Parental and grandparental age can alter the fitness of the progeny. For example, studies have found reduced fecundity, longevity, and memory in Drosophila melanogaster when parents were aged. These trans-generational effects can also be sex-biased, as aged female Drosophila appear to have a stronger negative influence on the longevity of their daughters, whereas aged males have some influence on the longevity of their sons.
Here we studied the effect of aging on neurodevelopment in the progeny in terms of changes to basic social behaviors such the social spacing between individuals and social avoidance of stressed flies. We also investigate the trans-generational effect on social behavior on progeny whose parents have been aged.
We have found that at older ages (30 days old, 90% survival and 50 days old, 50% survival) the distance between neighboring Drosophila increases, indicating that they are less social. Similarly, the social spacing between the progeny of aged Drosophila is also increased as compared to those with young parents. This suggests that the aging process contributes heritable change to the developing brain and therefore changes to social spacing. This also may indicate different aging mechanisms in germ cells versus somatic tissues resulting in a stronger effect in the progeny of aged parents than in the parents. Interestingly, the ability of individuals to avoid aversive stimuli is maintained throughout age and does not change the parents are aged, displaying maintenance of some social behaviors with age. We also show that it is enough to have an old father for the sons to be less social. We are currently investigating the effect of aged mothers as well.
We recapitulate the effect of old age of the parents on social spacing of their progeny by accelerating the aging process though increased metabolism (aging flies at 29C instead of the usual 25C) or via reactive oxygen species exposure (paraquat). In contrast, with delayed aging of the parents through caloric restriction, the progeny appeared more social.
Understanding the impact of aging is especially important as recently individuals with neuropsychiatric disorders like autism and schizophrenia have been linked to fathers over the age of 45. And although it is still unclear how exactly the aging process affects gametes leading to changes in neurodevelopment and thus specific social behaviors, the powerful model system Drosophila and its underused ability to display simple social interactions will allow us to identify the underlying mechanisms.