> Then----if reproductive energy can't go into shell growth, why is it
> that the female Busycons (and Lambis) are larger than the males?

Energy that goes into reproduction can't also be used for growth.  If
sexes are separate, and the female is larger than the male, then
presumably she spends more time growing before concentrating on
reproduction.  Since females usually put much more into reproduction
than males in terms of energy and nutrients (think how much bigger an
egg cell is than a sperm cell, plus whatever yolk, capsule, etc.),
females will typically gain more by being bigger and thus having more
room for storing nutrients, holding eggs, etc.  Even a small male can
produce excess sperm, so they don't need to be as large unless there's
other factors involved, e.g. competition with other males for mates
(more characteristic of vertebrates than mollusks).

Extreme examples of the effects of reproduction as a competitor with
growth come from cases where extra large individuals result if
reproduction is prevented.  One example is when larvae are able to
settle in a place, but right conditions for reproduction do not
occur.  It's been suspected that the many large shells from Bermuda
represent tropical taxa that get carried there as larvae in the Gulf
Stream and keep growing while waiting for the water to get a little
warmer for the summer breeding season.  Another way this can happen is
if a parasite damages the reproductive system.

Of course, in protandous hermaphrodites, individuals start out as
males and then become females.  Crepidula fornicata is a classic
example.  In this case, males would obviously generally be smaller
than females.  Human females sometimes complain about males being
immature, but for the poor female Crepidulas all males are immature.

(As has been discussed on the list some time ago, the species name
tends to cause suspicion but really comes from fornix, an arch.  You
can check with Meretrix meretrix as to what Romans did under arches.)

--
Dr. David Campbell
425 Scientific Collections Building
Department of Biological Sciences
Biodiversity and Systematics
University of Alabama, Box 870345
Tuscaloosa AL 35487-0345  USA

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