Stress levels of mother lizards have a direct psychological impact on their babies

A new study tested how a mother lizard’s stress during pregnancy changes her babies’ bodies and social lives. The team tracked growth and behavior from birth through the first months of life in a species that often lives in small family groups.

The key result is simple but surprising. Offspring of stressed mothers grew more slowly yet formed stronger social ties with family members and other lizards, and simply being near mom after birth did not reverse the prenatal effects.

The work was led by Dr. Kirsty Macleod of Bangor University’s School of Environmental and Natural Sciences (BU).

How lizard stress was tested

The researchers focused on glucocorticoids, hormones that rise during stress and can pass signals from mother to offspring during development.

Pregnant females received brief doses designed to mimic natural spikes, then their babies were observed in outdoor enclosures that allowed both staying near family and dispersing.

The species is Liopholis whitii, also called White’s skink, a medium sized, viviparous lizard native to Australia.

It often forms small families in which juveniles remain near a parent when good shelter is limited, a pattern linked to resource availability in the field.

Why stress matters

Glucocorticoids work within the body’s HPA axis, a system that helps animals respond to threats and return to balance. In many animals, time with kin can reduce stress responses, a pattern known as social buffering.

Early stress can also shape social tendencies later on. In zebra finches, developmental stress altered how connected young birds became within their flocks, shifting who they associated with and how often.

Prior work in reptiles hints at growth costs when mothers experience elevated glucocorticoids.

In another lizard, experimentally increased maternal corticosterone produced smaller, slower growing offspring, consistent with the growth pattern seen here.

How lizards changed with stress

Babies from stressed mothers were lighter at birth and stayed smaller across the juvenile period, with slower day by day growth rates reported in the statistical models of the new study.

The paper reported significant effects on mass at birth and over time, including p values of 0.04 at birth and 0.009 across the tracking window.

Social behavior shifted too. Offspring of stressed mothers showed stronger social associations with other individuals, including tighter connections to their mothers and siblings.

In addition, the network strength metric for these offspring was significantly higher, with p equal to 0.02.

The presence of the mother after birth did not undo the prenatal effects on sociality. The team found no evidence that simply being housed with the mother for a few weeks buffered the influence of prenatal stress on later social behavior in the semi-natural enclosures.

“Stress during pregnancy can affect how offspring grow and behave, including how they interact with others. It also suggests that, at least in these lizards, simply being near a parent after birth isn’t enough to undo the effects of prenatal stress,” said Dr. Macleod.

Early social effects

The team did detect one activity pattern tied to the early social setting and prenatal stress.

Among offspring from stressed mothers, those kept with their mother just after birth were observed active on more days than siblings reared alone, which could influence opportunities for exploration later.

That specific difference in daily activity did not translate into stronger social associations for the isolated group or a change in dispersal decisions.

It suggests that brief maternal association can affect how often juveniles are out and about without changing the strength of their social ties formed afterward.

At the same time, this lizard’s social environment has known effects in other contexts.

In the same species, maternal presence during early life can shape boldness and exploration, showing that parental tolerance can matter even when direct care is limited.

Significance of the study

The stronger social associations after prenatal stress may help offspring in tough conditions by increasing access to shelter or reducing conflict within familiar groups.

In White’s skinks, families can reduce aggression and create safer space, which can pay off when good crevices are scarce and competition is high.

The growth cost points to a tradeoff. Slower growth can carry risks, such as extended vulnerability before reaching adult size, and the new results show that these costs persisted for months in the juveniles monitored.

These findings sit alongside broader work on social buffering and developmental programming.

Not all species show the same pattern, and the balance between costs and social benefits will likely depend on habitat, predators, and how families organize themselves.

Future research on stress

Two questions now stand out. First, what physiological routes translate prenatal glucocorticoids into stronger social ties, for example through shifts in neuropeptides that regulate affiliation and tolerance.

Second, do these prenatal effects change when habitats vary in quality from year to year, or when free ranging animals face real predators and competition.

Answering those questions will help explain how family living forms and persists in species with simple parental care.

The work also invites a closer look at philopatry, the tendency to stay near home, because stronger associations between mothers and offspring could reflect both increased tolerance and a higher chance that juveniles delay dispersal.

Untangling those pieces will sharpen how scientists read social networks in the wild.

The study is published in the Journal of Animal Ecology.

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