I don't know for sure, but it sounds like a classic example of natural
selection.  Since Nucella lamellosa is an inshore, shallow water species of
rocky shores, its veligers are no doubt dispersed into all sorts of nearby
habitats by currents, tidal flow, and wave action.  If the newly formed
young of either smooth or frilly forms find themselves in a sandy, rock-free
habitat, they will not survive.  Both smooth and frilly forms, when they
find themselves in rocky, quiet waters, have equal chances of survival -
that is to say, neither form has an inate advantage over the other.  But
when a mix of smooth and frilly forms find themselves in a rocky surf zone,
the frilly ones are far more likely to be dislodged from the rocks by wave
action than the smooth ones.  Therefore they are selected against, at a very
early age, and only the more streamlined smooth individuals manage to
survive to adulthood in such a habitat.  Again, I'm not certain that this is
the mechanism at play, but it sounds to me like something similar must be
going on.

> ----------
> From:         Roland Anderson
> Reply To:     Conchologists of America List
> Sent:         Tuesday, March 30, 2004 2:52 PM
> To:   [log in to unmask]
> Subject:      Nucella lamellosa "frilliness"
>
> Hi All,
> Here in the Northeastern Pacific we have a marine gastropod, Nucella
> lamellosa, that has varying amounts of frills on its shells. It has been
> proposed that the outer coast versions are smooth, to prevent the waves
> from catching them, and those that live in protected bays like Puget Sound
> have the most frills (am I using the right term for the frills?). The
> problem is that in Puget Sound you can find both frilly and smooth forms,
> often on the same beach, but only smooth forms on the coast, with wave
> action. My qustion is then, why are smooth forms also found in protected
> waters?
> Roland
>

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