SUPERNUMERARY CHROMOSOMES OF HARVEST MOUSE, REITHRODONTOMYS MEGALOTIS

Chromosomes were analyzed from 282 field captured and 76 laboratory specimens of the Western Harvest Mouse, Reithrodontomys megalotis. The supernumerary chromosomes found in this species varied from 0 to 7 causing a variation in diploid number of from 42 to 49 with the modal class being 2n=44. The relative frequency of various numbers varied between populations, which were taken from Arizona, California, Nebraska, New Mexico and Utah. Laboratory breeding experiments and cytological evidence indicate differences in the rate of non-disjunction is responsible for interpopulational variation. A hypothesis is suggested to explain this variation as it relates to the evolution and zoogeography of the species. © 1969 Springer-Verlag.