Discrimination and hybridization in Peromyscus.

Abstract

Sympatric Peromyscus leucopus and ,E. maniculatus from Lyon County, Kansas, were tested for their ability to hybridize in natural surroundings from 24 May 1982 through 14 October 1982. Four metal enclosures, 5 ft. X 5 ft. X 3 ft., exposed to ambient conditions at the Ross Natural History Reservation, were used to house separately heterospecific pairs of both species combinations and homospecific pairs for control groups. The control pairs produced three litters during the course of study. ,E. leucopus female and ,E. manicula.tus male pairs produced no young. One female hybrid was produced from a P. leucopus male and,E. maniculatus female pair. Species discrimination criteria were determined by use of nesting preference. Test mice were given a choice of nesting closer to either homospecifics or heterospecifics of the opposite sex. Control teste consisted of giving test animals a choice of nesting "loser to homospecifics of opposite sex or empty nest boxes. ,E. leucopuB males and P. maniculatus females showed no significant difference in nesting preferences. ,E. leucopus females and 1:. maniculatus males did display an ability to discriminate. All control combinations failed to show significant differences in nesting preferences. Another facet of this research tested for olfactory discrimination. An olfactorium was constructed from a glass terrarium partitioned into three compartments. Each partition was pierced by a tunnel in which a microswitch, sensitive to the weight of a mouse, closed circuits to electro-magnetic pens which left a continuous record on a Kymograph recorder of tunnel passages by test mice. Total time spent by test mice in each end chamber, one previously occupied by homospecifics of opposite sex and one previously occupied by heterospecifics of opposite sex, was recorded. Control tests left one end compartment previously unoccupied, while homospecifics of opposite sex of the test mice occupied the other end chamber. R. maniculatus males spent significantly more time investigating E. leucopus female odors than homospecific female odors. All others showed no significant differences in their preferences. In control tests, P. maniculatus and E. leucopus males spent more time in previously unoccupied end chambers than in end chambers previously occupied by conspecific females. Females of both species did not prefer either end chamber significantly. However, results of these tests are inconclusive because of small sample size. These results suggest that natural hybridization is possible between P. maniculatus females and E. leucopus males and that reproductive isolation of these sympatric populations is probably behavioral.