Language
Country/Area
No result found
The mystery of parasitism: Why can't some organisms survive independently?
In nature, many organisms live by parasitism. These organisms are called obligate parasites or holoparasites. The only way they can survive is by relying on nutrients provided by the host, and if they cannot find a suitable host, they cannot complete their life cycle and cannot reproduce. The opposite is a facultative parasite, which can live without a host. So how did these parasites evolve such unique survival strategies?
Types of parasites
Extremophiles are widely distributed in various organisms, including viruses, bacteria, fungi, plants and animals. They must go through at least one parasitic stage before they can complete their development. Although controversial, viruses are generally considered obligator endoparasites that must invade living cells in order to exploit the cell's resources to reproduce.
"In the world of parasites, the art of survival lies in interaction and adaptation with the host."
For example, a species of the wasp family, such as Vespula austriaca, is a parasite that must live on Vespula acadica. In the Bombus of the insect kingdom, B. bohemicus is a parasite of B. locurum, B. cryptarum, and B. terrestris.
Host-parasite interactions
Life Cycle
The life cycle of a parasite is often focused on exploiting its host. When a host is infected, parasites complete their life cycle in different ways. Parasites that exclusively infect a single host species are said to have a direct life cycle, while those that infect multiple hosts are called complex or indirect life cycles, such as the Plasmodium parasite that causes malaria.
Intermediate host and final host
A parasite may use an intermediate host for a brief transition before ultimately reaching maturity in the first intermediate host, with its only place of reproduction being in the definitive host. For example, Ribeiroia ondatrae uses the blunt-edged arrow snail as its first intermediate host, amphibians and fish as second intermediate hosts, and birds as the final host.
Persistence of parasitic behavior
Different parasites can behave as permanent or temporary in their hosts. Permanent parasites, such as head lice, reproduce on their hosts for many generations, whereas transient parasites, such as the larval stage of harvestman mites, exhibit parasitic behavior only during a single stage of development.
Invasion Strategy and Host Defense
To establish parasitism in a susceptible host, extremophiles must effectively evade host defenses before, during, and after entry. Due to the diversity of parasite types, it is difficult to identify universal invasion strategies.
"The success of a parasite lies in its exquisite manipulation of the host's internal world."
For example, many bacteria and viruses enter host cells by passive uptake, while some enter by active entry. Some extreme parasitic wasps, such as Polistes atrimandibularis, infiltrate host communities silently by changing their chemical signatures to gain the host's trust.
Host Behavior Control
Changes in host behavior through infection are extremely common among parasites. This would classify some behavioral abnormalities as adaptive manipulation, but the researchers note that whether such behavioral changes are truly manipulations as claimed or purely side effects remains controversial. For example, rats infected with Toxoplasma gondii showed an increased attraction to cat urine.
"Behavioral changes may be a byproduct of long-term evolution of parasites and may not necessarily bring obvious benefits."
Extended phenotype and its evolution
Some of the observed behaviors of organisms are not the expression of their own genes, but rather are extended phenotypes under the influence of parasites. The evolutionary paths of behavioral manipulation can also be divided into three categories: one is manipulation dominated by parasites, and the other is manipulation driven by host responses. This also illustrates how parasites can further influence host behavior to promote their own spread.
Parasitic Mimicry: The Wisdom of the Hatchers
Parasitic birds such as jays and cuckoos reduce host rejection by mimicking the color and pattern of their host's eggs. This type of mimicry and competition allows the parasite to easily blend into the host's environment. Examples of some butterflies and ants also illustrate how parasites exploit the behavior of their hosts to survive and reproduce.
Extreme parasitism in evolution
According to current evolutionary biology theory, the relationship between host and parasite is likely to evolve towards an equilibrium state of severe disease rather than the traditionally believed equilibrium state of mutualism.
Humanity's understanding of parasites shows their importance in ecosystems. The existence of extreme parasites has inspired many studies in the fields of ecology and biology, asking us to think: What can we learn from these complex interactions of life?
