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 30ÊC, 25ÊC and
20ÊC 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 20ÊC, but least active at 30ÊC. Body temperature was
highest at 30ÊC and lowest at 20ÊC, 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.
S1 Fig. Soil temperature. Ambient temperatures (ÊC) in full sun, shade and at different soil
depths over five consecutive days.
S2 Fig. Daily mean Tb and activity. Mean body temperature (±SE) and mean activity counts
(±SE) for female and male highveld mole-rats over the 24h day at each of the three ambient
temperatures tested. Black bars indicate the dark phase of the light cycle and white bars indicate
the light phase.
S3 Fig. Actograms. Complete actograms for the duration of the experimental procedure are
presented for all animals. The black and white bars on top of the actograms shows the dark
and light phases during the LD cycles, during DD cycles no light is present. The number of
days are on the Y-axis.