The first big questions with any disease outbreak are 1) how many are going to die? and 2) can immunity develop? If immunity can develop then the impacts of the disease may be less severe.
One way to look at immunity is to sequence immune genes. There is a set of genes (a 'complex' of genes) that are known to be particularly important for immunity in vertebrates - these are called the Major Histocompatability Complex (MHC) genes. The MHC is divided into two main classes, and broadly speaking one class is more involved in the immune response to viruses - the MHC Class I. In Common frogs, this is a single gene, which makes our research reasonably straightforward.
We looked at this MHC Class I gene in set of frog populations with a long history of Ranavirus disease, and a set of populations with no history of disease. By sequencing the gene we were able to show consistent differences in the genetic code between frogs from each population type. The genes in frogs from infected populations were distinct. Frogs from infected populations were also more similar to each other than frogs from uninfected populations.
This finding was most likely the result of selection - frogs with certain immune gene sequences are more likely to survive infection. In a population that is infected, only those with particular immune gene sequences are able to survive, so the frogs in the population end up more similar to each other than they would be in an uninfected population.
This shows us that immunity may be evolving in infected frog populations. The next question is whether the virus is also evolving at a similar rate - and we end up with an arms race between the frog and the virus.
The full paper is available here.
One way to look at immunity is to sequence immune genes. There is a set of genes (a 'complex' of genes) that are known to be particularly important for immunity in vertebrates - these are called the Major Histocompatability Complex (MHC) genes. The MHC is divided into two main classes, and broadly speaking one class is more involved in the immune response to viruses - the MHC Class I. In Common frogs, this is a single gene, which makes our research reasonably straightforward.
We looked at this MHC Class I gene in set of frog populations with a long history of Ranavirus disease, and a set of populations with no history of disease. By sequencing the gene we were able to show consistent differences in the genetic code between frogs from each population type. The genes in frogs from infected populations were distinct. Frogs from infected populations were also more similar to each other than frogs from uninfected populations.
This finding was most likely the result of selection - frogs with certain immune gene sequences are more likely to survive infection. In a population that is infected, only those with particular immune gene sequences are able to survive, so the frogs in the population end up more similar to each other than they would be in an uninfected population.
This shows us that immunity may be evolving in infected frog populations. The next question is whether the virus is also evolving at a similar rate - and we end up with an arms race between the frog and the virus.
The full paper is available here.