Morphological divergence in endemic gastropods from Lake Tanganyika: implications for models of species flock formation

M. R. Johnston, A. S. Cohen

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Two thiarid gastropods endemic to Lake Tanganyika, which are both stenotopic and rock-dwelling, were investigated because they are believed to be equally subject to environmental barriers to dispersal. A model of allopatric divergence, faciliated by habitat fragmentation, predicts that variation among populations should be large relative to the variation within them, and that organisms equally subject to environmental barriers to dispersal should exhibit similar magnitude and character of morphological divergence. Spekia and members of the Lavigeria species flock appear only in rocky, wave-battered shoals and neither gastropod is known to exhibit wide dispersal. Intervening reaches of sandy and muddy substrates are thought to be barriers to gene flow. Interpopulation morphological variance is greater than intrapopulation variance for both genera, suggesting that divergence is allopatric. However, Spekia shows little morphological variability compared to shallow-water Lavigeria. In graphical analyses of factor scores, Lavigeria forms discrete clusters of morphology related to differences in environment, geographic distribution, and timing of larval broods, all indicative of speciation. The model of allopatric divergence controlled by environmental barriers to dispersal must be reviewed because of 2 incongruent results: sympatry of divergent morphs of Lavigeria, and the observation that members of Lavigeria show much greater endemic divergence than members of Spekia, even though they are thought to be equally poor dispersers. -from Authors

Original languageEnglish (US)
Pages (from-to)413-425
Number of pages13
Issue number5
StatePublished - 1987

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Palaeontology


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