Protist Transmission in Termites: Trophallaxis & Symbiosis

Lower termites depend on gut flagellated protists (parabasalids, oxymonads) to digest cellulose. These symbionts are transmitted vertically via proctodeal trophallaxis.

Transmission Process

1. Adult Workers harbor dense, diverse protist communities in hindgut paunches.
2. Trophallaxis: Adults exchange hindgut fluid (rich in protists, bacteria, enzymes) via anal-oral contact.
3. Newly Molted Nymphs lack protists (lost during molt). They solicit anal fluid from nestmates.
4. Ingestion: Nymph consumes fluid → protists colonize hindgut.
5. Establishment: Protists replicate; symbiosis restored.

Symbiotic Functions

• Cellulose → acetate, H₂, CO₂ (termite energy)
• Nitrogen fixation, recycling (urate → ammonia → amino acids)
• Lignin modification
• Pathogen defense (competitive exclusion)

Evolutionary Significance

• Obligate mutualism: Termites cannot survive without protists; protists cannot survive outside termite gut.
• Co-speciation: Protist phylogeny mirrors termite phylogeny.
• Higher termites (Termitidae) lost protists; evolved fungal combs (Macrotermitinae) or bacterial symbionts.

Trophallaxis is the social glue maintaining this 150-million-year-old partnership.