Testing the Mating System Model of Parasite Complex Life Cycle Evolution Reveals Demographically Driven Mixed Mating.

Area of Science:

• Evolutionary Biology
• Parasitology
• Genetics

Background:

• Many parasites utilize multiple hosts for development, but factors influencing host number evolution are poorly understood.
• A model suggests multihost life cycles in hermaphroditic parasites prevent inbreeding and inbreeding depression.

Purpose of the Study:

• To empirically test the mating system model's prediction that host loss evolves only when parasites lack inbreeding depression.
• To investigate the mating system of the hermaphroditic trematode *Alloglossidium renale*.

Main Methods:

• Developed a novel method to assess inbreeding depression using field-collected parasite samples.
• Compared genetically estimated selfing rates with demographic selfing rates derived from parasite mating systems.

Main Results:

• Results supported the model: the two-host trematode *Alloglossidium renale* exhibited no inbreeding depression.
• Genetic and demographic selfing rate comparisons indicated a mixed mating system.
• The observed mating system was fully explained by parasite demography, specifically infection intensities.

Conclusions:

• The study provides the first empirical support for the mating system model of parasite host number evolution.
• Lack of inbreeding depression facilitates the evolution of multihost life cycles in hermaphroditic parasites.
• Parasite demography plays a crucial role in shaping mating systems and potentially host-parasite interactions.