The Cichlid Fishes of Lake Malawi, Africa

Summary of Publication

Greenwood, P.H. 1984b. African cichlids and evolutionary theories. Pp. 141-154 in Echelle, A.A., and I. Kornfield (eds.), Evolution of fish species flocks. University of Maine at Orono Press.  

The species flock or flocks of haplochromine fishes in Lake Victoria, East Africa, appear to be an outstanding example of an extant punctuational evolutionary phase. During the 750,000-year history of the lake, its endemic haplochromine species have come to occupy a dominant position in the lake's ecology as a result of their extensive and diverse trophic specializations. Clearcut trends in the development of different anatomical specializations associated with the various feeding habits are discernible. The stages of derivation in any one morphocline are represented by distinct species, often with more than one species at a particular level of specialization still extant. Individual lineages in the flock thus seem to represent a form of cladistic gradualism rather than one of phyletic gradualism. The principal anatomical features involved in the radiation seem to have been brought about through simple changes in relative growth, and are manifest chiefly in syncranial characters and in oral and pharyngeal dentition.

It is suggested that this flock provides little evidence for the effects of natural selection or of species selection in its origin and development. On the other hand, it seemingly provides better evidence for the probability of punctuational evolutionary phases than do most of the paleontological examples cited by the proponents of the punctuated equilibrium theory. However, it does not provide any evidence to support a thesis that extraordinary genetic or epigenetic processes were involved in producing its pattern of speciation and morphological diversity.




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