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

Abstract

Studies on circadian entrainment have traditionally been performed under controlled laboratory conditions. Although these studies have served the purpose of providing a broad framework for our understanding of regulation of rhythmic behaviors under cyclic conditions, they do not reveal how organisms keep time in nature. Although a few recent studies have attempted to address this, it is not yet clear which environmental factors regulate rhythmic behaviors in nature and how. Here, we report the results of our studies aimed at examining (i) whether and how changes in natural light affect activity/rest rhythm and (ii) what the functional significance of this rhythmic behavior might be. We found that wild-type strains of fruit flies, Drosophila melanogaster, display morning (M), afternoon (A), and evening (E) peaks of activity under seminatural conditions (SN), whereas under constant darkness in otherwise SN, they exhibited M and E peaks, and under constant light in SN, only the E peak occurred. Unlike the A peak, which requires exposure to bright light in the afternoon, light information is dispensable for the M and E peaks. Visual examination of behaviors suggests that the M peak is associated with courtship-related locomotor activity and the A peak is due to an artifact of the experimental protocol and largely circadian clock independent.circadian rhythms | chronoethogram | courtship | period mutants | afternoon peak T he role of circadian clocks in the temporal regulation of behaviors has been studied mostly under controlled laboratory conditions (1). 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 (2-6). 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 (2-6). 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. Several features of the activity/rest rhythm (anticipation to twilight transitions and midday siesta) were absent under SN, and certain features of the rhythm such as crepuscular pattern and dominance of light over temperature were proposed to be artifacts of laboratory studies (4). The temporal profiles of neuronal expression of clock proteins, PERIOD and TIMELESS were also found to differ between laboratory and nature (6).At present, the available literature is limited to descriptions of rh...

The sexual dimorphic behaviour of adult Drosophila suzukii: elevated female locomotor activity and loss of siesta is a post-mating response

“…The monitor has been designed differently from the commonly used DAM2 Trikinetics monitors to reduce the risk of shadows being cast by the plastic housing. Such shadows might attract flies to the infrared beams as they seek shade from strong light and possibly lead to inaccurate reporting of activity (De et al, 2013).…”

“…This variability has been shown to be dependent on the age, sex and, in the case of females, mating status of the insects (Ho and Sehgal, 2005;Isaac et al, 2010;Koh et al, 2006). Some studies have compared circadian behaviour of D. melanogaster kept on the standard 12LD cycle with the behaviour of flies in either a seminatural outdoor environment or an incubator capable of simulating semi-natural conditions by gradually changing both temperature and light levels (De et al, 2013;Kannan et al, 2012;Menegazzi et al, 2013Menegazzi et al, , 2012Vanin et al, 2012). They have highlighted differences between the daytime activity of adult D. melanogaster in these more natural conditions compared with the standard laboratory 12LD cycle and constant temperature conditions and, in particular, the unexpected appearance in some studies of an afternoon peak of activity in semi-natural environments Vanin et al, 2012).…”

Drosophila circadian rhythms in seminatural environments: Summer afternoon component is not an artifact and requires TrpA1 channels

“…Another study performed under seminatural conditions at tropical latitudes has questioned the validity of the A component (8). These authors suggest instead that A represents a behavioral artifact as a result of flies avoiding the midday sun by sheltering in the shaded part of the glass activity tube where the TriKinetics infrared detectors are located, leading to inappropriate triggering of the sensor and high activity counts.…”

Control of Sleep-Wake Cycles in Drosophila

“…Indeed, we have data indicating that new groups of oscillators are recruited when flies are confronted with summer-like conditions. Such laboratory-based simplified environmental parameters are probably inadequate to explain the working of the network under the complex natural conditions that exist in the spatiotemporal niche inhabited by Drosophila in the wild (Menegazzi et al , 2013Vanin et al 2012;De et al 2013). In particular, daily temperature variations have a strong impact on the sleep-activity pattern and can even induce some morning and evening anticipatory activity in clockless flies (Vanin et al 2012;Menegazzi et al 2013).…”