How host-microbiome/holobiont evolution depends on whether the microbiome affects host lifespan or fecundity

Area of Science:

• Microbial ecology
• Evolutionary biology
• Theoretical biology

Background:

• The microbiome significantly impacts host physiology and fitness.
• Understanding host-microbiome coevolution is crucial for host and microbial benefit.
• The mode of symbiont transmission and the type of benefit provided influence coevolutionary outcomes.

Purpose of the Study:

• To investigate how host and symbiont evolution are shaped by symbiont benefits (lifespan vs. reproduction) and transmission modes.
• To model the conditions under which beneficial microbes evolve and are favored by hosts.
• To explore the role of horizontal and pseudovertical transmission in host-microbiome coevolution.

Main Methods:

• Adaptive dynamics modeling was employed to simulate host and symbiont interactions.
• The model considered two transmission strategies: steady horizontal release and release at reproduction (pseudovertical).
• The study analyzed scenarios where symbionts provide benefits to host lifespan or fecundity, and where these benefits incur costs to symbionts.

Main Results:

• Evolution of symbionts benefiting host fecundity necessitates pseudovertical (parent-to-offspring) transmission.
• Symbionts benefiting host lifespan can evolve without pseudovertical transmission.
• Intermediate levels of pseudovertical transmission are optimal for selecting beneficial symbionts when benefits are costly, due to increased competition.

Conclusions:

• The type of fitness benefit provided by symbionts and the mode of transmission are critical drivers of host-microbiome coevolution.
• Parent-to-offspring transmission is essential for the evolution of symbionts that enhance host fecundity.
• Host traits favoring beneficial symbionts can be lost if symbiont release at reproduction increases competition, highlighting the complexity of holobiont evolution.