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. 2021 Jul 1;11(1):13658.
doi: 10.1038/s41598-021-92816-6.

Gender differences in BaYaka forager sleep-wake patterns in forest and village contexts

Erica Kilius  1 , David R Samson  2 , Sheina Lew-Levy  3   4 , Mallika S Sarma  5 , Ujas A Patel  6 , Yann R Ouamba  7 , Valchy Miegakanda  8 , Lee T Gettler  9   10 , Adam H Boyette  11
Affiliations

Gender differences in BaYaka forager sleep-wake patterns in forest and village contexts

Erica Kilius et al. Sci Rep. .

Abstract

Sleep studies in small-scale subsistence societies have broadened our understanding of cross-cultural sleep patterns, revealing the flexibility of human sleep. We examined sleep biology among BaYaka foragers from the Republic of Congo who move between environmentally similar but socio-ecologically distinct locations to access seasonal resources. We analyzed the sleep-wake patterns of 51 individuals as they resided in a village location (n = 39) and a forest camp (n = 23) (362 nights total). Overall, BaYaka exhibited high sleep fragmentation (50.5) and short total sleep time (5.94 h), suggestive of segmented sleep patterns. Sleep duration did not differ between locations, although poorer sleep quality was exhibited in the village. Linear mixed effect models demonstrated that women's sleep differed significantly from men's in the forest, with longer total sleep time (β ± SE = - 0.22 ± 0.09, confidence interval (CI) = [- 0.4, - 0.03]), and higher sleep quality (efficiency; β ± SE = - 0.24 ± 0.09, CI = [- 0.42, - 0.05]). These findings may be due to gender-specific social and economic activities. Circadian rhythms were consistent between locations, with women exhibiting stronger circadian stability. We highlight the importance of considering intra-cultural variation in sleep-wake patterns when taking sleep research into the field.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Two fixed effect plots of ecological predictors on sleep duration quotas: nighttime sleep duration (TST) (left) and 24-h total sleep time (TTST) (right). Reference variables are set as village for location, and women for gender for all models. Both plots illustrate positive (indicated in blue) and negative (indicated in red) predictors of TST and TTST. The plotted lines indicate 95% confidence intervals of each predictor variable. For TST, only the location * gender interaction was a significant predictor variable. The location * gender interaction was also a negative predictor of TTST, while rainfall was a positive predictor. Values written above each plotted line are standard estimates of each predictor. Continuous predictors were scaled for comparability of the coefficients in the models.
Figure 2
Figure 2
Two fixed effect plots of ecological predictors on sleep quality measures: sleep efficiency (left) and Sleep fragmentation (right). For both plots, positive predictors on sleep quality are indicated in blue, while negative predictors are indicated in red. Values written above each confidence line are standard estimates of each variable. The plot on the left illustrates that humidity, temperature, moon phase, and the location * gender interaction effect all negatively influenced sleep efficiency in the BaYaka. The plot on the right illustrates that rainfall negatively influenced sleep fragmentation, while humidity, temperature, age, and the location * gender interaction effect were positive predictors of sleep fragmentation.
Figure 3
Figure 3
Functional linear modelling comparing 24-h sleep–wake patterns of BaYaka men and women. Women are represented by a red line and men represented by a black line. Women displayed a sharp, steady incline of activity in the morning and generally higher levels of mean activity throughout the day as compared to men, especially in the afternoon. Men show a decline in their activity towards noon, suggestive of resting and/or napping periods before the next peak of activity, and a steady decline throughout the evening. The bottom panel displays a permutation F test; the point-wise critical value (dotted line) displays the proportion of permutation F values at the significance level of 0.05 for every time point. Men and women have significantly different mean circadian activity patterns at the points when the observed F-statistic (represented as a solid line) crosses the critical value (dotted line).
Figure 4
Figure 4
Functional linear modelling comparing 24-h sleep–wake patterns of BaYaka in the forest and village locations. The forest location is represented by a red line and the village represented by a black line. Bottom part of the illustration displays the permutation F test; significant values of the F-statistic cross the line of the critical value (dotted line).
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