Below left: a Burmese Python with her clutch
of eggs. Image by Paul Tessier.
Right: shivering has been well-studied in the
Diamond Python. Image by fivespots.
evening (6-10pm), then steadily declining shortly
after midnight, and being lowest in the early morn-
ing (3-6am), with shivering ceasing around dawn.
When ambient temperatures were around 28 o C, the
python could maintain her body temperature at 32-
33 o C for 12 hours each day. At lower ambient
temperatures, she was still able to sustain a
temperature of 32 o C, but for a shorter duration of
eight hours.
Shivering thermogenesis is not a quirk of captive
conditions but has also been demonstrated in the
wild. Slip and Shine’s studies on Diamond Pythons
in the wild found that brooding females also used
metabolic heat production to maintain high, stable
body temperatures within a narrow range (around
31 o C), which was generally 9 o C above ambient
temperatures, but occasionally up to 13 o C higher.
The energetic expenditure and metabolic activity
involved in this activity is far from trivial: Harlow and
Grigg examined their female python’s oxygen
consumption when the snake was no longer brood-
ing (under identical ambient temperatures) and
found it to be just 4.8% of her maximum rate when
incubating her clutch! As such, metabolic rates of
brooding females can be 21-fold higher than when
they are non-brooding. The energetic cost was
evident when they monitored her weight: after 52
days of brooding and daily shivering, the female had
lost 278g (7% of her body weight) compared with
her weight two days after oviposition. It was noted
that she also fasted the entire time she was brood-
ing, and hence no energy was replaced through
diet, but none of the resultant weight loss was due
to voiding faeces or urine. Later, Slip and Shine
reported that female Diamond Pythons lost over
15% of their post-oviposition body weight while
brooding. The high energetic expenditure is likely
why females typically do not breed every year.
Given the energetic investment in shivering
thermogenesis, we would expect that there is a
benefit to this behaviour, and indeed, both field and
lab studies have found that this behaviour is clearly
adaptive. The resultant higher temperature-
mediated developmental rates have been shown to
induce earlier hatching, and the high incubation
temperatures have also been shown to enhance
offspring viability and quality. Pythons in particular
have often been shown to be very sensitive to low
temperatures during development, with embryos
dying when temperatures are too low. Experiments
on artificially-incubated python eggs have
suggested that at temperatures below 30 o C, eggs
take longer to develop, and fewer successfully
hatch; hatching ceases altogether if eggs are
incubated at 25 o C or less, with little signs of
development.
The faster developmen-
tal rates that occur under
higher temperatures