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WHEN THINGS CHANGE, CHANGE WITH THEM, OR WALK AWAY!

In 1949, Charles M. Bogert noticed that some organisms do not evolve in response to environmental change simply because, by moving to a different environment, they might avoid the change altogether. Over the years, lack of evolution owing to behavioural avoidance of such environmental change has come to be known as the "Bogert effect".

It is also widely appreciated that in addition to inter-generational change as a response to a changing environment, some organisms show change within their lifetimes, a phenomenon known as phenotypic plasticity. Where such plasticity involves improvement in survival or performance of an organism in a particular environment, following prior exposure to that environment, the response has come to be known as "Beneficial Acclimation".

What is not clear, however, is whether the Bogert effect might eliminate Beneficial Acclimation. At a time when environments are changing quickly and extreme events are increasing in frequency, knowing how organisms might respond to such change, and whether this varies with the mobility of the animal, is of considerable importance.

Now, two researchers from the Centre for Invasion Biology, in a paper recently published in one of Ecology’s highest ranking journals, Ecology Letters, have shown just how this might all play out.

Using the highly mobile, though flightless, adults and more sedentary larvae, of a sub-Antarctic kelp fly, Elrike Marais and Steven Chown have demonstrated that behaviour really does affect the extent of beneficial acclimation. They exploited the custom of virtually identical habitat use (kelp wrack on Marion Island) by fly adults and larvae to ensure that environmental change is similar among the stages.

Left: Trypot Beach at Marion Island. Kelp fly adults and larvae live amongst the stranded kelp wrack seen in the foreground. Right: An adult of the kelp fly, Paractora dreuxi. (Images© Steven Chown (left), Johan Grobbelaar (right)).


They then showed that the adults really do prefer low temperatures and seek them out, whilst the larvae are less fussy. Finally, in an elaborate and carefully designed set of trials, they demonstrated that when denied an opportunity for behavioural avoidance, the adults showed poor performance across a wide range of conditions when previously exposed to temperatures other than those they prefer. By contrast, if the larvae are initially exposed to low temperature they perform best at low temperature, and poorly elsewhere, while high temperature exposures result in the best performances at high temperature. That is, the larvae, that cannot move quickly out of harms way to adjust their physiological performance, or show beneficial acclimation. By contrast, the adults can simply move to where they find their preferred, low temperature conditions.

This study shows, for the first time, that phenotypic plasticity, one of the most significant initial responses to rapid environmental change is highly context sensitive. Moreover, it draws further attention to the importance of understanding the basic biology of organisms, and especially differences among their life stages, before attempting to gauge their sensitivity to change. Mobile adults are very different animals to sedentary larvae, a fact that models of animal responses to climate change can ill afford to ignore.

The full text of this work can be found at: Ecology Letters http://www3.interscience.wiley.com/journal/120749515/abstract (Digital Objective Identifier (DOI): 10.1111/j.1461-0248.2008.01213.x)

Marais, E. & Chown, S.L. 2008. Beneficial acclimation and the Bogert effect. Ecology Letters 11, 1027-1036.

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