CYP450 core involvement in multiple resistance strains of Aedes aegypti from French Guiana highlighted by proteomics, molecular and biochemical studies

Insecticide resistance is a worldwide threat for vector control around the world, and Aedes aegypti, the main vector of several arboviruses, is a particular concern. To better understand the mechanisms of resistance, four isofemale strains originally from French Guiana were isolated and analysed using combined approaches. The activity of detoxification enzymes involved in insecticide resistance was assayed, and mutations located at positions 1016 and 1534 of the sodium voltage-gated channel gene, which have been associated with pyrethroid resistance in Aedes aegypti populations in Latin America, were monitored. Resistance to other insecticide families (organophosphates and carbamates) was evaluated. A large-scale proteomic analysis was performed to identify proteins involved in insecticide resistance. Our results revealed a metabolic resistance and resistance associated with a mutation of the sodium voltage-gated channel gene at position 1016. Metabolic resistance was mediated through an increase of esterase activity in most strains but also through the shifts in the abundance of several cytochrome P450 (CYP450s). Overall, resistance to deltamethrin was linked in the isofemale strains to resistance to other class of insecticides, suggesting that cross- and multiple resistance occur through selection of mechanisms of metabolic resistance. These results give some insights into resistance to deltamethrin and into multiple resistance phenomena in populations of Ae. aegypti.

Genomic analysis ofPelements in natural populations ofDrosophila melanogaster

TheDrosophila melanogaster Ptransposable element provides one of the best cases of horizontal transfer of a mobile DNA sequence in eukaryotes. Invasion of natural populations by thePelement has led to a syndrome of phenotypes known as P-M hybrid dysgenesis that emerges when strains differing in theirPelement composition mate and produce offspring. Despite extensive research on many aspects ofPelement biology, many questions remain about the genomic basis of variation in P-M dysgenesis phenotypes across populations. Here we compare estimates of genomicPelement content with gonadal dysgenesis phenotypes for isofemale strains obtained from three worldwide populations ofD. melanogasterto illuminate the molecular basis of natural variation in cytotype status. We show thatPelement abundance estimated from genome sequences of isofemale strains is highly correlated across different bioinformatics approaches, but that abundance estimates are sensitive to method and filtering strategies as well as incomplete inbreeding of isofemale strains. We find thatPelement content varies significantly across populations, with strains from a North American population having fewerPelements but a higher proportion of full-length elements than strains from populations sampled in Europe or Africa. Despite these geographic differences inPelement abundance and structure, neither the number ofPelements nor the ratio of full-length to internally-truncated copies is strongly correlated with the degree of gonadal dysgenesis exhibited by an isofemale strain. Thus, variation inPelement abundance and structure across different populations does not necessarily lead to corresponding geographic differences in gonadal dysgenesis phenotypes. Finally, we confirm that population differences in the abundance and structure ofPelements that are observed from isofemale lines can also be observed in pool-seq samples from the same populations. Our work supports the view that genomicPelement content alone is not sufficient to explain variation in gonadal dysgenesis across strains ofD. melanogaster, and informs future efforts to decode the genomic basis of geographic and temporal differences inPelement induced phenotypes.

Genomic analysis of P elements in natural populations of Drosophila melanogaster

The Drosophila melanogaster P transposable element provides one of the best cases of horizontal transfer of a mobile DNA sequence in eukaryotes. Invasion of natural populations by the P element has led to a syndrome of phenotypes known as P-M hybrid dysgenesis that emerges when strains differing in their P element composition mate and produce offspring. Despite extensive research on many aspects of P element biology, many questions remain about the genomic basis of variation in P-M dysgenesis phenotypes in natural populations. Here we compare gonadal dysgenesis phenotypes and genomic P element predictions for isofemale strains obtained from three worldwide populations of D. melanogaster to illuminate the molecular basis of natural variation in cytotype status. We show that the number of predicted P element insertions in genome sequences from isofemale strains is highly correlated across different bioinformatics methods, but the absolute number of insertions per strain is sensitive to method and filtering strategies. Regardless of method used, we find that the number of euchromatic P element insertions predicted per strain varies significantly across populations, with strains from a North American population having fewer P element insertions than strains from populations sampled in Europe or Africa. Despite these geographic differences, numbers of euchromatic P element insertions are not strongly correlated with the degree of gonadal dysgenesis exhibited by an isofemale strain. Thus, variation in P element insertion numbers across different populations does not necessarily lead to corresponding geographic differences in gonadal dysgenesis phenotypes. Additionally, we show that pool-seq samples can uncover population differences in the number of P element insertions observed from isofemale lines, but that efforts to rigorously detect differences in the number of P elements across populations using pool-seq data must properly control for read depth per strain. Our work supports the view that euchromatic P element copy number is not sufficient to explain variation in gonadal dysgenesis across strains of D. melanogaster, and informs future efforts to decode the genomic basis of geographic and temporal differences in P element induced phenotypes.

The comparative biology of genetic variation for conditional sex ratio behavior in a parasitic wasp, Nasonia vitripennis.

Using genetic markers, we tracked the sex ratio behavior of individual females of the parasitic wasp, Nasonia vitripennis, in foundress groups of size 1, 2, 4, 8 and 16. Comparison of 12 isofemale strains extracted from a natural population reveals significant between-strain heterogeneity of sex ratios produced in all sizes of foundress group. Under simple assumptions about population structure, this heterogeneity results in heterogeneity of fitnesses. The strains differ in their conditional sex ratio behavior (the sex ratio response of a female to foundress groups of different sizes). Females of some strains produce more males as foundress group size increases (up to size eight). Females of another strain produce more males when not alone but do not respond differentially to group size otherwise. Females of two other strains show no conditional sex ratio behavior. Females of only two strains behave differently in foundress groups of size 8 and 16. Correlation and regression analyses indicate that the strains differ significantly in their fit to the predictions of an evolutionarily stable strategy (ESS) model of conditional sex ratio behavior. Such heterogeneity contradicts the notion that females of this species possess conditonal sex ratio behavior that is optimal in the ESS sense. The results imply that this ESS model is useful but not sufficient for understanding the causal basis of the evolution of this behavior in this species. This is the first report on the sex ratio behavior of individual females in multiple foundress groups in any species of parasitic wasp. Data of this type (and not foundress group or "patch" sex ratios) are essential for testing evolutionary models that predict the sex ratio behaviors of individuals. We suggest that a test for an ESS model include the answers to two important questions: 1) is the model quantitatively accurate? and 2) is there reasonable evidence to indicate that natural selection has caused individuals to manifest the ESS behavior?

Intra- and inter-specific variation in pupation behaviours of Drosophila from different habitats

Isofemale strains of Drosophila melanogaster and D. simulans were collected from wet and dry habitats in Tunisia. These strains were used to study the effect of habitat (collection site) and laboratory rearing temperature on larval pupation behaviour of these species. Results showed that D. melanogaster isofemale strains from the wet habitat pupated significantly higher in vials than those from the drier habitat. In contrast, the pupation behaviour of D. simulans isofemale strains was not affected by habitat type. Significant intraspecific variation in pupation behaviour was found for both species from both habitats. The distance pupated away from food in vials was positively correlated to the distance pupated from fruit in a field-like assay. Plasticity for pupation height was found at 16 and 32 °C for both species. Greater between-strain variation in pupation height was found for D. melanogaster at 32 °C and for D. simulans at 16 °C. The patterns of interspecific differences in larval pupation height paralleled those previously reported for adult behaviour patterns in these species.

The comparative biology of second sex ratio evolution within a natural population of a parasitic wasp, Nasonia vitripennis.

Correlation and regression analyses indicate that isofemale strains extracted from a population of the parasitic wasp, Nasonia vitripennis, differ in the fit of their second sex ratios (those produced in previously parasitized hosts) to the predictions of the theory of optimal facultative sex ratio adjustment. Under the theory's simple assumptions about population structure, there is significant heterogeneity of fitnesses among the isofemale strains. The reasons underlying these types of heterogeneity must be understood before we can make statements about the nature of sex ratio evolution in this species. These results suggest that comparative analyses are essential for testing the qualitative predictions of optimality models.

Genetic variation for sex ratio traits within a natural population of a parasitic wasp, Nasonia vitripennis.

By analyzing isofemale strains extracted from a natural population of Nasonia vitripennis, we detected variation for the sex ratios produced in fresh hosts (first sex ratios) and in previously parasitized hosts (second sex ratios). Under simple assumptions of population structure, this between-strain heterogeneity of first sex ratios results in heterogeneity of fitnesses. There is approximately ten percent difference in average fitnesses between the strains. (The fitnesses of second sex ratios are analyzed in the accompanying paper.) Average first and average second sex ratios are uncorrelated. There is significant between-female heterogeneity within some strains for first sex ratios but not for second sex ratios. In addition, the average direct-developing and diapause first sex ratios (but not second sex ratios) are significantly correlated. There are significant correlations between the direct-developing and diapause sex ratios produced by the same female. The strains differ in their effects on the sex ratio and size of another female's brood in the same host. Data on these types of variation for sex ratio traits are essential for further progress in the study of sex ratio evolution.

The Genetic Architecture of Cold Tolerance in Natural-Populations of Drosophila-Melanogaster and Drosophila-Simulans

Genetic analysis of cold tolerance was applied to samples of recently collected isofemale strains of Drosophila melanogaster and D. simulans from natural populations from diverse climates. The temperate zone locality of Melbourne was sampled twice for both species, once in 1986 and again in 1987. In 1987, D. melanogaster collections were also made in the humid tropics at Townsville and the wet/dry tropical locality of Darwin. D. simulans was also collected in Townsville in 1987 but it was not found in Darwin. Diallel analysis was performed for each population sample, so there were seven diallels, each with from 9 to 12 strains which were randomly chosen. Diallel analyses showed that cold tolerance was mainly controlled by additive genetic effects. This pattern was consistent across time, across populations and across species. It is proposed that natural populations of both members of the sibling species have the genetic architecture necessary for adaptive phenotypic response to selection by intermittent periods of low temperature.