ScienceDaily (Oct. 28, 2008) — Do mothers purposely expose their offspring to their own stress? If so, why?

The question arises because it is widely accepted that exposure to maternal stress during pre-natal development can have negative impacts on offspring following birth. To examine why a stressed mother would allow this to happen, evolutionary physiologists Oliver Love and Tony Williams examined how offspring exposure to the maternally-derived stress hormone corticosterone affect maternal fitness in free-living European starlings (Sturnus vulgaris).

They experimentally increased yolk levels of corticosterone to mimic the "signal" offspring receive indicating they have a low quality mother. They then paired corticosterone-exposed hatchlings with experimentally manipulated low quality mothers to examine how these mothers fared in raising stress-exposed young compared with "normal" young.

Finally, they followed mothers within and across years to determine the long-term effects of the original manipulation on future reproductive success and maternal survival.

Their results provide the first evidence that low quality mothers benefit in the long-term from exposing offspring to their own stress: corticosterone exposure better "matches" offspring demand to a mother's immediate offspring-rearing capability. Corticosterone-exposed sons were of lower quality at hatching and when paired with a low-quality mother these sons experienced increased mortality.

However, because these mothers now had fewer mouths to feed, and of the smaller, less-demanding sex (daughters), the offspring that survived were of better quality. More importantly, by reducing investment in their current reproductive attempt, these "matched" mothers began second broods in better condition, had increased future reproductive output, and increased survival compared to "mis-matched" mothers (low-quality mothers that raised "normal'" offspring).

In the long-term, natural selection therefore appears to favor low-quality mothers that expose offspring to quality-mediated stress.

Journal reference:

1. Oliver P. Love and Tony D. Williams. The Adaptive Value of Stress-Induced Phenotypes: Effects of Maternally Derived Corticosterone on Sex-Biased Investment, Cost of Reproduction, and Maternal Fitness. The American Naturalist, 2008; 172 (4): E135 DOI: 10.1086/590959

enlarge

Male and female nestling starlings face different developmental costs as they compete for access to the limited resources provided by a low quality mother. (Credit: Oliver P. Love)

Related Stories

Effects Of Stress Last For Life In Birds (Mar. 23, 2009) — Researchers have discovered the first direct evidence that exposure to stress in young birds affects the way they react to stress when adult. This research greatly improves our understanding of how ...  > read more

Mothers Pass On Disease Clues To Offspring (Jan. 9, 2009) — When there is a threat of disease during pregnancy, mothers produce less aggressive sons with more efficient immune systems, researchers have discovered. The new study provides the first evidence for ...  > read more

Penguin Chicks Exposed To Human Visitors Experience Spike In Stress Hormone (Sep. 28, 2005) — Newly hatched magellanic penguin chicks in breeding grounds with a large number of human visitors show a significant spike in levels of a stress-related hormone compared to chicks hatched in areas ...  > read more

Pregnancy And Lactation May Affect Maternal Behavior And Coping Skills (Sep. 21, 2006) — Hormonal changes occurring in female rats after they give birth to and nurse their offspring may cause long-term endocrine and neuroendocrine changes that help produce better mothering skills with ...  > read more

Search ScienceDaily

Men Are From Mars