Molecular evolution and genetic diversity of defective chorion 1 in Anastrepha fraterculus and Anastrepha obliqua (Diptera, Tephritidae).

Abstract

The family Tephritidae comprises numerous fruit fly species, some of which are economically significant, such as several in the genus Anastrepha. Most pest species in this genus belong to the fraterculus group, characterized by closely related species that are difficult to differentiate due to recent divergence and gene flow. Identifying genetic markers for their study is paramount for understanding the group's evolution and eventual phytosanitary control. Because there is variation in eggshell morphology among species in the genus, the study of the rapidly evolving defective chorion 1 (dec-1) gene, which is crucial for chorion formation and reproduction, could provide relevant information for Anastrepha differentiation. We compared transcriptome sequences of dec-1 from two of the most important pest species in the genus, Anastrepha fraterculus and Anastrepha obliqua to dec-1 sequences from Anastrepha ludens, which was used for structure prediction. Furthermore, we amplified a conserved exon across populations of these species. These data revealed three alternative transcripts in A. fraterculus and A. obliqua, consistent with patterns found in other Tephritidae; we obtained orthologous sequences for these other tephritids from NCBI to investigate patterns of selection affecting this gene at different hierarchical levels using different methods. These analyses show a general pattern of purifying selection across the whole gene and throughout its history at different hierarchical levels, from populations to more distantly related species. That notwithstanding, we still found evidence of positive and episodic diversifying selection at different levels. Different parts of the gene have shown distinct evolutionary rates, which were associated with the diverse proproteins produced by posttranslational changes of DEC-1, with proproteins that are incorporated in the chorion earlier in egg formation being in general more conserved than others that are incorporated later. This correlation appears more evident in certain lineages, including the branch that separates Anastrepha, as well as other internal branches that differentiate species within the genus. Our data showed that this gene shows remarkable variation across its different exons, which has proven to be informative at different evolutionary levels. These changes hold promise not only for studying differentiation in Anastrepha but also for the eventual management of selected pest species.