Natural pastures are among the most species-rich habitat types in Sweden and Europe, with a long history of human management in Sweden. Despite their importance, natural pastures are one of the least protected habitat types in Europe, and changes in land use in the form of intensified agriculture and overgrown land have led to a sharp decline over the past century. This means that species requiring specific habitats are being pushed out, while species less dependent on certain environments take over, resulting in decreased biodiversity.
For biodiversity to be preserved in the long term, it is crucial not only to conserve the number of species but also the genetic variation within species. Reduced genetic variation can lead to poorer adaptability and inbreeding within a species. To better understand how changes in land use affect genetic variation in different species, Zachary J. Nolen, BECC member and researcher at Lund University, investigated this in his doctoral thesis in biology. His research examines whether the loss of grasslands in southern Sweden has led to reduced genetic diversity in butterflies living in these environments.
Increased Inbreeding in the Mazarine Blue
The common blue, the silver-studded blue, and the mazarine blue are three relatively common Swedish grassland butterflies that were the focus of Zachary Nolen’s studies. While these species may seem quite similar on the surface, they differ in their habitat needs. The common blue can live in a wider range of environments, while the silver-studded blue and the mazarine blue have more specific requirements. This turned out to have major consequences for the species’ genetic diversity:
– When I compared different butterfly populations in southern Sweden, I found that species requiring more specialized habitats also had populations that did not come into contact with one another through dispersal. This meant that the populations of the specialised species differed more genetically from one another—and at the same time had less genetic variation within each population. In the mazarine blue, this led to more inbreeding, which in turn has made harmful mutations more common, reducing their chance of survival.”
To determine whether this inbreeding has been occurring for a long time or is a recent phenomenon, comparisons were made between contemporary samples and historical specimens from museum collections of common blue, silver-studded blue, and mazarine blue. This comparison showed that species thriving in a wider range of environments have maintained contact between populations and retained genetic diversity. For the mazarine blue, which needs more specific habitats, numbers have decreased sharply over the past century, and the inbreeding appears to have arisen in recent decades.
Important for Decision-making on Nature Restoration
Although the threats to the mazarine blue seem numerous, with inbreeding being a significant danger, it is not currently listed on Sweden’s Red List. And it is probably not alone in being affected by inbreeding, according to Zachary:
– My studies show that inbreeding may be common among other grassland insect species as well. We can use genetic data to find out which species are affected and identify groups that may be vulnerable. For these butterflies and other insects to survive in the long term, we need to restore connectivity between their habitats, helping them to disperse between populations again.
The results of Zachary Nolen’s research can be used as a basis for decision-makers, including in determining how Sweden will meet the requirements of the EU’s Nature Restoration Law. In this way, the parts of Sweden where inbreeding is most prevalent can serve as indicators of the areas most in need of habitat restoration.
Further reading
Zachary Nolen's Doctoral Thesis:
