Parasitism is a symbiotic relationship between two organisms where one (the parasite) depends on the other (the host), most often for food. Parasites usually exert some harm that can sometimes lead to their host’s death; however, some parasites have been observed to protect their host from other potentially harmful parasites. After all, they would need to find a new host (which is a risky venture) if their current one dies.
Parasitic species can have significant effects on their host’s interactions with other organisms, as well as the overall biodiversity in their ecosystem. They can regulate host population sizes, and some can even influence their host’s behavior and fitness (ability to survive and reproduce). For example, a mind-controlling parasite called Toxoplasma gondii lives in the brain of spotted hyena cubs in Kenya. T. gondii makes spotted hyena cubs more reckless–and more likely to be killed–around lions (hyenas’ top competitor for food) because Toxoplasma can only sexually reproduce in feline intestines. The parasite likely makes feline urine more alluring to infected hyena cubs, daring them to get dangerously closer to lions than the uninfected cubs would. This behavioral manipulation is just one example of the profound influence parasites can have on their hosts. Below are some of the reasons why parasites are important:
Biodiversity regulation - Parasites are ubiquitous (widespread) in nature. They can play a key role in regulating the populations of their hosts through various mechanisms, such as reduced reproductive success and direct mortality. This prevents any one species from becoming too dominant in an ecosystem, helping to maintain balance.
Evolutionary pressure - Parasites are a major driver of evolutionary processes. They are in a continuous evolutionary arms race with their hosts. Hosts evolve defenses against parasites, while parasites evolve strategies to overcome those defenses.
Food web dynamics - Parasites often serve as both prey and predator in an ecosystem, acting as trophic links between different species in a food web. For example, marine ecto (external) parasites that feed on the mucus, epidermal tissue, and/or blood of host fish are a primary food source for cleaner fishes.
Medical research - Parasites are excellent models for studying the immune system, host-pathogen interactions, and the evolution of both host and pathogen. For example, due to their effect on the immune system, parasites have been widely studied to develop vaccines.
Parasites are an incredibly abundant and diverse group of species; they can be animals, plants, fungi, or single-celled organisms (e.g., protozoa). Every habitat and ecosystem on Earth contains parasites, and it is estimated that every multicellular animal hosts at least one parasite species at some point in its life cycle. Orange County has a wide range of habitats (coastal, wetlands, chaparral, forests, etc.), each supporting a diverse community of species, including parasites. Below are some of the native parasitic species in Orange County.
Cochineal (Dactylopius coccus) is a sessile scale insect (i.e., an immobile, small bug with a protective shield-like cover) that infests various species of cactus in the genus Opunta. This ectoparasite (a parasite that feeds and/or lives on the surface of its host) infests any of the 200+ species of prickly pear cacti, which are native to subtropical parts of South America and Southwest United States, including Orange County.
Male cochineals have wings and they are much smaller than females. They do not have mouthparts so they are non-feeding adults and have a much shorter lifespan. Adult males only live for about a week after metamorphosis, and they will mate with as many females as they can before they die. Female cochineals are flightless and sessile. They cluster together on prickly pear pads, which they penetrate using their mouthparts to feed on cactus juice and flesh. Large abundance of cochineal can kill infected cacti.
Female cochineals and their eggs secrete carminic acid (red chemical) from their abdomen to protect themselves from desiccation (drying out) and insect predators. This chemical has been used by native tribes to dye fabrics; it has also been approved by the Food and Drug Association (FDA) to dye food and cosmetics.
Native people in Puebla, Tlaxcala and Oaxaca cultivated the parasitic cochineal and its host cactus to use the rich scarlet pigment to dye fabrics. This process showcases their thorough knowledge of both the insect and its cactus host.
Salt marsh bird’s beak (Cordylanthus maritimus) is found in coastal salt marsh habitats from San Luis Obispo to Northern Baja California. This plant is quite unique in that it is a root hemiparasite (a plant that is partially dependent on its host which has chlorophyll) and a halophyte (a salt-tolerant plant). Although salt marsh bird’s beak can photosynthesize, it still extends its haustorial roots (modified roots of a parasitic plant that penetrate a host plant to absorb nutrients and water) to adjacent plants’ roots to steal most of its water and nutrient requirements. It is a generalist when it comes to choosing its host, so it will try to parasitize any of its neighboring plants, such as shore grass, salt grass, and alkali heath.
Due to coastal development and environmental issues caused by global climate change, the salt marsh bird’s beak has been listed as endangered since 1978 in the U.S. It is considered a rare plant in Mexico, where it is listed as a threatened species. Even though salt marsh bird’s beak is parasitic, it supports various pollinators (e.g., bees) and contributes to the overall biodiversity in salt marsh habitats.
California dodder (Cuscuta californica) is a parasitic flowering plant in the morning glory family (Convolvulaceae) that is native to Orange County’s coastal sage scrub. Dodder species are holoparasites (plants that derive most, if not all, of their water and nutrient needs from their host plants). California dodders can only do limited photosynthesis; they do not have a root system or chlorophyll, and they have very small scale leaves that are short-lived. This parasitic plant looks like yellow-orange vines (that are actually weak stems) wrapped around its host plant; it produces tiny, white flowers (~3mm wide) that bloom from May-August, and fruits that are even tinier.
Although California dodders spend most of their lifetime without touching the soil, they do start off from the ground. Their seeds have temporary roots and sufficient nutrients to survive for 5-10 days before they must find a suitable host plant, after which the original root dies. Using their root-like structures called haustoria, California dodders survive by penetrating the tissues of its host plant to obtain water, minerals, and carbohydrates. Despite their ability to envelop and penetrate its host plant’s stems, dodder species are not usually fatal to their host plants.
When dodders penetrate their host’s stems, they essentially fuse vascular systems with their host. The vascular system allows transport of water, nutrients, and chemical cues throughout the plant body; it can act as a communication network that lets different plant parts “talk” to each other. When a dodder plant parasitizes multiple hosts, it can act as a network between its host plants. If a host plant within a dodder network is attacked by herbivorous insects, the dodder signals other hosts to activate their defense genes, making them more resistant to herbivory.
Dodders also have some human uses. Native Americans used California dodders that grew on buckwheat to treat black widow spider bites; however, no information was found on what part of the plant was used and how it was applied. Dodders were also used to treat nose bleeds by inserting them into the nostril, as well as scour pads for cleaning.
There are eight species of dodders that are native to California, and some have been observed to parasitize California buckwheat (Eriogonum fasciculatum), California croton (Croton californicus), sand aster (Corethrogyne filaginifolia), deerweed (Acmispon glaber), and various species of sage (Salvia species). As for its conservation status, the California dodder has a secure population size in the U.S.
American mistletoe (Phoradendron leucarpum) is a hemiparasitic flowering plant in the Santalaceae family that grows on woody shrubs and trees. It is native to many parts of the United States, including California. As photosynthetic hemiparasites, mistletoes are not completely dependent on their host plant; however, they still try to obtain most of their water needs from their host when possible.
Mistletoe berries are coated with viscin (packed with nutrients for birds), and each berry contains one seed. The seeds have special adaptations that aid in seed dispersal by animals. American mistletoes have white, sticky seeds that latch on birds’ beaks/feathers and on mammals’ furs. When these animals discharge the seeds or rub their beaks/feathers/fur on a tree, the seeds stick on the potential host tree. These sticky seeds contain haustorial roots that penetrate the host plant’s branches to eventually steal nutrients and minerals.
Mistletoes are both hemiparasitic to their host plants and are mutualists of various bird species that feed on their seeds, meaning both the birds and mistletoe benefit from this symbiotic relationship. Many species of birds use mistletoes for necessary resources such as food, refuge from predators, and nesting space for their young. For example, Phainopeplas (a species of flycatcher) rely heavily on mistletoes for both food and water (they don’t drink much water), and they have specialized digestive tracts to process the low-nutrient fruits. In return, Phainopeplas disperse mistletoe seeds to suitable locations for successful germination and growth.
Want to see some of these fascinating organisms in our local habitats? Join OC Habitats on our upcoming guided hikes, habitat restoration projects, and monitoring efforts! You can also learn about the native parasitic plants and animals in Orange County by tuning into two special podcast episodes available on our Spotify.
Comments