Arxiu d'etiquetes: host

Lying birds: Brood parasitism in birds, the continual struggle for survival

Some birds have development an interesting reproductive strategy to deceive other birds and put the eggs in their nests, so foster parents are forced to feed other chicks. But what is behind this strange behaviour?


The brood parasitism is a type of biological interaction between two organisms, in which one of them (the parasite) obtains resources from the other one (the host). In birds, the parasite obtains some benefits of parental cares from the host, developing a breeding strategy cold brood parasitism. The brood parasitism, although has been studied mostly in birds, also happens in other groups of vertebrates: for example in fish (Sato 1986, Baba et al. 1990) and some insects such as Himenoptera, Coleoptera and Heteropterous.

Brood parasitism –

According the characteristics of each relation, there are different types of brood parasitism:

  • Optional brood parasitism: the parasite species is capable of breeding a part of its own offspring and also, to parasite other individuals. A example in birds is in genus Coccyzus (Cuculidae).
  • Forced brood parasitism: hosts breed all the offspring of the parasite bird, as happens in common cucko (Cuculus canorus).
  • Intraspecific brood parasitism: host and parasite are of the same species. This is a common strategy in colonial species and in other species with nidifugous chicks.
  • Interspecific brood parasitism: host and parasite are the different species.

In addition parasites are classified, by their specialisation on one or several host species, in general parasites (parasite large number of species) or specialist (only parasite one or a few species).


Everything suggests that the main focus of this behavior was decreased the parental investment (less cost) increasing the chance of success (major benefits), although this is not always the case.

There are several hyphotesis to explain the origin of the brood parasitism in birds:

  1. Firstly, it is probably that parasites were displaced individuals that did not have any territory or lost their laying, and they try to lay their eggs in other nests to achieve greater breeding success (Sorenson 1998, Sandell y Diemer 1999).
  2. Other hypothesis suggests that this parasitism could be a stable strategy for evolution of the population, which has similar benefits to breed its own offspring (Eadie y Fryxell 1992).
  3. Finally, the third hyphotesis considers this parasitism like an additional strategy to the parent care and some individuals could be used it to reduce the sibling competition in their nest, or to reduce the number of chicks to feed without decreasing the breeding success (Moller 1987, Jackson 1993).



Hosts have learned to protect their offspring about the threat posed by brood parasitism.

Common cuckoo (Cuculus canorus) and rufous bush robin (Cercotrichas galactotes) have this relation, the first one lay a egg in the rufuos bush robin nest that it will be born before other chicks and kill them, capturing all the parental care.

One of the main host defences against brood parasites is the recognition and rejection of parasitic eggs. Because obligated brood parasites need appropriated individuals hosts for reproduction, such host defence-mechanisms simultaneously select for counter-defences in brood parasites, causing a coevolutionary arms race between hosts and parasites.

Rejection of parasitic eggs –



There is a particular case, the strategy of the great spotted cuckoo (Clamator glandarius) when is a parasite of the common magpie (Pica pica). The great spotted cuckoo lays an egg in the nest of common magpie and this chick possess adaptations to exploit the host parental care, it does not kill directly their siblings but has advantages in relation to begging behaviour and in the order of birth (cuckoo chick is born four or six days before magpie chicks.

Common magpie (Pica pica) –

Magpies have development a selective advantage to recognize and ejection of parasitic egg. However, it has been observed that cuckoos react to this behaviour returning to the parasitized nest and destroying it. This situation conditions the behaviour of the magpies in the future and they are forced to accept the parasite egg.

Eggs of cuckoo in magpie nest –
Cuckoo chicks are born some days before magpie chicks –
Development of cuckoo chicks in the nest –

The result of this evolutionary fight is the mafia-type behaviour of cuckoo that leads to a co-evolutionary arms race between species to avoid parasitism, in one hand, and maintain it, in the other one.

Great Spotted Cuckoo (Clamator glandarius) – Fveronesi1. Flickr, Creative Commons


  • Parasitism and nest predation in parasitic cuckoo (American Naturalist, 1995)
  • Mafia Behaviour and the Evolution of Facultative Virulence (Journal of Theoretical Biology, 1995.)
  • Magpie Host Manipulation by Great Spotted Cuckoos: Evidence for an Avian Mafia? (Evolution, 1997.)
  • Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs (PNAS, 2006)
  • Cover photo: Cuckoo chick in parasitic nest reciving food of host –



Zombie parasites: a reality of science fiction

Many horror films are based on organisms that have the ability to control the victim’s mind. In fact, there is some kind of real parasites and parasitoids which can control its host’s behaviour to guarantee its breeding. In this post, we will discuss some examples of those interesting parasites.


Parasitism is a type of predation where an organism (parasite) extracts a benefit at the expenses of another one (host). The parasites have lost the ability to synthesize some essential molecules that get through hosts, as well as parasitism is a mandatory relationship. There are many types of parasites, but the most interesting examples are zombies parasites.

The parasitic zombies have in common the ability to control and modify the behavior and physiology of the host to guarantee its breeding. Can you find them in different taxonomic groups (fungi, protozoa, nematodes, arthropods…). There are differents mechanisms to fulfill its objective, but the most important are: control the behavior of the host or induce him to suicide.


Glyptapanteles is a genus of parasitoid wasp that infects species of Lepidoptera Thyrinteina leucocerae in its larval phase. The larvae become caterpillars which grow and feed normally. In the final stages of development of the caterpillar,  the pupae of parasitoid wasp (the metamorphosis between larvae and the adult stage) are released and settled next to the caterpillar. Before his release, the pupae excrete an endocrine substance that modifies the behavior of the caterpillar forcing him to protect the small pupae. caterpillar stops feeding and move until the adult wasp emerges. At that time, the Caterpillar dies from starvation and exhaustion.

Thyrinteina leucocerae caterpillar protecting a group of pupae of Glyptapanteles sp. (Photo: José Lino-Neto)

Another example of  interesting parasitoid wasp, is the species Hymenoepimecis argyraphaga infecting Plesiometa argyra (a species of tropical spider). In this case, the female sticks to the abdomen of the spider its egg. When the hematophagous (which feed on blood) larvae hatches, injected a chemical substance that causes the host to create a cobweb that is capable of supporting the weight of the cocoon, rather than a cobweb to catch insects. The larvae then feeds the host until it dies and then create its cocoon in the cobweb. Then, it will transform into pupae and eventually will emerge as an adult.

Differences between a normal cobweb of Plesiometa argyra and a modified cobweb. Modified image of William G. Eberhard (Nature, 2000).

The above examples are parasitoids that they finally finished with the life of its host, but there are cases where once the parasitoid releases from the victim’s body, the host can continue to live. This is the case of the infection of the Ladybird Coccinella septempunctata by wasp species Dinocampus coccinellae. The  female wasp injects the eggs in the abdomen of the Ladybird that incubates them inside. When the larvae have been developed (without touching any host’s vital organ), are released and form a cocoon that will protect the Ladybird.  If the host gets to survive for seven days, when the larvae become adult Ladybug will recover and can continue with normal life cycle.

Coccinella septempunctata protecting a cocoon of wasp Dinocampus coccinellae. (Photo:Gilles San Martin)


Myrmeconema neotropicum is a nematode that infects tropical ants of the species Cephalotes atratus. These ants are completely black, but when they are infected with the parasite, their abdomen becomes reddish. This change allows the host camouflaged with certain berries and confuse frugivorous birds. In addition, this parasite is being able to change the behavior of ant and force her to rise to clear and unprotected areas to be located by the predators. The birds are hosts intermediaries, since thanks to their excrement, they get a greater dispersion of the eggs of parasites.

Differences between the abdomen of a Cephalotes atratus normal and an infected. (Photo: Steven Yanoviak)

Another species of nematode, namely Spinochordodes tellinii, infects to crickets Meconema Thalassinum (Orthoptera) species. The larvae of the parasite are in the water and are ingested by mosquitoes (intermediate host). Mosquitoes are swallowed up by Crickets and once in the intestine, the nematode grows up to triple the size of the insect. When the parasite is adult, modifies the behavior of the host causing and induces him to commit suicide in the water. Thus, the parasite is free in its middle order to breed.

Cricket (Meconema thalassinum) infected with the nematode Spinochordodes tellinii. (Photo: Alastair Rae)

The flatworm or platyhelminth Leucochloridium paradoxum infects snails of the species Succinea putris. The host eats the larvae of the parasite that develops into the digestive tract of the host to give rise to the sporocysts (a kind of sacks that contain thousands of larvae, known as cercarias). The sporocysts are directed towards the tentacles of the snail’s eyes and causes a very exaggerated inflammation that resembles a caterpillar. They also induce a change in the behavior of the snail, leading him away from protected areas and forcing them to expose in places where it can be seen by the birds. The movement of the tentacles draws the attention of the birds that eat the snail and spread through their feces the cercaria (next state of maturation of the parasite).

Life cycle of Leucochloridium paradoxum from Ophiguris (2009). The second image shows a parasite in the tentacle of the snail (Succinea putris) imitating a caterpillar. (Photo by Dick Belgers)

Finally, but no less important, highlights the parasitic fungus Ophiocordyceps unilateralis infecting species tropical ants (Camponotus leonardi). The host ingests the spores of the fungus. Once in the digestive system, it induces a change in the behaviour of the Ant, forcing her to climb to high places where anchor with jaws. Once there, the spores germinate through the host’s exoskeleton to release their reproductive structures.

Ant infected by Ophiocordyceps sp. See the reproductive structures of the fungus out of the exoskeleton of the host. (Photo: Alex Wild)

Today, however, the mechanisms used by these parasites zombies information continue to be investigated. Do you think that they seem to beings from a horror film? No,  it is not science fiction. It’s our surprising nature.



Evolution for beginners 2: coevolution

After the success of Evolution for beginners, today we’ll continue  knowing the basics of biological evolution. Why  exist insects that seem orchids and vice versa? Why gazelles and cheetahs are almost equally fast? Why your dog understands you? In other words, what is coevolution?


We know that it is inevitable that living beings establish symbiotic relationships between them. Some depend on others to survive, and at the same time, on elements of their environtment as water, light or air. These mutual pressures between species make that evolve together, and as one evolve as a species, in turn it forces the other to evolve. Let’s see some examples:


The most known process of coevolution is pollination. It was actually the first co-evolutionary study (1859) by Darwin, although he didn’t use that term. The first to use the word coevolution were Ehrlich and Raven (1964).

Insects existed long before the appearance of flowering plants, but their success was due to the discovery that nectar is a good reserve of energy. In turn, the plants found in the insects another way more effectively to carry pollen to another flower. Pollination by the wind (anemophily) requires more production of pollen and a good dose of luck to at least fertilize some flowers of the same species. Many plants have developed flowers that trap insects until they are covered with pollen and then set them free. These insects have hairs in their body to enable this process. In turn some animals have developed long appendages (beaks of hummingbirds, butterflies’ proboscis…) to access the nectar.

Polilla de Darwin (Xantophan morganii praedicta). Foto de Minden Pictures/Superstock
Darwin’s moth (Xantophan morganii praedicta). Photo by Minden Pictures/Superstock

It is the famous case of the Darwin’s moth (Xanthopan morganii praedicta) of which we have already talked about. Charles Darwin, studying orchid Christmas (Angraecum sesquipedale) saw that the nectar was 29 cm inside the flower. He sensed that there should exist an animal with a proboscis of this size. Eleven years later, Alfred Russell Wallace reported him that the Morgan’s sphinxs had proboscis over 20 cm long, and a time later they were found in the same area where Darwin had studied that species of orchid (Madagascar). In honor of both it was added “praedicta” to the scientific name.

There are also bee orchids that mimic female insects to ensure their pollination. To learn more about these orchids and the Christmas one, do not miss this post by Adriel.

Anoura fistulata, murcielago, bat
The bat Anoura fistulata and its long tongue. Photo by Nathan Muchhala

But many plants not only depend on insects, also some birds (like humming birds) and mammals (such as bats) are essential to pollination. The record for the longest mammal tongue in the world is for a bat from Ecuador (Anoura fistulata); its tongue measures 8 cm (150% of the length of its body). It is the only who pollinates one plant called Centropogon nigricans, despite the existence of other species of bats in the same habitat of the plant. This raises the question of whether evolution is well defined, and occurs between pairs of species or it is diffuse due to the interaction of multiple species.


The cheetah (Acinonyx jubatus) is the fastest vertebrate on land (up to 115 km/h). Thomson’s gazelle (Eudorcas thomsonii), the second (up to 80 km/h). Cheetahs have to be fast enough to catch a gazelle (but not all, at risk of disappearing themselves) and gazelles fast enough to escape almost once and reproduce. The fastest gaelles survive, so nature selects in turn faster cheetahs, which are who eat to survive. The pressure from predators is an important factor that determines the survival of a population and what strategies should follow the population to survive. Also, the predators will find solutions to possible new ways of life of their prey to succeed.

Guepardo persiguiendo una gacela. Foto de Federico Veronesi
Cheetah hunting a Thomson’s gazelle in Kenya. Photo by Federico Veronesi

The same applies to other predator-prey relationships, parasite-host relationships, plants-herbivores, improving their speed or other survival strategies like poison, spikes…


Our relationship with dogs since prehistoric times, it is also a case of coevolution. This allows, for example, to create bonds with just looking at them. If you want more information, we invite you to read this post where we talk about the issue of the evolution of dogs and humans in depth.

Another example is the relationship we have established with the bacteria in our digestive system, essential for our survival. Or with pathogens: they have co-evolved with our antibiotics, so using them indiscriminately has favored these species of bacteria to develop resistance to antibiotics.


Coevolution is one of the main processes responsible for the great biodiversity of the Earth. According to Thompson, is responsible for the millions of species that exist instead of thousands.

The interactions that have been developed with coevolution are important for the conservation of species. In cases where evolution has been very close between two species, if one become extint will lead to the extinction of the other almost certainly. Humans constantly alter ecosystems and therefore biodiversity and evolution of species. Just declining one species, we are affecting many more. This is the case of the sea otter (Enhydra lutris), which feeds on sea urchins.

Nutria marina (Enhydra lutris) comiendo erizos. Foto de Vancouver Aquarium
Sea otter (Enhydra lutris) eating sea urchins. Photo by Vancouver Aquarium

Being hunted for their fur, urchins increased number, devastated entire populations of algae (consumer of CO2, one of the responsible of global warming), seals who found refuge in the algae nonexistent now were more hunted by killer whales… the sea otter is therefore a key species for the balance of this ecosystem and the planet, as it has evolved along with urchins and algae.

Coevolutive relations between flowers and animals depend on the pollination of thousands of species, including many of agricultural interest, so we must not lose sight of the seriousness of the issue of the disappearance of a large number of bees and other insects in recent years. A complex case of coevolution that directly affects us is the reproduction of fig.


As we have seen, coevolution is the evolutionary change through natural selection between two or more species that interact reciprocally.

It is needed:

  • Specificity: the evolution of each feature of a species is due  to selective pressures of the feature of the other species.
  • Reciprocity: features evolve together.
  • Simultaneity: features evolve simultaneously.



What are parasitoid insects and what are they useful for?

Almost everybody could explain you more or less accurately what both parasites and predators are. But could everybody say you what a parasitoid is?

Animals (and especially insects) set up a lot of different symbiotic relationships, but often we find organisms whose relationship is somewhere between one and another (this is not a matter not of black or white!). In the case of parasitoid insects, we talk about organisms that establish a symbiotic relationship with traits of both predator-prey relationships and a parasitic ones.

Read this article to find out what parasitoid insects are, which is their origin and which kind of parasitoid insects exist. They are more useful than they seem to be!

Parasites, parasitoids and predators

Parasitoids are not exclusively insects, but the greater part of parasitoids belong to the subphyllum Hexapoda. For this reason, I will focus my explanation on parasitoid insects.

Before giving you further explanations, we must make the differences between parasitoids, parasites and predators clear.

In a parasitic relationship, parasites benefit at the expense of other organisms, the hosts, which are damaged in result. But despite of hurting it, parasites try to keep their hosts alive as long as possible in order to keep on benefiting from them, so parasites rarely kill their hosts.

Aedes albopictus female (tiger mosquito or forest mosquito) biting its host (Public domain).

In a predator-prey relationship, predators feed on a lot of organisms (the prey) throughout their life cycle in order to keep on developing. Unlike parasite organisms, predators don’t try to keep their prey alive so long, because the purpose of preying on other organisms is to obtain energy as faster as possible (for example, mantids, dragonflies…).

Mantis eating a prey (Picture by Avenue, CC).

Finally, between parasitism and predation we find parasitoid organisms: insects with a parasitic larval stage that develop by feeding on a single host, which is usually another insect or arthropod. In contrast with parasites, parasitoids larvae kill their hosts to complete their life cycle; so, in which sense are they different from predators? The answer is that parasitic larvae only need to feed on a single host to reach adulthood. While parasitoid larvae are a parasitic life form, parasitoid adults tend to be herbivores or predators.

common awl parasitoids 001a
Caterpillar of the lepidopteran species Hasora badra surrounded by wasp cocoons of the family Braconidae (Picture by SoonChye ©).

Origin and diversity of parasitoids

Parasitoid insects are present in many insect orders (Coleoptera, Diptera..), but the greater part of them is located in the Hymenoptera order (bees, wasps and ants). Because of that, in this section I will focus on talking only about the origin and diversity of hymenopteran parasitoids.

The most important and also evolved group of hymenopterans is the suborder Apocrita, which includes wasps, bees and ants. In turn, the suborder Apocrita is divided in two artificial groups:

  • Aculeata: they don’t have a parasitic larval stage. The ovopositor (an organ that females use to lay their eggs) has been transformed into a sting that inoculates venom (organisms of this group are also called “stinging wasps and bees”).
Sting of a female bee (Apidae) (Public domain).
  • “Parasitica”: they have a parasitic larval stage. Adult females of the group Parasitica have a long and sharp ovopositor they stab into different surfaces (wood, another insect…) so they can lay their eggs inside. In contrast with Aculeata, Parasitic hymenopterans don’t sting (they’re not venomous).
Parasitoid female bee of the species Megarhyssa macrurus, family Ichneumonidae, with its long and sharp ovopositor she use to lay their eggs (Picture by Bruce Marlin, CC).

About 77% (66.000 species more or less) of parasitoid insects known nowadays belong to the Parasitica group, and most of them are wasps.

Origin of hymenopteran parasitoids

To understand the origin of certain morphological, anatomical or conductual traits of an organism, we often have to study the traits of a “sister taxon” or “sister group”, i.e. a group more closely related to the group in question than any other group (they share the most recent common ancestor).

The sister group of Apocrita is the family Orussidae (from the Symphyta suborder), which is also considered the most ancient groups of hymenopterans.

Orussus coronatus (Fam. Orussidae) (Public domain).

It’s believed that the common ancestor of Apocrita and Orussidae had first developed a parasitic life form among hymenopterans. This conclusion is based on the studies about ecologic traits of current Orussidae specimens: some of these organisms establish a positive relationship with some symbiotic xylophagus fungi (i.e. fungi that feed primarily on wood); these fungi usually develop inside a sort of tiny baskets located over the surface of ovopositors, so they can be inoculated inside the wood the Orussidae feed on when laying. Thus, fungi process wood to obtain a product that can be digested by Orussidae. However, there exist Orussidae specimens which don’t establish this kind of symbiotic relationship and parasite other specimens instead (especially the ones that possess symbiotic fungi). Thus, these parasitic Orussidae obtain nutrients by feeding on other Orussidae members and obtain more energy in result.

So, this being an ancient group it’s believed that the observed behavior in some current Orussidae members could be a reflection of the ancient origin of parasitism and parasitoids among the Hymenoptera order.

Types of parasitoids

Even if there are many ways to classify parasitoids, we can divide these organisms mainly into two groups: the ones that stop host’s development when laying inside it and the ones that don’t stop host’s development. Let’s talk about these two groups:


Idiobiont parasitoids paralyze or prevent further development of hosts when laying, so parasitoid larvae could have a reliable and immobile source of food at their birth.

Usually, idiobionts attack hosts that are concealed in plant tissues (for example, wood) or exposed hosts that possess other kinds of physical protections, so female parasitoids have developed long and sharp ovopositors that allow them to pierce these barriers.

Liotryphon caudatus female (Hymenopteran of the family Ichneumonidae, superfamily Ichneumonidea) with her long and sharp ovopositor (Picture by CNC/BIO Photography Group, Biodiversity Institute of Ontario, CC).

Idiobiont parasitoids can be both ectoparasitoids and endoparasitoids (i.e. if larvae attack hosts from outside or inside host’s body), although mostly are ectoparasitoids. Moreover, parasitoid larvae feed on hosts only on the last development stages until the moment they reach adulthood.

Ectoparasitoid idiobiont females first inject venom into the host, to induce temporary or permanent paralysis, and then ovoposits on or near the immobilized host. In some cases, females that have just layed their eggs stay near the lay to protect it and also to prevent host to be eaten by other organisms.

Femella d’un himenòpter de la subfam. Pimplinae (fam. Hymenopteran female from the subfamily Pimplinae (family Ichneumonidae) stabbing her ovopositor in a trunk surface to lay eggs (Picture by Cristophe Quintin on Flickr, CC).

Generally, idiobiont adult females don’t have any preference when looking for a place to proceed on egg laying, so larvae feed on a wide variety of organisms.


Most of parasitoid insects (and especially hymenopterans, dipterans and coleopterans) are koinobionts.

Unlike idiobionts, almost all koinobionts are endoparasitic and lay their eggs directly inside the host, which can be both exposed and concealed. However, the trait that truly differentiates koinobiont parasitoids from idiobiont parasitoids is the fact that koinobionts allow the host to continue its development while feeding on it. Thus, the parasitic larvae feed on the host while growing inside host’s body without causing it any damage…until the moment larvae reach the adulthood, when they emerge from the body of the host, causing its death.

Aleiodes indiscretus female (Hymenopteran from the family Braconidae, superfamily Ichneumonoidea) inoculating eggs inside the body of a gypsy moth larvae (Lymantria dispar) (Foto de domini públic).

Once the parasitic larvae are inside host’s body begin to grow to reach the pupal stage. Until this moment, larvae use different mechanisms to avoid or block the immune response of the host (for example, by placing eggs in hosts tissues where immune system doesn’t work). So, larvae can develop by feeding on host’s nutrients until the moment they metamorphose, when adult parasitoids emerge from inside the body of the host, killing it consequently.

Due to the close relationship established by parasitoids and hosts, koinobiont parasitoids tend to be less generalist than idiobionts when looking for a suitable host.

Ecological function of parasitoids

Parasitoids, like predators or parasites, perform an important ecological role because they act as natural regulators of other organisms populations. So, parasitic larvae kill a lot of organisms that could damage the environment or even other organisms if their populations grow excessively. Thus, the disappearance of parasitoids (just like predators or parasites) could entail an excessive increase of some animal populations (especially other insects populations).

For that reason, parasitoids are considered as a great biological control agent against different plagues in gardens and crops.

Tobacco hornworm (Manduca sexta) being attacked by a parasitoid wasp of the superfamily Braconidae. In this picture, the larvae of the wasp have reached the pupal stage (white rice-shaped cocoons) and, at the end of pupation, adults will emerge, killing the hornworm. Tobacco hornworm is considered a harmful plague for plants of the family Solanaceae (like tobacco, tomato and potato) (Foto de R.J Reynolds Tobacco Company Slide Set).

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  • Notes from the subject “Biology and Biodiversity of Arthropods” taken during my Biology studies at Universitat  Autònoma de Barcelona (UAB).
  • Timothy M. Goater, Cameron P. Goater, Gerald W. Esch (2013). Parasitism: The Diversity and Ecology of Animal Parasites. Ed. 2. Cambridge University Press.
  • Vincent H. Resh, Ring T. Cardé (2009). Encyclopedia of Insects. Ed.2. Academic Press.
  • Donald L. J. Quicke (2014). The Braconid and Ichneumonid Parasitoid Wasps: Biology, Systematics, Evolution and Ecology. John Wiley & Sons.

Main image by Ton Rulkens (Flickr, CC).


Symbiosis: relationships between living beings

Predation, parasitism, competition… all living beings, besides interacting with the environment, we relate to other living beings. What types of relationships in addition to those you know? Do you feel like to know them?


The group of all living beings in an ecosystem is called biocenosis or community. The biocenosis is formed in turn by different populations, which would be the set of individuals of the same species occupying an area. For survival, it is imperative that relations between them are established, sometimes beneficial and sometimes harmful.


They are those that occur between individuals of different species. This interaction it is called symbiosis. Symbiotic relationships can be beneficial to a species, both, or harmful to one of the two.

Detrimental to all the species involved:

Competition: occurs when one or more resources are limiting (food, land, light, soil …). This relationship is very important in evolution, as it allows natural selection acts by promoting the survival and reproduction of the most successful species according to their physiology, behavior …

Las selvas son un claro ejemplo de competencia de los vegetales en busca de la luz. Selva de Kuranda, Australia. Foto de Mireia Querol
Rainforests are a clear example of competition between vegetals in the search for light. Kuranda rainforest, Australia. Photo by Mireia Querol
One species has benefits and the other is detrimented:
  • Predation: occurs when one species (predator) feeds on another (prey). This is the case of cats, wolves, sharks
foca, león marino,
Great white shark (Carcharodon carcharias) jumping to depretade a marine mamal, maybe a sea lion. Photo taken from HQ images.
  • Parasitism: one species (parasite) lives at the expense of other (host) and causes it injury. Fleas, ticks, pathogenic bacteria are the best known, but there are also vertebrate parasites, like the cuckoo that lay their eggs in the nests of other birds, which will raise their chicks (brood parasitism). Especially interesting are the “zombie parasites”, which modify the behavior of the host. Read this post to learn more!
    Carricero (Acrocephalus scirpaceus) alimentando una cría de cuco (Cuculus canorus). Foto de Harald Olsen
    Reed warbler (Acrocephalus scirpaceus) feeding a cuckoo’s chick (Cuculus canorus). Photo by Harald Olsen

    Parasites that live inside the host’s body are called endoparasites (such as tapeworms), and those who live outside ectoparasites (lice). Parasitism is considered a special type of predation, where predator is smaller than prey, although in most cases does not cause the death of the host. When a parasite causes illness or death of the host, it is called pathogen.

    Cymothoa exigua es un parásito que acaba sustituyendo la lengua de los peces por su propio cuerpo. Foto de Marcello Di Francesco.
    Cymothoa exigua is a parasite that replaces the tongue of fish with their own body. Picture by Marcello Di Francesco.

Kleptoparasitism is stealing food that other species has caught, harvested or prepared. This is the case of some raptors, whose name literally means “thief.” See in this video a case of kleptoparasitism on an owl:

Kleptoparasitism can also occur between individuals of the same species.

One species has benefits and the other is not affected:
  • Commensalism: one species (commensal) uses the remains of food from another species, which does not benefit or harm. This is the case of bearded vultures. It is also commensalism the use as transportation from one species over another (phoresy), as barnacles attached to the body of whales. The inquilinism is a type of commensalism in which a species lives in or on another. This would apply to the woodpeckers and squirrels that nest in trees or barnacles living above mussels. Finally, metabiosis is the use of the remains of a species for protection (like hermit crabs) or to use them as tools.
    El pinzón carpintero (Camarhynchus pallidus) utiliza espinas de cactus o pequeñas ramas para extraer invertebrados de los árboles. Foto de
    The woodpecker finch (Camarhynchus pallidus) uses cactus spines or small branches to remove invertebrates from the trees. Picture by Dusan Brinkhuizen.
    Both species have benefits:
  • Mutualism: the two species cooperate or are benefited. This is the case of pollinating insects, which get nectar from the flower and the plant is pollinated. Clownfish and anemones would be another typical example, where clown fish gets protection and food scraps while keeps predators away and clean parasites of the sea anemonae. Mutualism can be optional (a species do not need each other to survive) or forced (the species can not live separately). This is the case of mycorrhizae, an association of fungi and roots of certain plants, lichens (mutualism of fungus and algae), leafcutter ants

    Las hormigas Atta y Acromyrmex (hormigas cortadoras de hogas) establecen mutualismo con un hongo (Leucocoprinus gongylophorus), en las que recolectan hojas para proporcionarle nutrientes, y ellas se alimentan de él. Se trata de un mutualismo obligado. Foto tomada de Ants kalytta.
    Atta and Acromyrmex ants (leafcutter ants) establish mutualism with a fungus (Leucocoprinus gongylophorus), in which they gather leaves to provide nutrients to the fungus, and they feed on it. It is an obligate mutualism. Photo taken from Ants kalytta.


They are those that occur between individuals of the same species. They are most beneficial or collaborative:

  • Familiars: grouped individuals have some sort of relationship. Some examples of species we have discussed in the blog are elephants, some primates, many birds, cetaceans In such relationships there are different types of families.
  • Gregariousness: groups are usually of many unrelated individuals over a permanent period or seasonal time. The most typical examples would be the flocks of migratory birds, migration of the monarch butterfly, herds of large herbivores like wildebeest, shoal of fish

    El gregarismo de estas cebras, junto con su pelaje, les permite confundir a los depredadores. Foto tomada de Telegraph
    Gregariousness of these zebras, along with their fur, allow them to confuse predators. Photo taken from Telegraph
  • Colonies: groups of individuals that have been reproduced asexually and share common structures. The best known case is coral, which is sometimes referred to as the world’s largest living being (Australian Great Barrier Reef), but is actually a colony of polyps (and its calcareous skeletons), not single individual.
  • Society: they are individuals who live together in an organized and hierarchical manner, where there is a division of tasks and they are usually physically different from each other according to their function in society. Typical examples are social insects such as ants, bees, termites

Intraspecific relations of competition are:

  • Territorialityconfrontation or competition for access to the territory, light, females, food can cause direct clashes, as in the case of deer, and/or develop other strategies, such as marking odor (cats, bears), vocalization

    Tigres peleando por el territorio. Captura de vídeo de John Varty
    Tiger figthing for territory. Video caption by John Varty
  • Cannibalism: predation of one individual over another of the same species.

And you, as a human, have you ever thought how do you relate with individuals of your species and other species?