Distant relative, close neighbour: The house mouse

The house mouse (Mus musculus) is one of the most well-known and widespread rodents in the world. Although small in size, it plays a significant role in both ecosystems and human life. Found in homes, warehouses, fields and laboratories, the house mouse is extremely adaptable, enabling it to survive in a variety of environmental conditions.

The importance of the house mouse is twofold. In the domestic context, it is often seen as a pest that can damage stored food and materials and transmit disease. On the other hand, in the world of science, the house mouse plays a key role as a model research organism. Thanks to its small size, short life cycle and genetic similarity to humans, it has become an indispensable tool in medical, genetic and biological research.

In this article, we will take a closer look at this fascinating rodent, discussing its classification, appearance, lifestyle, ecological significance, as well as its role in science and households. We will discover the benefits and challenges of having a house mouse and why it is worth getting to know this small but extremely important inhabitant of our planet better.

Classification and appearance

The house mouse belongs to the following zoological classification categories:

• Kingdom: Animalia (Animals)
• Phylum: Mammalia (Mammals)
• Order: Rodentia (rodents)
• Family: Muridae (mice and rats)
• Genus: Mus
• Species: Mus musculus

Physical characteristics

The house mouse is a small rodent with a distinctive appearance. Its basic physical characteristics are as follows:

• Size: An adult house mouse is between 7.5 and 10 cm long, with an additional tail length of 5 to 10 cm.
• Weight: The average weight of an adult mouse is between 12 and 30 grams, although this can vary slightly depending on the availability of food and environmental conditions.
• Appearance: House mice have a slender body covered with short, smooth fur, which can range in colour from light grey to dark brown. The belly is usually lighter in colour, whitish or light grey. The head is relatively small, with large, round ears and distinctive black eyes. The tail is almost as long as the rest of the body, covered with scales and sparse fur.

The house mouse’s characteristic physique enables it to move freely in various environments, including confined spaces and on a variety of surfaces. Small, sharp claws and strong hind legs allow it to run and jump quickly, which helps it avoid predators and find food.

Habitat and distribution

The house mouse originally inhabited temperate areas, where it found shelter in natural habitats such as meadows, bushes and forests. Over time, however, thanks to its exceptional adaptability, it has adapted to living in a variety of environments, including near human settlements.

Geographical distribution

The house mouse is one of the most widespread mammals in the world. It can be found on all continents except Antarctica. It is found in both temperate and tropical zones as well as in regions with extreme climatic conditions such as deserts and subarctic areas. Its global spread is largely the result of human activity, which unknowingly transported mice along with goods over long distances.

Preferences regarding the living environment

The house mouse has a strong preference for settling near humans, where it can easily find shelter and food. In natural conditions, it inhabits a variety of habitats, but its environmental preferences can be categorised into several key aspects:

• Shelter: House mice prefer places that offer numerous hiding places and protection from predators. These include, for example, burrows in the ground, dense vegetation, haystacks, outbuildings, and various nooks and crannies in houses and warehouses.
• Availability of food: Mice are omnivores and can adapt to a wide variety of diets. In their natural habitats, they feed on seeds, fruits, insects and small invertebrates. In the vicinity of human habitation, they take advantage of leftover food, cereals and stored food products.
• Climate: Although house mice can live in different climates, they prefer areas with moderate weather conditions. In extreme temperatures (very cold or hot), they seek shelter in human buildings, which offer more stable thermal conditions.

Lifestyle and behaviour

The house mouse is mainly nocturnal. It is most active from dusk till dawn, when it goes out in search of food and to explore its environment. During the day, it usually hides in its hiding places, protecting itself from predators and other dangers. The nocturnal lifestyle allows it to avoid many predators and use the resources of the environment more effectively.

Feeding habits

The house mouse is omnivorous, which means that its diet is very diverse. In their natural habitats, house mice feed mainly on seeds, fruit, insects and small invertebrates. In the vicinity of human dwellings, their diet is considerably extended to include foodstuffs stored by humans. Mice often raid pantries, eating cereals, nuts, bread and leftover food. They are also known to damage food packaging, leading to significant losses in households and warehouses.

Social behaviour and group hierarchy

House mice are social animals that live in groups of a few to several individuals. These groups have a complex social structure and hierarchy. The group is usually led by a dominant male, who has priority access to food and females. The hierarchy is maintained through various social behaviours such as grooming and aggressive and defensive rituals.

Female mice also form a hierarchy, although it is less pronounced than among males. Cooperation and socialisation are crucial for the group’s survival, especially in difficult environmental conditions. Young mice learn from older individuals how to obtain food and avoid dangers.

House mice communicate using ultrasound, which is inaudible to humans, as well as olfactory and tactile signals. These forms of communication are essential for maintaining group cohesion and coordinating activities such as foraging and defence against predators.

The lifestyle and behaviour of the house mouse are perfectly adapted to its environment, which allows it to successfully survive and reproduce in a variety of conditions, both in nature and in close proximity to humans.

Reproduction

The life cycle of the house mouse is relatively short, which allows for a rapid increase in population. After birth, the young mice are completely dependent on their mother. They are hairless, blind and deaf, and weigh about 1 gram. Within a few days, they start to grow fur, and after about two weeks, their eyes open.

The young mice start eating solid food at around three weeks old, although they can still be fed with their mother’s milk. At around four weeks old, they become independent and start to leave the nest. A house mouse reaches sexual maturity at 6-8 weeks, which means that they can reproduce and increase the population.

Mating season and reproduction methods

House mice reproduce all year round, but the highest number of litters occurs in the warmer months. Females are polyestrous, which means they have several estrous cycles throughout the year, each lasting about 4-6 days. During estrus, the female releases pheromones that attract males.

Mating behaviour includes ultrasonic vocalisations, which play an important role in communication between individuals. After mating, the female can store the male’s sperm in special structures, allowing fertilisation even a few days after the mating act.

Pregnancy and litter size

The pregnancy of a house mouse lasts only a short time, usually 19 to 21 days. The female gives birth in a well-hidden nest, which can be in a burrow, under a pile of materials or in a quiet corner of a building.

Each litter usually has 4 to 12 young, although this number can vary depending on the environmental conditions and the female’s health. Under favourable conditions, the female can have 5 to 10 litters per year, which leads to a rapid increase in population.

Thanks to their short reproductive cycles and large number of offspring, house mice are extremely effective at colonising new areas and maintaining population numbers. This is one of the key characteristics that makes them so ubiquitous and difficult to control in human environments.

Role in the ecosystem

The house mouse plays an important role in the ecosystems in which it occurs. It is a key element of trophic networks, which means that it participates in many ecological interactions. Thanks to their omnivorous nature, mice influence the populations of plants, insects and other small organisms. Through their foraging activities, house mice contribute to seed dispersal, which promotes the regeneration of vegetation in some ecosystems.

Role as prey and predator

The house mouse plays a dual role in the ecosystem – it is both prey and predator. As a prey, it is an important source of food for many predators such as birds of prey (e.g. owls), mammals (e.g. foxes, martens) and snakes. The high reproductive rate of the house mouse ensures a constant food supply for these predators, which helps to maintain their populations.

On the other hand, as a predator, the house mouse preys on a variety of small invertebrates, including insects, larvae and other small organisms. By controlling the populations of these organisms, mice contribute to the maintenance of balance in ecosystems.

Impact on biodiversity

The impact of house mice on biodiversity is complex and depends on the ecological context. In natural habitats where mouse populations are part of sustainable ecosystems, their presence can support biodiversity through activities such as seed dispersal and insect population regulation.

However, in introduced ecosystems where house mice are not a natural component of the fauna, they can pose a threat to local biodiversity. In such cases, mice can compete with native species for resources, introduce new diseases and prey on local invertebrate and small vertebrate species that have no natural defences against these new predators. An example of the negative impact of the house mouse is their activity on islands, where they can threaten populations of endemic bird species by plundering nests and eating eggs.

House mice as pets

Advantages and disadvantages of keeping a house mouse as a pet

Advantages:

• Small size: House mice do not take up much space, making them ideal pets for people living in small apartments.
• Low maintenance: Keeping mice is relatively cheap, both in terms of purchasing food and the equipment needed.
• Curiosity and interaction: Mice are intelligent and curious, which makes them interesting animals to observe. They can also be taught simple tricks.
• Short life cycle: Thanks to their short lifespan, breeders can quickly observe generational changes, which is interesting for biology and genetics enthusiasts.

Disadvantages:

• Short lifespan: Mice only live on average 1.5 to 3 years, which can be emotionally difficult for their keepers.
• Need for care: Despite their small size, mice require regular care, cleaning of the cage and monitoring of their health.
• Specific odour: Mice can give off a specific odour, especially males, which can be bothersome in closed rooms.
• Mobility: They are very active and fast, which can make them difficult to handle and easy to escape.

Keeping and caring for a house mouse

Cage:

• Size: A mouse cage should be spacious with adequate ventilation but small bars to prevent escape.
• Substrate: Use a suitable substrate such as wood shavings (dust-free), paper or special rodent substrate that absorbs moisture and odours well.
• Equipment: The cage should contain a running wheel, hiding places, tunnels and toys to chew on to stimulate the mice’s natural behaviour.

Hygiene:

• Cleaning: The cage should be cleaned regularly, removing dirty substrate and food scraps to prevent the growth of bacteria and unpleasant odours.

Feeding and health tips

Feeding:

• Diet: Special rodent mixes available in pet shops should form the basis of the mice’s diet, as they provide the right proportions of proteins, fats and carbohydrates.
• Fresh food: You can supplement the diet with fresh vegetables (e.g. carrots, broccoli), fruit (e.g. apples, bananas) and small amounts of protein (e.g. boiled egg).
• Water: Mice should have constant access to fresh, clean water, preferably in a ball-shaped drinking bottle that prevents spillage.

Health:

• Monitoring your mice: Regularly observe your mice for signs of illness, such as changes in appetite, behaviour, breathing or coat appearance.
• Veterinarian: If you notice signs of illness such as weight loss, diarrhoea, or breathing difficulties, consult a small animal veterinarian immediately.
• Prevention: Avoid exposing mice to stress, noise, and drastic temperature changes to prevent health problems.

All in all, pet mice can be wonderful pets for people who are willing to provide them with the right living conditions, care and attention. With proper care, a suitable diet and regular health checks, mice can lead healthy and active lives, bringing joy to their owners.

Pet mice in science

The house mouse (Mus musculus) is one of the most important model organisms used in scientific research. Its importance in science is due to several key characteristics:

• Genetic similarity to humans: Mice share about 95% of their genes with humans, making them ideal models for studying human genetics and biology.
• Short life cycle: Rapid maturation and short lifespan allow several generations to be observed in a relatively short period of time, which is beneficial for studying inheritance and development.
• Ease of breeding: Mice are easy to breed in laboratory conditions, enabling a large number of experiments to be conducted under controlled conditions.
• Availability of genetic tools: Many genetic techniques have been developed, such as mutagenesis, transgenesis or CRISPR technology, which allow the modification of mouse genes, which is crucial in the study of gene functions and disease mechanisms.

Examples of research in which house mice have played a key role

1. Cancer research: Transgenic mice, which are genetically modified to develop certain types of tumours, are used to study the mechanisms of carcinogenesis and to test new cancer therapies.
2. Diabetes research: Mice with mutations in genes related to glucose metabolism are used to study the pathophysiology of type 1 and type 2 diabetes and to test drugs.
3. Immune system research: Mice are used to study the function of the immune system, including immune responses to infections and autoimmunology.
4. Neurobiological research: Mouse models are used to study neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, as well as brain function and behaviour.
5. Genomics: The mapping of the mouse genome and comparative genomics studies provide important information about the function of genes and their evolution.

Ethics and controversies of using mice in research

The use of mice in scientific research is essential for progress in many areas of biology and medicine, but it also involves numerous ethical controversies:

• Animal welfare: One of the main issues is to ensure adequate housing and care conditions to minimise animal suffering. The 3Rs principles (replacement, reduction, refinement) are applied to replace animals with other methods, reduce the number of animals used and refine methods to reduce pain and stress.
• Alternative methods: There is continuous development of alternative research methods such as cell cultures, computer models and organ-on-a-chip technologies that can replace or supplement animal testing.
• Regulations: In many countries, there are strict regulations regarding the use of animals in scientific research, requiring approval from ethics committees and adherence to specific care standards.

Despite the controversy, house mice remain an invaluable research tool, contributing to numerous scientific discoveries and medical advances. The ethical conduct of animal research, along with the development of alternative methods, is crucial for sustainable scientific progress.

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