In brief A new Stanford study explores how fruit fly populations maintain genetic diversity amid changing environments, which is crucial for survival against future challenges.
The research provides direct evidence to support the theory of “dominance reversal” in genetics.
Findings indicate that genetic variants can act as dominant or recessive based on environmental conditions – which gives the flies long-term pesticide resistance.
Populations live in rapidly changing environments – droughts come and go, food sources change, human activities reshape habitats. For scientists, this raises a fundamental puzzle: How do populations maintain the genetic diversity needed to survive future challenges when natural selection should eliminate variants that aren’t useful for long periods?
Researchers at Stanford have addressed this puzzle by tracking the evolution of fruit fly populations in an outdoor orchard where they controlled pesticide exposure over time, and paired experiments with mathematical modeling. Their new paper, published Sept. 15 in Nature Ecology and Evolution, offers the first direct evidence to support the theory of “dominance reversal” in a changing environment over time.
Classically, we think of genetic variants (alleles) as strictly dominant or recessive – dominant alleles dominate expression of traits and recessive alleles are only outwardly expressed if there isn’t a dominant allele around. In the case of dominance reversal, the same genetic variant is dominant when helpful (providing the flies with resistance in pesticide-rich environments) but recessive when harmful (reducing fitness in pesticide-free environments).
“Let’s say you haven’t used pesticides for 20 years. The moment you add pesticides again, they’ll rapidly respond and resist them,” said senior author Dmitri Petrov, professor of biology in the School of Humanities and Sciences (H&S). “It’s like the flies have a hidden shield. When they don’t need it, it’s not in their way. But it’s ready as soon as they are threatened.”
The researchers suggest this mechanism may be widespread in nature, helping maintain genetic diversity for different environmental challenges that change over time. “What we’re seeing could be a general mechanism for populations to hold on to genetic variants they might need for future environmental shifts,” said Marianthi Karageorgi, who is the lead author and a research scientist in the Petrov Lab.
“For example, synthetic insecticides are often analogs of plant chemical defenses,” Karageorgi added. “So, this mechanism could have been operating in nature for millions of years – helping insects maintain resistance to chemical defenses that vary seasonally with host plant availability.”
Evolution in an experimental orchard
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