The Biological Bulletin, Vol 191, Issue 1 33-41, Copyright © 1996 by Marine Biological Laboratory

PHYSIOLOGY

Subunit Composition of the Crustacean Hemocyanins: Divergence in Incipient Speciation

C. P. Mangum and A. L. McKenney
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187-8795

The monomeric subunit composition of the oxygen carrier hemocyanin was examined in samples of the Sesarma reticulatum complex and of Uca minax, both of which are believed to be in the process of speciation. The samples were taken on the Atlantic and Gulf of Mexico coasts, from disjunct populations that are believed to have been isolated by the Florida peninsula since the retreat of the last glacier. In Atlantic and Gulf samples of the S. reticulatum complex, which is believed to be in the terminal stages of speciation, the hemocyanins differed qualitatively. Several electrophoretic bands found in one group, including an invariant band, were totally absent from the other. This difference exceeds that reported in a previous investigation of a variety of polymorphic allozymes in this species complex. It also exceeds the physiologically labile differences in hemocyanins found previously within a panmictic species of brachyuran crustaceans. In U. minax, which is believed to have diverged less, Atlantic and Gulf animals expressed the same number of electrophoretic bands at exactly the same positions. Nonetheless, highly significant differences in band frequencies distinguished both Atlantic samples from the Gulf sample, and somewhat less significant differences distinguished the Atlantic cold temperate zone samples from the warm temperate zone ones. The phenotypes of the major bands, defined as those present in high densities, qualitatively distinguished Atlantic from Gulf animals, but they did not differentiate the two Atlantic samples. The difference between Atlantic and Gulf members of this species also exceeds that found previously among polymorphic allozymes. These findings further support the hypothesis that the hemocyanins are among the first proteins to diverge structurally in brachyuran speciation.