Researchers discover rapid and predictable genome evolution in three hybrid ant populations

Credit: Lotta Sundström

In the last decade, the DNA sequencing revolution has revealed that mating between two different species—the once rare hybridization—is actually common throughout the tree of life. This came as a surprise – crossbreeding was mostly considered harmful, as the offspring were not always viable and could be sterile like mules. However, many studies have shown that hybridization can have beneficial results and help populations adapt to new environments.

In humans, for example, Tibetan populations were adapted to the low oxygen concentrations found at high altitudes 50,000 years ago thanks to genetic material obtained through hybridization between modern and archaic humans, now extinct populations (such as Neanderthals). This year, the Nobel Prize in Physiology or Medicine was awarded to Svante Pääbo (Max Planck Institute) for his work on human evolution, including gene exchange between modern and archaic humans.

Understanding the consequences of hybridization, that is, producing hybrid offspring by mating between two different species, is important because it is a common phenomenon in nature. By transferring genetic material between species, it can also help populations adapt to new challenging environments such as a warming climate. One of the key aspects of hybridization is predictability, which is also an important research question: If we could reproduce the same hybridization event several times, how often would we get similar results?

Populations evolve both rapidly and predictably due to natural selection.

Researchers at the University of Helsinki took advantage of different hybrid tree ant populations identified in Southern Finland to examine whether hybridization was predictable. They found that after multiple hybridization events between the two tree ant species, different hybrid populations evolved independently in the same direction. Today they are quite similar to each other in terms of genetic composition, suggesting that the outcome of hybridization is predictable. The researchers also determined that hybridization occurred less than 50 ant generations ago, about 125 years ago, making it a case of fairly rapid evolution in the wild.

“Since hybridization is also common in many other species other than ants, our results may help us understand the implications of it more generally. In the long run, our study will help us better understand the impact of hybridization in the wild and evaluate whether it will help species cope with changing environments,” he says. Associate Professor Jonna Kulmuni from the Faculty of Biology and Environmental Sciences, University of Helsinki. She has been leading ant research for 15 years.

A small step in knowledge or a giant leap forward?

“A bit of both. Finnish wood ants provide an opportunity to observe many, very recent hybridization events, and despite this innovation, the amount of predictability we found is remarkably high,” explains faculty researcher Pierre Nouhaud. Biological and Environmental Sciences, University of Helsinki.

“In the meantime, our study also confirms previous results from a handful of species, including humans, suggesting that the patterns we see in tree ants are fairly general.”

DNA contains information about the evolutionary history of populations.

For this study, the research group collected hybrid individuals in Finnish forests close to the Tvärminne Zoological Station in Southern Finland. DNA accumulates mutations as it is passed from parents to offspring, so it contains information about the evolutionary history of populations.

Accessing this background required the researchers to reconstruct the first reference genome for red wood ants. The researchers then sequenced and analyzed the hybrid genomes using supercomputers from the Finnish IT science center (CSC). Some analyzes were done in collaboration with scientists from Scotland and Portugal.

Reconstructing past evolutionary histories using computer simulations

“We are dealing with recent events on an evolutionary time scale with fewer than 50 ant generations that have had little time to leave footprints in DNA sequences. This means that it can be difficult to distinguish between competing hypotheses. We performed computer simulations in our study. Nouhaud took this uncertainty into account. “It considers different evolutionary scenarios to add value and ensure our results are robust.”

The article was published in the journal PLOS Biology.

The ant research group will then monitor the genetic composition of hybrid populations over several years to find evidence for adaptation and test whether the hybrids can combine the temperature ranges of both species, which could help tree ants cope with a warming climate. According to Nouhaud, this can be quite important because tree ants are a key species of boreal forest: they provide food for many species, contribute to the nutrient cycle, prey on many other insects. Without them, Finnish forests would certainly look quite different.

More information:
Pierre Nouhaud et al., Rapid and predictable genome evolution in three hybrid ant populations, PLOS Biology (2022). DOI: 10.1371/journal.pbio.3001914

Provided by the University of Helsinki

Quotation: Researchers report rapid and predictable genome evolution in three hybrid ant populations (2022, 21 Dec) retrieved from on Dec. 21, 2022 they discovered.

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