Category Science

Even the tiniest living things may be parasites. The micro-organisms that cause malaria and sleeping sickness, for example, are parasites that need more than one host to complete their life cycles. The diseases are spread by infected insects, which bite human beings to feed on their blood and in so doing pass on the infection. The organisms multiply in the person’s body, causing illness. The cycle is completed when an infection-free insect bites the person and in its turn becomes a carrier of the disease.

Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the ability for a foreign virus, once introduced into an individual of a new host species, to infect that individual and spread throughout a new host population. Steps involved in the transfer of viruses to new hosts include contact between the virus and the host, infection of an initial individual leading to amplification and an outbreak, and the generation within the original or new host of viral variants that have the ability to spread efficiently between individuals in populations of the new host Often seen in emerging viruses where one species transfers to another, which in turn transfers to humans. Examples include covid-19, HIV-IDS, SARS, Ebola, swine, rabies, and avian influenza. Bacterial pathogens can also be associated with CST.

The exact mechanism that facilitates transfer is unknown; however, it is believed that viruses with a rapid mutation rate are able to overcome host-specific immunological defenses. This can occur between species that have high contact rates. It can also occur between species with low contact rates but usually through an intermediary species. Bats, for example, are mammals and can directly transfer rabies to humans through bite and also through aerosolization of bat saliva and urine which are then absorbed by human mucous membranes in the nose, mouth and eyes. Note: the document used as a reference does not use the words urine or saliva so this citation is questionable. A host shifting event is defined as a strain that was previously zoonotic and now circulates exclusively among humans.

Similarity between species, for example, transfer between mammals, is believed to be facilitated by similar immunological defenses. Other factors include geographic area, interspecies behaviours, and phylogenetic relatedness. Virus emergence relies on two factors: initial infection and sustained transmission.

A parasite is a living thing that benefits from a relationship with another species but actually causes harm to that species. Some fungi are found on dying birch trees and can also live for a while on the wood after the tree has died.

Cuckoos do not raise their own young. They are said to be brood parasites. They lay a single egg in a nest that already contains several eggs while the parent bird is away. Although cuckoo eggs are often slightly bigger than the other eggs, the female cuckoo has the extraordinary ability partially to match the colour of her egg to the others. The eggs are hatched by the host bird. The young cuckoo is bigger and stronger than the other nestlings and demands more food. To ensure that it receives all the food brought to the nest by the foster parents, it pushes the other young birds out of the nest.

When she’s ready to lay an egg, a female cuckoo canorus swoops to the unattended nest of a smaller species. She then swallows one of the eggs that have been laid there and lays one of her own—a behavior known as brood parasitism.

Sometimes potential victims revolt. The parents that inhabit the nest may mob the cuckoo mom, preventing her from dropping off her egg; they may push out cuckoo eggs before they hatch, or they may even abandon the nest.

But often the cuckoo mom gets away undetected, leaving her parental duties behind, and the nest’s owners return none the wiser. C. canorus is known to have passed its eggs on to more than 100 host species, according to the International Union for Conservation of Nature.

When the cuckoo chick hatches, it ejects other eggs or hatchlings to get all the space—and food—for itself. Hungry as a whole brood, the outsize baby devours everything brought by its foster parents—in the photo above, the provider is a reed warbler, a common host.

Franka Slothouber, a retired photo editor who’s an avid wildlife photographer, observed the birds’ behavior in 2014 in Amsterdam, where she lives. “The poor warbler almost disappears in the wide-opened mouth of its ‘adopted’ baby,” Slothouber says. And yet “the warbler couple is convinced this chick is theirs and treats it accordingly, by feeding it until it can look after itself.”

In tropical waters, clownfish have a symbiotic relationship with sea anemones. They live among the anemone’s tentacles, unharmed by its stings but enjoying protection from predators. In turn, the clown-fish seem to protect the anemone from some predators too. They may even lure fish into the anemone’s tentacles, where they can be caught and digested.

Clownfish and sea anemones both live in saltwater habitats. There are numerous species of clownfish, and they come in a variety of colors from orange to black. Their colorful appearance kind of looks like a clown’s face paint, so it’s no wonder they got the name clownfish.

Sea anemones look likes plants, but they’re actually a predatory animal that belongs in the same phylum as coral and jellyfish. They kill their prey with their nematocysts, which are poisonous cells that can be found in the sea anemone’s tentacles. These special cells can be shot out of the sea anemone, thus delivering venom to potential prey.

Although there over 1,000 species of sea anemones, only about 10 species of sea anemones have a symbiotic relationship with clownfish, and not all species of clownfish are compatible with those 10 species of anemone. Certain species of clownfish pair up with certain species of anemone. By now you’re probably wondering how a fish and a sea anemone work together to have a mutualistic relationship.

When both partners benefit equally from a partnership, they are said to be in a symbiotic relationship. There are many such relationships in the natural world. For example, when a bee goes to a flower to collect nectar, it also brings about pollination by carrying pollen on its furry body from one flower to the next. Both the bee and the flower benefit.

A symbiosis is an evolved interaction or close living relationship between organisms from different species, usually with benefits to one or both of the individuals involved. Symbioses may be ‘obligate’, in which case the relationship between the two species is so interdependent, that each of the organisms is unable to survive without the other, or ‘facultative’, in which the two species engage in a symbiotic partnership through choice, and can survive individually. Obligate symbioses are often evolved over a long period of time, while facultative symbioses may be more modern, behavioral adaptions; given time, facultative symbioses may evolve into obligate symbioses.

Endosymbiosis is a symbiotic relationship, occurring when one of the symbiotic partners lives within the body of the other. Endosymbiosis can take place either within the cells (intercellular symbiosis) of the ‘host’ organism, or outside the cells (extracellular symbiosis). On the other hand, ectosymbiosis is a symbiotic relationship in which one organism lives on the body surface of the host, including the lining of the digestive tract, or exocrine glands such as mucus or sweat glands.

Mutualisms are a form of symbiosis in which both symbiotic partners benefit from the interaction, often resulting in a significant fitness gain for either one or both parties. Mutualisms can take the form of resource-resource relationships, service-resource relationships, or service-service relationships.

Resource-resource mutualisms (also known as ‘trophic mutualisms’) happen through the exchange of one resource for another between the two organisms involved. Resource-resource mutualisms most often occur between an autotroph (a photosynthesizing organism) and a heterotroph (an organism which must absorb or ingest food to gain energy). Most plants have a trophic mutualism called a mycorrhizal association, which is a symbiosis between the roots of the plants and a fungus. The fungus colonizes the plants roots and is provided with carbohydrates, sucrose and glucose. In exchange, the plant benefits from the fungi’s higher water and mineral absorption capabilities.

Service-resource mutualisms occur when the symbiotic partner provides a service in exchange for a resource reward. One of the best known examples of this is the exchange between plants and their pollinators. While visiting the plants to gain a supply of energy-rich nectar, the pollinator (insects, birds, moths, bats, etc.), provides the plant with the service benefit of being pollinated, while ensuring their own pollen is distributed when the pollinator visits more plants of the same species.

All living things are linked in complicated food. Webs, relying on each other for nourishment, but some animals and plants have very special relationships, where a partnership may benefit one partner or both.

Relationships are an important component of life. In such relationships, plants or animals of different species may be dependent on one another for survival. They may share habitats or lifestyles or interact in a specific way to benefit from the presence of another organism.

We often refer to animals living in tandem as ‘associates.” The relationship between associates and their hosts can be described as mutualistic, commensal, or parasitic. In a mutualistic relationship, both animals benefit from living together. Commensal organisms cause no harm to their hosts, but receive some benefit from living with them. Parasites actually feed off their host organism, thus causing harm to the host.