Adult Emergence Rhythm of Fruit Flies Drosophila melanogaster under Seminatural Conditions

Abstract

In insects, the role of circadian clocks in the temporal regulation of adult emergence rhythm under natural conditions has not previously been reported. Here we present the results of a study aimed at examining the time course and waveform of emergence rhythm in the fruit fly Drosophila melanogaster under seminatural condition (SN). We studied this rhythm in wild-type and clock mutant flies under SN in parallel with laboratory condition (LAB) to examine (1) how the rhythm differs between SN and LAB, (2) what roles the circadian clock protein PERIOD and the circadian photoreceptor CRYPTOCHROME (CRY) play in the regulation of emergence rhythm under SN, and (3) whether there is seasonality in the rhythm. Under SN, wild-type flies displayed tightly gated emergence, peaking at "dawn" and gradually tapering down toward the evening, with little or no emergence by night, while in LAB, flies emerged throughout the light phase of light-dark (LD) cycles. The period loss-of-function mutant (per ( 0 )) flies were arrhythmic in LAB but displayed weak rhythmic emergence under SN. Under SN, cry mutants displayed less robust rhythm with wider gates, greater variance in peak timing, and enhanced nighttime emergence compared to controls. Furthermore, flies showed seasonal variation in emergence rhythm, coupled either to light or to humidity/temperature depending on the severity of environmental conditions. These results suggest that adult emergence rhythm of Drosophila is more robust in nature, is coupled to environmental cycles, and shows seasonal variations.

Significance of activity peaks in fruit flies, Drosophila melanogaster , under seminatural conditions

“…Studies were conducted in an experimental enclosure under SN (3). Based on the light profile (dawn, ∼0600 hours; dusk, ∼1800 hours), we designated specific intervals of time as morning (M, 0400-1000 hours), afternoon (A, 1000-1600 hours) and evening (E, 1600-2200 hours).…”

“…Most assays were done on virgin male CS flies (unless specified) of age [3][4] ) and their genetic controls (w 1118 and CS) were also used. The activity recordings and behavioral assays were done in June to July 2012 and January to February 2013 in an outdoor enclosure (3).…”

“…Because simplified laboratory protocols are far removed from the reality of nature, these studies are limited in their ability to reveal the true features of circadian behavior in nature. For instance, laboratory studies mostly use square waves of one zeitgeber (time cue) such as light or temperature, or in rare cases, a combination of the two, quite unlike multiple, simultaneous, stochastic, and gradually changing factors in nature (2)(3)(4)(5)(6). Few recent studies on activity/rest and adult emergence rhythms of fruit flies, Drosophila melanogaster, under seminatural (SN) conditions reported significant differences in the patterns of these rhythms from those observed in the laboratory (2)(3)(4)(5)(6).…”

“…For instance, laboratory studies mostly use square waves of one zeitgeber (time cue) such as light or temperature, or in rare cases, a combination of the two, quite unlike multiple, simultaneous, stochastic, and gradually changing factors in nature (2)(3)(4)(5)(6). Few recent studies on activity/rest and adult emergence rhythms of fruit flies, Drosophila melanogaster, under seminatural (SN) conditions reported significant differences in the patterns of these rhythms from those observed in the laboratory (2)(3)(4)(5)(6). For instance, adult emergence rhythm was more robust under SN compared with the laboratory, and even the period null (per 0 ) flies exhibited rhythmicity (3).…”

“…Few recent studies on activity/rest and adult emergence rhythms of fruit flies, Drosophila melanogaster, under seminatural (SN) conditions reported significant differences in the patterns of these rhythms from those observed in the laboratory (2)(3)(4)(5)(6). For instance, adult emergence rhythm was more robust under SN compared with the laboratory, and even the period null (per 0 ) flies exhibited rhythmicity (3). An additional afternoon (A) peak of activity was reported under SN (4), which had never been observed in any standard laboratory protocol.…”