Hosts do not simply outsource pathogen resistance to protective symbionts

Area of Science:

• Ecology
• Evolutionary Biology
• Microbiology

Background:

• Microbial symbionts often provide hosts with protection against natural enemies.
• The impact of this 'extrinsic' protection on the evolution of host 'intrinsic' immunity to pathogens remains largely unknown.
• It's hypothesized that extrinsic protection might allow hosts to downregulate intrinsic immune defenses.

Purpose of the Study:

• To investigate how protective microbial symbionts influence the evolution of host intrinsic immunity.
• To test if pea aphids (Acyrthosiphon pisum) with protective symbionts exhibit reduced intrinsic resistance to pathogens.
• To explore the relationship between symbiont presence, intrinsic resistance, and host plant association.

Main Methods:

• Comparative analysis of pea aphid biotypes with varying symbiont communities.
• Assessment of intrinsic resistance levels in aphid clones with and without protective symbionts.
• Evaluation of host plant effects on intrinsic resistance.

Main Results:

• Pea aphid biotypes frequently harboring protective symbionts exhibited higher intrinsic resistance, contrary to the initial hypothesis.
• No significant difference in intrinsic resistance was observed between clones with and without protective symbionts within the same biotype.
• Host plant species did not strongly influence the level of intrinsic resistance.

Conclusions:

• The findings challenge the notion that extrinsic protection from symbionts leads to reduced intrinsic immunity.
• Selection may favor the concurrent evolution of both symbiont acquisition and enhanced intrinsic resistance in pathogen-rich environments.
• Combined intrinsic and extrinsic resistance offers a potentially more robust defense strategy for hosts.