Progressive invasion and allopatric speciation can also explain distribution patterns of rock‐dwelling cichlids from southern Lake Victoria: a comment on Seehausen and van Alphen (1999)

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Abstract
I show that distribution patterns of rock‐dwelling haplochromine cichlids in the south‐eastern part of Lake Victoria can be explained by allopatric speciation alone. Observed patterns are consistent with a progressive invasion of different lineages from older ( = deeper) parts of the lake, after which some lineages speciate more frequently than others. Based on a quantitative analysis of distribution data, Seehausen and van Alphen conclude that a high percentage of sympatric speciation (17.5%) is essential to explain the patterns. In my view this conclusion has its origins in an unjustifiable assumption. Seehausen and van Alphen assume that the unresolved phylogeny is balanced. However, allopatric speciation would typically result in imbalanced phylogenies.