Mouse pups are born helpless and require extensive parental care from both mothers and fathers. Maternal behaviors in mice include nest building, nursing, pup retrieval, and aggression to protect the litter. Pups communicate their needs through ultrasonic vocalizations which stimulate maternal care. Communal nesting with multiple females provides benefits like improved thermoregulation and defense. While infanticide can occur, paternal behaviors like huddling, grooming and play also contribute to pup survival when tolerated by the mother. Genetics, experience, stress, and pup communication all influence the display of nurturing behaviors in mice.

1. Nurturing
Behavior
in Mice- I

2. Parental Care
Parental care can be defined to include "all non-
gametic investments in offspring following
fertilization".
Parental investment may be either: -
Direct: "an immediate physical influence" on the
young that increases survivorship,
Indirect: which includes "acts a parent may
in the absence of the young which increase the
latter's survivorship"

3. Maternal Behavior
Maternal behavior influences the probability of
survival
It includes: -
 nest building by one or both parents
 incubation
 feeding behaviors
 protection of the young
 training of young

4. The size of the mother also influences litter size
(larger females producing more ova)
Fertilization is possible about 10–12 h after
ovulation and gestation lasts for 19–21 days.
Parturition usually takes place during the night.
Maternal characteristics

5. Pup development
At birth : the young weigh approximately 1 g, are hairless (except for
whiskers), blind, deaf, have undeveloped motor skills and are fully
dependent on their mother for nutrition and thermoregulatory control.
4th or 5th day postpartum: Hearing ability seems to appear
~6th day postpartum: the pups are completely covered with a thin coat of
first hair. between day
12th and 14th day postpartum: They open their eyes (after this the first
extensive activity outside the nest occurs)
~ 16th day postpartum: litters are often seen nursing.
17 days postpartum: the pups start to eat solid food and the first signs of
weaning are noted

6. Mouse pup appearance by age [video

7. Nest building
All mice build nests in which they sleep
Types of mouse nests: -
Sleeping nests or thermoregulatory nests:
small, often saucer shaped open nests built by non-
pregnant mice
Brood nests or maternal nests: Built by the female
approximately 4 days after mating, 2–3 times the size of a
sleeping nest, with one or two entrances and completely
enclosed

8. Mice are born ectothermic and have poor thermoregulatory
abilities up to 2–3 weeks of age
Brood nest is important for successful rearing of young
Maternal nest is prepared very early in gestation (differs from other
altricial species e.g. rats and rabbits)
Role of the hormones: Progesterone and oestradiol in eliciting maternal
nest building
Mean nest weight decreased after oestradiol treatment and increased
after implantation of progesterone or a combination of oestradiol and
progesterone; these hormones seem to act in synergy to facilitate
maternal nest building.
Pup vocalization also influences nest building

9. General aspects of maternal
behavior
Maternal behavior starts during early gestation with the preparation of
the brood nest.
During the first 3 weeks, nursing occupied 92% of the maternal
behavior
Weaning seems to take place gradually
The weaning age of 23 days is judged from a drop-in nursing activity to
less than 1%.
Weaning is completed by day 25.

10. Maternal
Behaviors
Maternal
moving
Nursing
Maternal
grooming

11. Mouse pups are born without hair.
When they begin to grow their first coat, their eyes are still closed.
Dam grooms their coats for them.
Serves a physiological and psychological purpose
Strengthens the maternal-social bond.
How much the mother grooms her own pups; influences later
corticosterone responses to stress in the pups
Maternal grooming

12. Maternal moving
When a dam moves a pup, she will pick it up in her mouth and move it to
a safe area (nest)
Rarely needs to move or rearrange the entire litter
Individual newborn pups rarely stray on their own from a warm nest
In response to their ultrasonic cries, the dam locates and retrieves the
lost pups back to the nest
Pup-retrieval (type of maternal moving)- [videos]

13. Nursing
Mice are an altricial species.
Dependent on mother's milk as a source of food
The amount of milk received can affect a pup's adult weight and
aggressiveness.
Weaning weight of male pups can have long term effects on their
ability to become dominant adults.
A dam uses olfactory cues in her milk and urine to establish a unique
social identity for her litter

14. Maternal aggression
Aggressive behavior of a lactating female defending her offspring
Predation by non-conspecifics is probably rare
Major predators of neonate rodents are conspecifics
Both pregnant and lactating females display maternal aggression
(attacks have rapid onset and are potentially damaging in nature)

15. Males often flee or react with defensive postures, but in some cases,
they retaliate and kill the offspring.
Hrdy’s sexual selection hypothesis: Males benefit from killing
nonrelated pups as this allows the female to return to oestrus
Maternal aggression functions to protect the litter from infanticidal
intruders
The intensity of aggression increased with increased litter size.
Female mice discriminate between infanticidal and non-infanticidal
males
Maternal aggression (cont…)

16. Nurturing
Behavior
in Mice- II

17. Factors affecting maternal
behavior: -
Pup behavior and vocal communication
External stimuli from the pups are crucial for maintaining maternal
care
Born with non-functional auditory systems: use vocalizations
First 2–3 weeks postpartum: pups emit a variety of ultrasonic
vocalizations (USVs) when isolated from the mother
Three categories of infant calls:
 ultrasounds,
 audible squeals
 clicks

18. Ultrasonic sounds categorized according to response triggered in
mother:
 pure ultrasounds inducing pup approach and retrieving
 broadband pain calls to signify injury
 low-frequency wriggling calls eliciting maternal behavior and
particularly licking
Moving pups do not act as an effective stimulus for releasing
maternal behavior in mothers who are deaf
Pup behavior and vocal communication (cont…)

19. Experience improves maternal behaviour as demonstrated
by higher survival in second versus first litters
Stress: -
 Multiple protocols can be used: Acute and Chronic stress can
be generated
 Though nest building capacity remains unchanged, the
mother’s capability in defending her pups decreases
 They also decreased rates of grooming, nursing, and time
spent in the nest

20. Genetic influence
Transgenic studies with null mutations have demonstrated
several individual genes involved in the regulation of maternal
behavior.
Many mutant, knockout and transgenic mice, display poor
maternal behavior or complete inability to rear offspring
Mutant mouse staggerer: The mice fail in removing the amniotic
membrane, leading to pups dying from being choked, and
surviving pups ignored and dying of cold or hunger
hubb/hubb mutation: These mice tend to be sensitive to
disturbance of their cages, responding with infanticide and
cannibalism
Mecp2-deficient mouse: High incidence of infanticide

21. Pups of fosB mutant mice: scattered around the cage and neglected by
the mother
Wild Type fosB mutant

22. Communal
care
The sharing of parental
responsibility by multiple
individuals
Example, communal nesting
Multiple females raise young in the
same nest
Result of individuals congregating
around clumped resources, or may
also be an adaptive strategy,
improving thermoregulation and
nest defense.

23. Communal nursing
If several females are housed together, they build and keep their
pups in a communal nest in which they may also share the nursing
Pups benefit in terms of increased growth and survival.
Especially in an environment with limited food supply for the dam
(inadequate milk supply, offspring survival difficult)
Each communal nesting female spend less time nursing than a
solitary female
Relatedness of communally nesting females and their offspring
Nest mates have the same father and females are often related

24. Three conditions under which communal nesting
benefits participants: -
(1) Improving heat retention, with consequent improved
pup survival and growth
(2) Increasing pup growth due to increased milk production
by two or more females
(3) Fewer pups are lost to predators because of higher nest
defense.

25. Infanticide and Cannibalism
Infanticide is defined as ‘‘the killing of conspecific preweaning young’’
House mice are reported to be infanticidal under certain circumstances
D’Amato (1993) reported sexually naive males to be more infanticidal
than sexually naive females
Males killed pups indiscriminately while female mice discriminated first
by familiarity to the pups, and secondly on the degree of relatedness
Female mice sometimes also kill own offspring
Evidence of female mice reducing litter size when food is restricted, and
stress has been suggested to cause females to neglect, kill, or eat their
young
No evidence of females actively killing pups (‘maternal cannibalism’ )

26. Role of the father: Paternal behavior in
mice
Presence of a male can be important both pre- and post-natally
Male rodents perform all direct parental activities displayed by female
such as:
 huddling—sleeping with, crouching over, or adopting the nursing position
with the young;
 grooming—cleaning, licking, or otherwise grooming the young;
 retrieving—carrying or transporting the young from place to place,
generally returning to the nest;
 play—engaging in play behavior with the young;
 tutoring— behavioral patterns that facilitate learning by the young;
 providing food—bringing food to the young;
 greeting—engaging in species typical greeting displays;
 manipulation in nest—manipulating the young while in the nest

27. Naive wild house mice typically kill the young
Paternal behavior observed:
 mice that remain with their parents while the parents rear a
subsequent litter
 cohabitation by a male with a female throughout her pregnancy
Only those males paired with minimally aggressive females
display appreciable paternal behavior.
Complete parenting behavior when housed individually with the
young
Role of the father: Paternal behavior in
mice (cont…)

28. Female may increase the chances of survival of the pups by permitting
males to help care for young
Males "prove" themselves as non-infanticidal then only allowed near the
pups
Female mice play a definite role in encouraging paternal relationships
between male mice and their pups.
Ultra-sonic noises emitted by females under stress triggered paternal
behaviour
The females also released olfactory signals in the form of pheromones,
which triggered the same reaction in the males
[video]
Role of the father: Paternal behavior in
mice (cont…)