532.

House Mouse

Mus musculus

French: Souris domestique / German: Hausmaus / Spanish: Raton casero

Taxonomy. Mus musculus Linnaeus, 1758,

Uppsala, Sweden.

The species shows high variability in color and size in function of the environment, and this has led to the naming of a high number of synonyms. The genome of Mus musculus was one of the first to be sequenced, and this species has been intensively studied as a model of evolution. A mtDNA study, coupled with a surveyof 19 microsatellite loci, provides a good summary of intraspecific variation. Genetic diversity is high within this species, and seven phylogroups have been identified: domesticus, in North Africa and Western Europe; musculus in Eastern Europe, Central Asia and China; castaneus in Madagascar, Kenya, Pakistan, India, and South-east Asia; and two unnamed clades, one from central Iran, the other from south-east Iran. In addition is the form gentilulus from the Arabian Peninsula, and an undescribed clade from Nepal commented by H. Suzuki and colleagues in 2013. According to E. A. Hardouin and colleagues in 2015, the Iranian Plateau is a hotspot for the genus, having at least four house-mouse lineages, and it has played a central role in the species’ evolution. In the commensal house mouse from the mountains of north Italy, various populations have different karyotypes within the range 2n = 22-40. Race domesticus with 22 chromosome pairs is distinct because the Robertsonian metacentric they possess results from the fusion of different acrocentrics of the standard 2n = 40 chromosome karyotype. This species belongs to the subgenus Mus, and a “ M. musculus clade” was named including M. m. castaneus, M. spicilegus, M. macedonicus, and M. spretus . Four subspecies recognized.

Subspecies and Distribution.

M.m.musculusLinnaeus,1758—EEurope,CAsia,andChina.

M.m.castaneusWaterhouse,1843—Kenya,Madagascar,Pakistan,India,andSEAsia.

M. m. domesticus E. Schwarz & H. K. Schwarz, 1943 — W Europe and N Africa. M. m. gentilulus Thomas, 1919 — Arabian Peninsula. Also three unnamed geographic lineages from C & SE Iran and Nepal. Now introduced worldwide, except Antarctica (modern introductions not shaded on the map).

Descriptive notes. Head-body 70-103 mm, tail 67-104 mm, ear 12-17 mm, hindfoot 14-20 mm; weight 12-39 g. The House Mouse is a medium-sized Mus . It has a uniform grayish-brown dorsal and a paler ventral pelage. Tail is as long as head-body length. On the skull, the third upper molaris reduced in size, the upper incisors are notched. Females bear five pairs of mammae. Chromosomal complementis 2n = 40, FNa = 38 but, due to many Robertsonian fusions occurring in the species, diploid number may be as low as 22.

Habitat. Mostly commensal and found in a very wide range of man-made habitats. Nominotypical musculus is found both in houses and in the wild. It does not make sophistcated burrows and can nest in a wide variety of environments, including meat-storing cold chambers to cereal storage buildings. In Morocco,it is found in houses, barns, and haystacks, as well as in fallow fields. Wild nominotypical musculus in south France are found in wetter habitats than are those of the sympatric Western Mediterranean Mouse ( M. spretus). Wild populations have a preference for irrigated fields, pond margins, beds of bulrushes, and green-oak woodland, while the Western Mediterranean Mouse favors xeric habitats, such as garrigue and maquis. The two species cohabit only in barrier beaches of Languedoc (France), where sandy dunes and salty water ponds alternate.

Food and Feeding. House Mice are omnivorous, with invertebrates forming the greater part of the diet, followed by seeds and other plant material.

Breeding. Reproduction in commensal populations tends to reflect food availability; litter size and frequency seem to be lower in winter. Gestation period is 20-25 days, and a female may bear 1-11 embryos. In the wild, reproduction reaches a peak in spring and autumn.

Activity patterns. House Mice are terrestrial, and crepuscular and nocturnal.

Movements, Home range and Social organization. The House Mouse is flexible in its social life. In commensal populations, females are not aggressive toward each other, while in non-commensal situations there is a high degree of intolerance. House Mice live in colonies or extended family clans. In wild mice, each colony is dominated by a single male (for an average of 3-9 subordinate males), which is able to mate more often than the others (54% vs. 46%), and is actively approached by females. Over time, young males are able to kill the dominant one and set up territorial systems from which they chase all rival males but not the females; those males that are not territorial become subordinate males. Females move between territories, with no male attempting to keep them to itself, but they reproduce only with the territorial males that hold the richest areas. In 1975, J. A. Lloyd reported changes in social structure following population size increase, with two different populations evolving in response to different factors: territoriality was established by males in both populations; males would move around their territories, and, when they met other males, thetwo would stand up, become immobile with the tails and hairs erected, ears elevated, and the tips of their noses almost touching; either one mouse retreated or one attacked and chased the other; social structure and population regulation evolved differently in these two populations, with reproduction related to these changes. Similarly the subgroups in House Mouse colonies or demes have a limited number of individuals, and members are aggressive toward strangers to their group. Such subgroups are composed of a dominant male, 2-5 females and up to three subordinate males and juveniles. House Mice have strong female groups, with close kin associated in a territory; they offer little spatial avoidance toward males, which are polygynous.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The House Mouse is considered a pestbecause of the damageit causes in houses and stores.

Bibliography. Bonhomme & Searle (2012), Canova & Fasola (1993), Church et al. (2009), Denys etal. (2015), Hardouin et al. (2015), Lekagul & McNeely (1977), Lloyd (1975), Marshall (1977a), Moro & Bradshaw (2002), Quéré & Le Louarn (2011), Reimer & Petras (1967), Shimada et al. (2010), Singleton & Hay (1983), Suzuki, Nunome et al. (2013), Suzuki, Shimada et al. (2004), Wolff, R.J. (1981, 1985).