Geographic variation in sleep and metabolic function is associated with latitude and temperature

Abstract

19Regulation of sleep and metabolic homeostasis are critical to an animal's survival and under 20 stringent evolutionary pressure. Animals display remarkable diversity in sleep and metabolic 21 phenotypes; however, an understanding of the ecological forces that select for, and maintain, 28populations collected from unique geographic localities. These studies reveal remarkable 29 diversity in sleep, starvation resistance, and energy stores. We found that increased sleep 30 duration is strongly associated with proximity to the equator and elevated average annual 31 temperature, suggesting that environmental gradients strongly influence natural variation in 32 sleep. Further, we found variation in metabolic regulation of sleep to be associated with free 33 glucose levels, while starvation resistance associates with glycogen and triglyceride stores. 34Taken together, these findings reveal robust naturally occurring variation in sleep and metabolic 35 traits in D. melanogaster and suggest that distance from the equator and median temperature is 36 a significant evolutionary factor in sleep regulation and architecture. 50Determining the relationship between sleep and metabolic function, and how evolution shapes 51 these processes, is critical for understanding the function of sleep and basis for sleep differences 52 between and within species. 53The fruit fly Drosophila melanogaster presents a powerful model for investigating genetic 54 interactions between sleep and metabolic processes (Erion et al., 2012; Yurgel et al., 2014 (Shaw et al., 2000). Flies acutely modulate their sleep in accordance with 59 nutrient availability, and starvation potently inhibits sleep and initiates foraging, thereby 60 providing a system to investigate the relationship between sleep and metabolic regulation 61 (Keene et al., 2010; Lee and Park, 2004; Linford et al., 2012 (Cirelli et al., 2005; Koh et al., 2008; Rogulja and Young, 2012), naturally occurring 68 variation has also been leveraged to identify the genetic architecture regulating these processes 69 (Harbison et al., 2009a(Harbison et al., , 2013 95San Diego) with stock numbers provided in Table 1. Flies were reared and maintained on a 12:12 96 light-dark cycle in humidified incubators at 25°C and 65% humidity (Percival Scientific, Perry, IA). 97Unless otherwise noted, all flies were maintained and tested on standard cornmeal/agar 98 medium. 100 | Behavioral Analysis 101Mated female flies aged 3-5 days were briefly anesthetized using CO 2 and then individually 102 placed into plastic tubes containing standard food. Flies were then acclimated to these 103 conditions for at least 24hrs prior to testing. Fly activity was monitored using DAM2 Drosophila 124were assigned a positive value, while measurements to the west were assigned a negative value. 125Since the altitude measurements were not normally distributed, the Log 10 of altitude was used. BY 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder fo...