Experimental evolution of infectious behaviour in a facultative ectoparasite.

Area of Science:

• Evolutionary biology
• Parasitology
• Animal behavior

Background:

• The evolution of parasitic lifestyles from free-living ancestors is a significant puzzle in evolutionary biology.
• Transitional symbiotic strategies, like facultative parasitism, are proposed as evolutionary stepping stones towards obligate parasitism.
• A prerequisite for this hypothesis is the existence of heritable genetic variation in the infectious behavior of transitional symbiotic strategies.

Purpose of the Study:

• To experimentally evolve infectivity in a facultative parasite.
• To estimate the additive genetic variation for infectious behavior.
• To test the hypothesis that facultative parasites possess heritable variation in infectivity.

Main Methods:

• Artificial selection was applied to a facultative parasitic mite (Macrocheles muscaedomesticae) for increased or decreased infectivity.
• Infectiousness was quantified by mite attachment to a host (Drosophila hydei) and modeled as a threshold trait.
• Heritability of infectious behavior was estimated, and infection prevalence was monitored for 20 generations post-selection.

Main Results:

• Mites responded positively to selection for increased infectivity.
• Realized heritability of infectious behavior was significantly non-zero, estimated at 16.6% (±4.4% SE).
• Selected lines maintained relatively high infection levels for 20 generations, indicating genetic stability.

Conclusions:

• This study provides the first estimate of heritability and additive genetic variation for infectious behavior in a facultative parasite.
• The findings suggest that natural selection can act on facultative parasitic strategies.
• This has significant implications for understanding the evolutionary pathways leading to obligate parasitism.