Stimulus selection (light) in four subspecies of deermice (Peromyscus maniculatus)

Abstract

Four subspecies of deermice (Peromyscus maniculatus) were selected from habitats along a gradient from mesic hardwood forests (gracilis), tall grass prairie (bairdi), short grass prairie (nebrascensis), to desert grassland (labecula) in effort to relate the light preferences of the mice to the habitat of their origin. Six individuals of each subspecies were maintained in dark chambers for 25 days, during which they could turn on a dim light for 30 seconds on ten of these days. Mice from the mesic habitats turned the lights on more frequently (light reinforcement) than mice from xeric habitats. The same subspecies that exhibited light reinforcement when raised in laboratory light conditions failed to show light reinforcement when raised in total darkness. The circadian periodicities also differed significantly among the subspecies. Conclusions drawn from the results were: (1) selection for light is genetically influenced as indicated by subspecific differences, (2) some genotypes are readily modified by environmental light conditions than others, and (3) natural selection in each environment appears to contribute to the degree of genetic fixation or genetic plasticity.