The Scientist - USA (2022 - Spring)

SPRING 2022 | THE SCIENTIST 55

Similarly, experiments from a few years earlier point to bacteria’s

use of TEs to adapt to acute stress.

Chuong, who says his group’s unpublished work in cattle has

suggested that TEs can be activated by immune responses after

eons of being silenced, says it’s plausible that TEs are a “major

source of variation... that could be selected upon” during times

of extreme stress, especially when that stress is novel and sudden,

such as infection with a deadly pathogen. In such cases, he says, “I

think transposons and their activity are much more likely to pro-

vide an outsized source of variation compared to littler mutations.”

Other circumstantial evidence for rapid, TE-driven adapta-

tion is found in mosquitoes. In the last 60 years or so, Anophe-

les coluzzii mosquitoes have become the scourge of sub-Saharan

Africa and primary vectors of malaria. One of the reasons for this

is that the insect species adapts well to urban environments—

something entomologists hadn’t expected, because their close rel-

atives, A. gambiae, are highly susceptible to pollutants and pes-

ticides that are generally more abundant in densely populated

areas. It turns out that urban A. coluzzii mosquitoes may have

specific TE insertions near genes involved in insecticide resistance

and immunity more generally, according to a preprint posted by

González Pérez and colleagues last April.^9 Similar insertions have

been linked to pesticide tolerance in other mosquito species, so

while the findings haven’t been subjected to formal peer review

and are “very preliminary,” says González Pérez, they point to TEs

as the driver of the mosquitoes’ ecological flexibility.

Lukas Schrader, an evolutionary biologist at the Univer-

sity of Münster in Germany, meanwhile, has been investigat-

ing the role of TEs in invasive species. Similarly to popula-

tions responding to a novel pathogen or other stressor, species

entering new environments may need to evolve quickly to

survive. When the researchers examined the genomes of the

heart node ant Cardiocondyla obscurior, their TEs immedi-

ately stood out. There were 34 areas “where over seventy per-

cent of the genomic region is just encoded by transposable ele-

ments,” Schrader explains.^10 In the rest of the genome, TEs

account for less than 1 percent. Comparing the ant species’ two

lineages, one of which is found only in Latin America while the

other is found around the globe, the team discovered that while

the less invasive ants didn’t lack these “TE islands,” those of

the global ant lineage appeared to be more active, suggesting

transposons’ confinement to certain regions that might help

the species be particularly good at invading novel habitats, he

says. The majority of the ant’s genome “is highly conserved,

and encodes the basic necessities for being an ant, and then

[they] have the super quickly evolving part that’s more specific

towards being an invader.”

Ultimately, Schrader says, although TEs are genomic parasites

in the strictest sense, they’re not all bad. “I think we’re going to

see more and more cases where TEs help explain cases of rapid

adaptive changes.” g

References

1. A.E. van’t Hof et al., “The industrial melanism mutation in British peppered
   moths is a transposable element,” Nature, 534:102–5, 2016.


2. B. McClintock, “The origin and behavior of mutable loci in maize,” PNAS,
   36:344–55, 1950.


3. A. Ullastres et al., “Regulatory regions in natural transposable element
   insertions drive interindividual differences in response to immune challenges
   in Drosophila,” Genome Biol, 22:265, 2021.


4. M.-C. Carpentier et al., “Retrotranspositional landscape of Asian rice revealed
   by 3000 genomes,” Nat Commun, 10:24, 2019.


5. A. Porquier et al., “Retrotransposons as pathogenicity factors of the plant
   pathogenic fungus Botrytis cinerea,” Genome Biol, 22:225, 2021.


6. G.E. Rech et al., “Stress response, behavior, and development are shaped
   by transposable element-induced mutations in Drosophila,” PLOS Genet,
   15:e1007900, 2019.


7. M. Bogaerts-Márquez et al., “Temperature, rainfall and wind variables underlie
   environmental adaptation in natural populations of Drosophila melanogaster,”
   Mol Ecol, 30:938–54, 2021.


8. C. Esnault et al., “Transposable element insertions in fission yeast drive
   adaptation to environmental stress,” Genome Res, 29:85–95, 2019.


9. C. Vargas-Chavez et al., “Uncovering transposable element variants and their
   potential adaptive impact in urban populations of the malaria vector Anopheles
   coluzzii,” bioRxiv, doi:10.1101/2020.11.22.393231, 2021.


10. M. Errbii et al., “Transposable elements and introgression introduce
    genetic variation in the invasive ant Cardiocondyla obscurior,” Mol Ecol,
    30:6211–28, 2021.

© ISTOCK.COM, INDIANOCEANIMAGERY

I think we’re going to see more and more

cases where TEs help explain cases

of rapid adaptive changes.

—Lukas Schrader, University of Münster