Natural selection in the origin: how does selection act on snails’ shell
colour in the source of a diversified population?
Abstract
The mechanisms of adaptive radiation with phenotypic diversification and
further adaptive speciation have been becoming clearer through a number
of studies. Natural selection is one of the primary factors that
contribute to these mechanisms. It has been demonstrated that divergent
natural selection acts on a certain trait in adaptive radiation.
However, it is not often known how natural selection acts on the source
of a diversified population, although it has been detected in
phylogenetic studies. Our study demonstrates how selection acts on a
trait in a source population of diversified population using the
Japanese land snail Euhadra peliomphala simodae. This snail’s
shell colour has diversified due to disruptive selection after migration
from the mainland to islands. We used trail-camera traps to identify the
cause of natural selection on both the mainland and an island. We then
conducted a mark-recapture experiment on the mainland to detect natural
selection and compare the shape and strength of it to previous study in
an island. In total, we captured and marked around 1,700 snails, and
some of them were preyed on by an unknown predator. The trail-camera
traps showed that the predator is the large Japanese field mouse
Apodemus speciosus, but this predation did not correlate with
shell colour. A Bayesian approach showed that the stabilising selection
from factors other than predation acted on shell colour. Our results
suggest that natural selection was changed by migration, which could
explain the ultimate cause of phenotypic diversification in adaptive
radiation that was not due to predation.