Hybrids of the hard clam (Mercenaria) have been found in the Indian River
Lagoon (Dillon and Manzi, 1989) and in Cedar Key (Arnold et al. 2004).
These hybrids are between the Atlantic species Mercenaria mercenaria and the
Gulf species Mercenaria campechiensis.  Ribbed mussels (Geukensia sp.) have
also been found to hybridize in the Indian River Lagoon (Sarver et al.
1992).
Hope this helps,
John

Arnold WS, Walters SL, Fajans JS, Peters SC, and Bert TM (2004) Influece of
congeneric aquaculture on hard clam (Mercenaria spp.) population genetic
structure.  Aquacult. Int. 12: 139-160.

Dillon RT Jr. and Manzi JJ (1989) Genetics and shell morphology in a hybrid
zone between the hard clams Mercenaria mercenaria and M. campechiensis.
Mar. Biol. 100: 217-222.

Sarver SK, Landrum MC and Foltz DW (1992) Genetics and taxonomy of ribbed
mussels (Geukensia spp.).  Mar. Biol. 113: 385-390.



----- Original Message -----
From: "Lee Spencer" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 30, 2005 12:26 PM
Subject: Re: hybrids


> In a biological sense, large scale hybridization at the population level
is
> termed reticulate evolution. It is reportedly common in some scleractinian
> coral phylogenies, modern African cichlid fishes and some plant groups
such
> as oaks (see Veron 1996; Sylvester-Bradley 1977). I know of no reports of
it
> within the mollusks. At a lower scale, hybridization occurs among
> individuals within different species populations, for example within
> vertebrate groups such as the white-tailed and mule deer of North America
> and also is some warbler groups, etc., but it occurs infrequently enough
> that the species remain distinct. I am not sure of the scale your question
> addresses.
>
> From a cladistic analysis point of view, hybridization at the reticulate
> evolution scale is problematic since members of two presumably
monophyletic
> groups fuse to form a third group which may then be monophyletic
afterwards.
> It is a struggle with which I am currently dealing. Computer based
character
> analysis programs such as PAUP have no way to address whether or not a
> reticulate event is more parsimonious. If anyone out there has any ideas
on
> how to address this issue, I would welcome them.
>
> Lee Spencer
>
> Veron, J. E. N. 1996. Evolution in corals, IN George D. Stanley, ed.
> Paleobiology and biology of corals, The Paleontological Society Papers,
> 1:7-37. (ISSN 1089-3326)
>
> Sylvester-Bradley, P. C. 1977. Biostratigraphical tests of evolutionary
> theory, IN Erle G. Kauffman and Joseph E. Hazel, eds. Concepts and Methods
> of Biostratigraphy, Dowden, Hutchinson & Ross, Stroudsburg, Penn. (ISBN
> 0879332468)
>
>
>

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