Foraging alters resilience/vulnerability to sleep disruption and starvation in Drosophila

Abstract

Recent human studies suggest that genetic polymorphisms allow an individual to maintain optimal cognitive functioning during sleep deprivation. If such polymorphisms were not associated with additional costs, selective pressures would allow these alleles to spread through the population such that an evolutionary alternative to sleep would emerge. To determine whether there are indeed costs associated with resiliency to sleep loss, we challenged natural allelic variants of the foraging gene (for) with either sleep deprivation or starvation. Flies with high levels of Protein Kinase G (PKG) (for(R)) do not display deficits in short-term memory following 12 h of sleep deprivation. However, short-term memory is significantly disrupted when for(R) flies are starved overnight. In contrast, flies with low levels of PKG (for(s), for(s2)) show substantial deficits in short-term memory following sleep deprivation but retain their ability to learn after 12 h of starvation. We found that for(R) phenotypes could be largely recapitulated in for(s) flies by selectively increasing the level of PKG in the α/β lobes of the mushroom bodies, a structure known to regulate both sleep and memory. Together, these data indicate that whereas the expression of for may appear to provide resilience in one environmental context, it may confer an unexpected vulnerability in other situations. Understanding how these tradeoffs confer resilience or vulnerability to specific environmental challenges may provide additional clues as to why an evolutionary alternative to sleep has not emerged.

Fig. 1.

foraging differentially confers resilience/vulnerability to SD and starvation. (A) for^R flies do not compensate for 12 h of SD with a subsequent increase in sleep, whereas both for^s and for^s2 mutants exhibit a sleep rebound typical of Cs flies. % sleep recovered is calculated for each individual as a ratio of the minutes of sleep gained above baseline during 48 h of recovery divided by the minutes of sleep lost during SD; *P < 0.05, modified Bonferroni test. Data are presented as mean ± SEM. (B) STM is impaired in for^s flies following 12 h of SD, whereas for^s2 mutants display impairments both during baseline and following SD. In contrast, for^R flies maintain normal STM following SD. (C) When placed in starvation before lights out, for^R flies display significantly less sleep than during the previous baseline night and do not exhibit a sleep rebound when placed back onto food the following morning. Neither for^s flies nor for^s2 mutants respond to starvation with an increase in waking. Cumulative sleep lost or gained during starvation. (D) STM is impaired in for^R flies when waking is induced by starvation. for^s flies maintain STM following a night of starvation. Surprisingly, for^s2 mutants have normal STM following a night of starvation. (E) STM is impaired in for^s/for^s2 flies under baseline conditions compared with starved siblings. Sleep-deprived for^s/for^s2 flies show no further STM impairments relative to baseline. (F) for^s flies survive longer than for^R and for^s2 flies during chronic starvation (n > 27 per group).

Fig. 2.

Sleep deprivation does not block LTM in for^R flies. (A) for^R females increase sleep following social enrichment relative to isolated siblings, whereas for^s and for^s2 females do not. *P < 0.05, modified Bonferroni test. Data are presented as mean ± SEM. (B) for^R flies have intact LTM that is not disrupted when sleep-deprived for 4 h immediately after training (T+SD). Trained for^s flies have intact LTM during baseline but are impaired when sleep-deprived following training. for^s2 mutants have impaired LTM; courtship was not evaluated in for^s2 flies following SD (ND). NS, nonsignificant. *P < 0.05, modified Bonferroni test. (C) Following spaced training for courtship conditioning, for^R males, but not for^s or for^s2 flies, sleep significantly more than their naïve siblings; *P = 0.03.

Fig. 3.

Expressing foraging in the MB confers resilience to sleep deprivation. (A–C) When UAS-for is expressed using c739-GAL4/for^s (A) and 30y-GAL4/for^s (B) drivers, no sleep rebound is observed after 12 h of SD. Parental lines display a sleep rebound. Interestingly, w; for^s,201y/for^s;UAS-for flies (C) and their parental controls exhibit a sleep rebound; *P < 0.05, modified Bonferroni test. Data are presented as mean ± SEM. n.s., nonsignificant. (D and E) As expected, w; for^s,c739/for^s, w; for^s;UAS-for/+, and w; for^s;30y parental lines display significant reductions in STM following 12 h of SD, whereas both w; for^s,c739/for^s;UAS-for/+ (D) and w; for^s;30y/UAS-for (E) flies retain STM following SD. (F) During baseline, UAS-dicer²/+;30y/UAS-for^RNAi flies show deficits in STM, whereas both parental controls learn; performance remains low after SD in all genotypes. However, UAS-dicer²/+;30y/UAS-for^RNAi flies display STM following starvation. (G–I) Courtship conditioning fails to induce LTM in w; for^s,c739/for^s;UAS-for/+ (G) and w; for^s;30y/UAS-for (H) but is intact in the parental lines. w; for^s,201y/for^s;UAS-for/+ flies and parental controls have intact LTM (I).

Fig. 4.

for overexpression in the MBs alters response to starvation. (A–C) w; for^s,c739/for^s;UAS-for/+ and w; for^s;30y/UAS-for flies exhibit a for^R-like response to 15 h of starvation, whereas the parental lines retain the for^s phenotype; for^s;UAS-for/+ data are replotted in B and C to facilitate comparisons. In contrast, w; for^s,201y/for^s;UAS-for/+ flies and their parental controls (w; for^s,201y/for^s) exhibit a for^s response to starvation (C). Data are presented as mean ± SEM. (D–F) Survival during chronic starvation is not altered when UAS-for is expressed in MB α and β lobes but is increased when UAS-for is expressed in MB γ lobes.