Females live longer when they have help raising offspring
Female birds age more slowly and live longer when they have help raising their offspring, according to new joint research.
Researchers studied the relationship between ageing and offspring-rearing patterns in the Seychelles warbler and found that females who had assistance from other female helpers benefitted from a longer, healthier lifespan.
The findings help explain why social species, such as humans, which live in groups and cooperate to raise offspring, often have longer lifespans. The study was led by researchers at UEA and the University of Groningen in the Netherlands, in collaboration with the University of Leeds and the universities of Sheffield and Wageningen, and with Nature Seychelles.
Dr Hannah Dugdale, from the Faculty of Biological Sciences, said "Our Seychelles warbler study system is ideal for this analysis as the birds do not leave the study island so if we do not see them we know they have died rather than emigrated. This has allowed us to discover this exciting relationship between sociality and ageing"
Professor David S Richardson, from UEA’s School of Biological Sciences, said: “There is a huge variation in lifespan between different species, and also between individuals within a species. But we know very little about what causes one individual to live a long healthy life, and another to die young. Or indeed, why individuals in one species live much longer than individuals in another similar species.
“Finding out more about what causes biological ageing is really important. And, until now, there has been very little known about the relationship between sociality and ageing within species.”
Many species have cooperative breeding systems – in which offspring are cared for not only by their parents but also by other adult members of the group called ‘helpers’. These helpers are often – but not always – grown-up offspring from previous years. The research team used more than 15 years of data on the breeding patterns of Seychelles warblers living on the small island of Cousin, in Seychelles, to study associations between cooperative caregiving and ageing.
As well as studying how quickly individuals’ chances of dying increased as they grow older, the team also used the length of the birds’ telomeres as a measure of their condition. Telomeres are found at the end of chromosomes and act as protective caps to stop genes close to the end of the chromosome being damaged – like the hard plastic ends of a bootlace.
Professor Richardson said: “Our previous work has shown that telomere length can be a good indicator of an individual’s biological condition relative to its actual age – a measure of an individual’s biological age so to speak. So we can use it to measure how quickly different birds are ageing.
“In the Seychelles warbler the majority of helpers are female - and they assist with incubating the eggs and providing food for the chicks. This means that the parents don’t need to do as much work when they have help.
“We found that older dominant females really benefit from having female helpers – they lose less of their telomeres and are less likely to die in the near future. This shows they are ageing slower than females without helpers. Interestingly, these older female mothers were also more likely to have female helpers.
“Meanwhile the survival of elderly birds who were not assisted by helpers declined rapidly with age.
“The birds only need one female helper to show the effect of delayed ageing, and indeed most only have either one or no helpers. Very few may have two or three helpers, but there were not enough of those to determine whether there would be a greater benefit in having more helpers.”
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‘Breeders that receive help age more slowly in a cooperatively breeding bird’ is published in the journal Nature Communications on March 21, 2019.