Mus musculus: Profile of the Common House Mouse

The house mouse, Mus musculus, is one of the most numerous mammals on Earth, its history intertwined with human civilization. This relationship has carried it to nearly every corner of the globe. This small rodent is a common sight in human-occupied landscapes, from agricultural fields to dense urban centers. Its adaptability has allowed it to thrive alongside people, making it a significant species in both ecological and scientific contexts.

Physical and Behavioral Characteristics

The house mouse is a small rodent, weighing between 12 and 30 grams with a body length of 7.5 to 10 centimeters. A distinctive feature is its long, scaly tail, which is often as long as its body. Its fur is a grayish-brown color, though laboratory and domesticated varieties can range from white to black. The mouse has a pointed snout, large rounded ears, and prominent eyes that aid its nocturnal lifestyle.

These animals are characterized by their nocturnal behavior, though some activity can occur during the day. They live in social groups that are often territorial, with males sometimes fighting to defend their area and access to mates. Females can have between five and ten litters per year, with each litter containing four to eight young. The gestation period is short, lasting 19 to 21 days, and the young are weaned and independent within about three weeks.

In the wild, their lifespan averages around 18 weeks, though they can live longer in protected environments. As omnivores, house mice have a varied diet that includes grains, seeds, and fruits. Near humans, they readily consume nearly any available food scraps. This dietary flexibility is a factor in their success.

Habitat and Global Distribution

Believed to have originated in Central Asia, Mus musculus achieved a near-global distribution by following human migration and trade. This has made it one of the most widespread terrestrial mammals. Its ability to live in close association with people, a relationship known as commensalism, is central to its success. The mouse benefits from the shelter and food found in human settlements.

The species thrives in and around human-made structures like homes, farm buildings, and warehouses, which provide shelter from predators and stable food supplies. While most common in urban and suburban areas, Mus musculus is also found in natural habitats like fields and woodlands. In these wilder settings, it often faces competition from other native small rodents.

The house mouse constructs nests from soft, shredded materials, often tucked away in secluded areas within buildings. In the wild, they may build tunnel systems ranging from a simple chamber to a complex network. The range an individual mouse covers depends on food availability. Where food is abundant, its territory may be only a few square meters, but it can expand if resources are scarce.

Significance in Scientific Research

Mus musculus is a model organism in biomedical research, and its use has led to many scientific advancements. A primary reason for its use is the high degree of genetic similarity it shares with humans, allowing researchers to study human diseases in a living system. The complete mouse genome was sequenced in 2002, enabling the creation of “knockout mice,” where specific genes are inactivated to study their function and connection to disease.

The practical aspects of working with house mice also contribute to their importance in a laboratory setting. Their small size makes them easy to house in large numbers. Their rapid reproductive cycle and short lifespan are advantageous for multi-generational studies, allowing scientists to observe the effects of genetic changes over several generations in a relatively short period.

This species has been used in many research fields, including:

• Immunology
• Genetics
• Developmental biology
• Cancer research

Studies using mice have been important to understanding the immune system’s response to pathogens, the genetic basis of inherited diseases, and the mechanisms that drive tumor growth. Modeling complex human conditions in mice provides a platform for testing new drugs and therapies before human trials.

Relationship with Humans

The relationship between humans and house mice is complex, defined by both conflict and companionship. For most of history, Mus musculus has been viewed as a pest. It infests buildings, contaminates stored food with its droppings, and causes structural damage by gnawing on materials like wood and wiring. This behavior results in economic losses and poses health risks, as mice can act as vectors for various pathogens.

In contrast to its role as a pest, the house mouse has also been domesticated. Through selective breeding, a variety of “fancy mice” have been developed, prized for their unique fur colors, patterns, and docile temperaments. These domesticated mice are kept as pets around the world. This practice highlights the species’ dual role as both a nuisance and a companion.

This domestication for companionship is separate from the breeding of laboratory mice for scientific utility. Both practices, however, stem from the same species and showcase the versatile relationship between Mus musculus and humans.