Darryl McLennan, John D. Armstrong, David C. Stewart, Simon Mckelvey, Winnie Boner, Pat Monaghan and Neil B. Metcalfe
Much of the study of molecular biology inevitably focuses on active genes. However, chromosomes also consist of ‘non-gene’ regions that play an essential role in keeping the cells functioning. These include the telomeres, which form caps at the ends of chromosomes in almost all multicellular species. Cell division is slightly flawed, in that chromosomes are not able to fully replicate each time that a cell divides. As a result, chromosomes shorten in length with each round of cell division. Because telomeres cap the ends of chromosomes, it is the telomeres that experience this loss, thus protecting the central part of the chromosome that contains the active genes.
However, after a number of rounds of cell division, the telomeres may shorten to such an extent that the genes may become vulnerable to this loss of parts of chromosomes. At this point, that cell may shut down, as a way of protecting the individual as a whole. For this reason, biologists generally consider telomere length to be a good indicator of how healthy a cell is (as well as how healthy the individual is). In support of this, studies across a number of different species have shown that telomere length can be used to predict lifespan.
In our study of a wild migratory Atlantic salmon population, we predicted that a shorter telomere length at the time of entering the sea would be associated with a reduced likelihood of surviving the marine stage of the life cycle. However, contrary to expectations, juvenile salmon with the shortest telomeres at the start of their migration had the greatest probability of returning from it. We suggest that this surprising association may arise from a trade-off. Juvenile salmon spend their early years in fresh water and must therefore undergo many physiological and biochemical changes in preparation for life at sea. Therefore, if these juvenile salmon are investing a large proportion of their energy reserves in this preparation for salt-water life, they may be investing less energy into the maintenance of their telomeres.
Image caption: ecologist at work.