How does
hibernation work? What do insects do?
During hibernation the animal’s body temperature drops and their breathing and heart beat slow down significantly this reduces the energy consumption. For example, a hibernating woodchuck's heart rate slows from 80 to 4 beats per minute, and its temperature drops from 98 F to as low as 38 F. However if their body temperature drops too low the animal will wake up and shiver to raise their temperature.
How do animals know it is
time to hibernate?
This is still being widely
researched. It is believed that hibernating animals have something in their
blood called HIT (Hibernation Inducement Trigger). Recent research suggests
that it is some kind of opiate, chemically related to morphine. HIT is
triggered as the days become shorter, the temperature changes, food becomes
scarce and as a result hibernation occurs. How and why it happens are still a
mystery.
Insects
Insects all behave slightly
differently during winter, each adopting separate approaches to staying warm
including:
Communal living
This is when insects find
warmth in numbers. Honey bees group together for warmth and ants head deep
underground with large food supplies where the stay sharing body heat
throughout winter.
Torpor
This is a temporary state
of sleep which keeps the insect still and unmoving in order to conserve heat
and energy. Some insects do this at night and during the day come out of torpor
to continue as normal.
Diapause
This is a long term state
of suspension. This allows the insects life style to be in sync with the
seasonal climate. If the conditions are too cold to find food or migrate the
insect will pause during development.
Eggs of
the praying mantis only emerge during the spring.
Larvae
of caterpillars curl up in leaves and only spin their cocoons in the spring.
Pupa Black
swallowtails spend
winter as chrysalids, emerging as butterflies when warm weather returns.
Adult Mourning
cloak butterflies hibernate as adults for the winter, tucking themselves behind
loose bark or in tree cavities.
Antifreeze
Many insects are prepared
for the cold weather because they produce their own antifreeze. During the autumn
insects produce glycerol which gives the insect the ability to allow body
fluids to drop below freezing points without causing ice damage. Glycerol also
lowers the freezing point, making insects more cold-tolerant, and protects
tissues and cells from damage during icy conditions in the environment. In
spring, glycerol levels drop again.
http://insects.about.com/od/adaptations/p/wintersurvival.htm
Another interesting question is what cues are used by insects to go into hibernation or come out of it. If the cue for leaf eating insects is temperature - but the cue for trees to produce their first leaves is day length - there will be times when they are out of sync. Not surprisingly, caterpillars emerging from eggs in early spring are VERY mobile and also VERY tolerant of starvation. Makes sense.
ReplyDeleteDuncan (whose PhD thesis was on feeding ecology of plant feeding insects!)
I am unsure about all insects as there are such wide ranges that hibernate in different ways in relation to different stimuli. However when researching insects that use diapause, I did discover that in some species diapause only occurs in relation to the environmental conditions. However in other species the diapause period has become an obligatory part of their life cycle.
ReplyDeleteThis is most often seen in temperate zone insects, for these insects diapause is caused by what is known as changes in the photoperiod which is the relative lengths of day and night. When 50% of the population is in diapause, egologists call this the critical day length. Insects that enter disapause after this time are known as long day insects. The critical day length is a genetically determined property.
http://9e.devbio.com/article.php?id=211