Transgenic sperm marking system in Ceratitis capitata does not appear to impair fitness.

A powerful sperm-marking system based on the spermatogenesis-specific Ceratitis capitata β2t-tubulin (Ccβ2t) promoter has been developed for the medfly. Several lines have been generated in which the reporter genes tGFP or DsRedEx are expressed in a stable, persistent and sex-specific manner at spermatogenesis level. Our aim was to obtain direct sperm visualization, both for applied and basic purposes: firstly, to provide an efficient tool for improving the monitoring of ongoing SIT programs and secondly, to improve the analysis of medfly mating physiology regarding sperm transfer, storage, competition, and use. Fluorescent sperm can be isolated from testes or spermathecae. The marking itself does not cause general disadvantages in preliminary laboratory competitiveness assays. Some of the transgenic lines showed fitness costs, probably due to the presence of the transgene, the genetic bottleneck during the line’s establishment, or its particular insertion into the genome. However, males of one sperm-marked line showed no significant reduction in their overall fitness, transmitting their genes to the next generation in a competitive way. Therefore, transgenic sperm-marking could serve as a major improvement for monitoring medfly SIT programmes. Moreover, mating physiology, cryptic female choice, sperm competition, sperm quality, and other postcopulatory sexual behaviours can now be analyzed using this novel tool. An enhanced knowledge of these basic biological processes will provide additional means to further improve environmentally safe, biological pest management approaches.