Locomotor Activity and Body Temperature Patterns over a Temperature Gradient in the Highveld Mole-Rat (Cryptomys hottentotus pretoriae)

Abstract

African mole-rats are strictly subterranean mammals that live in extensive burrow systems. High humidity levels in the burrows prevent mole-rats from thermoregulating using evaporative cooling. However, the relatively stable environment of the burrows promotes moderate temperatures and small daily temperature fluctuations. Mole-rats therefore display a relatively wide range of thermoregulation abilities. Some species cannot maintain their body temperatures at a constant level, whereas others employ behavioural thermoregulation. Here we test the effect of ambient temperature on locomotor activity and body temperature, and the relationship between the two parameters, in the highveld mole-rat. We exposed mole-rats to a 12L:12D and a DD light cycle at ambient temperatures of 30°C, 25°C and 20°C while locomotor activity and body temperature were measured simultaneously. In addition, we investigated the endogenous rhythms of locomotor activity and body temperature at different ambient temperatures. Mole-rats displayed nocturnal activity at all three ambient temperatures and were most active at 20°C, but least active at 30°C. Body temperature was highest at 30°C and lowest at 20°C, and the daily cycle was highly correlated with locomotor activity. We show that the mole-rats have endogenous rhythms for both locomotor activity and body temperature. However, the endogenous body temperature rhythm appears to be less robust compared to the locomotor activity rhythm. Female mole-rats appear to be more sensitive to temperature changes than males, increased heterothermy is evident at lower ambient temperatures, whilst males show smaller variation in their body temperatures with changing ambient temperatures. Mole-rats may rely more heavily on behavioural thermoregulation as it is more energy efficient in an already challenging environment.

Ambient Temperature as a StrongZeitgeberof Circadian Rhythms in Response to Temperature Sensitivity and Poor Heat Dissipation Abilities in Subterranean African Mole-Rats

“…During Cycle 1 , animals were subjected to 10L:14D and constant T a of 25 °C, and lights went on at 0700 h and off at 1700 h (Figure 1a). To investigate whether the circadian rhythms of LA of CHM and GC are capable of entraining to T a cycles in the absence of light, we subjected animals to complete darkness (DD) and a simulated T a cycle, Cycle 2 , mimicking the natural range of temperatures experienced by these animals in their burrow systems (18-28 °C) (Roper et al, 2001; Haupt et al, 2017) (Figure 1b). Cycle 2 was followed by constant conditions (DD, T a = 25 °C), C ycle 3 , to differentiate whether any observed rhythms were due to masking or entrainment (Figure 1c).…”

“…The subterranean niche provides a relatively thermostable environment (Bennett et al, 1988; Šumbera et al, 2004; Holtze et al, 2018; Šumbera, 2019) as well as a shelter from above-ground predators and temperature extremes (Bennett and Faulkes, 2000; Finn et al, 2020), but the burrow systems have hypoxic and hypercapnic atmospheres with poor ventilation, high humidity, and limited access to light (Kennerly, 1964; Darden, 1972; Roper et al, 2001; Ivy et al, 2020; Logan et al, 2020). Although the burrow systems of African mole-rats are considered to possess a muted T a range, a minor T a range does exist (~10 °C) (Roper et al, 2001; Haupt et al, 2017). Furthermore, the LA of mole-rats under natural conditions has been suggested to be constrained by the risk of overheating during bouts of activity (Šklíba et al, 2014; Oosthuizen et al, 2021; Vejmělka et al, 2021), but there is no direct evidence to support this.…”

“…The LA patterns of African mole-rats have been extensively investigated and shown to entrain to photic stimuli, which suggests the possession of endogenous rhythms and a functional circadian system (Oosthuizen et al, 2003; Vasicek et al, 2005; Schöttner et al, 2006; De Vries et al, 2008; Streicher et al, 2011; Haupt et al, 2017; van Jaarsveld et al, 2019). Nevertheless, the degree of rhythmicity and ability to entrain varies within and between species (reviewed by Bennett (2009)).…”

RhythmicAlly: Your R and Shiny–Based Open-Source Ally for the Analysis of Biological Rhythms

“…7b). Data for the mole rats have been published (Haupt et al, 2017), but that of the ice rats are not yet published. Finally, we also analyzed circatidal rhythms in activity/rest behavior of the mangrove cricket ( Aptorenemobius asahinai ; Fig.…”

“…The mole rat was recorded for 25 days under LD12:12 at 30 °C and then under DD at 30 °C. The mole rat data have been published elsewhere (Haupt et al, 2017). All activity data sets are binned in 15-min intervals, and the body temperature data are collected at 1-h intervals.…”