Hybrid ants rapidly evolve to remove harmful genes • Earth.com
Despite the fact that there are many mechanisms that prevent interbreeding in nature between two different species, hybridization is a widespread phenomenon that has shaped the genomes of many today. species, including humans. When the genomes of two different species are combined through successful breeding, this provides a source of genetic novelties that can be crucial in helping populations adapt to changing environments. Understanding the evolution of hybrid genomes is therefore important because it can shed light on the formation of species barriers, the costs and benefits of hybridization, and the function of genes and their interactions.
Researchers at university of Helsinki knew that two species of ants, Formica aquilonia and F. polyctena have multiplied and formed hybrid populations in several different locations in Finland. The researchers took advantage of these known hybrid populations to measure how fast and predictable genome evolution is in nature after hybridization. In this case, predictability concerns the genetic outcome after hybridization and the question of whether the genetic outcomes would be similar if the same hybridization could be done again.
The researchers collected 39 ants from three different hybrid populations in the forests of southern Finland near the Tvärminne zoological station. They then generated whole-genome DNA sequences from these individuals and compared them to the genomes of 10 individual ants from both parent species found in areas where the hybrids and parent species overlap. For this, they collaborated with researchers from Scotland and Portugal and used the supercomputers of the IT Center of Finland (CSC). In total, the researchers analyzed about 1.6 million single nucleotide polymorphisms at locations in the ant genomes.
The results were published in the journal PLOS Biologyshowed that for three different hybrid populations, hybridization between the two ant species did not occur until about 125 years ago, equivalent to 50 ant generations. After hybridization, three separate hybrid populations evolved independently toward the same genetic outcome. This means that today the genomes of ants in hybrid populations are remarkably similar in genetic makeup, even though they started out different at the time of hybridization.
To explain this unexpected finding, the researchers tested for evidence of gene flow between hybrid populations and between hybrids and parent species. They found no evidence of gene flow and concluded that other mechanisms must be involved to explain this rather rapid evolution of the three hybrid populations toward similar genomes. They suggest that natural selection against deleterious genes in hybridizing species with the smallest effective population size (and presumably a higher load of deleterious alleles) could explain how hybrid populations became genetically similar in such a short time.
When Pierre Nouhaud, a researcher at the University of Helsinki’s Faculty of Bio and Environmental Sciences, answered whether these results were a small step or a great leap forward, he replied: “A little bit of both! Finnish wood ants make it possible to observe several very recent hybridization events, and the predictability we found is remarkably high despite this recency, which is quite new. Meanwhile, our study also confirms previous results from a few species, including humans, suggesting that the patterns we see in wood ants are quite general.
“On the evolutionary time scale, we are dealing with recent events, less than 50 ant generations, which had very little time to leave footprints in the DNA sequences,” adds Nouhaud. “This means that it can be difficult to distinguish between competing hypotheses. In our study, we ran computer simulations based on different evolutionary scenarios to account for this uncertainty and ensure that the results are robust.
The researchers emphasize that hybrid genomes provide powerful insights into evolution because they are exposed to strong and often opposing selective forces. In this way, evolution has shaped the hybrid genomes in a predictable way so that the genomes of different hybrid populations are now similar. This indicates that the selective pressures were similar in each hybrid population and this led to the removal of harmful genes from the genomes.
“Since hybridization is also common in many species other than ants, our results can help to understand its consequences more generally,” says associate professor Jonna Kulmuni from the University of Helsinki’s Faculty of Bio and Environmental Sciences. “In the long term, our work would help to better understand the effects of hybridization in nature and assess whether it could help species cope with changing environments,” he says.
Next, the ant research team will monitor the genetic makeup of the hybrid populations over several years to find evidence of adaptation and test whether hybrids can combine the temperature ranges of both species, which might help forest ants survive global warming. According to Nouhaud, this can be quite important because forest ants are key species in boreal forests: they provide food for many species, promote nutrient cycling and hunt many other insects. Without them, Finnish forests would certainly look completely different.
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Factor: Alison Bosman, Earth.com Staff writer
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