Shell colour diversification induced by ecological release: A shift in natural selection after a migration event

Area of Science:

• Evolutionary Biology
• Ecology
• Genetics

Background:

• Ecological release is a key driver of adaptive diversification.
• The precise mechanisms of natural selection shifts during ecological release remain unclear.

Purpose of the Study:

• To investigate how natural selection changes strength and direction during ecological release.
• To understand the diversification of shell color in *Euhadra peliomphala simodae* following island migration.

Main Methods:

• Utilized trail camera traps to identify predators and assess predation frequency.
• Conducted mark-recapture experiments and collected microhabitat use data.
• Employed Bayesian estimation to analyze selection pressures on shell color.

Main Results:

• The large Japanese field mouse (*Apodemus speciosus*) was identified as a predator, with higher predation on the mainland.
• Island snails exhibited broader microhabitat use (ground and arboreal) compared to mainland snails.
• Natural selection on shell color shifted from stabilizing on the mainland to disruptive on the island, independent of predation.

Conclusions:

• Ecological release significantly modified natural selection, leading to phenotypic diversification in shell color.
• Factors other than predation were responsible for stabilizing selection on shell color on the island.