Wednesday, August 09, 2006

Displaced Finch Characteristics May Never Find Their Way Back!

` Whatever in the hell I was thinking when I titled this....
` Long ago, I'd read Beak of the Finch by John Weiner, a book that detailed Rosemary and Peter Grant's studies of Galapagos finch evolution! It's good to know that they're still at it....

Published online: 13 July 2006; | doi:10.1038/news060710-11
Evolution caught in the act
Smaller beaks in Galápagos finches make finding food easier.

` Here's basically what came from the hand of Heidi Ledford:

` Peter and Rosemary Grant from Princeton University have been going at this since 1973, and they have just found but one more example that Galápagos finch beaks change in response to small acts of evolution.
` In Science, they have recently published a paper about the medium ground finch, Geospiza fortis, and the large ground finch, Geospiza magnirostris as they struggle to survive on Daphne Major (a barren rock just north of Santa Cruz).
` The medium ground finch manages to survive on small seeds, although the ones with big enough beaks are able to eat the larger seeds of Tribulus cistoides. These seeds are shaped like an orange wedge and have two long spines sticking out the back - the medium finches with big beaks are able to twist off the ends.
` Unfortunately for them, in 1982, a few large ground finches had flown onto Daphne Major and established a colony! They were already better adapted for eating the large seeds, and so they mainly subsisted on those types of things. It hasn't been until recently that there have been enough of them to deprive the medium finches (with sufficient beakage) of their extra food source.
` A drought in 2003 and 2004 has brought on an even more dramatic struggle, causing many of both species to die of starvation. Interestingly, the medium finches with the smallest beaks could most easily pick up the tinier seeds compared with finches that had larger beaks. Because the big seeds were already being eaten by the large finches, the finches that found it easier to grab up mere crumbs had an advantage.
` In 2004 and 2005, the average finch that was captured and measured by the Grants had a smaller beak than the average of ones living the year before. "Small-beaked birds survived better than the large-beaked birds, to a strong extent, during the drought," says Peter Grant.
` Inevitably, only the smaller-beaked birds were around to pass on their genes to the next generation. Also, the Grants observed that the medium ground finches were only half as likely to eat the larger seeds as they had been before.
` When two similar species sharing the same habitat diverge, this is called character displacement, and helps each species survive as they compete for resources. The reason this study is so newsworthy is that it is probably the most thorough observation of character displacement to date.
` "People have inferred character displacement," says Jeffrey Podos, an associate professor of biology at the University of Massachusetts, Amherst. "But to actually see it as it happens is quite a triumph. To be in the right place at the right time to observe something like this is really just incredible."
` The fact that the island is so small and sparsely populated by just a few plants and animals is what allows Peter and Rosemary to study and measure wildlife like this.

` In the meantime, it looks like the large ground finches have an established-enough population that they will continue shrinking the beak size of the medium ground finches.
` Good for them for surviving.
` Of course, one can also observe other signs of short-term evolution in other species on the island, including plants. Ever since I read that book, I've been wanting to get myself up there and check out the simplified ecosystem.

` ...Offhandedly, I also went ahead and found some more about the Grants' finch studies in the journal Science:

Darwin's Avian Muses Continue to Evolve

Carl Zimmer

On page 707 of this issue, two biologists review 30 years of evolution among Darwin's finches in the Galápagos. They report that climate change has been a powerful influence guiding the evolution of the finches--and its effects turn out to be surprisingly complex. In addition, the two species on the volcanic island of Daphne Major can and sometimes do interbreed, and their hybrids--far from being mulelike reproductive dead ends--are a source of fresh genetic variability.

` And what is this article he refers to? It's by the Grants - they say;
` Evolution can be predicted in the short term from a knowledge of selection and inheritance. However, in the long term evolution is unpredictable because environments, which determine the directions and magnitudes of selection coefficients, fluctuate unpredictably.
` These two features of evolution, the predictable and unpredictable, are demonstrated in a study of two populations of Darwin's finches on the Galápagos island of Daphne Major. From 1972 to 2001, Geospiza fortis (medium ground finch) and Geospiza scandens (cactus finch) changed several times in body size and two beak traits. Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual.
` Hybridization occurred repeatedly though rarely, resulting in elevated phenotypic variances in G. scandens and a change in beak shape. The phenotypic states of both species at the end of the 30-year study could not have been predicted at the beginning. Continuous, long-term studies are needed to detect and interpret rare but important events and nonuniform evolutionary change.
` Well, that's probably about all that most people can take on this subject (which is kinda sad, really), so I'd better get going.


Galtron said...

'Displaced Finch Characteristics May Never Find Their Way Back?' are you implying that the change might be permanent?

NO! The poor mutants! Doomed to evolve! The Daphne Finches might never find their way back to being normal! They may even *gulp!* become a distinct species from the other medium beaked finches someday!!!!
The poor things.......

S E E Quine said...

` 'Tis a tragedy! Remember that time before the invention of language, when everyone slept in trees? Now life is full of pollution and giant corporations and bad movies!
` For the old days, chum! For the old days!

Galtron said...

Oh, yes, for the old days when we were killed in storms and eaten by sabertooth tigers and starved in droughts and died from smallpox a lot!

S E E Quine said...

` I miss smallpox. *snf*