Temperature regulation in invertebrates and fishes
Invertebrates:
Many Arthropods
have mechanism for surviving temperature extremes.
Temperature zone
insects avoid freezing by reducing the water content in their tissues as winter
approaches. Other insects can produce glycerol or other glycoproteins that act
as antifreeze. Some moths and humble bees warm up prior to flight by shivering
contractions of their thoracic flight muscles. In most large flying insects
blood circulating through the flight muscles carries heat from the thorax to
the abdomen which gets rid of the heat. Certain cicadas that live in the
Sonoran desert have cooling by evaporation like vertebrates.
When threatened
with overheating, these cicadas extract water from their blood and transport it
through large ducts to the surface of their body, where it passes through sweat
pores and evaporates. In other words these insects can sweat. Porching
dragonflies and butterflies can regulate their radiation heat gain by postural
adjustments to sun. To prevent over heating many ground dwelling arthropods
(beetles, locusts and scorpions) raise their bodies as high off the ground as
possible to minimize heat gain from the ground. Some caterpillars and locusts orient
with reference to both the sun and wind to vary both radiation heat gain and convective
heat loss. Some desert dwelling beetles can exude waxes from thousands of tiny
pores on their cuticle. These ‘wax blooms’ present dehydration and also are
extra barrier against the desert sun.
Many black
beetles may be more active earlier in the day because they absorb more
radiation and heat faster. Conversely white beetles are more active in hotter
parts of the day because they absorb less heat.
Fishes:
The temperature
of the surrounding ater determines the body temperature of most fishes. Fishes
that live in extremely cold water have “antifreeze” material in their blood.
Poly alcohols (e.g. sorbitol, glycerol) or water soluble peptides and
glycopeptides lower the freezing point of blood plasma and other body fluids.
These fishes
also have proteins or proteins sugar compounds that stunt the growth of ice
crystals that begin to form. These fishes stay flexible and swim freely in a
super cooled. Some active fishes maintain a core temperature significantly
above the temperature of the water. Blue fin tuna and great white shark have
major blood vessels just under the skin. Branches deliver blood to the deeper,
powerful red swimming muscles, where smaller vessels are arranged in a counter
current heat exchanger called miraculous net. The heat that these red muscles
generate is not lost because it is transferred in rete mirabile from venous
blood passing outward to cold arterial blood passing inward from the body
surface.
This arrangement of blood vessels enhances vigorous activity by
keeping the swimming muscles several degrees warmer than the tissue near the
surface of the fish. This system has been adaptive for these fishes. Their
muscular contraction can have four times as much power as those of similar
muscles in fishes with cooler bodies. Thus they can swim faster and range more
widely.
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