Parasitism and Mutualism

Parasitism and Mutualism Notes

Definition: Symbiosis refers to the intimate and enduring relationship between two or more organisms of different species.
Implications: The relationship determines the fate of individuals of one species based on their interaction with another species.
Types of Outcomes:
- Mutualism (++): Both species benefit from the relationship.
- Parasitism (+-): One species benefits at the expense of the other.
- Commensalism (+0): One species benefits while the other is unaffected.
- Amensalism (-0): One species is harmed while the other is unaffected.

Parasites: Typically do not kill their hosts; they draw resources from them.
Parasitoids: Lay eggs in a host; larvae consume the host, eventually leading to the host's death.

Traits: Small size, short generation time, rapid multiplication within the host.
Associated with: Disease.
Infection Duration: Short in relation to host lifespan, typically transmitted directly from host to host or via a carrier (e.g., viruses, bacteria).

Traits: Larger size, longer generation time, usually do not complete life cycle in a single host.
Transmission: Can occur directly between hosts or via carriers/intermediate hosts (e.g., flatworms, roundworms, lice).

Over 4000 species of parasitic plants exist.
Haustorium: A modified root that penetrates host tissues to connect with vascular tissue.
Types:
- Hemiparasites: Photosynthetic, drawing water and nutrients from the host's xylem.
- Holoparasites: Non-photosynthetic, obtaining all resources from the host's phloem and xylem.

Ectoparasites: Live on the surface of hosts (e.g., skin, feathers).
Endoparasites: Live within hosts, potentially affecting blood and organ systems.
Life cycles can involve multiple hosts and stages; definitive hosts are where parasites achieve sexual maturity, and intermediate hosts support lifecycle stages.

Direct Transmission: Occurs between hosts without intermediate organisms (e.g., through air or water).
Indirect Transmission: Involves an intermediate vector that transmits the parasite from one host to another.

Behavioral Defenses: Hosts can groom to remove ectoparasites, relocate to areas with fewer parasites (e.g., deer using dense, shaded spots).
Immune Defenses:
- Inflammatory Response: Triggers release of histamines, increased blood flow, and white blood cell activity.
- Cysts: Hard encapsulated structures around parasites to isolate them.

Parasitism may lead to decreased fitness (e.g., smaller egg sizes in infected females).
Altered behaviors in hosts can increase vulnerability to predators (e.g., rabbits with tularemia, killifish with trematodes).

Emerging Infectious Diseases: Diseases that have recently increased in incidence or range.
Lyme Disease Example: Transmission through ticks that obtain bacteria from infected animals, affected by human-induced environmental changes.

In cases where parasites are less harmful and actually beneficial, relationships can shift from parasitism to mutualism (e.g., tapeworms aiding in host growth).
Type of Mutualists:
- Obligate: Cannot survive without the interaction.
- Facultative: Can survive without the interaction.

Coral-Algae Symbiosis: Corals obtain most of their energy from symbiotic algae (zooxanthellae), while algae receive shelter.
Plant-Bacteria Relationships: Legumes associate with nitrogen-fixing bacteria (Rhizobium) to receive nitrogen, while bacteria gain carbon from plants.
Mycorrhizal Fungi: Assist plants in nutrient uptake while receiving carbon, with endomycorrhizae and ectomycorrhizae being types of interactions.

Defense: Examples where one species helps defend another, like alkaloids from fungi in grasses that deter grazers.
Reproduction: Pollinators like insects and birds that not only gain food but also help fertilize plants by transferring pollen; might incur energy costs to the plant.

Ants and Myrmecochore Plants: Seeds that ants collect for their elaiosome (food body) to consume, helping disperse the seeds.
Fruit-Eating Animals: Consume fruit while ensuring seeds are not eaten, promoting germination away from the parent plant.