Investigations of the ecology of planktonic marine organisms run into the problem of reconciling the anonymity of morphological uniformity with the potential for ubiquitous distribution in the continuity of the oceans and the observed genetic diversity. Foraminifera are good model organisms for disentangling protist biogeography, not only because they have left an unusually complete fossil record, but also because living forams display high rates of small-subunit ribosomal RNA evolution.
Darling et al. find that one widespread morphospecies has evolved into several types with distinct global distribution patterns that seem to have arisen during Northern Hemisphere cooling in the Quaternary. Subsequently, gene flow has been restricted by the equatorial oceans and especially by the Gulf Stream. Adaptations for survival at cold temperatures have since developed and are related to niche: that is, living within ice brine channels, in subpolar oceans, in upwellings, and so on. -- CA
Proc. Natl. Acad. Sci. U.S.A. 104, 5002 (2007).
