Littorinid snails

We are using the comprehensive phylogeny of the littorinid snails to answer evolutionary questions while discovering new snail habitats.

Littorinid snails, commonly known as periwinkles, are found on intertidal hard surfaces on almost all shores of the world. Their well-established phylogeny serves as a model for diversification of invertebrates in global shallow marine environments.

Reinforcement analysis

The phylogeny of the littorinid snails is now so comprehensive that deeper evolutionary questions are being tested using them as model organisms.

Reinforcement, the evolutionary selection against hybrids between emerging species, has been suggested as a final step in speciation. The process is controversial and field evidence is hard to find.

We are comparing the differences in genital traits between close littorinid relatives in overlapping and separated geographic areas. If reinforcement is operating, we would expect a greater difference in genital characteristics between similar species that overlap geographically, and less difference between similar species that are geographically separate. 

We have confirmed this predicted genital difference in 147 of the 153 worldwide littorinid species.

Western Ghats of India

Most littorinids are marine, but a single genus (Cremnoconchus) is found in mountain waterfalls in the Western Ghats of India.

We have discovered these snails branching out into new ecological niches, many of which are threatened by development and pollution. We are urging for their conservation so that these new species may be better studied.

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Glossary

Reinforcement

When two groups of a previously separated species come back together, there may be breeding between them that produces hybrids. If the differences in ecological niche between the two groups are large enough, the hybrids will not be suited for either. As a result the hybrids will be weaker, and therefore not likely to survive and pass on their genes.

This process is reinforcement, or the Wallace effect, where breeding between two distinct groups is discouraged. Eventually the groups become two different species, unable to interbreed.