Flies in the North

Abstract

The circadian clock plays an important role in adaptation in time and space by synchronizing changes in physiological, developmental, and behavioral traits of organisms with daily and seasonal changes in their environment. We have studied some features of the circadian activity and clock organization in a northern Drosophila species, Drosophila montana, at both the phenotypic and the neuronal levels. In the first part of the study, we monitored the entrained and free-running locomotor activity rhythms of females in different light-dark and temperature regimes. These studies showed that D. montana flies completely lack the morning activity component typical to more southern Drosophila species in an entrained environment and that they are able to maintain their free-running locomotor activity rhythm better in constant light than in constant darkness. In the second part of the study, we traced the expression of the PDF neuropeptide and the CRY protein in the neurons of the brain in D. montana adults and found differences in the number and location of PDF- and CRY-expressing neurons compared with those described in Drosophila melanogaster. These differences could account, at least in part, for the lack of morning activity and the reduced circadian rhythmicity of D. montana flies in constant darkness, both of which are likely to be adaptive features during the long and dark winters occurring in nature.

Selection for reproduction under short photoperiods changes diapause-associated traits and induces widespread genomic divergence

“…Photoperiodic reproductive diapause has evolved multiple times in arthropod species, including within the genus Drosophila (Hand et al, 2016), and the interaction between PTM and circadian clock also seems to vary between species (Meuti and Denlinger, 2013). D. montana is a northern Drosophila species with a robust reproductive diapause, unimodal daily activity rhythm and an ability to maintain free-running locomotor activity rhythm in constant light, but not in constant darkness (Kauranen et al, 2012). This and other D. virilis group species also differ from a more southern species, D. melanogaster, at the neuronal level, for example, in the expression pattern of the blue light photopigment cryptochrome (CRY) and the neuropeptide pigment-dispersing factor (PDF) (Kauranen et al, 2012;Hermann et al, 2013).…”

“…D. montana is a northern Drosophila species with a robust reproductive diapause, unimodal daily activity rhythm and an ability to maintain free-running locomotor activity rhythm in constant light, but not in constant darkness (Kauranen et al, 2012). This and other D. virilis group species also differ from a more southern species, D. melanogaster, at the neuronal level, for example, in the expression pattern of the blue light photopigment cryptochrome (CRY) and the neuropeptide pigment-dispersing factor (PDF) (Kauranen et al, 2012;Hermann et al, 2013). D. virilis group species (including D. montana) probably lost CRY and PDF expression in their long (l-LNvs) and small (s-LNvs) ventrolateral clock neurons, respectively, but gained PDF expression in their central brain, under selection from environments subject to major photoperiodic changes throughout the year with extremely long photoperiods in summer (Menegazzi et al, 2017;Beauchamp et al, 2018).…”

“…Locomotor activity rhythm of the flies was traced in Trikinetics Drosophila High Resolution Activity Monitors (Waltham, MA, USA) (N=27-32 females and males per replicate; see Table 3) with 9 consolidated infrared beams per tube. Flies were collected 1-2 days after emergence and entrained under LD 19:5 for 6 days, after which their free-running rhythmicity was measured in LL for 8 days at 17°C (see Kauranen et al, 2012).…”

“…Flies that did not survive throughout the experiment (both entrained and free-running conditions) were excluded from the analysis. For more detailed information on the locomotor activity analysis, see Kauranen et al (2012). The data were made binary with values of 0 for arrhythmic flies and 1 for rhythmic flies to determine whether selection had affected flies' ability to retain their activity rhythm in constant light (LL).…”

Interaction of light regimes and circadian clocks modulate timing of pre-adult developmental events in Drosophila

“…For instance, differences in the activity/rest rhythm seen in fruit fly populations maintained under semi-natural conditions did not correlate with changes at the molecular or neural levels [46]. Similarly difference in activity/rest rhythm of different Drosophila species was found to occur in spite of very little difference at the molecular and neural levels [47,48]. The fact that all the four populations of the faster developing flies underwent changes in the same direction (BD1-FD1 = 0.44 h; BD2-FD2 = 0.71 h; BD3-FD3 = 0.41 h; BD4-FD4 = 0.52 h; [11]), suggests that the period differences are not because of random genetic drift but due to the imposed selection for faster pre-adult development.…”