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The Alcon blue butterfly is distributed very patchily throughout Denmark and the rest of Europe. In the past century the populations of the Alcon blue have become more fragmented, probably due to changes in agricultural land use, and many populations have become extinct. For example, the Alcon blue used to be found all across the Jutland peninsula in Denmark, but is now mostly confined to the North and West coasts and the islands of Læsø, Fanø and Rømø, with a few small remnant populations in the interior (Stoltze 1998). The map below shows the current distribution of the Alcon blue in Denmark. |
| Alcon blue butterflies are not strong fliers, so that there is very little dispersion between populations.
This means that there is likely to be very little exchange of genes (gene flow) between the different populations. This can be important for the butterflies in several ways. Gene flow is one way of maintaining the genetic diversity within the populations of any species. Without gene flow, populations tend to lose genetic diversity, which means they can adapt less quickly to environmental changes, and can cope less well with a wide range of parasites and diseases. Low gene flow also means that each population can easily evolve to be different from the other populations, so that there is greater potential for the evolution of new races and even species. |  |
| Hence it is important to know the genetic structure of the populations of the Alcon blue both for the conservation of this rare species and to understand how it has evolved and how it is continuing to evolve. An unusual feature of the Alcon blue is its use of different primary host ants in different parts of its range. In order to understand how this feature has evolved, and to find out whether what we call the Alcon blue is really several cryptic species that use different host ants, it is necessary to look at the genetics of Alcon blue populations. |
 | The genetics of populations can be examined in several different ways. The first approach that was taken at the University of Aarhus by Rebekka Gadeberg and Koos Boomsma was to examine different allozyme alleles from several populations.
The picture to the left shows how the frequency of several different allozyme alleles in Alcon blue populations changes across the Jutland peninsula. The colours show the proportion of individuals in a population with that allele from purple (none) to red (all individuals). This seems to show that the populations on the west coast and interior of Jutland are rather different genetically from those in the North and far south of Jutland. The study confirmed that gene flow between populations is indeed low for the Alcon blue. The study also found more homozygotes (individuals having two copies of the same allele; one from their father and one from their mother) in several populations than would be predicted if there were random mating. There are several reasons that this could come about, but one possibility is that there really are two different subspecies or cryptic species of the Alcon blue in Denmark, possibly using two different host ants. |
| Research is currently underway at the University of Aarhus to develop DNA markers to look at the population genetics of the Alcon blue butterfly. These are potentially more powerful than allozymes, and should allow us to look at the genetics of the Alcon blue in more detail. We are also examining the ecology of the populations in Denmark in more detail, particularly which host ants they are using. This will allow us to link host specificity to genetic make-up of the different populations and to determine whether we have host races, subspecies or cryptic species. |
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