Myo-inositol as a main metabolite in overwintering flies: seasonal metabolomic profiles and cold stress tolerance in a northern drosophilid fly

Abstract

SUMMARYCoping with seasonal changes in temperature is an important factor underlying the ability of insects to survive over the harsh winter conditions in the northern temperate zone, and only a few drosophilids have been able to colonize sub-polar habitats. Information on their winter physiology is needed as it may shed light on the adaptive mechanisms of overwintering when compared with abundant data on the thermal physiology of more southern species, such as Drosophila melanogaster. Here we report the first seasonal metabolite analysis in a Drosophila species. We traced changes in the cold tolerance and metabolomic profiles in adult Drosophila montana flies that were exposed to thermoperiods and photoperiods similar to changes in environmental conditions of their natural habitat in northern Finland. The cold tolerance of diapausing flies increased noticeably towards the onset of winter; their chill coma recovery times showed a seasonal minimum between late autumn and early spring, whereas their survival after cold exposure remained high until late spring. The flies had already moderately accumulated glucose, trehalose and proline in autumn, but the single largest change occurred in myo-inositol concentrations. This increased up to 400-fold during the winter and peaked at 147nmolmg -1 fresh mass, which is among the largest reported accumulations of this compound in insects. Supplementary material available online at

More complex than expected: Cold hardiness and the concentration of cryoprotectants in overwintering larvae of five Erebia butterflies (Lepidoptera: Nymphalidae)

“…The AutumnCold treatment temperatures, to which the alpine and freeze-avoidant E. cassioides larvae were exposed, likely crossed a threshold for a decrease in SCP (Vesala et al, 2012). The larvae dramatically increased their cryoprotectant concentration and decreased their SCP.…”

How consistent are the transcriptome changes associated with cold acclimation in two species of the Drosophila virilis group?

“…Changes to the composition of phospholipids in the cell membrane are thought to be particularly important for cold acclimation, as it allows cells to maintain their physiological function in sub-optimal temperatures (Hazel, 1995;Koštál et al, 2003). Our previous work has shown the major metabolite produced in overwintering D. montana flies to be myoinositol (Vesala et al, 2012a), which functions in many processes including regulation of cell development and growth (Loewus and Loewus, 1983). It also is a precursor of inositol phospholipids leading to production of inositol phosphates that function as second messengers (Downes and Macphee, 1990).…”

Hemolymph metabolites and osmolality are tightly linked to cold tolerance ofDrosophilaspecies: a comparative study

“…However, small increases in trehalose are found on a whole-organism level after both rapid cold hardening and long-term cold acclimation in larval and adult D. melanogaster (Overgaard et al, 2007;Koštal et al, 2011a;Colinet et al, 2012). Further, whole-organism levels of trehalose (and glucose) were found to increase during autumn and winter in D. montana (Vesala et al, 2012). However, interestingly, feeding with dietary sugars does not increase cold tolerance of D. melanogaster even though it increases the general level of sugars (Colinet et al, 2013).…”

“…Glycerol is a very important cryoprotectant in many freeze-avoiding insect species (Zachariassen, 1985) and has also been found to be associated with increased cold tolerance in cold-sensitive species like the flesh fly and the tropical beetle A. diaperinus (Chen et al, 1987;Yoder et al, 2006;Michaud and Denlinger, 2007;Lalouette et al, 2007;Teets et al, 2012). Glycerol has not previously been associated with cold tolerance in Drosophila (Kelty and Lee, 1999;Overgaard et al, 2007;Koštal et al, 2011a;Colinet et al, 2012), but D. montana does accumulate large amounts of another polyol, myoinositol, as a cryoprotectant (Vesala et al, 2012). However, analysis of the entire spectra without removal of the contaminated areas did not show any strong signals for these compounds.…”

“…In coldacclimated adult D. melanogaster, several amino acids increased and in D. melanogaster larvae, long-term cold acclimation increased levels of proline in particular (Koštal et al, 2011a). Furthermore, in D. montana, proline varies seasonally, showing a maximum in the winter (Vesala et al, 2012), while fluctuating thermal regimes and diapause lead to increased levels of many amino acids (e.g. lysine, isoleucine and leucine) in the tropical beetle Alphitobius diaperinus and codling moth Cydia pomonella, respectively (Lalouette et al, 2007;Rozsypal et al, 2013).…”