The 5 differences between ectothermic and endothermic animals

Animals are, regardless of gender and species, open systems. As such, we are in constant relationship with the environment, obtaining energy in the form of organic matter, receiving and dissipating heat, exchanging gaseous substances with the environment and excreting potentially toxic compounds, among others things.

In the midst of this maelstrom of dynamism, some living beings have more control over their own internal environment than others, with the associated costs that this entails.

It is estimated that, on Earth, there are 8.7 million species of living beings, although today just over 2 million of them have been discovered. With such overwhelming diversity, just look for a few examples to realize that, in the natural world, the condition of the human being is almost anecdotal. For example, the vast majority of living beings on the planet are unable to regulate their internal temperature with metabolic mechanisms, although our species can.

Based on this premise (and perhaps with the intention of breaking some anthropocentric preconceptions), today we present you

the key differences between endothermic and ectothermic animals.

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What are the differences between endothermy and ectothermy in animals?

The terms "endothermy" and "ectothermy" refer to the ability of a living being (or lack thereof) to modulate its body heat. In any case, in nature not everything is black or white: as you will discover in later lines, neither Endothermic animals are immune to temperature changes, nor are ectotherms incapable of generating heat from the everything. Let's see the clearest differences between both biological strategies.

1. Endotherms generate metabolic heat to maintain their temperature, and ectotherms not so much

We start by laying the foundations. From a biological point of view, An endothermic animal is one that is capable of producing heat in relevant quantities and, therefore, can maintain its internal temperature within a favorable range, regardless of the environmental conditions expected for the ecosystem in which it lives. The classic endotherms are mammals and birds.

On the other hand, An ectothermic animal is one that generates very little metabolic heat and, therefore, must regulate its internal temperature through behavioral activitiessuch as going out in the sun for energy or in the shade to lower your metabolic rate. Within this group are all invertebrates, fish, reptiles and amphibians. As 53% of the world's fauna are insects, it can be assumed that the vast majority of living beings are ectotherms.

Exceptions that challenge the rule

The reality is that this classifying criterion, no matter how widespread it may be, is reductionist. Ectothermic animals generate less metabolic heat than endotherms, but this does not mean that they completely lack thermogenesis mechanisms.

For example, the snake species Python bivittatus significantly increases your body temperature through jerky contractions of your muscles. It does so when it is rolled up to its eggs, in order to transmit heat to them and protect them from the elements. Sea turtles of the Dermochelys coriacea species also maintain an internal temperature much higher than the marine aquatic environment, since they generate heat with their constant muscular activity.

Even more interesting is knowing that, in insects, moths and other flying invertebrates also defy this rule. For example, while flying, they can direct the hemolymph from the chest to the abdomen in a directional way, in order to dissipate the excess heat produced during movement. As you can see, some ectotherms can modulate their internal temperature, although it is often said that they cannot.

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2. A different mitochondrial load

In any case, these generalizations do have a series of biological bases, although they are increasingly being questioned. For example, Endotherms have, on average, been shown to have more mitochondria per cell than ectotherms. Mitochondria are the energy generators of organisms, since cellular respiration takes place here, or what is the same, the conversion of organic matter into energy.

As homeotherms have more mitochondria, they can generate more metabolic heat, enough not to constantly depend on environmental constraints. However, this energy does not come from nowhere: it is obtained from the diet, specifically from organic compounds such as carbohydrates, fats and proteins. Because the metabolism of the homeotherm is much more demanding, it must consume more food in greater quantities compared to the ectotherm.

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3. Endotherms can hibernate, while ectotherms cannot

At an informative level, the term "hibernation" is often used to designate any decrease in the activity of a living being in adverse conditions. Again, this generality errs as reductionist, since the reality is that ectotherms are unable to hibernate.

Hibernation is a state of minimal activity and metabolic depression, usually associated only with mammals (for birds it is more correct to use the term "torpor"). In this state of vital reserve, homeothermic animals minimize their internal temperature, the rhythm heart rate decreases, the respiratory rate drops and, consequently, the metabolism falls to its minimum possible.

In this state, the animal is sound asleep and does not get up until adverse conditions are over.. Hibernating mammals must eat a lot before this stage begins, as they must rely on their energy reserves in the form of adipose tissue to survive.

In the case of ectotherms (especially reptiles), the proper term is "brumation". A misty reptile is not completely asleep, as it must be activated to drink water and respond to stimuli, for example. In addition, a lizard can eat during its brumation, although it may not search for prey as hard as it did before. In other words, "metabolic depression" is less drastic in brumation.

4. Endotherms are less dependent on external temperature

The greatest evolutionary disadvantage of ectothermy is the dependence on the external environment. As a general rule, reptiles, fish, and amphibians are clumsier in the morning and at night., since it is colder (due to the lack of incidence of sunlight) and, therefore, your metabolism irreparably lowers. As an advantage associated with this state, at least they need much less food to maintain their body, so this exchange "pays off."

Endotherms are less dependent on the environment to maintain their body temperature, but this does not mean that they are immune to environmental variations. Without going any further, when a human being is exposed to -30 ° C, he freezes and dies in less than a minute.

The heat dissipation and generation mechanisms are very effective in endotherms, but not infallible: below 30 ° C of body temperature, a person loses consciousness, tension drops drastically, and their heart beats rapidly. imperceptible. As you can imagine, in these cases the outcome without treatment is death.

5. Ectotherms have lower metabolic rates

We have already evidenced this reality at multiple points throughout space, but it is worth highlighting it again. By “relying” on the environment to generate heat, ectotherms do not have to obtain as much energy in the form of organic matter and, therefore, tend to move less. Many predatory ectotherms follow the vital strategy of the sit and wait: they wait for a prey to pass in front of them, as chasing it is too costly on an energy level.

Also, if you think of a scorpion, a tarantula, a snake or a lizard, you will see that their life strategy is not even comparable to that of a bird. Ectotherms move less, are less generally active, and only run for short intervals of time when they feel in danger. In general, ectothermy results in a lower average activity rate (although there are exceptions).

Resume

As you can see, nature shows us, once again, that human self-imposed rules are broken much more than it seems. The determinism of our thinking has led us to believe for decades that ectotherms are incapable of generating heat, but this is not the case. From insects to reptiles, there are many examples of supposedly ectothermic animals that thermoregulate, even if not constantly.