Studies On The Wing Vibration During Courtship In Drosophila Serrata

In Drosophila, the males' courtship, which can make the females calm down, plays a vital role in the successful copulation. The courtship song generated by wing vibration is species-specific and the main element in most Drosophila species. It involves a lot in the sexual selection, speciation and evolution. In Drosophila montium species-subgroup, the copulatory courtship after mounting is dominant, while the precopulatory courtship before mounting has gradually been lost. Why the precopulatory courtship might come to be lost in the montium subgroup? What is the genetic mechanism? All these questions have not been addressed so far. In order to answer these questions, the Drosophila serrata, which is losing the precopulatory courtship, was focused on in the present study. Based on the careful observation and analysis of the courtship behavior, the phenotypic selection on the wing vibrating before mounting in the first courtship was conduced for the genetic background; A 24 hours separating-gathering experiment on mated pairs was performed for the learning and memory background; A comparison of the copulation duration and the number of offspring between males with and without wing vibration of mated pairs was applied for the biological significance of the wing vibration before mounting in the first courtship; Suppression Subtractive Hybridization(SSH) c DNA libraries were constructed from male flies with and without wing vibration before mounting in the first courtship. Candidate genes associated with odor, learning and memory were selected from the SSH libraries for the further investigation of the gene expression. The following results were obtained:1) The courtship behavior of D. serrata: The courtship behavior was carefully observed and note-taken when the videos were recorded and repeatedly played back. During the courtship, the wing vibration took place in three stages: a) Before mounting in the first courtship(only for about 27% males) with a small angle(smaller than 45 degrees). b) After mounting in the first courtship with a bigger angle(larger than 45 degrees). c) Before and after mounting in multiple courtships with a bigger angle(larger than 45 degrees). The following questions were raised according to above observation of the courtship behavior: Why the males use different strategies in different courtship stages? Why and how a relative ratio of 1:4 for males with and without wing vibration before mounting in the first courtship was maintained in the D. serrata? Is there any genetic factor involved in this phenomenon? Or just as Hoikkala's saying that males of this species still have ability to court before mounting, they just do not use this ability.2) Phenotypic selection on males with and without wing vibration before mounting in the first courtship: according to the results of the phenotypic selection, the increasing trend of the wing vibration before mounting in the first courtship in the strain Y indicated that this behavior might be controlled by multiple genes, and other environmental factors might also involve in triggering this behavior. The strain Y might be controlled by more dominant genes, while more recessive genes might be involved in the strain N for the character selected.3) The biological significance of male's wing vibration before mounting in the first courtship: No significant difference was found between the pairs with and without male's wing vibration in copulation duration. More offspring were produced by the pairs with male's wing vibration than that from the pairs without male's wing vibration. The biological significance on increasing offspring number might put in effort through its contribution on the sperm competition in the postmating. Further studies might be worth to be conducted for addressing this issue.4)24 hours separating-gathering experiments for the learning and memory background: The significant difference was found on the average rate of male's wing vibration between pairs with wing vibration and without wing vibration before mounting in the first courtship. It is very noticeable that after 24 hours separating, the way of wing vibration of reencountered males returned to be the small angle as that of the virgin males performed in the first courtship, but as the way with big angle in the multiple courtships right after the first copulation. The results suggested that the male's wing vibration in the multiple courtships might be the consequence of the learning from the wing vibration during the first copulation. Whereas, the memory of such learning might be the short term one.5) The SSH c DNA library and expressive pattern of candidate genes associated with the odor, learning and memory: 329 sequences were identified from the library PY, Five genes, obp56 g, 14-3-3zeta, Deasat1, Argk, Cyp9b2, were selected from identified genes associated with pheromone binding protein, learning and memory for the gene expressive pattern by the q RT-PCR. These genes expressed significantly higher in males without wing vibration than that in the males with wing vibration. The males without wing vibration might possess better skill on the odorant detection and learning, so that they can mount females without wing vibration to avoid the energy consumption. It could be concluded that the males adjusted the courtship strategy according to their odorant detection, learning and memory.6) The effect of the female rejection on the courtship strategy: The wing vibration before mounting in the first courtship is the only stage which females do not show obvious repelling behavior. Females always show repelling behavior after mounting and in the second courtship and multiple courtships, males usually vibrate wings in response to the female's repelling behavior and show persistent courting. In D. serrata, females' rejecting behavior might be the potential vital factor for inducing males' wing vibration and the courtship strategy.In conclusion, the present study focused on the behavior of males' wing vibration in the courtship, and tried to understand its mechanism from behavioral, genetic, molecular approaches. The results obtained from the present study provided new ideas on the behavioral mechanism and would also shed light on understanding of the evolutionary genetics of courtship behavior in Drosphila.