Parasitism

Parasitism can differ based on characteristics, size, and relation with the hosts. They can function as both predators and prey. Some classical forms of parasitism in nature are:

1. Ectoparasitism

Ectoparasitism involves one organism residing on the outer surfaces of another (ectoparasites), tapping into its host for essential resources. Those parasites often attach themselves to the host, utilizing ingenious adaptations to feed on blood, tissues, or other nutrients. Common examples include ticks, fleas, and leeches, which secure their livelihood while affecting their host’s well-being.

2. Endoparasitism

In endoparasitism, the parasites (endoparasites) reside within their host’s body. These internal invaders establish their presence within various organs, often altering the host’s health and functions. Intestinal parasites, like tapeworms and roundworms, reside in the digestive system, while intracellular parasites, such as the Plasmodium responsible for malaria, infiltrate host cells to satisfy their needs.

Endoparasites can be intestinal (inhabiting the host’s digestive system), for example, tapeworms and roundworms, or intracellular (take residence within the host’s cells), such as Plasmodium parasite causing malaria.

3. Mesoparasitism

Mesoparasitism represents a unique type of parasitic interaction where the parasite relies partially on its host for resources while still possessing some capacity for independent survival. Certain plants containing chlorophyll for photosynthesis perform this intermediate form of parasitism, deriving nutrients from the host plant’s vascular system at the same time.

4. Obligate Parasitism

Obligate parasitism epitomizes a one-sided relationship where an organism (obligate parasite) relies entirely on a host for survival, lacking the ability to live independently. They have evolved specialized adaptations for parasitic living and cannot complete their life cycle without a host. An example of obligate parasitism is the tapeworm, which cannot do digestion or reproduction outside its host’s digestive system.

5. Facultative Parasitism

Facultative parasitism offers a glimpse into those organisms that can lead a parasitic or a free-living lifestyle. These adaptable organisms can survive and reproduce independently, but under certain conditions, they may choose to exploit a host for resources. The ability of some fungi and bacteria to switch between parasitic and non-parasitic modes of existence is called facultative parasitism.

Variations on Parasitism

Beyond the classic forms, parasitism also has some variations:

• Hyperparasitism involves a parasite that parasitizes another parasite. In this intricate relationship, the secondary parasite preys upon the primary parasite, exploiting a host. Hyperparasitism can create complex chain interactions within ecosystems, with multiple layers of dependence and exploitation.
• Social parasitism occurs when one species uses the behaviors or resources of another species. A classic example is the cuckoo bumblebee, which invades the nest of a host bumblebee species, killing the host queen and using the worker bees to care for its own young.
• Brood parasitism involves one species laying its eggs in the nest of another, leaving the host to raise the young parasite. This phenomenon is notably seen in birds, where the parasitic species’ eggs hatch alongside or before the host’s eggs. The common cuckoo and its interactions with various bird species exemplify this parasitism.
• Kleptoparasitism refers to the act of stealing food or resources from another organism. Rather than directly living on or within the host, the kleptoparasite takes advantage of the host’s efforts. Seabirds like skuas and frigatebirds often engage in kleptoparasitism by harassing other birds to steal their recently caught prey.
• Sexual parasitism involves one sex of a species exploiting the reproductive efforts of the other sex. In some cases, males may coerce or manipulate females into mating, often leading to detrimental effects on the female’s well-being or reproductive success.
• Adelphoparasitism is a rare form of parasitism observed in insects like ants. In this relationship, a parasitic ant infiltrates the nest of a host ant species and is cared for as if it were one of the host’s own. The parasitic ant may exploit the host’s resources or even kill its queen to establish dominance.

Over half the organisms have a parasitic phase at some point in their life cycle.

Some common examples of parasitism in nature are:

In Humans

Several intestinal parasites can affect human health. The tapeworm (Taenia spp.) and roundworm (Ascaris lumbricoides) are examples of parasites that infect the human digestive system, causing discomfort, malnutrition, diarrhea, and other health issues.

Some parasites live in the blood. Blood parasites like the malaria parasite (Plasmodium) are transmitted through mosquito bites, causing malaria in humans. Blood parasitism is also found in most species of cuckoos and all cowbirds. Such birds do not build their nests and thus lay their eggs in the nests of other species with the hope that they will raise them. The parasitism in cowbirds does not harm the host. However, the cuckoo may remove some host eggs.

Liver flukes are endoparasites that infect the livers of various animals, including humans. They can cause serious health issues and diseases.

In Plants

Parasitism is not limited to animals; it also occurs in the plant kingdom. Some plants, known as parasitic plants, derive nutrients from other plants.

One example is the parasitic mistletoe plants, attaching themselves to trees and deriving nutrients from their host’s sap. While mistletoe is a holiday tradition, its parasitic nature can weaken trees over time. The other example is the dodder, which lacks chlorophyll and attaches itself to the host plant to extract water and nutrients.

In Insects

Certain species of insects, such as some types of ants, practice social parasitism. These parasites infiltrate the colonies of other ants and manipulate their behavior to serve their needs. They may steal food, exploit the colony’s resources, or even control the host ants into caring for the parasite’s young.

Certain species of wasps lay their eggs inside other insects. On hatching, the wasp larvae thrive on the host’s tissues, eventually causing death.

Thus, parasitism, like predation, is a consumer-resource interaction, but unlike them, the parasites are much smaller than their hosts and do harm the host.

In Fishes

Monogeneans and trematodes are common ocean flatworms that attach to fish gills, skin, and other external surfaces. These parasites use those host cells to complete their lifecycle. Fishes become infected through direct contact with contaminated water or intermediate hosts.