INFORMATION

SPECIES:
Peromyscus leucopus (White-footed Mouse)

STOCK:
LL. Subspecies P. leucopus originally from near Linville, North Carolina.

HISTORY:
The LL stock originated from 38 animals wild-captured between 1982 and 1985. This is a closed colony outbred stock.

All founders were collected from a single site less than 0.5 hectares in area, most near a single large brush-pile. Deer mice (P. maniculatus nubiterrae) were collected at the same site, but in substantially fewer numbers. No animals were collected that were intermediate or suggested that hybridization was occurring between these species. Other studies of these two species in Appalachia suggest that they share, rather split, a niche (Hawkins and Cranford 1992; Wolff 1996; Barry et al. 1984). One interpretation is that P. leucopus are gradually displacing P. maniculatus in the Appalachians as a post-Pleistocene process.

Nearly all of the originally captured animals were fertile in inter-se crosses and 38 founders contributed to the gene pool of the laboratory stock. The stock has been closed since 1985. In the laboratory sib-sib mating is avoided and the mice are otherwise mated essentially at random. In 2003 the stock was about 20 generations into captivity, with some overlap among generations. Fertility is excellent.

MORPHOLOGY:
Morphologically, the LL animals are typical for the species. We do not classify them to subspecies, inasmuch the boundary between P. l. leucopus and P. l. noveboracensis occurs essentially at Linville NC (Hall 1981) with no discrete morphological discontinuity apparent. Adult weights range from 18 – 24 g. Head and body length averages 96mm and the tail length is 69mm. The dorsal coat of the adult animal is a rich brown and the underside is uniformly white. The dorsal pattern is sharply delineated from the underside. The eyes are slightly more protruding than those of deer mice and more narrowly set. The tail is bi-colored but the dorsal stripe is not distinctly defined.

As a species, P. leucopus is distributed mostly in upland hardwood forests from Yucatan northward to New England in the eastern half of North America. It also occurs in wooded river valleys in the Great Plains. Seventeen subspecies are recognized. White-footed mice are among the most common native rodents in the eastern United States.

REPRODUCTION:
Animals are sexually mature by 55 days age. The estrous cycle is five days. Gestation is 23 days, except in lactating females where it is delayed by 4-6 days to 28 or 30 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 28-30 day intervals. About 80% of the pairs are productive within 3 months. There may be a lag in breeding during midwinter under natural lighting. Mean number per litter is 4.1. Usual litters are 3-6 and rarely exceed 8. Mean newborn weight is 1.8 grams.

HUSBANDRY:
Peromyscus can be maintained using standard laboratory mouse methodology. A maximum of six animals can be house in a 7" X 10" plastic cage. Feed and water are presented ad libitum. Nutritionally complete commercial laboratory rodent feed is advised. Do not use rabbit or guinea pig feed. Supplements of fresh vegetables, raisins, sunflower seed, etc., are unnecessary, and may be detrimental. Except for breeding, sexes should be house separately. Peromyscus are reasonably cold tolerant, but ambient temperature should never exceed 33C. Optimum temperature is 22-25C.

BREEDING:
Pairs are established individually, and checked regularly for pregnancies or litters. Copulatory plugs are inconspicuous in Peromyscus and are not a reliable indication of mating. Lighting is very important, with a 16:8 light-dark cycle satisfactory. Continuous light will produce anestrus. Breeding difficulties are sometimes overcome by reducing the light cycle to 12:12, then advancing it to 16:8 over a 3 week interval. The male should be retained with the female throughout. Introduction of a strange male to a pregnant female may block the pregnancy. Litters should be removed by 25 days of age, and may be ear or toe marked at this time. It is convenient to tag each mating cage with a card to maintain a record of breeding performance.

BEHAVIOR AND HANDLING:
Peromyscus are considerably more active than laboratory mice and will readily escape if not properly guarded. P. leucopus are especially active and capable of jumping 20 inches or more. A handling table with a 10 inch high barricade is useful. Although the animals will bite if improperly handled, they rarely bite without provocation. Gentle handling is advised, and the animals become accustomed to regular gentle handling. The skin at the neck is loose and the animals may be held by the scruff of the neck. The animals may also be restrained by cupping the palm of the hand over the animal, without applying pressure, and picking the animal up by the tail. Peromyscus are much more active at night than during the day. Their repertoire of behavior is greater than that of laboratory mice, and they exhibit many activities and routines of circling, jumping, climbing, etc. White-footed mice are much more arboreal than prairie deer mice and usually nest in stumps or tree hollows, whereas prairie deer mice nest in shallow burrows, presenting an area for comparative behavioral analysis.

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