Symbiosis Nature

Symbiosis (Greek: 'living together') describes close, long-term biological interactions between species. Types: mutualism (both benefit — clownfish and anemone, mycorrhizal fungi and tree roots, nitrogen-fixing bacteria and legumes, oxpecker birds and rhinos); commensalism (one benefits, other unaffected — barnacles on whales, remora fish on sharks, cattle egrets following cattle); parasitism (one benefits at the other's expense — tapeworms, malaria, mistletoe, cuckoos). Symbiosis is not a biological curiosity — it is fundamental to all ecosystems. The mitochondria in all eukaryotic cells (including human cells) were once free-living bacteria that formed a symbiotic relationship with ancestral cells approximately 2 billion years ago; without this event, complex multicellular life would not exist. The gut microbiome (38 trillion bacteria) is the most intimate ongoing symbiosis in a human body. Coral reefs' existence depends entirely on the symbiosis between coral polyps and photosynthetic algae (zooxanthellae).