Circadian rhythmicity is involved in photoperiodic time measurement in the aphidMegoura viciae

Abstract

The photoperiodic clock in the vetch aphid Megoura viciae is generally accepted to be based on a non-circadian mechanism or "hourglass", as no evidence has been found for the involvement of the circadian system in the photoperiodic response. By using a recently-devised protocol which discriminates between single and repeated night length measurement, we demonstrate here that long-night measurement in Megoura is executed in a repetitive way, and thus that its photoperiodic clock is based on a circadian oscillator after all. However, it is also apparent that the determination of short nights is not repetitive.

Photoperiodic Time Measurement in Insects: A Review of Clock Models

“…For the blowfly, C. vicina, a damping circadian clock also had been suggested from other experiments by Vaz Nunes et al (1990a) in which it was found that DD had the same inductive value as about 5 long-night (LD 8:16) cycles. Vaz Nunes and Hardie (1993) demonstrated with this protocol that the photoperiodic clock in the aphid, M. viciae, is based on a self-sustained or slightly damped circadian oscillator instead of an hourglass as was generally accepted (Lees, 1973;Saunders, 1982b); in this species, n cycles of LD 12:60 or LD 12:36 resulted in the same incidence of ovipara producers as did 3n or 2n cycles of LD 12:12, respectively. Therefore, the Veerman-Vaz Nunes protocol gave a variety of results.…”

“…More recently, Vaz Nunes and Hardie (1993) found experimental evidence for a circadian clock in M. viciae despite the typical hourglass responses in NandaHamner experiments observed at various temperatures (Lees, 1986). These results show that a negative Nanda-Hamner response does not necessarily mean that the clock is based on a noncircadian (hourglass) mechanism.…”

“…It has been observed that the effects of temperature on long nights and short nights are rather different in that short nights appear much more sensitive to temperature than do long nights (Goryshin and Tyshchenko, 1973;Hardie, 1990;Saunders, 1992;Vaz Nunes and Hardie, unpublished). Moreover, in the vetch aphid, M. viciae, and the large cabbage white butterfly, Pieris brassicae, long and short nights seemed to be determined in different ways (Vaz Nunes and Hardie, 1993;Vaz Nunes, 1994;Dumortier, 1994), and in some cases only long nights were accumulated, not short nights (Goryshin and Tyshchenko, 1973;Saunders, 1981b). These observations are difficult to explain if the difference between a short night and a long night is simply the coincidence or noncoincidence of ϕ i with light, respectively.…”

“…Although its clock appeared to be circadian, Nanda-Hamner and Bünsow responses were negative. A possibility, suggested by Vaz Nunes and Hardie (1993) and tested by Vaz Nunes (1994), was that long nights were measured repetitively but that measurement of short nights was nonrepetitive. This assumed differential effect of long and short nights was one of the reasons for the development of a totally new model, the double circadian oscillator model (Model 13), by Vaz Nunes (1998a), in which any scotophase is measured by two independent (damping or nondamping) circadian oscillatory systems and is given a positive value by the one (LN) system if long or is given a positive value by the other (SN) system if short.…”

Neuroanatomical Approaches to the Study of Insect Photoperiodism†

“…Nowadays, it is generally accepted that the circadian oscillator is involved in insect photoperiodism. Even in M. viciae , Vaz Nunez and Hardie (27) proved the involvement of circadian oscillation by a newly devised protocol. However, it is still unclear whether the circadian oscillator is involved in the time measurement itself.…”