Rare but evolutionarily consequential outcrossing in a highly inbred zoonotic parasite

Area of Science:

• Parasitology
• Evolutionary Biology
• Population Genetics

Background:

• The zoonotic parasite Trichinella spiralis is suspected to exhibit frequent inbreeding, producing genetically uniform larval cohorts.
• Understanding genetic variation distribution is crucial for parasite population dynamics and evolutionary outcomes.

Purpose of the Study:

• To investigate the extent of inbreeding in Trichinella spiralis populations within wild boars in Extremadura, Spain.
• To determine the distribution of genetic variation among parasite larvae and identify parental lineages.

Main Methods:

• Analysis of genetic variation using variable microsatellite markers.
• Genotyping of 1379 Trichinella spiralis larvae from 41 wild boar hosts.
• Assessment of genetic differentiation among parasite subpopulations.

Main Results:

• Strong evidence of inbreeding was found, with distinct parasite subpopulations arising from multiple wild boar pairs.
• Two-thirds of parasite cohorts originated from inbred parents, and 10% showed fixation at all assayed genetic loci.
• Mixed infections, originating from more than one parental pair, were identified in one-third of wild boars, potentially slowing genetic diversity loss.

Conclusions:

• Inbreeding is prevalent in Trichinella spiralis, creating genetically distinct subpopulations.
• Mixed infections and subsequent outcrossing play a role in maintaining heterozygosity and polymorphism, enforcing regional population cohesion despite inbreeding.
• Epidemiological conditions may influence evolutionary trajectories in different geographic regions.