Exploring the impact of early-life adversity on starlings
Research indicates that in humans, adverse early-life experience impacts later cognition. This can be manifested in impulsive and addictive behaviour, dietary choices, obesity and anxiety disorders. But there is scant knowledge about whether this applies to other species. Altricial birds – whose young, like humans, are born underdeveloped and dependent on parents for survival – are good research subjects. Young, nested birds are immobile, so food and care can be accurately measured, and as parents don’t recognise their young, the birds can be hand-reared. A lot of data also exists linking offspring health to brood size, establishing a framework for benign experimentation. As Daniel Nettle, the project coordinator of European Research Council funded COMSTAR explains, they chose to study starlings because they are abundant, social and adapt well to laboratory environments. Amongst the project’s findings was the discovery that early stress and adversity speeds up ageing, corroborated partly through telomere measurements. Telomeres are DNA caps on chromosomes. Research in humans suggests they shorten with age. The team also found that early experience affects patterns of fat storage and appetite regulation. “Here it gets complex, because adversity can make for either thinner or fatter adults. Nonetheless, this has implications for all kinds of health issues, like obesity and metabolic disorders,” says Nettle.
Learning from social foraging
The link between early-life experience and later cognition and behaviour, in species other than humans, is fragmentary. Research favourites, rodents and monkeys, have been studied the most, with few bird studies. Inter-species comparisons are practically non-existent. To manipulate early experience, the team hand-reared four siblings from a family, giving each different combinations of the same amount of food over their first couple of weeks. The chicks were then introduced to flocks. “So, we had siblings sharing genes, living in the same adult environment, but with different ‘childhood’ experiences,” adds Nettle. To study the behaviour and physiology of these birds in adulthood, the team devised a number of behavioural tasks, measuring food motivation, risk-taking and tolerance to delayed gratification. Human studies of the same traits were also carried out for comparison. A ‘social foraging system’ was developed – a machine in the starlings’ environment which automatically dispensed food. “Nothing like this had been made before. It required precision engineering and software interfaces, with suitability for constant use by starlings, without human interference,” remarks Nettle. When birds wanted to forage, they flew to the machine and perched; fitted with electronic tags, each individual was identified and weighed. The bird then had to press a key for food. The team altered variables such as predictability of food delivery or degree of competition. In one experiment, one key led to a small but immediate reward, another to a larger, but delayed, reward. The human equivalent elicited cash rewards. “We found that siblings with different early lives approached risk differently, for example with some less able to estimate time intervals, despite having indistinguishable adult environments. Early comparisons suggest similar findings in humans,” explains Nettle. Another noteworthy finding was that more stress in the initial weeks of life, accelerated telomere shortening in starlings. “Measuring telomere length remains technically difficult and they are not precise indicators of biological age,” notes Nettle. “However, developing our techniques taught us a lot about biomarkers so we contributed to the science of telomere measurement.” The team are now concentrating on human development, drawing on studies which have tracked cohorts from childhood to adulthood.
Keywords
COMSTAR, starling, bird, adversity, childhood, adulthood, food, telomere, behaviour, cognition, ageing
