Vertical transmission does not always lead to benign pathogen-host associations

Area of Science:

• Evolutionary biology
• Pathogen dynamics
• Disease ecology

Background:

• Pathogens can transmit horizontally between hosts or vertically from parent to offspring.
• Vertical transmission is often assumed to reduce pathogen virulence.
• Previous models often neglect the host's evolutionary response.

Purpose of the Study:

• To investigate the evolutionary consequences of vertical transmission in pathogen-host systems.
• To determine if vertical transmission consistently leads to less virulent pathogens.
• To identify conditions under which vertical transmission may increase pathogen virulence.

Main Methods:

• Utilized a game-theory model to simulate coevolution between hosts and pathogens.
• Incorporated host evolutionary responses into the transmission dynamics.
• Analyzed scenarios with varying transmission modes and host population growth rates.

Main Results:

• Vertical transmission does not invariably result in less virulent pathogens.
• Scenarios exist where vertical transmission drives increased pathogen virulence.
• Reduced host damage from horizontal infections, high costs of infection clearance, and rapid host population growth favor less virulent outcomes.

Conclusions:

• The relationship between vertical transmission and pathogen virulence is complex and context-dependent.
• Host evolutionary responses are critical in shaping virulence evolution.
• Findings challenge the long-held assumption that vertical transmission always attenuates pathogens.