I was not aware that two spp from different genera or families could be
very difficult to distinguish- esp. gastropods, which have those
wonderful inventions called "protoconchs", but i guess we learn
something every day...
At any rate, to be moderately concise, Mytilus edulis L. and M.
trossulus Gould are indeed classical examples of "crypto-species".
They were not conclusively separated until the mid-1980s, when it was
noticed that some mussel farms on the Atlantic coast of Nova Scotia were
having a hard time with fragile, elongate shells that often broke while
being washed, while others in different areas -such as Prince Edward
Island- never had this problem. An enterprising researcher for the
Fisheries Dept. figured out that there were in fact two very similar spp
involved, which could be easily differentiated by a particular enzyme
one always produced, but the other one never did (and of course DNA, but
that sort of thing is quite expensive for an industrial situation, where
you might wish to periodically check on your stock). They could also
usually be told apart just by shape and shell thickness, but the amount
of overlap in morphology was high enough to cause considerable
difficulty: there just *didn't* seem to be any way of determining if a
specimen in the "grey zone" was edulis or trossulus!! A number of
papers were written on the subject, and i came across one (which ref. i
didn't record, alas!) which fairly convincingly showed that one could
indeed differentiate them via conchological (ie, shell-related) features
alone, but the mathmatics involved was "convoluted", to be polite!!
The REAL question involved here, is "Is it ALWAYS possible to
differentiate molluscan spp using shell features alone??" I think the
answer so far is yes, but i'm not certain- any takers on this one???
Not hard to find in Halifax,
-Ross M.
|
