Evolutionary Fuel: Researchers Study Maintenance of an Ancient Chromosomal Inversion
According to Zachariah Gompert, an evolutionary geneticist from Utah State University, genetic diversity serves as the primary driving force behind evolution. However, as natural selection and random genetic drift occur over centuries, this reservoir of genetic variation gradually diminishes.The capacity of T. knulli to thrive on Redwood trees can be attributed to a chromosomal inversion, which is a structural modification that occurs within its genome. This alteration in the chromosome’s structure enables T. knulli to exhibit this specific adaptation.
The preservation of genetic variation and its implications for adaptation have long intrigued scientists. Addressing this query, Zachariah Gompert, an associate professor in the Department of Biology and also the USU Ecology Center at Utah State University, alongside colleagues from the University of Montpellier, John Innes Center, National Autonomous University of México, Querétaro, University of Nevada, Reno, and University of Notre Dame, delves into their investigation, published in the online edition of the Proceedings of the National Academy of Sciences on June 12, 2023.
The research focused on stick insects of the Timema genus, which exhibit a broad diet encompassing numerous plant species.
Gompert explains, “We explored the mechanisms that maintain genetic variation within a species and its impact on adaptation.” He notes that there are over a dozen species of Timema in western North America, characterized as generalists capable of consuming various plants. However, one species, Timema knulli, thrives exclusively on Redwood trees, which other Timema species struggle to utilize.
The ability of T. knulli to exploit Redwood trees stems from a chromosomal inversion, a structural alteration within its genome. Unlike gene mutations that involve changes in DNA sequences, a chromosomal inversion occurs when a segment of a chromosome breaks in two places, undergoes a 180-degree rotation, and is reintegrated at the original breakpoints.
Gompert elaborates, “With an inversion, substantial sections—30 million DNA bases, in this case—of the chromosome are reversed.”
The research team discovered that this chromosomal inversion in T. knulli is ancient, estimated to have occurred around 7.5 million years ago. Remarkably, contemporary T. knulli populations still retain both versions of the alleles—the one enabling them to thrive on Redwood trees as a host plant, and the original version that enhances survival on the ancestral flowering plant—favoring the heterozygous form.
Gompert suggests that environmental diversity and gene flow among migrating stick insect populations contribute to the persistence of both the new and ancestral chromosomal variants or polymorphism. This phenomenon could provide these organisms with an advantage in an ever-changing world by facilitating ongoing evolution and adaptation.
Rather than being detrimental, the intricate evolutionary processes linked to this inversion confer resilience against the loss of genetic variation and potentially foster long-term survival, according to Gompert.
Read the original article on PHYS.
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