Coexistence and origin of trophic ecotypes of pygmy whitefish, Prosopium coulterii, in southwestern Alaskan lake

Ecologically, morphologically, and genetically distinct populations within single taxa often co-exist in postglacial lakes and have provided important model systems with which to investigate ecological and evolutionary processes such as niche partitioning and ecological speciation. Within the Salmonidae, these species complexes have been well studied, particularly within the Coregonus clupeaformis-C. laveratus (lake and European whitefish, respectively) group, but the phenomenon has been less well documented in the other whitefish genera, Prosopium and Stenodus. Here, we examined the morphology, feeding biology, and genetic structure of three putative forms of the pygmy whitefish, Prosopium coulterii, that were first reported from Chignik Lake, southwestern Alaska, over 40 years ago. Field collections and morphological analyses resolved a shallow water (< 5 m depth) low gill raker count form (< 15 first arch gill rakers), a deepwater (> 30 m), low gill raker form, and a deepwat...