Biological Clocks in Mosquitoes - Section 2
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"that within a certain range of photoperiods the phase-setting effects of light-on and light-off reinforce each other; the range over which this reinforcement occurs coincides with that of the photoperiod which is usually encountered by this species throughout its natural geographical range" (Taylor, 1969b).From that idea came the rationale for the experiments with other mosquito species, which are reported and considered in the present paper. The Ae. aegypti LLt = 26h is such that the circadian-controlled E and M peaks match a daylength of 13-14h, that is the range for latitudinal range of up to 30°N or S. The Cx. p. molestus LLt @ 30h, however, would match a wider range of Summer daylengths.
This development in the concept is followed from hereon by the use of sine waves plotted with periods reflecting the Summer daylengths of the known geographical range of the particular species. The periodicity will be referred to as Lt and Dt. It is illustrated by the histograms of Cx. p. molestus activity shown in Figure 37, with the sine wave Lt = 30h, and Dt = 22.5h.
Figure 37
The main coincidence of the OFF SINE and ON SINE peaks is between L12h and L16h of light, coinciding with the natural range of the species, and the origins of the laboratory colony - from Iran, 40°N, where maximum L = 15h (Chiba et al., 1992).
To return to the geometric expression used above for the Ae. aegypti results, the speed per hour with Lt = 30h is 12° per hour. When combined with Dt = 22.5h, or 16° per hour, an LD 16:8 will give the ON SINE peak (180°) at 15h after light-on, but the OFF SINE peak will fall at 8 X 16° = 128°, plus 16 X 12° = 192°, a total of 320°.
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©1998, 2010 - Brian Taylor CBiol FSB FRES 11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K. Comments to dr.b.taylor@ntlworld.com |