P polionotus subgriseus Oldfield Mouse-PO Stock
Peromyscus polionotus (Oldfield Mouse)
PO. Subspecies P. p. subgriseus originally from Ocala National Forest, Florida.
The PO ("polionotus Ocala") stock originated from 21 ancestral mice wild caught in 1952 by Paul G. Pearson at Ocala National Forest, Florida, and thence shipped to L. R. Dice at the Laboratory of Vertebrate Biology at the University of Michigan. At the LVB a breeding stock was established and maintained for several years as a closed colony. About 1956 a sub-colony was established by W. B. McIntosh at Ohio State University and from this colony the stock presently at the Peromyscus Genetic Stock Center was established in 1962 with a founder population of 19 individuals. P. polionotus is interfertile in captivity to a limited extent with the larger and darker deer mouse, P. maniculatus. The two species are allopatric in distribution. Since the 1920s experimental hybridization between oldfield mice and deer mice has been used in investigations of natural selection, speciation and genetic isolating mechanisms. Reciprocal hybrids exhibit about a 12-gram difference in mean adult weight and a six-fold difference in placental size. Most recently, the demonstration of genomic imprinting in P. maniculatus X P. polionotus hybrids is of considerable interest (Vrana et al. 1998, 2000 ).
Peromyscus polionotus is the smallest species of the genus with an average adult weight of 16+2 g. Its range is limited to the five southeastern-most states of the US. Fourteen subspecies are recognized based primarily upon intensity of pigmentation. This species prefers sandy soils and beach dunes where the mice construct an elaborate burrow with a distinctive pattern of tunnel and nest chamber features (Dawson et al. 1988). Coat coloration varies with the predominant soil color. Inland populations are darker and beach forms are pale, and in the case of the Santa Rosa Island FL form, nearly white (Sumner, 1929). The pale forms are often called "beach mice" to distinguish them from the darker inland subspecies.
All breeding of captive animals at all three institutions used individually ear-marked animals and breeding records were meticulously maintained. Animals were bred without deliberate selection except to avoid sib-sib and parent-offspring mating. A bottleneck in the breeding program about 1978-1980 reduced the founders of the current stock to 13 individuals. Hence, the stock has a relatively high inbreeding coefficient estimated at ~.30. It is about 35-40 generations into captivity. The stock is wild-type in coat color and exhibits no abnormalities, and is essentially like the wild ancestral animals. About 75-80% of mated pairs produce weaned young. P. polionotus is mostly a monogamous breeder. Litter size is 1 - 6, typically 3. Animals are sexually mature by 60 days age. The estrous cycle is five days. Gestation is 22 days, except in lactating females where it is delayed by 4-5 days to 26 or 27 days. Breeding is optimized when animals are continuously retained in breeding pairs. The females enter postpartum estrus about 12 hours after delivery and remate. Thus, serial litters are born at 26-27 day intervals. Young are removed from the parental cages (weaned) at a minimum of 25 days. Females may be productive for up to five years.
Old field mice are easily handled and survive well in standard animal care facilities with temperature maintained at 22-25° C.