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The Adaptive Response of Salmon to Global Warming
From Patrick J. Michaels and Craig D. Idso of Cato.
"…the extinction horrors of climate change may be a “fish story”
Perhaps the myth-iest chestnut in the scary global warming meme is
that our dear earth’s panoply of species is adapted only to the current
climatic regime, and changing that regime means certain death, i.e.
extinction.
That’s an easy, simplistic sell, but it denies some of the subtleties
of organismal biology. Four decades ago, scientists realized that
evolution has preserved a variety of responses to environmental change.
It turns out that our enzymes, the basic material that catalyze life as
we know it, actually change their shape as climate changes. Whether this
is because we have so much information stored in our DNA that has
survived countless generations and a variety of climates, or whether the
response is simply built into the enzymes is unknown, but it is
ubiquitous. It even has a catchy name: “Phenotypic Plasticity.”
Before your eyes glaze over, a little explanation is in order.
Each one of us has a genotype, which is our DNA, and each of us has
an expression of that, our “phenotype.” Obviously not all genes express
themselves—if they did, our physiological destiny would be eminently
predictable, but it is not. Instead, we all carry strands of DNA that
could theoretically cause major disease that generally do not express
(or “penetrate” in the lingo of biology), and we also have DNA that
could probably defeat many of the aging processes, that similarly do not
express.
Instead, organisms display “plastic” responses when their environment
changes. And so, species-related concerns over potential CO2-induced
global warming may be dramatically overblown. And, though they don’t get
much publicity, scientists are continually documenting our amazing
adaptability.
Consider one of our most important marine sources of food: the salmon
family. What happens when the oceans warm? In the words of Anttila et al.
(2014), “a population has the options of either [1] migrating to more
suitable environments (if any are available and accessible), [2]
acclimating to the new temperature by exploiting its phenotypic
plasticity, or [3] adapting through natural selection.” Recognizing
these options, Anttila et al. set out to investigate which of these paths Atlantic salmon (Salmo salar) might pursue in response to future increases in temperature.
To achieve their objective, the team of seven researchers gathered
specimens of two wild Atlantic salmon populations from the northern
(coolest) and southern (warmest) extremes of their European
distribution, which range spans a distance of over 3,000 km. Eggs from
both groups were hatched in a salmon nursery and thereafter the
juveniles were acclimated for three months at temperatures of either
12°C or 20°C. The salmon were then evaluated and tested for cardiac
performance, as “cardiac function has been observed to limit the
tolerance to high temperatures.” This was accomplished by subjecting the
salmon to temperatures well above their acclimated state, whereupon
their cardiac performance was evaluated.
In describing their findings, the seven scientists report the salmon
populations “differed very little in their acute cardiac response to
temperature, but instead showed considerable cardiac plasticity in
response to thermal acclimation that surprisingly was largely
independent of the latitudinal and climatic origin of the populations.”
In other words, regardless of the acclimation temperature, 12°C or 20°C,
both salmon populations exhibited a similar stress response as
temperatures increased. They also found that acclimation to 20°C
consistently raised the temperature at which various measures of acute
cardiac stress were observed. For example, they write “although cardiac
collapse starts at 21°C-23°C with a maximum heart rate of ~150 beats per
minute (bpm) for 12°C-acclimated fish, acclimation to 20°C considerably
raises this temperature (27.5°C) and maximum heart rate (~200 bpm).”
The results of the Anttila et al.’s analysis indicate that
the response of Atlantic salmon to temperature stress–-as evaluated by
cardiac performance-–is “largely dependent on individual thermal history
and largely independent of local adaptation,” as offspring of both
populations displayed phenotypic plasticity in adapting to the two
acclimation temperatures. Such findings are encouraging, as the
researchers state they “emphasize that acclimation remains a feasible
possibility for survival in a warmer future, with physiological
plasticity replacing the immediate need for local adaptation,” adding
that “this plasticity might aid northern Atlantic salmon populations to
compensate for a warmer future.”
Although this response represents only one of the three options by
which to face the challenge of potential future global warming, it
appears to be more than sufficient to overcome the worst possible
scenarios. In addition, Anttila et al. optimistically add
“natural selection has the potential to improve thermal tolerance in
Atlantic salmon beyond the demonstrated benefits of high thermal
plasticity,” particularly through transgenerational changes in
temperature tolerance in which the heritability of thermal tolerance is
passed down from parents to offspring.
All in all, therefore, the future looks bright for Atlantic salmon!
Reference: Anttila, K., Couturier, C.S., Overli, O.,
Johnsen, A., Marthinsen, G., Nilsson, G.E. and Farrell, A.P. 2014.
Atlantic salmon show capability for cardiac acclimation to warm
temperatures. Nature Communications 5: 10.1038/ncomms5252."
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