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. 2021 Oct 19;11(22):15534-15544.
doi: 10.1002/ece3.8080. eCollection 2021 Nov.

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

Shun Ito  1 , Takahiro Hirano  1   2 , Satoshi Chiba  1   2 , Junji Konuma  3
Affiliations

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

Shun Ito et al. Ecol Evol. .

Abstract

Ecological release is often attributed to the rapid adaptive diversification of phenotypic traits. However, it is not well understood how natural selection changes its strength and direction through the process of ecological release. Herein, we demonstrated how shell colour of the Japanese land snail Euhadra peliomphala simodae has diversified via a shift in natural selection due to ecological release after migration from the mainland to an island. This snail's shell colour diversified on the island due to disruptive selection after migration from the mainland. We used trail camera traps to identify the cause of natural selection on both the mainland and the island. We then conducted a mark-recapture experiment while collecting microhabitat use data. In total, we captured and marked around 1,700 snails on the mainland, some of which were preyed upon by an unknown predator. The trail camera traps showed that the predator is the large Japanese field mouse Apodemus speciosus, and the predatory frequency was higher on the mainland than on the island. However, this predation did not correlate with shell colour. Microhabitat use on the island was more extensive than on the mainland, with snails on the island using both ground and arboreal microhabitats. A Bayesian estimation showed that the stabilizing selection on shell colour came from factors other than predation. Our results suggest that the course of natural selection was modified due to ecological release after migration from the mainland, explaining one cause of the phenotypic diversification.

Keywords: colour diversification; disruptive selection; ecological release; land snail; mammal predator; mark–recapture; stabilizing selection; trail camera.

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Conflict of interest statement

The authors have no conflict of interest to declare.

Figures

FIGURE 1
FIGURE 1
Maps of the study sites on the Izu Peninsula. Euhadra peliomphala simodae is found on the Izu Peninsula (mainland) and on the Izu Islands including Niijima Island. The survey was conducted in both the Izu Peninsula and the Niijima Island
FIGURE 2
FIGURE 2
Frequency distribution of shell colour on marked snails in (a) Izu Peninsula and (b) Niijima Island (modified from Ito & Konuma, 2020). Shell colour was quantified using the luminance value Y using a photograph of the snail, with higher values representing brighter colours. In the Izu Peninsula, most of the snails had bright shells whereas in Niijima, snails with dark and bright shell colour existed with almost equal frequency
FIGURE 3
FIGURE 3
Images of preyed empty shells and the large Japanese field mouse Apodemus speciosus. (a) Preying on a live snail in front of a trail camera. (b) Shells left in place after the trail camera captured A. speciosus preying on snails. (c) Empty shells predated by A. speciosus found during the mark–recapture survey. The shells are characterized by cracked tops and shattered shells
FIGURE 4
FIGURE 4
The relationship between survival rate and shell colour in (a) Izu Peninsula and (b) Niijima Island (modified from Ito & Konuma, 2020); (I) juvenile, (II) adult. This shape represents natural selection that worked on shell colour. In the Izu Peninsula, natural selection was estimated after excluding the effects of predation. The solid and dashed lines indicate the median and the 95% Bayesian confidence interval of the posterior distribution obtained from Markov chain Monte Carlo simulations, respectively
See this image and copyright information in PMC

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