| The red imported fire ant, Solenopsis invicta Buren, originating from the Parana river in South America, is one of the most dangerous invasive species and has caused damage to human being, ecosystem, agriculture and economy. In order to explore the relation between photoperiod and diurnal rhythm of S. invicta foraging worker, a video-computer recording system was used to record the foraging activity of fire ant workers from foraging arena box kept under three patterns of photoperiods(12L:12D, 24 L, and 24D) in the laboratory. Meanwhile, the real-time quantitative PCR(RT-PCR) was used to detect Sifor(S. invicta foraging gene)expression of foragers sampled at 8:00, 12:00, 16:00, 20:00, 0:00, and 4:00 within a 24-h duration. The main results are as follows:1. Diurnal rhythm of foragers under three cycles of photoperiodUsing a video-computer recording system to record the foraging amount of fire ant workers and Cosinor model was used to simulate the activity. Under 12L:12D cycle(control), the foraging activity of workers was a single-peak pattern, in which the peak appeared at 23:41 at midnight and the valley occurred at 11:41. When colonies reared in 12L:12D were moved to 24 L,the peak and valley of worker foraging activity was similar to 12L:12D, However, when other colonies were moved to 24 D, its peak and valley moved to 21:21 and 9:21. The result showed that foraging activity pattern for fire ant foragers was an endogenous mono-peak model. Although the foraging activity pattern of foragers outside nest remained closely similar, it could result in phase shift of the pattern.2. Dynamics of Sifor expression under 3 cycles of photoperiodThe expression pattern of the foraging gene(Sifor) for S. invicta, was studied using the real-time quantitative PCR, foragers reared under three cycles of photoperiod and the foragers were sampled at 8:00, 12:00, 16:00, 20:00, 0:00, and 4:00. The rhythm of foraging gene expression was plotted based on the c DNA data at six time points and then the Cosinor model was used to simulate.the observed data. The results showed the expression pattern was 24 hour-cycle pattern with mono-peak. The lowest transcription level was at 14:00~15:00 and the highest was at 2:00~3:00 for worker Sifor under 12L:12D. When colonies were moved to 24 D,the lowest relative expression of Sifor appeared at 7:00~8:00 and the highest one was at 19:00~20:00. When the colonies were moved to 24 L, the lowest expression level of Sifor from worker individuals appeared at 14:00~15:00 and the highest was at 2:00~3:00.When the colonies in control photoperiod were moved to the cycles of 24 D or 24 L the expression level of forager Sifor at each point for 24 h-cycle did show irregular trend after treatment.3. Impact of photoperiod change on Sifor expression from foragersWhen colonies reared under 12L: 12 D were moved to 24 L or 24 D, Sifor expression at each sample time with the exception of Sifor at 0:00 under 24 D was up-regulated. Compared with Sifor related expression and the foraging intensity under 24 L or 24 D, there have no correlation.4. Correlation between Sifor expression and diurnal rhythm of fire ant foragersThe study implied that Sifor expression pattern seemed similar to those diurnal rhythm of foraging activity. However, Sifor expression pattern in comparison with the foraging rhythm under each of three cycles, the highest peak of Sifor transcription delayed for 3h under 12L:12D, for 3h under 24 L, and ahead for 1 h under 24 D. In addition, the correlation between Sifor expression level and the foraging intensity was significantly positive under three cycles of photoperiod. The analysis proposed that foraging activity of fire ants could be regulated by the foraging gene Sifor.The consequences could provide clue to further explanation molecular mechanism of circadian rhythm of fire ant foragers. |
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