Parents’ nutrition affects offspring lifespan — but not in the way you think
By varying the environment of many organisms — from worms to primates, we can alter their physiology, which in turn alters their development time, lifespan, the rate they reproduce, the survival rate of their offspring, their body size, and so on. These changes occur due to a plasticity of phenotypes, or the ability for certain observable characteristics within an organism to mould and change according to environmental changes — despite the genes remaining the same. This can mean two organisms, with two identical genotypes (think identical twins) can end up observably different, because environmental changes can change the expression of those genotypes. A famous example of this in humans is the Kelly twins, one brother, Scott, spent 340 days on the International Space Station orbiting around 400km above the earth, while the other brother, Mark, relaxed in retirement in Tucson, Arizona. The stressors of space life triggered observable differences in Scott’s appearance, physiology, immune system, and cognitive function.
In nature (and indeed in life!), environmental changes and stresses can take many forms, such as temperature or climatic, presence of parasites or disease, presence of predators, or changes in food availability and nutrition. We know these factors change phenotypes of individuals (remembering phenotypes are observable characteristics of an organism), but evidence is also mounting to suggest it can also change the phenotypes of their offspring. In our latest study, we have altered the diets of fruit fly parents to observe both how diet alters the fitness of the parents but of the offspring as well. Evidence so far demonstrates that when the diet of the parent is altered, effects are passed from parent to offspring — beyond the transfer of genes alone. But, is the diet that is optimal for parents, optimal for their offspring? Traditional thinking tells us that there may be an advantage for offspring to have an environment that matches their parents. Evidence for this concept so far is mixed. It may be that a plant raised in the same type of light as its maternal plant does better, but how does this generalise to other organisms? If we expect that offspring have a diet that matches their parents might live longer, will that be true for all diet combinations? Which parent passes on the strongest effects (especially since most studies don’t consider both parents)? We sought to answer these questions by challenging both the parents and both sexes of offspring with a diet of either higher or lower sucrose, so that we could observe the effects of all possible combinations of diets represented in our study.
Instead of finding that offspring lived longer if they ate a diet that matched one or more of their parents — we found that if the diets matched between the parents (i.e. Mum and Dad both ate either high or low sucrose) they lived longer than if say Mum ate low sucrose and Dad ate high sucrose. Offspring from these “matched” parental combinations however, did not live as long as offspring from combos where parents ate two different diets respectively. This highlights to us that a diet combination that is optimal for parents, may not actually be optimal for their offspring. If you are acquainted with life history theory, at this point you may be wondering, but what about the trade-off between reproduction and lifespan? Maybe you will find that those offspring from those “mismatched” parental combos lived longer, but reproduced less. Sorry to disappoint, but in our measure of reproduction we find that more eggs were again produced by the daughters from parents who ate mismatched diet combinations.
Disentangling what this all means is the next step, and indeed seeing whether these effects will hold consistent for further generations, such as grand offspring, and for more combinations of diets, here we have only altered sucrose content, what if we alter protein? What our work does highlight is the need for these studies to consider both maternal and paternal effects together if we hope to understand how the interaction between the two affects the health and fitness of subsequent generations.