Background: In the tephritidsCeratitis,BactroceraandAnastrepha, the genetransformerprovides the memory device for sex determination via its auto-regulation; only in females is functional Tra protein produced. To date, the isolation and characterisation of the genetransformer-2in the tephritids has only been undertaken inCeratitis, and it has been shown that its function is required for the female-specific splicing ofdoublesexandtransformerpre-mRNA. It therefore participates intransformerauto-regulatory function. In this work, the characterisation of this gene in eleven tephritid species belonging to the less extensively analysed genusAnastrephawas undertaken in order to throw light on the evolution oftransformer-2.Results: The genetransformer-2produces a protein of 249 amino acids in both sexes, which shows the features of the SR protein family. No significant partially spliced mRNA isoform specific to the male germ line was detected, unlike inDrosophila. It is transcribed in both sexes during development and in adult life, in both the soma and germ line. The injection ofAnastrepha transformer-2dsRNA intoAnastrephaembryos caused a change in the splicing pattern of the endogenoustransformeranddoublesexpre-mRNA of XX females from the female to the male mode. Consequently, these XX females were transformed into pseudomales. The comparison of the elevenAnastrephaTransformer-2 proteins among themselves, and with the Transformer-2 proteins of other insects, suggests the existence of negative selection acting at the protein level to maintain Transformer-2 structural features.Conclusions: These results indicate thattransformer-2is required for sex determination inAnastrephathrough its participation in the female-specific splicing oftransformeranddoublesexpre-mRNAs. It is therefore needed for the auto-regulation of the genetransformer. Thus, thetransformer/transfomer-2 > doublesexelements at the bottom of the cascade, and their relationships, probably represent the ancestral state (which still exists in the Tephritidae, Calliphoridae and Muscidae lineages) of the extant cascade found in the Drosophilidae lineage (in whichtrais just another component of the sex determination gene cascade regulated bySex-lethal). In the phylogenetic lineage that gave rise to the drosophilids, evolution co-opted forSex-lethal, modified it, and converted it into the key gene controlling sex determination.

We found that the sex-ratio of an amphigenic strain of Sciara ocellaris varied widely from progenies with few males to progenies containing a larger proportion of males, with single-sex progenies being rare. The sex-ratio distributions were dependent on the temperature at which the stocks of flies were raised, with the sex-ratio distributions being symmetrical (i.e. about 50% males) at 18 °C and 20 °C while at the higher temperatures of 24 °C and 28 °C the distributions were skewed toward a high proportion of females with the mean proportion of males decreasing to about 30-37% per progeny. Temperature-shift experiments showed that high temperatures were effective only during the last stages of female pupal development plus a period after adult emergence, stages corresponding to oocyte maturation. When imagine females were exposed to temperatures as low as 12 °C the sex-ratio distributions of their progeny were skewed toward a high proportion of males per progeny. No differential fecundity was involved in these progeny sex-ratio modifications. Egg-to-adult survival was lower at 18 °C and 28 °C but no correlations with skewing in the sex ratio distributions were observed, indicating that modifications in progeny sex-ratio did not involve the differential survival of a particular sex

The South American fruit fly Anastrepha fraterculus (Wiedemann) is a complex of cryptic species, the so-called “Anastrepha fraterculus complex”, for which eight morphotypes are currently recognized. A previous analysis of ITS1 in samples of the Anastrepha fraterculus complex, while revealing high distinctiveness among samples from different localities of South America, Central America, and Mexico, no direct association was made between sequence type and morphotype. In the present report, a correlated analysis of morphometry and ITS1 data involved individuals belonging to the same population samples. Although showing a low level of intra-populational nucleotide variability, the ITS1 analysis indicated numerous inter-population sequence type variants. Morphotypes identified by morphometric analysis based on female wing shape were highly concordant with ITS1 genetic data. The correlation of genetic divergence and morphological differences among the tested samples gives strong evidence of a robust dataset, thereby indicating the existence of various taxonomic species within the A. fraterculus complex. However, the data revealed genetic and morphological variations in some regions, suggesting that further analysis is still required for some geographic regions.