The researchers found that females who did survive to motherhood were likely to be more 'heterozygous'. This is where an individual possesses a higher level of genetic variation and is associated with higher fitness in many species. Whilst these females are more likely to survive and breed, their pups will only have the same advantage if they too are heterozygous. However, the heterozygous characteristic is not inherited; it depends on which male the female mates with and so arises mostly through chance. This means that many seals are born who are not heterozygous and are therefore less able to cope with the changing environment.
Co-author, Dr Joe Hoffman from Bielefeld University explains:
"We found that, over the last two decades, the proportion of breeding females that are highly heterozygous has increased, as these individuals are more likely to survive the changing conditions. Strong selection by the environment can drive rapid evolution. However, in this case the seals do not appear to be evolving because surviving females do not pass their high heterozygosity on to their offspring.
"Therefore, with each new generation, the process of selection has to start all over again, with only those individuals that happen to be born more heterozygous having a good chance of survival. As the climate continues to change, many fur seal pups are not surviving to adulthood and the population is declining."
Climate change is already altering environmental pressures on many species, and scientists do not yet know how populations will cope with these new environments. This study shows that natural selection on a fur seal population has altered as a result of climate change and that the seals have been unable to evolve in response.
Impacts on one species can affect a whole ecosystem.
|Contact: Paul Seagrove|
British Antarctic Survey