Genetic structure and symbiotic profile of worldwide natural populations of the Mediterranean fruit fly, Ceratitis capitata.

Background: The Mediterranean fruit fly, Ceratitis capitata, is a cosmopolitan agricultural pest of worldwide economic importance and a model for the development of the Sterile Insect Technique (SIT) for fruit flies of the Tephritidae family (Diptera). SIT relies on the effective mating of laboratory-reared strains and natural populations, and therefore requires an efficient mass-rearing system that will allow for the production of high-quality males. Adaptation of wild flies to an artificial laboratory environment can be accompanied by negative effects on several life history traits through changes in their genetic diversity and symbiotic communities. Such changes may lead to reduced biological quality and mating competitiveness in respect to the wild populations. Profiling wild populations can help understand, and maybe reverse, deleterious effects accompanying laboratory domestication thus providing insects that can efficiently and effectively support SIT application.

Results: In the present study, we analyzed both the genetic structure and gut symbiotic communities of natural medfly populations of worldwide distribution, including Europe, Africa, Australia, and the Americas. The genetic structure of 408 individuals from 15 distinct populations was analyzed with a set of commonly used microsatellite markers. The symbiotic communities of a subset of 265 individuals from 11 populations were analyzed using the 16S rRNA gene-based amplicon sequencing of single individuals (adults). Genetic differentiation was detected among geographically distant populations while adults originated from neighboring areas were genetically closer. Alpha and beta diversity of bacterial communities pointed to an overall reduced symbiotic diversity and the influence of the geographic location on the bacterial profile.

Conclusions: Our analysis revealed differences both in the genetic profile and the structure of gut symbiotic communities of medfly natural populations. The genetic analysis expanded our knowledge to populations not analyzed before and our results were in accordance with the existing scenarios regarding this species expansion and colonization pathways. At the same time, the bacterial communities from different natural medfly populations have been characterized, thus broadening our knowledge on the microbiota of the species across its range. Genetic and symbiotic differences between natural and laboratory populations must be considered when designing AW-IPM approaches with a SIT component, since they may impact mating compatibility and mating competitiveness of the laboratory-reared males. In parallel, enrichment from wild populations and/or symbiotic supplementation could increase rearing productivity, biological quality, and mating competitiveness of SIT-important laboratory strains.