for all partitions except in the case of micro-geographical differentiation within ecotypes, and the microsatellites (putatively neutral) showed an identical pattern to noncandidate loci. Thus, variation in candidate loci is determined partially independent by divergent natural selection (in addition to stochastic forces) at each locality, while noncandidate loci are exclusively driven by stochastic forces. These results support the evolutionary history described for these particular populations, considered to be a clear example of incomplete sympatric ecological speciation.

The Genetic Basis of Sexually Selected Variation

Sexually selected traits contribute greatly to phenotypic diversity, yet we have historically understood little about their genetic basis and how that basis may affect their evolution. Recent work in developmental and quantitative genetics has provided both mechanistic and statistical descriptions of genotype-phenotype maps for sexually selected traits. These studies expose generally complex genetic architectures; genotype-phenotype maps are polygenic with allelic effects that are pleiotropic and highly context-dependent. At the same time, developments in quantitative genetics have provided new insights into the microevolutionary potential of standing variation and indicate genetic constraints on the contemporary evolution of male sexually selected characters, mate preferences, and also male mating success itself. Understanding the extent to which these constraints are a function of genetic architecture will require a tighter integration of developmental, molecular, and quantitative genetic approaches in a variety of model systems. Emerging genomic technologies offer an unprecedented opportunity to deepen our understanding of sexual selection as an evolutionary process.

Screening and identification of male-specific DNA fragments in common carps Cyprinus carpio using suppression subtractive hybridization

In this study, a sex subtractive genomic DNA library was constructed using suppression subtractive hybridization (SSH) between male and female Cyprinus carpio. Twenty-two clones with distinguishable hybridization signals were selected and sequenced. The specific primers were designed based on the sequence data. Those primers were then used to amplify the sex-specific fragments from the genomic DNA of male and female carp. The amplified fragments from two clones showed specificity to males but not to females, which were named as Ccmf2 [387 base pairs (bp)] and Ccmf3 (183 bp), respectively. The sex-specific pattern was analysed in a total of 40 individuals from three other different C. carpio. stocks and grass carp Ctenopharyngodon idella using Ccmf2 and Ccmf3 as dot-blotting probes. The results revealed that the molecular diversity exists on the Y chromosome of C. carpio. No hybridization signals, however, were detected from individuals of C. idella, suggesting that the two sequences are specific to C. carpio. No significant homologous sequences of Ccmf2 and Ccmf3 were found in GenBank. Therefore, it was interpreted that the results as that Ccmf2 and Ccmf3 are two novel male-specific sequences; and both fragments could be used as markers to rapidly and accurately identify the genetic sex of part of C. carpio. This may provide a very efficient selective tool for practically breeding monosex female populations in aquacultural production.

The genetic architecture of insect courtship behavior and premating isolation

The genetic architecture underlying reproductively isolating traits may have substantial impacts on the likelihood and pace of speciation. Recent studies of a key premating barrier, courtship, provide sufficient data to assess the degree to which behaviorally isolating traits are controlled by many or few loci, and help to investigate whether the same loci underlie both intraspecific and interspecific behavioral differences. Of the behavioral courtship traits examined, 69% (25 of 36) were found to be mediated by few loci of relatively large effect. This apparent prevalence of major loci suggests that changes in courtship behavior may often evolve quickly, which in turn may drive rapid speciation through premating isolation. Although both intraspecific and interspecific courtship differences are commonly controlled by major loci, intraspecific and interspecific differences usually involve different loci or traits. This finding provides evidence that different sets of processes and genetic changes characterize microevolutionary change in courtship-related traits, in contrast to change during speciation.