Postprandial Sleep in Short-Sleeping Mexican Cavefish

Abstract

Interactions between sleep and feeding behaviors are critical for adaptive fitness. Diverse species suppress sleep when food is scarce to increase the time spent foraging. Postprandial sleep, an increase in sleep time following a feeding event, has been documented in vertebrate and invertebrate animals. While interactions between sleep and feeding appear to be highly conserved, the evolution of postprandial sleep in response to changes in food availability remains poorly understood. Multiple populations of the Mexican cavefish, Astyanax mexicanus, have independently evolved sleep loss and increased food consumption compared to surface-dwelling fish of the same species, providing the opportunity to investigate the evolution of interactions between sleep and feeding. Here, we investigate the effects of feeding on sleep in larval and adult surface fish, and in two parallelly evolved cave populations of A. mexicanus. Larval surface and cave populations of A. mexicanus increase sleep immediately following a meal, providing the first evidence of postprandial sleep in a fish model. The amount of sleep was not correlated to meal size and occurred independently of feeding time. In contrast to larvae, postprandial sleep was not detected in adult surface or cavefish, which can survive for months without food. Together, these findings reveal that postprandial sleep is present in multiple short-sleeping populations of cavefish, suggesting sleep-feeding interactions are retained despite the evolution of sleep loss. These findings raise the possibility that postprandial sleep is critical for energy conservation and survival in larvae that are highly sensitive to food deprivation.

Keywords: cavefish; circadian; evolution; feeding; sleep.

Figure 1

Sleep, feeding, and postprandial sleep behaviors across three populations of wild‐type Astyanax mexicanus. (A) Twenty days post fertilization fish were briefly fed before 24‐hour behavioral sleep recordings. At ZT0 the following day, fish were assayed for feeding behavior until ZT2, immediately after which, we recorded sleep behaviors between ZT2 and ZT6. (B) Sleep profiles of wild‐type surface, Pachón, and Tinaja fish were taken over the course of the experiment. Lines and error bars represent the mean ± SEM. (C) Cross‐population comparison of total sleep duration immediately following the feeding experiment. Letters indicate significant differences between populations. Cavefish slept significantly less than surface fish (ANOVA: F_2, 34 = 8.123, p = 0.0013; Tukey's HSD for surface‐Pachón, p = 0.0202; Tukey's HSD for surface‐Tinaja, p = 0.0024). (D) Cross‐population comparison of the number of Artemia eaten during the 2‐h feeding experiment. Letters indicate significant differences between populations. Tinaja ate significantly more than surface fish (ANOVA: F_2, 76 = 3.91, p = 0.0242; Tukey's HSD for surface‐Tinaja, p = 0.0178).

Figure 2

Postfeeding increase in larval Astyanax mexicanus sleep duration is not dependent on daily feeding time. Twenty days post fertilization larvae were fed over a 45‐min window before ZT2 (A, D, G), ZT6 (B, E, H), or ZT10 (C, F, I). (A–C) Sleep profiles of surface, Pachón, and Tinaja larvae, in minutes per hour, averaged across the daylight cycle. Lines and error bars represent the mean ± SEM. (D–F) Cross‐population comparison of total sleep duration in hours over the 14‐hour light cycle. Letters represent significant differences between populations. (D) Total sleep duration around a ZT2 feeding window was significantly different between populations of A. mexicanus (ANOVA: F_2, 113 = 20.81, p < 0.0001). (E) Total sleep duration around a ZT6 feeding window was significantly different between surface and cave populations of A. mexicanus (ANOVA: F_2, 113 = 8.48, p = 0.0004; Tukey's HSD for Surface‐Pachón, p = 0.001 and Surface‐Tinaja, p = 0.0069). (F) Total sleep duration around a ZT10 feeding window was significantly different between surface and cave populations of A. mexicanus (ANOVA: F_2, 81 = 11.64, p < 0.001; Surface‐Pachón, p = 0.0003; Tukey's HSD for surface‐Tinaja, p = 0.0002). (G–I) Percentage change in sleep duration for the 4‐hour period following feeding from total daytime sleep calculated as (proportion of postprandial sleep − proportion of total sleep)/proportion of total sleep. All conditions were significantly different from zero (see Table S1). Letters indicate significant differences between populations. (G) Percent change of postprandial sleep after ZT2 feeding window. There was no significant difference across populations in the percentage of increase in postprandial sleep (ANOVA: F_2, 104 = 3.36, p = 0.0417). (H) Percent change of postprandial sleep after ZT6 feeding window. There was no significant different in the percentage of increase in postprandial sleep between surface and Pachón cavefish, but surface fish had a significantly greater increase in sleep than Tinaja cavefish (ANOVA: F_2, 96 = 5.758, p = 0.0072; Tukey's HSD for surface‐Tinaja, p = 0.0101). (I) Percent change of postprandial sleep after ZT10 feeding window. Pachón cavefish had a significantly greater percent increase in postprandial sleep than both surface and Tinaja cavefish (ANOVA: F_2, 111 = 4.727, p = 0.0107; Tukey's HSD for surface‐Pachón, p = 0.0298; Tukey's HSD for Pachón‐Tinaja, p = 0.0275).

Figure 3

Postprandial sleep in larval Astyanax is only dependent on the amount of food consumed for surface fish fed before ZT2. Correlation of amount of Artemia nauplii consumed with sleep duration in the 4 hours following feeding with a simple linear regression for surface (A–C), Pachón (D–F), and Tinaja (G–I). (A, D, G) Larvae were fed before ZT2. (B, E, H) Larvae were fed before ZT6. (C, F, I) Larvae were fed before ZT10.

Figure 4

Feeding results in robust increases in sleep duration in larval surface, Pachón, and Tinaja populations of Astyanax mexicanus. (A–C) Four‐hour sleep profiles comparing the sleep of fed (colored) and unfed (black) individuals in each population. Lines and error bars represent the mean ± SEM. (D–F) Fed fish sleep significantly more during the 4 hours following feeding than unfed fish, regardless of the population. (D) Surface: Mann–Whitney U = 524, n _fed = 77, n _unfed = 55, p < 0.0001. (E) Pachón: Mann–Whitney U = 310.5, n _fed = 52, n _unfed = 47, p < 0.0001. (F) Tinaja: Mann–Whitney U = 546.5, n _fed = 45, n _unfed = 49, p < 0.0001. (G–I) Fed fish are less likely to wake while asleep, and more likely to fall asleep while awake, than unfed fish. (G) Surface: P(Wake) Mann–Whitney U = 1317, n _fed = 77, n _unfed = 76, p < 0.0001; P(Doze) Mann–Whitney U = 1347, n _fed = 77, n _unfed = 75, p < 0.0001. (H) Pachon: P(Wake) Mann–Whitney U = 663, n _fed = 66, n _unfed = 52, p < 0.0001; P(Doze) Mann–Whitney U = 802, n _fed = 69, n _unfed = 52, p < 0.0001. (I) Tinaja: P(Wake) Mann–Whitney U = 369, n _fed = 40, n _unfed = 38, p < 0.0001; P(Doze) Mann–Whitney U = 229, n _fed = 40, n _unfed = 34, p < 0.0001. Horizontal lines represent quartiles. Asterisks represent significant differences between fed and unfed groups.

Figure 5

Adult Astyanax do not display postprandial sleep behavior. (A, B) Sleep profiles of adult Surface, Pachón, and Tinaja, in minutes per hour. Lines and error bars represent the mean ± SEM. (A, C) Fish were not fed over the course of the day. (B, D) Fish were provided food from ZT5.5 (indicated by the arrow and dotted black line in B) to ZT6. (C, D) Cross‐population comparison of total sleep duration in hours over the 24‐hour day. Letters represent significant differences between populations. (C) Total sleep duration in 24 hours was significantly different between unfed surface and cave populations of Astyanax mexicanus (ANOVA: F_2, 28 = 15.5, p < 0.0001; Tukey's HSD for Surface‐Pachón, p < 0.0001 and Surface‐Tinaja, p = 0.0015). (D) Total sleep duration was significantly different between fed surface and cave populations of A. mexicanus (ANOVA: F_2, 25 = 15.04, p < 0.0001; Tukey's HSD for Surface‐Pachón, p < 0.0001 and Surface‐Tinaja, p = 0.0008). (E–G) Four‐hour sleep profiles comparing the sleep of fed (colored) and unfed (black) individuals in each population: surface (E), Pachón (F), and Tinaja (G). Lines and error bars represent the mean ± SEM. (H–J) There were no significant differences in sleep during the 4 hours following feeding, regardless of the population. (H) Surface: Mann–Whitney U = 88, n _fed = 12, n _unfed = 15, p = 0.9317. (I) Pachon: Mann–Whitney U = 31.5, n _fed = 8, n _unfed = 8, p > 0.9999. (J) Tinaja: Mann–Whitney U = 22.5, n _fed = 8, n _unfed = 8, p > 0.2. (K–M) There were no significant differences in activity state transitions between fed and unfed fish. (K) Surface: P(Wake) t = 0.271, df = 22, p = 0.7888; P(Doze) t = 2.041, df = 22, p = 0.054. (L) Pachon: Mann–Whitney U = 24, n _fed = 8, n _unfed = 8; P(Wake) p = 0.4667; P(Doze) p = 0.4667. (M) Tinaja: Mann–Whitney U = 23, n _fed = 8, n _unfed = 8; P(Wake) p = 0.5714; P(Doze) p = 0.1319). Horizontal lines represent quartiles.