This interesting paper was published online some weeks ago:
Nussle S, Bornand CH, Wedekind C (2009) Fisheries-induced selection on an Alpine whitefish: quantifying genetic and environmental effects on individual growth rates. Evolutionary Applications (in press)
There was a closed, steadily and intensively fished population, and growth of nearly all individuals in the population could be analysed based on scale samples collected over 25 years. The authors estimated selection differentials, and found consistent changes in growth but no changes in maturation schedule or energy allocation to reproduction. The conclusion was that 1/3 of the change seen in growth could be an evolutionary response to fishing, the rest environmental.
After reading the paper, I started to wonder this: if 33% of the change in growth was an evolutionary response to fishing, but no shifts were seen in maturation, how common this kind of response might actually be in exploited fish populations? Perhaps studies investigating phenotypic impacts of fishing should start to pay much more attention on shifts in growth, rather than only those in maturation.
2 Comments
Hmmm…
The logic in the paper was that heritability of growth may be around 0.3 (they did not estimate heritability for the study population), so therefore 33% of the change is an evolutionary response. I could not find any part of the analysis that took the environment into account (there seemed to be no environmental data whatsoever- please correct me if I’ve missed it).
Anyway, just wondering what your viewpoint is about how likely this is to be an evolutionary response. Or would you still put this in the speculation department?
Yes, the logic was that 33% might be evolutionary response so rest must be environmental, but there was no analyses to investigate which environmental mechanisms were behind the changes. I would say that from fisheries management point of view assumed evolutionary change is of minor importance as environmental change is of much larger scale, and therefore investigating mechanisms behind those should be of larger importance. But generally the study does not provide evidence on evolution, because selection does not automatically lead to it, and it also remained undetected which other factors affected growth in the population.
But looking from the point of view of studies on fisheries induced evolution, one of the major assumptions has been that fishing leads to evolution of maturation reaction norms, but changes in growth are predominantly environmental. The whitefish study suggests that the case might be other way round.