Lateral plate morph genetics revisited: Evidence for a fourth morph in three-spined sticklebacks

The view that four (not three) lateral plate morphs exist in the three-spined stickleback Gasterosteus aculeatus is supported in this paper. The morphs are: trachura (= completely plated), semiarmata (= partially plated), leiura (= low plated), and leiura-with-keel (= low-plated-with-keel). 2. Two one-locus and four two-locus models of lateral plate morph inheritance are identified and reviewed. A new genetic model for a two-locus system comprising one major gene with three alleles and one dominance modifier gene with two alleles is advocated. 3. Predictions of different models are explicitly examined using the existent data. 4. Results of 10 new crosses that distinguished the form leiura-with-keel are presented. The segregation ratios obtained are best explained by the new model. 5. Adaptive value of plate morph differentiation is not clear. Different aspects of selection on the morphs are discussed.