Induction of diapause in Drosophila melanogaster: photoperiodic regulation and the impact of arrhythmic clock mutations on time measurement.

Abstract

The fruit fly Drosophila melanogaster displays an ovarian diapause that is regulated by photoperiod.Newly eclosed female flies (Canton-S wild type) exposed to short days (<14 hr of light per day) at 12'C (or 100C) enter a fairly shallow reproductive diapause. Females exposed to long days (16 hr of light per day) at the same low temperature undergo ovarian maturation. The short day induced diapause continues for 6-7 weeks under a 10:14 light/dark cycle at 120C but is terminated rapidly after a transfer to higher temperature (18 or 250C) or to long days (18:6 light/dark cycle).Females from three strains homozygous for alleles of the period (per) locus, reportedly arrhythmic for behavioral circadian rhythms, and females that possessed two overlapping deletions of per were also capable of discriminating between long and short days, although, when compared with the wild-type flies, the critical day length was shifted to shorter values by -2 hr. It is concluded that the period locus is not causally involved in photoperiod time measurement.The majority of insects inhabiting the temperate zones develop and reproduce during the summer months but become dormant as winter approaches. Although ecological distinctions are becoming blurred, this dormancy may be a direct response to unfavorable conditions (i.e., cold torpor or quiescence), or it involves programmed responses to seasonal changes in day length (or photoperiod), which results in interruptions or alterations in endocrine regulation (i.e., diapause). Photoperiodic regulation of diapause has been documented for a large number of species representing -13 insect orders (1).A central problem in the study of photoperiodism is the nature of the "clock" used by organisms to discriminate long days from short days (or short nights from long nights) as the seasons change. The mechanism of this time measurement remains obscure, but a favored model suggests that night length is measured by a clock based on the system of circadian oscillations, which also regulate overt daily rhythms (2-4). In the 50 years since its formulation, this proposition has become known as "Hunning's hypothesis." D. melanogaster occupies an almost unique position in biological research because of its amenability for molecular and genetic analysis. Therefore, the nature of its overwintering strategy, whether diapause or quiescence, is also of considerable interest. To our knowledge, no published observations on this aspect of its biology have appeared, although it would be surprising if some attention had not been given to the problem, especially since the circadian system is known to underlie photoperiodic time meaurement [at least in D. auraria (13)], and the clock or period (per) locus is being subjected to intensive molecular and genetic analysis (14-17).This paper describes experiments with D. melanogaster in which newly eclosed adults were exposed to a range of photoperiods at temperatures somewhat lower than those normally used in routine laboratory maintenance and experimentation in an a...

Diapause in Drosophila melanogaster females: a genetic analysis

“…Diapause has been investigated for many Drosophilids [for example, Drosophila robusta (Carson & Stalker, 1948;Levitan, 1951), Drosophila littoralis (Lumme et at., 1974;Lumme & Oikarinen, 1977;Lumme, 1978), Drosophila deflexa Duda (Basden, 1952(Basden, , 1954a, Drosophila subobscura (Basden, 1954b), Drosophila auraria complex (Kimura, 1984), D. melanogaster (Saunders et al, 1989;Izquierdo, 1991), also see review by Lumme & Lakovaara, 1983]. However, the genetic resources available for the study of this phenomenon in species other than D. metanogaster are limited.…”

“…Until recently, D. ine/anogaster was thought of as a 'day-neutral' species, devoid of an overwintering response, having no diapause (Saunders, 1976). However, Saunders et at.…”

“…Ovarian diapause was therefore measured by considering whether flies were in the stage of ovarian development necessary for the onset of vitellogenesis. Saunders et al (1989) showed that ovarian diapause is induced in D. metanogaster at the critical temperature of 12°C and a photoperiod of 10 h of light and 14 h of darkness (IOL:14D) (Saunders et at., 1989).…”

“…Juvenile hormone is thought to regulate vitellogenesis (Bownes, 1980(Bownes, , 1989, and ovarian diapause (Saunders et at., 1990). Genes regulating diapause and cold hardiness have not yet been localized in any Drosophila species (Denlinger, 1991 Prior to the initiation of diapause, flies were maintained at 20°C, under a 1 2L: 1 2D cycle, with lights on at 0800 h. The sensitive stage for the induction of diapause in D. melanogaster is before eclosion and up to 10 hours after eclosion (Saunders et at., 1989). To test for diapause, we collected newly emerged males and virgin females, within 9 h of eclosion, and placed them into vials at densities of approximately 50 flies with equal sex ratios.…”

Photoperiodic Time Measurement in Insects: A Review of Clock Models

“…Does this occur in the same cells (neurons) as that regulating overt rhythmicity, or are the two rhythmic systems functionally separate? So far, these questions have been addressed only for the photoperiodic control of ovarian diapause in D. melanogaster (Saunders et al, 1989;Saunders, 1990). In this study, critical night lengths were found to be identical in a short-period mutant (per s ), a long-period mutant (per L2 ), and the wild type (Canton S) from which they were originally isolated (Konopka and Benzer, 1971); if a per-regulated feedback loop also was operating in photoperiodic time measurement, then large effects of these mutations on critical night length would have been expected.…”