“Evolution is driven by constant tugs-of-war”

A few tiny seed beetles move around inside a glass jar in the lab. A number of deceased members of the same species rest in peace among the eggs they have recently laid on the bottom of the jar, but some individuals are still in their prime. They in fact belong to a population that can live for an average age of 57 days, equivalent to 160 human years.

“These seed beetles of the species Acanthoscelides obtectus live twice as long as normal, are much larger, and age much more slowly. In only 400 generations, we have almost created a new species,” says Göran Arnqvist, professor of animal ecology at the Department of Ecology and Genetics.

This experiment at the Evolutionary Biology Centre started back in 1986, and exhibits major differences in evolution compared to other beetle populations in the lab. All the populations are kept in the same protected environment free of predators, parasites and diseases. But their living conditions differ in one crucial way: the long-lived seed beetles are prevented from reproducing until they have lived for ten days.

“All female beetles produce eggs from the very first day of their lives which means they can be fertilised from day one. But in this seed beetle experiment, both sexes were forced to stay alive until day ten in order to make any genetic contribution to the next generation at all,” Arnqvist says.

Metabolism very important

These seed beetles also enjoy fixed routines around food, ambient temperature and humidity, which contribute to them ageing slowly and living longer. When genetic influences are propagated in this way, researchers can see how the insects change over time, even after only 10 to 20 generations. It’s become clear how important metabolism is for a long life.

“There, we can compare this to other species in nature, including mammals. If you have a fast metabolism then you don’t live long. Quite simply, it’s more advantageous for an individual to have a slower metabolism for a longer lifespan. In addition, males have a faster metabolism.

One problem with a metabolism that is fast is that it forms free radicals: a type of cellular component that is harmful to the cell and can lead to mutations, for example. But are these findings transferable to other animals, such as humans? Can they in fact provide answers to how we can manage our own metabolism and increase our lifespan?

“I’m not a medical doctor, but I don’t know of any data supports, for example, dietary supplements to combat free radicals having any impact on our longevity,” Arnqvist says. “It’s best to stick to already well-known lifestyle factors that can help to slow ageing, such as avoiding negative stress, exercising, eating a balanced diet and not drinking too much alcohol”.

‘Dark matter’ in the genome

One thing that his research group is now seeking to find out is how the so-called non-coding DNA interacts with other elements that encode for proteins in the genome. In the seed beetles, the proportion of DNA that code for proteins in the genome is only around 30 per cent. What the remaining 70 per cent do is largely unknown.

“In humans, a large portion of the genome consists of DNA that do not encode for proteins. This portion is sometimes referred to as ‘dark matter’, and we know very little about what it does. But some of it has to do with how genes are expressed,” Arnqvist says.

His interest in biology came early in his life. During his childhood, he was often out in the woods picking mushrooms and berries with his parents. At the age of twelve he joined Nature and Youth Sweden (Fältbiologerna), which made a strong impression on him and deepened his interest in animals and nature. After completing the science programme in upper secondary school, Göran Arnqvist studied at Umeå University where he defended his PhD in animal ecology in 1992.

After that, it was off to the United States for a number of postdoc fellowships, the longest being for three years in Albuquerque, New Mexico. In 1996, he returned to Sweden and ended up in 2002 in Uppsala, where he was offered a senior lectureship.

“At Uppsala University, we are very good at evolutionary biology; in fact we’re among the top ten universities in the world in this field. I’ve had many collaborations with groups of researchers from all over the world over the years. Right now I’m collaborating mainly with researchers in Serbia, England, Canada, Austria, Germany and France.”

Big data sets require more computing power

Uppsala University’s strengths include its work with multi-year model systems, which includes beetle and zebra fish model systems. To analyse the big data sets generated, you need special methods and high-performance computer systems, which are located in nearby SciLifeLab and Uppmax.

“These infrastructures are a fantastic resource for us. As we get more and more efficient methods for sequencing DNA, data volumes grow exponentially and thus also the computing power we need. Our needs are great, but so far we have had the time slots we need for this.”

One area he has been researching for a long time is evolutionary conflicts between males and females. In 2019, his group published an article in the journal Nature Ecology & Evolution on how different gene variants are maintained in populations in cases where the sexes benefit from different gene variants. At the same time, evolutionary conflicts can lead to a balance between the sexes in genes that control metabolism and reproduction. The result is a genetic diversity that has higher odds of withstanding diseases and environmental changes, for example.

These conclusions are in line with Göran Arnqvist’s previous studies. In his 2005 book Sexual Conflict, he described how sexual selection is continuously pulling their shared genome in opposite directions. Such conflicts contribute to the evolution of a great variety of those traits that distinguish the sexes and thus contribute to the diversification of lineages.

Evolutionary tug-of-war for good and ill

But at times, evolution expresses itself in extreme ways, as demonstrated by a study published by his research group in Current Biology in 2012. In the seed beetle species Callosobruchus maculatus, the male’s copulatory organ is covered in spines. The longer the spines, the greater the individual’s reproductive success and the more viable their offspring. But these spines also cause significant injury to the female’s reproductive tract.

According to Göran Arnqvist, there is an explanation as to why evolution goes to such extremes.

“If sexual selection is strong enough and advantageous for one sex, it can lead to the evolution of traits that are harmful to the other sex. In this system, however, females have developed a series of adaptations that allow them to cope quite well. Such evolutionary tugs-of-war between the sexes can also lead to maintaining diversity in gene variants,” Arnqvist says.

One of the seed beetles, the most enthusiastic climber of them, has been allowed to come out of the glass jar. Arnqvist places it in a Petri dish under a microscope. The seed beetle continues to crawl around for a while but then stops, and starts to carefully clean its mouth parts.

“It’s most probably an older female, you can see that she has laid all her eggs,” he says.

What are you looking for now in your research?

“I want to understand what specific genetic changes in the genome are responsible for a long life span. But I also want to understand how the genome creates phenotypes, meaning the traits we can see in individual organisms. In many ways this is a formidable challenge for us biologists, because it’s so incredibly complex,” Arnqvist says and adds:

“Evolution – it’s such an enormous creative force!”

Anneli Björkman