Unusual Lateral Plate Variation of Threespine Sticklebacks (Gasterosteus aculeatus) from Knik Lake, Alaska

Abstract

Lateral plate phenotypes of Gasterosteus aculeatus from Knik Lake, Alaska form a continuum which cannot be divided objectively to conform to the trimorphic lateral plate morph concept in current use. This case indicates the range of possible lateral plate phenotypes possible in G. aculeatus and brings into question the general applicability of the lateral plate morph concept and underlying genetic models for lateral plate trimorphism. We consider the possibility that abdominal and caudal keel plate phenotypes are potentially genetically independent and that a polygenic model for plate phenotypes may be more appropriate. Pronounced directional asymmetry of lateral plate number was observed in specimens with greater than seven plates per side. This asymmetry does not have obvious functional significance. We suggest that this and other cases of pronounced directional asymmetry may represent stochastic fixation in phylogeny and thus may be useful characters in systematics.