Geographic Variation in the Brook Stickleback, Culaea inconstans, and Notes on Nomenclature and Distribution

Abstract

Clinal variation in dorsal and pelvic spine lengths was observed in the brook stickleback, Culaea inconstans, in an examination of 1366 specimens from 62 localities. Mean spine length was longest in the Wisconsin to Ohio area and generally decreased to the west, north, and east of this area. Shortest spines were observed in the northwestern part of the range of the species. A population in New Mexico, believed to be relict, was highly variable, but most specimens had long spines. Pelvic spines, and the supporting skeleton, were absent in most specimens from five localities in Alberta. Pelvic skeleton size and body depth were generally greatest in the area east of Wisconsin and least in the northwestern part of the range. Although C. inconstans is generally described as being naked, a series of about 30–36 small bony scutes was found along the lateral line in all populations examined. No marked geographic variation was observed in number of pectoral rays, caudal rays, soft dorsal-fin rays, soft anal-fin rays, gill rakers, scutes, or vertebrae. The nomenclature and distribution of C. inconstans are reviewed. The historical origin of clinal variation in spine length is discussed.