Animal Symbiosis

Definition: Symbiosis translates to "living together" and denotes a persistent, intimate association between two or more unrelated organisms.
- Originated in 1876.
Key Characteristics:
- Involves at least one organism benefiting from the relationship.
- Types include: Parasitic relationships, mutualistic relationships, and others that are more difficult to categorize.

Symbiotic interactions are classified based on the effect of the symbiont on the host organism, which can be:
- Mutualism (both benefit)
- Commensalism (one benefits, other unaffected)
- Parasitism (one benefits at the expense of the other)

Moray Eel and Prawn/Shrimp:
- Host: Moray eel
- Symbiont: Prawn/Shrimp
- The shrimp removes parasites from the eel's skin, benefiting both parties.

Mutualism (Plus-Plus)
- Definition: Both organisms benefit from the association.
- Example: Plant pollinator interactions. Pollinators collect nectar and pollen while aiding in plant reproduction by transferring pollen between flowers.
- Examples of mutualistic relationships:
- Corals and coral reefs with fish.
- Mycorrhizal fungi with plants for nutrient absorption.
Commensalism (Plus-Zero)
- Definition: One organism benefits, while the other is unaffected.
- Example: Staphylococcus aureus bacteria living on human skin; they benefit from nutrients without harming the host.
- Characters of commensalism:
- Provides habitat or nutrients without affecting the host organism.
Parasitism (Plus-Negative)
- Definition: One organism benefits at the expense of the other.
- Example: Mosquitoes feeding on human blood, providing nourishment for the mosquito while causing discomfort and potential health issues for the human host.
- Characteristics of parasitism include:
- Parasites can live inside (endo) or on the outside (ecto) of the host.
- Examples include ticks and intestinal worms.

The interactions can change depending on environmental or situational context:
- Example: Brittle stars and sponges can exhibit both commensal and parasitic relationships depending on the reproductive stage of the sponge.

Types of Mutualism
- Facultative: Organisms can survive independently but gain benefits from each other.
- Obligate: Organisms depend on each other for survival.
- Endosymbiosis: A type of obligate mutualism where one organism lives inside the other (e.g., mitochondria and chloroplasts).

Horizontal Transmission: Symbionts are obtained from the environment (e.g., bacteria from contact).
Vertical Transmission: Symbionts are inherited from the mother (e.g., bacteria in eggs).

Endosymbiosis has led to the formation of vital eukaryotic organelles:
- Mitochondria: Originated from a symbiotic relationship with protoeukaryotic cells and proteobacteria.
- Chloroplasts: Resulted from eukaryotic cells engulfing cyanobacteria, allowing photosynthesis in plants.

Endosymbiosis enables organisms to acquire new traits and live in environments that would otherwise be inhospitable (e.g., corals thriving in low-nutrient water through dinoflagellate symbionts).
Mycorrhizal fungi help plants fix nitrogen from atmospheric sources, allowing them to inhabit nitrogen-poor soils.

Nutrition
- Example: Cleaner shrimp removing parasites from moray eels for mutual food benefit.
- Ruminants: Utilize bacterial symbionts to digest cellulose in grasses (e.g., cows, termites).
- Zombie Worms: Deep-sea organisms that host bacteria to digest bone.
Defense
- Example: Clownfish and sea anemones; clownfish get protection, while sea anemones benefit from being cleaned of parasites.
- Shrimp and Gobies: Goby provides security to shrimp, which excavates the burrow.
- Defensive Symbionts: Such as Hamiltonella defensa in aphids, offering toxicity protection.
Communication
- Many organisms use bioluminescent bacteria for signaling and predator evasion.
Dispersion (Dispersive Mutualism)
- Example: Yucca plant and yucca moth; the moth pollinates while laying its eggs, providing food for the emerging caterpillars.

Definition: One organism benefits, the other suffers. Includes endoparasites and ectoparasites.
Effects on Hosts: Parasites may manipulate host behavior to enhance transmission likelihood.
- Parasitoids: Larvae that develop in and typically kill their host (e.g., wasps on caterpillars).
- Example: Trematode parasites in fish manipulating predator behavior for transmission.
- Zombie Ant Fungus: Manipulates ant behavior for spore dispersal.

Coral Bleaching: A critical environmental issue where stress leads to the expulsion of dinoflagellate symbionts from coral, resulting in bleaching and potentially dying coral ecosystems.
- Coral reefs are biodiversity hotspots, and their disruption poses severe risks to marine environments.

Symbiosis Importance: A crucial concept in ecology and evolution that underlies many life forms and ecosystems.
- Understanding mutualism, commensalism, and parasitism sheds light on ecosystem dynamics.
Relevance: Each type of relationship can have profound implications for species survival, biodiversity, and ecosystem health.