Wednesday, October 19, 2005

Or is it?

If there is one hope for the Antarctic organisms threatened by rising ocean tempertures, its phenotypic plasticity.... the ability to be flexible in response to environmental change.

When we usually think of populations of organisms responding to a change in the environment (rising temperatures, new or better predators, new diseases) we often think in terms of genetic changes. In most populations of animals, there is usually genetic variation for any given trait (phenotype)... for example, some animals will be genetically programmed to have taller necks, or more body fat (better able to withstand lower temperatures), or brighter coloration. If the environment changes, some genetic variants within the population will be favored and produce more offspring, while others will die out or fail to reproduce. The end result is that when the population is viewed as a whole, both the the trait in question and the underlying genetics can be seen to change over time... natural selection and evolution at work.

Phenotypic plasticity is the ability to alter ones traits (neck size, fat layer, coloration, etc.) without undergoing a genetic change. The plant or animal may sprout spines in response to predators, change color to better blend in to the background, or produce more offspring when food is abundant.... without changes in the underlying genes. Whats interesting is that this ability to respond to the environment is genetic. When environmental conditions change rapidly, an organism that can alter its traits will do better than one that takes a gamble on its genes and either lives or dies as a result.

I mentioned in my last post how global warming is like a giant man-made experiment in adaptation... well, one of the ways plants and animals are adapting to the rapid changes in climate is to evolve the ability to adapt. In this weeks Science there is an article on how climate change is causing Great Tits (Parus major) to become more flexible as to when they lay their eggs. Great Tits, like most passerine birds, feed their young on caterpillars. In order to ensure their young will have an ample food supply, they try to time the laying of their eggs so that when the eggs hatch, the number of caterpillars available to feed them will be at its peak. Because the growth rate of caterpillars is directly affected by the climate, if the birds want to get the most caterpillars for their chicks they have to breed earlier in warm years than they do in cold years. With recent changes in climate, the Great Tits have been getting more and more out of sync with the caterpillars they depend on, as the caterpillars now peak two weeks earlier, around when the Tits are laying their eggs - not when they are hatching.

What Nussey et al. have found in their review of 30 years of Dutch bird data is the emergence of a sub-population of Great Tits that has become much more flexible in its response to rising temperature and caterpillar emergence. While the Great Tit population as a whole is in decline, these adaptable birds are managing to hold their own and produce more offspring than their less adaptable peers. Its still early in this 'grand experiment', but the outcome looks like these birds that have evolved flexibility will take over and replace their more 'conservative' bretheren. The next big question is whether these birds can evolve enough flexibility to survive as the pace of climate change increases.