Zivanovic, Goran, Concepció Arenas, and Francesc Mestres. "Temporal and habitat adaptations in Drosophila subobscura populations: changes in chromosomal inversions." Genetica 153, no. 1 (2025): 16.

 What They Did

In 2023, the researchers collected Drosophila subobscura fruit flies from Jastrebac Mountain in Serbia, revisiting oak and beech forest locations that had been previous collection sites in 1990 for the oak forest and in 1990, 1993, and 1994 for the beech forest. Male flies from the 2023 collection and their descendants were crossed with flies from a reference strain. The researchers dissected at least eight larvae from each cross to examine their chromosomes. In particular, they looked at the different patterns of inversions, areas where part of the original chromosome was detached, flipped, and replaced. (For example, a nucleotide sequence of TGATTCGG might change to AGTTTCGG).

Previous research had identified many D. subobscura chromosomal inversions as cold-adapted, warm-adapted, or not thermally adapted. Therefore, the researchers were able to quantify the degree of imbalance in warm- or cold-adapted chromosomes for each collection site. Multivariate analysis showed that some of the chromosomal variation among groups of fruit flies depended on time, with those from the 2023 oak and beech site similar to each other, those from the 1993 and 1994 beech sites differing, and those from the 1990 oak and beech sites differing even more.

Among the flies in the beech forest, the imbalance towards warm-adapted chromosomes increased from 1990 to 1994 but did not change from 1994 to 2023, suggesting that the degree of adaptation reached its maximum in 1994. The flies at the oak site did not show a significant change in the degree of adaptation between 1990 and 2023.

 

Further Exploration

A good number of inversions have been in the human genome for a while and aren’t reported in laboratory DNA analysis because they’re considered natural variants. Since this information came from a document about chromosomal disorders (see https://rarechromo.org/media/information/Other%20Topics/Inversions%20FTNW.pdf), I assume the context is a DNA analysis to find out if one has any chromosomal issues that might affect fertility or the health of one’s children.

Most of the time, chromosomal inversions don’t cause any problems. This might be because they’re usually less than 1000 base pairs (see https://pmc.ncbi.nlm.nih.gov/articles/PMC2946949/). Since most human DNA doesn’t code for proteins, an inversion of only a few hundred base pairs might not affect protein coding at all. At the same time, other functions have been found for some of that non-coding DNA, and I wonder what effects inversions would have on other functions (see https://www.quantamagazine.org/the-complex-truth-about-junk-dna-20210901/). Sections of DNA with inversions are a lot less likely to recombine with non-inverted analogous chromosomes during meiosis, so there’s more tendency for genes in or near the inversion to be inherited together. This is also part of how sex chromosomes work: inversions make the Y chromosome largely unable to recombine with the X chromosome.

It appears that the process that generates some of the inversions in D. subobscura also results in additional copies of some segments of DNA. These extra copies might provide an advantage in tolerating different climate conditions (see https://www.nature.com/articles/srep30715). I’d love to know exactly how the inversions affect fruit fly climate adaption, but that’s a rabbit hole for another day!

Image credit: Martin Cooper (adapted from original collage image to show only the adult fruit fly).

https://commons.wikimedia.org/wiki/File:Drosophila_(Sophophora)_subobscura_(male)_collage.jpg