Arxiu d'etiquetes: aposematism

Animal mimicry: now you see me…

What do you see in the picture above? Maybe snakes… or maybe not? All animals try to enhance their survival rates, and one of the most effective ways to achieve this goal is by looking similar to some environmental elements, either by camouflaging or by imitating traits from other organisms. Mimicry is a complex and surprisingly phenomenon present in almost every animal taxa acting as an evolutionary driving force. Do you know what types of mimicry exist and which animals do perform each one? Are you ready to read more about this topic? If that’s the case, keep reading!

Mimicry vs camouflage (or crypsis)

The word mimicry (that derives from the Greek term mimetikos = “imitation”) was firstly being used to describe people who have the ability to imitate. From 1851 on, its use extended to other life forms.

Sometimes, the term mimicry is used as a synonym of “camouflage or crypsis”. Although these two words are sometimes confused and used equally, from a biological point of view they are well differentiated terms:

  • Mimicry: the ability an organism develops to imitate one or more traits from another organism (with which it’s unrelated) so that it can obtain some benefit.
  • Camouflage (or crypsis, from the Greek word kryptos = “hidden”): the ability an organism has to be unnoticed by its predators (or prays) by copying some environmental traits or by developing a disruptive coloration that allows it to hide.

Some authors consider that camouflage includes only to the ability an animal has for imitating morphological traits from some environmental elements, such as different natural surfaces, plants or even sessile animals (i.e. immobile animals) like corals and sponges (as you can see on the picture below). On the other hand, mimetic animals go further and try to imitate not only morphological traits, but physiological and behavioral, looking for a response from other animals.

Can you see the camouflaged seahorse? (Picture by Stephen Childs, CC).

To sum up: the main objective of mimetic animals is to trick the senses (e.g. sight, hearing, smell…) of the other organisms they live with, in order to induce them a specific behavior that gives mimetic animals a benefit in return.

Types of mimicry

There are different ways to classify the different types of mimicry, but I will show you two main groups of mimicry, in which we will see different subtypes: defensive mimicry and non-defensive mimicry.

Defensive mimicry

The defensive mimicry is specially performed by animals that have lots of predators, so their survival rates depend on avoiding their predators.

BATESIAN MIMICRY

Venomous and poisonous animals tend to develop flashy traits (especially flashy morphological traits, like coloration and menacing sounds) which alert other animals about their danger. This phenomenon is known as aposematism (when an animal has a flashy coloration we talk about aposematic coloration). In the Batesian mimicry, the mimetic organism (that is usually harmless and edible) copies the flashy traits of a venomous or poisonous organism present in its habitat in order to make predators think it’s a harmful species. Thus, the mimetic organism avoids being caught and eaten by predators.

Poisonous Coral Snake (on the left) and non-poisonous Scarlet King Snake or False Coral Snake (on the right). The second one imitates the aposematic coloration of the first one (Source: oakdome.com).

 

MÜLLERIAN MIMICRY

Sometimes, there are various poisonous or venomous species coexisting at the same time in the same habitat that are all being very hunted by predators (and sometimes by the same predator). In some of these cases, even when only one of these species has an aposematic trait to dispel predators, the rest of them try to mimic it and develop this trait (or traits). In contrast with de Batesian mimicry, in this model all species are harmful at some degree.

Try to think that all these species finally develop the same aposematic coloration: when predators prey on one of these species and are harmed in result, probably they won’t attack again any species that has the same coloration pattern. Thus, predation pressure will be distributed within the species matrix.

Different geographical forms of both Heliconius erato (top row) and Heliconius melpomene (bottom row). Heliconius melpomene is a widespread neotropical species well known for its geographic diversity in color pattern. Throughout its range, H. melpomene is co-mimetic with Heliconius erato (which is generally less abundant than H. erato). Both have a disgusting flavor when being eaten (source: heliconius.org).

 

MERTENSIAN MIMICRY

This is an unusual type of mimicry (only a few cases in snakes are known), and it occurs when a harmful species copies an aposematic trait (e.g. coloration) of a less dangerous organism. What could this mechanism be useful for?

Mimetisme_angIn the picture above, we can see that predators that feed on a harmful organism die (e.g. because it’s poisonous), so that the information “this animal is poisonous and mortal, don’t eat it!” won’t be transmitted to the rest of the predator population nor the next generations of predators. Thus, this harmful prey will remain preyed by predators. On the other hand, predators that feed on a less harmful prey and stay alive will have the chance to transmit this information to the rest of the population, so that predators will stop feeding on this prey.

In light of this situation, what do the most harmful organisms do? they try to imitate the aposematic traits of less harmful organisms (like coloration or shape) so that predators that feed on these less harmful organisms and stay alive, learn that all organisms with the same traits are dangerous. So, the predation pressure will fall for all preys.

Non-defensive mimicry

One of the most important types of mimicry within the non-defensive mimicry is the Peckhammian mimicry.

AGRESSIVE OR PECKHAMIAN MIMICRY

Unlike defensive mimicry, in this case are predators (or parasites) the ones that develop the traits of a more or less harmless species (or even of a beneficial one) in order to be unnoticed by their preys or hostages.

peses
Plagiotremus rhinorhynchos (on the right) is an aggressive mimetic species that imitates another fish known as Laborides dimidiatus or bluestreak cleaner wrasse. Plagiotremus rhinorhynchos (family Blenniidae) imitates youth specimens of Labroides dimidiatus (family Labridae) both morphologically and behaviorally. Many species of fishes enter corals in order to be cleaned from parasites by Labroides dimidiatus. Taking advantage of this situation, P. rhinorhynchos get close to these coral fishes by mimicking the bluestreak cleaner wrasse in order to feed on their tissues (Pictures: the left one by Karelj, CC  and the right one by JennyHuang, CC).

Aggressive mimicry can be confused with some camouflage or crypsis mechanisms, as sometimes these two terms can be overlapped or maybe show no evident differences. This is the case of some abyssal fish species which have one or more filaments of their dorsal fins transformed into lures (sometimes these lures are bioluminescent). These lures sometimes mimic the shape of the abyssal fish’s preys, so those preys feel strongly attracted by them. Some authors propose that preys could be the model organisms and that abyssal fishes would modified their dorsal fin through an evolutionary process.

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Abyssal fish on a photogram from the film ‘Finding Nemo’ (© Pixar, 2003).
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Abyssal fish…a way more real than the one showed above (with its luminescent lure) (Image source: http://www.bogleech.com/nature/).

A curious case: the automimicry

The automimicry (also known as intraspecific mimicry) is a special case of mimicry that takes place when an organism transforms some part of its body in order to seems like another part of its own body or even of the body of another member of its species (e.g. a male that mimics a trait from females). The objectives of this type of mimicry are to obtain some benefit from other organisms or maybe to be unnoticed by their predators or preys.

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The northern pygmy owl (Glaucidium californicum) has two big dark spots behind its head which remind of two big eyes (picture by Michael Durham).

Mimicry makes animals to evolve!

Mimicry is one of the processes that makes animals to evolve faster (do you want to learn more about evolutionary processes? Enter this link!).

These changes may occur in a higher or lower speed. So, what about those animals that mimic other organisms? Mimetic animals are in constant selective pressure to look more like their models in order to go unnoticed and improve their survival, but at the same time imitated organisms (the models) are also under selection to sharp their ability to discern between models and imitators.

.            .             .

Thus, mimicry is an incredible evolutionary engine: a perpetual struggle between mimetic organisms and imitated ones in order to improve their respective survivals.

REFERENCES

  • Bone Q., More R. Biology of fishes. 3a ed. Taylor & Francis.
  • Campbell, N.A., Reece J. B. 2007. Biología. Ed. Médica Panamericana.
  • Cheneya K.L., N. Justin M. 2009. Mimicry in coral reef fish: how accurate is this deception in terms of color and luminance?. Behavoural ecology, Oxford Journals. Vol 20. P. 459-468.
  • Harper D. Online Etymology Dictionary.
  • Kashyap H. V. 2001. Advanced Topics In Zoology. Ed. Orient Blackswan.
  • Sarmiento O.F., Vera F., Juncosa E. J. 2000. Diccionario de ecología: paisajes, conservación y desarrollo sustentable para Latinoamérica. Ed. Abya Yala.

Main picture source: www.yedirenkhaber.com.

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Migration in danger! The disappearance of the monarch butterfly

Generally, we tend to think of migration as an event exclusively linked to complex organisms (like mammals or birds). But there are always exceptions: the North American populations of the monarch butterfly (Danaus plexippus) cover a distance of almost 5000km (more than some complex animals!) in order to reach their hibernation areas, where there can be concentrated thousands of specimens during the winter. Unfortunately, the migration phenomenon depend on many factors that are being damaged by anthropogenic pressure nowadays, so that the future of these populations and also their migration are in danger.

Throughout this article, you will learn some of the most curious biology traits of these organisms, the main causes that could be endangering their populations and the consequences that this would entail.

INTRODUCTION

The monarch butterfly (Danaus plexippus) is a butterfly of the Nymphalidae family. It’s also probably one the most well-known butterflies of North America due to its long migration, that their specimens perform from the north of EEUU and Canada to California coast and Mexico, covering a distance of almost 5000km to reach their hibernation areas. It’s, by far, the insect that performs the widest and large migration of all.

Specimen of monarch butterfly (Danaus plexippus) with its typical color pattern: white, black and orange (Picture by Peter Miller on Flickr, Creative Commons).

Although the North American populations of this species are the most known worldwide due to their migration pattern, there are also monarch butterflies in some Atlantic islands (Canary islands, Azores and Madeira), and sometimes also as eventual migrators that reach the coasts of Western Europe (United Kingdom and Spain). Moreover, they were introduced in New Zealand and Australia during the XIX century.

LIFE CYCLE

The life cycle of this species is very unique. First of all, they’re considered specialist butterflies: they lay their eggs exclusively over plants of the Asclepias genus (also known as milkweeds), and their newborn caterpillars (which are black, white and yellow striped) feed only on these plants. This is a very interesting fact, because the plants of this genus contain cardiac glycosides that are progressively assimilated by the caterpillar tissues, which let them to acquire a disgusting taste that prevents them to be predated. This taste will last during their adult phase.

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Caterpillar of a monarch butterfly (Picture by Lisa Brown on Flickr, Creative Commons).

Once completed the larva phase, the metamorphosis take place so that the caterpillars become adult butterflies colored in black, white and orange. Both caterpillar and butterfly color patterns carry out a communicative function: it’s a mechanism to warn other animal of their toxicity, fact which is known as aposematic mimicry (this phenomenon is very frequent in a lot of group of animals, even in mammals).

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Phases of the metamorphosis of the monarch butterfly (Picture by Steve Greer Photography).

The adult phase also has some particularities: during the mating season (April-August) some generations of adults are generated, and each of them has a life expectancy of a few weeks, more or less. Then, an awesome event takes place: the butterflies of the generation born at the end of August (when temperatures get low and days became shorter) stops the maturing process of their reproductive organs (phenomenon known as diapause) so they can spend their energy on enlarging their life expectancy to 9 months. This generation is known as “Methuselah generation” due to its longevity.

The increase of their longevity allows this generation to cover the long distance required to reach the hibernation areas during the autumn (Mexico and California coast) and then to come back to the north of America at the end of the winter.

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Hundreds of monarch butterflies flying over the place called ‘El Santuario ‘El Rosario” (Mexico) (Picture by Luna sin estrellas on Flickr, Creative Commons).

A ROUND TRIP: THE GREAT MIGRATION

Although the monarch butterfly isn’t only located in North America, there is no evidence nowadays showing that the other populations of monarch butterflies do such a long migration. It’s believed that the fact that only these populations of butterflies go on a trip this long is due to the wide spreading of plants of the Asclepias genus over all North America that took place in the past. Scientists suggest this event allowed the monarch butterflies to spread progressively to the south.

WHICH PLACES DO THE BUTTERFLIES VISIT?

A migration is always a complex process. In this case, the migration to the south is divided into two simultaneous migrations:

  • The east migration: this trip is made by those butterflies that fly from the east of the Rocky Mountains, South of Canada and a big part of USA to the central part of Mexico (90% of all the monarch butterflies located in North America go on this trip).
  • The west migration: this trip is made by those butterflies that fly from the west of the Rocky Mountains, South of Canada and a little part of USA to the California coast (10% of all the monarch butterflies located in North America go on this trip).
Migratory patterns of the monarch butterfly in North America (round trip) (Sources: Monarchwatch.org y Monarch Alert).

Once in the winter habitats, the butterflies plunge into a lethargic state until the next spring, when they become sexually active and start mating before heading again to the north.

It’s a very surprising event seeing all the butterflies sleeping together and covering all the plants and trees of the winter habitats!

Thousands of butterflies gather over the vegetation (Picture by Carlos Adampol Galindo on Flickr, Creative Commons).

PROTECTED AREAS

There exists a lot of protected areas all over the places where the butterflies go through.

One of the most important protected areas is the Monarch Butterfly Biosphere Reserve (Mexico City), which is considered a World Heritage Site by the UNESCO since 2008.

Monarch Butterfly Biosphere Reserve (Picture by Michelle Tribe on Flickr, Creative Commons).

And why are these butterflies so protected? Besides the fact that their migration pattern is considered an incredible phenomenon, they are pollinators that contribute to the pollination of the wild flora and also of the crops of North America.

THE ‘QUEEN’ IS IN DANGER!

Although there exists a huge effort to protect them, the migratory phenomenon of the North American monarch butterflies is in danger nowadays due to the anthropic pressure, which could also put their populations at risk in the future.

According to the data generated by the WWF, the surface of the winter habitats occupied by these butterflies has decreased 94% in 10 years, going from 27,48 acres occupied in 2003 to only 1,65 acres in 2013. This is the lower value registered in the last 20 years.

Decresing of the surface occupied by the monarch butterflies in the winter habitats (Data form WWF website).

Even though the surface occupied by these organisms has been fluctuating over the years as a part of a natural process, this pronounced decreasing that has taken place in only a few years suggests that butterflies are stopping their annual migrations to the south.

Total occupied area by the butterflies in their winter habitats since 1993 to 2013 (WWF-Telcel-CONANP).

This recession has also been registered in other species of butterflies at different emplacements all over the world, so there must exist some kind of factor in common with the ones affecting the North American monarch butterfly populations.

WHAT COULD BE THE MAIN CAUSES OF THIS RECESSION?

According to the WWF, the main causes that could being putting in danger the migration process of the monarch butterflies are:

  • The reduction of the surface occupied by plants of the Asclepias genus: as we said above, the caterpillars feed exclusively on these plants. But the use of certain herbicides and the changes on the rain patterns could being limiting their dispersal over a big part of North America.
  • Deforestation: cutting down trees massively and the subsequent desertization could being reducing their winter habitats.
  • Extreme climate: the global change, which entails changes in temperature and rain patterns, could being putting at risk the survival of adult butterflies, preventing them to reach the longevity required to carry out complete migrations.

WHICH EFFORTS ARE MADE TO PROTECT THESE POPULATIONS?

As I said above, monarch butterflies are an essential part of the pollination net of North America and also iconic insects, so there exists a big interest on protecting them.

Nowadays, most of the protected areas of North America are making a big effort to improve the quality of their habitats. Among them, the Monarch Butterfly Biosphere Reserve (Mexico) along with the WWF are trying to restore the woods where butterflies hibernate and also promoting a sustainable tourism (enter this link to see more information).

 .            .            .

The case of the monarch butterfly is only one of a huge list of animals in danger. Nowadays, a lot of animals with complex migration patterns and wide spreading areas are suffering similar pressures, mostly of them with an anthropogenic origin. There’s still so much work to do, and it depends on all of us.

REFERENCES

Main picture by Carlos Adampol Galindo on Flickr.

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Danger, poisonous mammals!

We usually associate snakes, spiders, jellyfish, etc. as venomous animals par excellence, but did you know that there are poisonous mammals? In this article we will discover who are they and the nature and use of their poisons.

THE PLATYPUS

The platypus (Ornithorhynchus anatinus) is the most famous among the poisonous mammals, and not just for this feature. With a peak like a duck and oviparous (laying eggs), when it was discovered some scientists thought it was a fraud.

platypus ornitorrinco ornitorinc
Platypus (Ornithorhynchus anatinus). Photo by Jonathan Munro

They belong to the order monotremes, which means “one hole” in reference to the cloaca, the end of the digestive and reproductive systems. Some evolutionary biologists refer to them as the “missing linkbetween reptiles and mammals, as they have characteristics of both groups. Monotremes are the only mammals that lay eggs, but his body is covered with hair and the young are fed with breast milk. They are distributed by Australia, Tasmania and New Guinea.

Platypuses have a spur on the hind legs, which only in the case of males, release poison produced by femoral glands (located in the leg). The male uses it mainly to defend their territory and establish their dominance during the mating season, although if it is bothered also uses it as a defense. This poison can kill small animals, including dogs, and cause severe pain and swelling in humans. This pain can last days or months.

Platypus spur, espolón ornitorrinco
Spur on the hind leg of a platypus. Photo by E. Lonnon

Toxins are four proteins, three of which are unique to the platypus. They are like the defensins (DLP, defensin-like proteins). These are globular proteins, small and compacted, involved in the activation of pain receptors. Understanding how these toxins act it has special interest because they cause a lasting and severe pain; it may open new chances in the synthesis of analgesic drugs.

short-beaked echidna, equidna de nariz corta, equidna de nas curt
Short-beake echidna (Tachyglossus aculeatus). Photo de Tony Britt-Lewis

Echidnas (family Tachyglossidae) complete the order of monotremes with the platypus; consequently they are also oviparous. The family consists of four species, with the common characteristic of having the body covered with dense hair and spines. They are mainly insectivores specializing in ants and termites.

Like the platypus, they also have spurs behind the knees, but their secretions are not poisonous. The substances are used to mark their territory, according to the recent studies.

SLOW LORIS

As we saw in a previous post, lorises are primates in the prosimians suborder. They are nocturnal, arboreal and feed primarily on insects, vegetables and fruits. The slow lorises (Nycticebus) living in Southeast Asia, are the only poisonous primate. They possess poison glands on the elbows (brachial gland), and poison their body with arms and tongue, which can also join saliva and be transmitted by bitting.

lori pigmeo, nycticebus pigmaeus,
Pygmy slow loris (Nycticebus pigmaeus). Photo by Ch’ien C. Lee

In this case the poison is used as a defense against predators, causing them pain, inflammation, necrosis (cell death) in the area of the bite, hematuria (blood in urine) or in some cases anaphylactic shock (allergic reaction) which can lead to death, even in humans (some are threatened by the illegal pet trade and traditional Chinese medicine). The poison also serves as protection for the young, they are licked by their parents and the poisonous secretion is distributed throughout the coat. Being poisonous, unusual among primates, can help counteract the disadvantages of its slow movements. Exudate from glands, as in echidnas, can also give olfactory information of range and territory between individuals of loris (Hagey et al., 2007).

Loris de Kayan (Nycticebus kayan). foto de Ch'ien C. Lee
Kayan loris (Nycticebus kayan). Photo by Ch’ien C. Lee

Toxins are polypeptides (generated when glandular secretion is mixed with saliva) and an unidentified steroid. Secretion is similar to the allergen Fel d 1 which is in the domestic cat and cause allergies in humans (Hagey et al., 2006; Krane et al., 2003).

It is believed that slow lorises even have converged evolutionarily with cobras, for his defensive behavior when threatened, whistling and raising his arms around his head. (Nekaris et. al, 2003).

Loris, cobras, evolucion, convergencia
Mimicry between loris and cobras. 1. Javan slow loris, 2 y 3. Spectacled cobra, 4. Bengal slow loris. Photo by Nekaris et. al.

In the following video a lazy lori is disturbed and hisses like a snake while trying to bite:

SOLENODON OR ALMIQUI

They are small and nocturnal mammals, basically insectivores, that live in the West Indies. The Hispaniolan solenodon (Solenodon paradoxus), also known as the Dominican solenodon, Haitian solenodon or agouta, lives on the island de La Española (Dominican Republic and Haiti) while The Cuban solenodon or almiqui (Solenodon cubanus) is distributed throughout Cuba. They are considered living fossils because they have similar characteristics to primitive mammals of the end of the Mesozoic Era (kingdom of the dinosaurs).

solenodonte de La Española (Solenodon paradoxus
Hispaniolan solenodon (Solenodon paradoxus). Photo by Eladio M. Fernández.

Unlike other poisonous mammals, toxic saliva is produced under the jaw (submandibular glands), which is transported by pipes to the front of the mouth. The second incisor teeth have a groove where toxic saliva accumulates to promote their entry into the wounds. They are the only mammals that inject venom through its teeth, similar to the way snakes do.

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Paradoxus Solenodon lower jaw incisor showing the groove. Photo by Phil Myers

The main function of this venom is to immobilize prey, as well as insects they can hunt small vertebrates such as reptiles, amphibians and birds.

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Cuban solenodon (Solenodon cubanus). Photo by Julio Genaro.

This poison may have been developed to keep alive but immobilized prey during times of shortage, to aid in digestion, minimize energy expenditure in the struggle for hunting and face prey even twice as big as them. This venom is not deadly to humans.

SHREWS

The northern short-tailed shrew (Blarina brevicauda), the Eurasian water shrew (Neomys fodiens) and the Mediterranean water shrew (Neomys anomalus) also have submandibular glands similar to solenodons. They are distributed by North America (northern short-tailed shrew) and Europe and Asia (water shrews), including the Iberian Peninsula.

Musaraña colicorta americana (Blarina brevicauda). Foto de Gilles Gonthier.
The northern short-tailed shrew (Blarina brevicauda). Photo by Gilles Gonthier.

The short-tailed shrew can consume up to three times its weight in food per day. Their saliva is the most poisonous and uses it to paralyze their prey, to eat them or keep them alive in times of shortage. The water shrews also store its immobilized prey under rocks.

Musgaño (Neomys anomalus). Foto de rollin Verlinde.
Mediterranean water shrew (Neomys anomalus). Photo by Rollin Verlinde.

These animals attack from behind and bite the neck of its prey so that the poison acts more quickly, affecting the central nervous system (neurotoxins). The respiratory and vascular system is also affected and causes seizures, incoordination, paralysis and even death of small vertebrates.

Musgaño patiblanco-Neomys_fodiens, Wasserspitzmaus
Eurasian water shrew (Neomys fodiens). Photo by R. Altenkamp.

Its teeth don’t have grooves as the solenodons do, but a concave surface to store the toxic saliva.

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Lower jaw of Neomys anomalus. Photo by António Pena.

It is suspected that other mammals also produce toxic saliva similarly, as the European mole (Talpa europaea) and other species of shrew, but there are no conclusive studies.

MANED RAT

The maned rat or crested rat (Lophiomys imhausi), lives in Africa and  uses his poisoned hair to protect themself from predators.

Rata crestada Lophiomys_imhausi, rata de crin, maned rat
Maned rat (Lophiomys imhausi). Photo by Kevin Deacon

Unlike other mammals that produce their own poison, the crested rat gets toxin (called ouabain) from the bark and roots of a tree (Acokanthera schimperi). Chews the bark and the mixture of saliva and toxins are distributed on the body. Their hairs are cylindrical whith a perforated microscopic structure, which favors the absorption of venom. In case of danger, it bristles and shows his brown coat with white stripes, warning of its potential danger. This strategy of persuasion based on brightly colored warning is known as aposematism present in many animals, such as bees.

In this BBC video you can see a crested rat and a hair under the microscope absorbing ink, showing its porous structure:

It is unknown how it is immune to the toxin, since it is the same substance used by some African tribes for hunting such large animals like elephants.

Ouabain is a glycoside which controls the heartbeat, causing infarcts if absorbed in large quantities. The study of the mechanisms that protect the crested rat of a substance that regulates the heartbeat, can help develop treatments for heart problems.

European hedgehogs (Erinaceus europaeus) have similar behavior (smearing the body with foreign poison), but it is not established whether the objective is defensive because it does not scare away predators.

In conclusion, strategies, practices and nature of the poison in mammals are varied and their study may have important medical implications for drug development and increase awareness of the evolutionary relationships between different groups of living animals (reptiles-mammals) and their ancestors.

REFERENCIAS

MIREIA QUEROL ALL YOU NEED IS BIOLOGY