Evolution of generalism under Muller's ratchet

Area of Science:

• Evolutionary biology
• Parasitology
• Genomics

Background:

• Host-range expansion in parasites is typically viewed as an adaptive strategy.
• Environmental heterogeneity and trade-offs are considered key drivers of parasite adaptation.
• Alternative non-adaptive mechanisms for host-range expansion remain underexplored.

Purpose of the Study:

• To propose a novel hypothesis for the non-adaptive evolution of broad host range in parasites.
• To introduce the concept of Ratchet-Driven Generalism (RDG) as an alternative explanation.
• To outline genomic predictions and testing strategies for RDG.

Main Methods:

• Theoretical framework development.
• Literature review and synthesis.
• Proposal of comparative genomic analyses.

Main Results:

• Ratchet-Driven Generalism (RDG) posits that loss of sexual recombination leads to Muller's ratchet.
• Deleterious mutations accumulate, causing genomic erosion and loss of host-specific adaptations.
• Reduced selection efficacy allows genotypes viable across multiple hosts to persist, resulting in generalism.

Conclusions:

• Broad host range may arise non-adaptively due to genomic decay in parasites with reduced recombination.
• RDG predicts observable genomic signatures of functional degradation and altered selection.
• This generalism may be transient, with continued erosion increasing extinction risk.