Nature
PUBLISHED
When fruit flies are exposed to a temperature shock, the gene regulation responses that form part of their adaptation can be passed on to at least four generations of descendants, even if temperatures level out. The researchers who discovered this pattern think it is likely to apply to other animals as well.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Changes in environmental conditions always favor members of a population with genes suited to the new circumstances, and heat tolerance is no exception. These genes then become more likely to be passed on to the next generation in a classic example of the intersection of Darwin and Mendel’s discoveries. However, adaptation can also happen more quickly when epigenetics promotes the expression of genes that are now beneficial and suppresses those that no longer suit conditions.
To explore how these general principles play out in practice in a hotter environment, female Drosophila melanogaster fruit flies were collected in Finland and Spain so they would be used to strikingly different climates. The researchers exposed their subjects to heat shock in the lab and studied the consequences for their genetics, the proportion of their eggs that reached adulthood, and how long the offspring took to develop.
All living organisms are known to produce molecules known as heat shock proteins (Hsps) after experiencing extreme heat, so the rise in these molecules was expected. However, the genes responsible are quite varied, and the researchers wanted to get a higher resolution view of how the flies’ bodies would respond.
Both populations expressed genes that assist with coping in high temperatures more strongly after the heat shock, but for the Spanish flies the response was more ordered and effective. The Finns turned up potentially useful genes, but in a less effective way – like the person who has never experienced extreme heat and has read tips like drinking water, but doesn’t know how much to consume.
Eggs laid within two days of the heat shock were less likely to be viable and to reach adulthood more quickly, but in the arid zone, fly eggs laid later developed more quickly as well. The authors think this might be an evolved response to move fast before the heat returned.
Flies reach adulthood and breed so fast, the team were able to track the descendants of those exposed to heat over generations and compare them with controls. Each generation showed fewer genetic differences from the controls than its predecessors, since the heat was not repeated, but differences persisted in regard to the expression of 23 genes.
That lasting effects were greater among the flies of Spanish descent, which continued to develop more rapidly four generations later, presumably because this has proven an effective response when heat-shocks occur, something the Finns would not have encountered.
If a single shock generations before could lead to these differences in distant descendants, repeated events associated with a hotter world may well cause rapid evolution. Eventually those that have experienced more of these shocks might struggle to breed with their counterparts from more consistent climates.
Given that results differed even within one species, the work doesn’t predict how a specific animal, particularly a vertebrate with such different ancestry, will react to a hotter world. Nevertheless, lead author Dr Ewan Harney of the University of Liverpool thinks there are lessons to be learned. By identifying specific genes whose expression remained affected, and the mechanisms for some changes, the team have given researchers studying other animals potential research targets.
“The transgenerational effects in gene expression and development time we observed demonstrate that stress might not only select for better adapted flies, but could facilitate evolution,” Harney said in a statement. “Understanding why some variants can respond transgenerationally better than others could be important in identifying at-risk populations as the Earth’s climate continues to change.”
The study is published open access in Molecular Biology and Evolution.
