Introduction
Many relationships in our environment go unnoticed because the organisms involved are so small. Parasitic relationships are a prime example of this, as many of the species that participate in this relationship are microscopic - and are not limited to just birds or insects but also bacteria and fungi. Parasites are defined as an organism that lives in or on another organism (its host) and benefits by deriving nutrients at the other's expense. Parasites generally do not kill their host directly, but may cause a disease in the host that could be fatal. An example of this is toxoplasmosis, in which the parasite Toxoplasma gondii infects their host and may cause an infection, Toxoplasmosis, which is a leading cause of death from food-borne illnesses.
Types of Parasitism
There are several types of parasitism, including obligate, which is when the organism is unable to complete the life cycle without a suitable host. One example of this is Ophiocordyceps unilateralis - a fungus that can be found in South American rainforests. Its main goal is to reproduce which it accomplishes by taking control of the host’s body and guiding it to another environment with conditions suitable for the parasite to infect more organisms and continue its life cycle.
Another type of parasitism is facultative parasites, and they are the opposite of obligate parasites as they are organisms that do not need a host to complete their life cycle. One parasite that possesses this trait is Strongyloides stercoralis which is a round worm from the nematode group which mainly infects humans but is also known to occur in dogs as well. They are facultative parasites because they are able to produce offspring that are free living without the help of a host.
The third type of parasitism is mesoparasitism which is when a parasite, copepods for example, enter the host’s body through an opening such as the ear or mouth and remain - embedded there absorbing nutrients from the host.
The final types of parasitism are endoparasitism and ectoparasitism. These parasites are classified as ones that live inside the host and outside the host, respectively. A great example of these ectoparasites are ones that affect dogs as they are very common. Tick lives on the outside of the host sucking on their blood for nutrients. Tapeworm is an endoparasite that lives inside of the host's small intestine, stealing nutrients from the food that travels through the digestive system.
Variations of Parasitism
Along with types of parasitism, there are also variations of parasitic behaviors that are all very different from each other. Brood parasitism is when the hosts act as parents to offspring that don't belong to them and were placed by another organism and this is common in birds such as the Pin-tailed Whydah. Social parasitism occurs when a parasite takes advantage of interspecific interactions between other animals like the Bombus bohemicus, which is a bumblebee that invades the hives of other bees and seizes reproduction while also making the host workers raise the offspring.
Kleptoparasitism is when parasites steal food gathered by the host and this is clearly seen in some species of birds such as skuas (pictured above). Hyperparasitism is when a parasite feeds on another parasite. This is common in insects in which some of them lay their eggs inside or near another host which has been in contact with another parasite. Sexual parasitism is a unique situation which can be seen in some species of anglerfish in which the female acts as the host and protects the male while he is kept only for reproductive purposes. The final variation of parasitism is adelphoparasitism in which the host and the parasite are closely related to each other. This can be seen in the citrus blackfly in which some unmated females lay eggs in fully developed larvae of their own species.
Organisms
Here are some examples of parasites that can be found in Orange County!
Pacific Lamprey (Entosphenus tridentatus) are ectoparasites that can be found along the Pacific Coast. They are eel-like fish that lack jaws, fins, scales, and can grow up to 2.5 feet long. They are facultative parasites that feed by attaching themselves to a host or in this case another fish such as salmon or rock fish and they accomplish this by use of their rounded like sucker mouth that comes equipped with 3 large anterior teeth and plenty of smaller teeth located on the posterior. The life cycle of these fish is typical as they have a larval stage, juvenile stage, and adult stage. They don't become parasitic until their juvenile stage in life, before they are primarily feeding on algae. This could be in order to prevent competition for food with their offspring for food allowing them to mature and continue the life cycle.
Euhaplorchis californiensis is a trophically transmitted (spread when eaten by the host) endoparasite that can be found in many different species living in the salt-water marshes of Southern California. This parasite resides in three different hosts: shorebirds, snails and killfish in a constant cycle. The way this relationship works is that the Euhaplorchis californiensis will start out as eggs released from the bird droppings which are then consumed by snails where they develop into infected cercariae (larval form of trematodes) that infect killfish - producing cysts inside of its brain cavity and affecting the behavior of the fish, causing them to be more erratic and likely to be caught by shorebirds scanning the surface of waters for food. The shorebirds consume these infected fish and the parasite finds a new home in the gut of the shorebirds where more eggs will be produced and distributed throughout the water environment by the stool of the host.
Conclusion
The life cycle of a parasite varies from organism to organism, but the main premise for each one is growth, reproduction, and transmission. But one thing for sure is that parasites play an important role in the ecosystem, mainly in the host’s behavior and fitness, and are able to influence population sizes that can have effects on the other species around them and their interactions. There is some speculation that there are far more species that are parasitic than those that are just free living and they are often overlooked and neglected despite their abundance in the species population. This is important because there are still plenty of other parasites that have yet to be researched and discovered so the extinction of other organisms may cause the loss of a host for many parasites and cause them to follow suit.
Look out for next week's blog featuring more parasites native to Orange County!
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