Are endosymbioses mutualistic?

Area of Science:

• Microbiology
• Symbiotic relationships
• Ecology

Background:

• Many organisms host non-parasitic microorganisms, forming endosymbiotic relationships.
• These endosymbioses are commonly presumed to be mutualistic, benefiting both partners.
• Microorganisms often provide essential metabolic functions like nutrient fixation or degradation.

Purpose of the Study:

• To critically evaluate the evidence for mutualism in microbial endosymbioses.
• To investigate the benefits, if any, that microorganisms receive from their hosts.
• To explore methodologies for demonstrating microbial benefit or harm in symbiotic associations.

Main Methods:

• Literature review and synthesis of existing research on microbial endosymbioses.
• Analysis of metabolic contributions of microorganisms to host organisms.
• Discussion of challenges in quantifying benefits and harms for symbiotic microbes.

Main Results:

• Scant empirical evidence supports the mutualistic nature of many assumed endosymbioses.
• The benefits conferred by hosts to their resident microorganisms are often not clearly demonstrated.
• Existing research primarily focuses on host benefits, neglecting microbial perspectives.

Conclusions:

• The widespread assumption of mutualism in microbial endosymbioses may be inaccurate.
• Further research is needed to rigorously assess the fitness consequences for microorganisms.
• Developing methods to quantify microbial costs and benefits is crucial for understanding symbiosis.