Fight between two terms Ectotherms & Poikilotherms.

1. Temperature Regulation
in Ectotherms
Presented By
Nida Sajjad
Physiology of Adaptation
MPhil Zoology
University of Sargodha

2. Contents
 What are ectotherms?
 Ectothermy and poikilothermy
 Temperature independence of ectotherms
 Adaptations for cold environment
 Freeze avoidance and tolerance
 Adaptations in other ectotherms
 Advantages and disadvantages
 Conclusion

3. What are Ectotherms?
 Any animal whose regulation of body temperature depends on external sources, such as
sunlight or a heated rock surface.
 The ectotherms include the fishes, amphibians, reptiles, and invertebrates.
 The body temperatures of aquatic ectotherms are usually very close to those of the water.
 Ectotherms do not require as much food as warm-blooded animals (endotherms) of the same
size.
 They occur in every ecological niche on Earth.
 They are unable to maintain their body temperature as endotherms do.

4. Poikilothermy And Ectothermy
 Both are the same thing.
 Two terms simply emphasize different aspects of one phenomenon.
 Poikilothermy emphasizes the variability of body temperature.
 Ectothermy emphasizes that outside conditions determine the body
temperature.

5. How Ectotherms Achieve Temperature
Independence?
 It is actually Independence from maintenance of temperature within narrow
range.
 Behavioral Adjustments
 Ectotherms cannot control their body temperature physiologically.But they
can regulate their body temperature behaviorally.
 Such as desert lizards, exploit hour-to-hour changes in solar radiation to keep
their body temperatures relatively constant.
 Behavioral patterns help to maintain a relatively steady body temperature of
36 to 39 C while the air temperature varies between 29 and 44 C.
 The desert iguana of the southwestern US prefers a body temperature of 42 C
when active and can tolerate a rise to 47 C, a temperature that is lethal to all
birds and mammals and most other lizards.

7. Metabolic Adjustments
 Even without the help of the behavioral adjustments, most ectotherms can
adjust their metabolic rates to the prevailing temperature such that the
intensity of metabolism remains mostly unchanged. This is called
temperature compensation.
 It involves complex biochemical and cellular adjustments.
 These adjustments enable a fish or a salamander to benefit from almost the
same level of activity in both warm and cold environments.

8.  ADAPTATIONS TO COPE WITH COLD
ENVIRONMENT

9. Thermal Environments of Cold-hardy
Ectotherms
 Avoidance often is an animal's primary means for protection from
extreme temperatures.
 If migration to warmer climes is not an option, survival may depend
on finding an overwintering site, or hibernaculum, that insulates from
damaging cold.
 For example, some toads and terrestrial turtles, being proficient
excavators, descend into the soil column and overwinter below the
reach of frost. Various snakes and woodland salamanders evade frost
by following abandoned rodent burrows.

10. Servival benefits at overwintering site
 To survive in winter cold-hardy ectotherms must seek thermally buffered sites.
 Ideal hibernaculum conceals its occupant from potential predators, permits gas exchange,
and prevents excessive desiccation.
 Some species prefer relatively exposed sites from which they can readily detect
environmental cues stimulating spring emergence.
 For others, such as plant gall-inhabiting insects and the hatchlings of some turtles there is
no choice in the matter: winter is passed in the very place where one hatches.
 Even locally, temperatures can range from mild to severe, depending on site characteristics
and the physical features of individual hibernacula, and, being subject to the vagaries of the
weather, can vary markedly from year to year.
 Within hibernacula, prevailing temperatures follow a pronounced seasonal rhythm.They
can detect tolerable temprature.

11. Freeze Avoidance
 Ice-nucleating Agent (INAs)
 Any agent that promotes the formation of ice crystals.
 An organism must remain free of INAs to carry out physical phenomenon of supercooling in
a freeze-avoidance strategy.
 Many inorganic particulates, microorganisms, proteins, and organic residues can organize
water molecules into a crystalline arrangement.
 INAs occur in overwintering sites of many ectotherms and may enter the body through
orifices or ingested with food.
 Many freeze-avoiding ectotherms prepare for dormancy by eliminating ingested INAs, and
by inhibiting endogenous ice-nucleating proteins.
 Physical contact with ice can invade the body and initiate freezing.
 Species that rely on supercooling for winter survival can reduce the risk of such "inoculative
freezing" by selecting hibernacula that limit their exposure to environmental ice.
 Ectotherms accumulate one or more cryoprotectants in advance of winter to avoid icing.

12. All are of low molecular mass and benign in
high concentrations
Class Examples Known From
Carbohydrates
polyhydric alcohols (glycerol,
sorbitol, ethylene glycol);
sugars (glucose, trehalose)
bacteria, marine and terrestrial
invertebrates, amphibians,
reptiles
Amino acids & derivatives
taurine, glycine, proline,
alanine, asparagine, glutamic
acid, lysine
bacteria, marine and terrestrial
invertebrates
Methylamines
glycine betaine,
glycerophosphorylcholine,
trimethylamine oxide
bacteria, marine invertebrates,
beetles
Urea
Terrestrial gastropods,
amphibians, reptiles
Table 1: Cryoprotectants used in animal freeze-avoidance and freeze-tolerance.

13. Freeze Tolerance
 Freeze tolerance is an adaptation for the survival of
tissue freezing under ecologically-relevant thermal and
temporal conditions.Found in arthropods, molluscs,
nematodes, annelids, amphibians, and reptiles.
 It is molecular and physiological responses that limit
injury to cells and tissues.
 Control of the freezing process is key to survival in
ectotherms.
 Many invertebrates, which are prone to supercool
owing to their small size, freezing is initiated by INAs in
the hemolymph or other tissues.
 Ectotherms vary markedly in their limits of freeze
tolerance.
 No ectotherm can withstand the freezing of more than
50-80% of their body water.
Taxon Examples
Lower Lethal
Temperature (°C)
Marine
invertebrates
(intertidal)
barnacles, bivalves,
gastropods
-20
Terrestrial
invertebrates
free-living
nematodes,
centipedes, flies,
beetles, butterflies
and moths, wasps
-80
Amphibians salamander, frogs -40 (frogs, -6)
Reptiles turtles, lizard, snake -4
Table 2: Thermal limits of freeze tolerance in
animals

14. More Adaptations in some other ectotherms
 BEHAVIORAL
 In cold weather, honey bees huddle together to retain heat and some vibrate their
flight muscles to generate heat. Butterflies and moths may orient their wings to
maximize exposure to solar radiation in order to build up heat before take-off.
 Gregarious caterpillars, such as the Forest Tent caterpillar, benefit from basking in
large groups for thermoregulation.
 PHYSIOLOGICAL
 Diving reptiles conserve heat by heat exchange mechanisms, whereby cold blood
from the skin picks up heat from blood moving outward from the body core, re-
using and thereby conserving some of the heat that otherwise would have been
wasted.
 The skin of bullfrogs secretes more mucus when it is hot, allowing more cooling by
evaporation.

15. Junonia lemonias is basking under the sun.
A six-foot-long black snake basking in
the Inverness, Florida sunshine on a cool
morning.

16. Pseudemys turtles basking for warmth are ectothermic.

17. Advantages and disadvantages
 They depend on ambient conditions to reach operational body
temperatures.
 But endotherms maintain nearly constant high operational body
temperatures by internal heat produced by metabolically active organs
(liver, kidney, heart, brain, muscle) or by specialized heat producing
organs like Brown Adipose Tissue (BAT).
 Ectotherms have lower metabolic rates than endotherms because
endotherms rely on higher food consumption, and on food of higher
energy content. Such requirements may limit the carrying capacity of a
given environment for endotherms as compared to ectotherms.
 As ectotherms depend on environmental conditions for thermoregulation,
that’s why they are more sluggish at night & in early mornings.
 Diurnal ectotherms need to heat up in the early sunlight before they can
begin their daily activities. In cool weather the foraging activity of such
species is restricted to the day time in most vertebrate ectotherms, and
in cold climates most cannot survive at all.

18.  In lizards, most nocturnal species are geckos specialising in "sit and
wait" foraging strategies. Such strategies do not require as much energy
as active foraging, and do not require hunting activity of the same
intensity. From another point of view, sit-and-wait predation may require
very long periods of unproductive waiting.
 Endotherms cannot in general afford such long periods without food,
but suitably adapted ectotherms can wait without expending much
energy.
 Endothermic vertebrate species are therefore less dependent on the
environmental conditions and have developed a higher variability (both
within and between species) in their daily patterns of activity.