Local adaptation to parasite selective pressure: comparing three congeneric co-occurring hosts

Area of Science:

• Ecology
• Evolutionary Biology
• Marine Biology

Background:

• Organisms may adapt defenses to local parasite pressure.
• Local adaptation can be limited by larval dispersal patterns.
• Understanding host-parasite interactions is crucial for predicting evolutionary responses.

Purpose of the Study:

• To investigate if local adaptation in snail defenses against trematode parasites is influenced by population exposure and larval dispersal.
• To determine if direct developing snail species exhibit local adaptation to parasite risk differently than broadcast spawning species.

Main Methods:

• Common garden experiment comparing susceptibility of three littorinid snail species to trematode infection.
• Snail populations were sourced from sites with varying historical trematode infection risk.
• Larval dispersal mode (direct development vs. broadcast spawning) was used as a proxy for population openness.

Main Results:

• Two snail species with direct development (Littorina obtusata, Littorina saxatilis) showed reduced susceptibility in populations with high prior infection risk.
• This pattern of local adaptation was not observed in the broadcast spawning snail species (Littorina littorea).
• The lack of local adaptation in L. littorea may be due to broad larval dispersal or other unmeasured factors.

Conclusions:

• Locally recruiting intertidal snails can adjust their defense strategies based on localized trematode infection risk.
• Broad larval dispersal in broadcast spawning species may hinder or prevent local adaptation to spatially variable parasite pressure.
• Larval dispersal mode is a key factor mediating the potential for local adaptation in host defense.