Haast's Eagle - a snapshot of rapid speciation

[Monad]

Using genetic analysis scientists have proved that the giant eagle that used to prey on moa's in New Zealand was not descended from the larger wedge tail, as had been assumed, but from the much smaller little eagle. Further more it was so close genetically that their common ancestor would have been less than a million years ago meaning that Haast's eagle underwent massive evolutionary change to adapt to the new predation opportunities in the NZ ecosystem in a very short space of time.

http://news.bbc.co.uk/1/hi/sci/tech/4138147.stm

[braces_for_impact]

Dr Bunce said: "Even more striking was how closely related genetically the two species were. We estimate that their common ancestor lived less than a million years ago.

"It means that an eagle arrived in New Zealand and increased in weight by 10 to 15 times over this period, which is very fast in evolutionary terms. Such rapid size change is unprecedented in birds and animals."

That does seem awfully fast. How does this relate to what we know about the speed of of evolution as related to size change in other animals?

[RBH]

That does seem awfully fast. How does this relate to what we know about the speed of of evolution as related to size change in other animals?It's a million or so generations, which ain't an eyeblink. And pure size is a developmental variable, and is likely under the control of regulatory genes that govern gene expression. For example, genes that control growth hormone secretion are very influential in determing phenotypic body size.

And one more time, evolution is not committed to single rate "constant speedism". Depending on several circumstances (pop variability, strength of selection, complexity of genetic control of a feature), morphological changes can occur at rates varying by many orders of magnitude. Measured rates range from a few tenths of a darwin in some very stable fossil lineages to hundreds of thousands of darwins in radiative evolution in cichlids. See here (http://hcgs.unh.edu/Staff/streelman/pdfs/Streelman&Danley.2003.pdf)for a review of some of the variables involved in an instance of rapid adaptive radiation.

RBH

[MrDarwin]

One of my own favorite examples is the Hawaiian Silversword Alliance (http://www.botany.hawaii.edu/faculty/carr/silversword.htm). This group has radiated into 3 genera and a few dozen species, many of them radically different from each other, apparently from a single colonization event about 5 million years ago. What's especially interesting is that, despite their morphological disparity, they have all retained the ability to interbreed and the hybrids are often fertile. In fact they can even cross with their nearest relatives on the North American mainland, which look nothing like them.

[Flint]

A million years should be plenty of time provided (1) like dogs, the potential for such a size range was already present in the genome; and (2) there was a reasonably strong selection pressure for size. The time span is probably long enough to make the probability of a suitable mutation less than prohibitive as well (bearing in mind that ANY helpful mutation is fine, and we're not only considering the probability of a size-related mutation. A size change just happens to be what we got. Had things gone differently, we might be marveling over how fast this eagle lost the ability to fly, gained the ability to swim, etc.)

[travc]

Size is a trait that is typically highly variable, with a good bit of that variability being heritable.

One thing to remember is that phenotypic traits are not genetic traits. Phenotypic traits are often the product of many different genetic products and are often highly influenced by the environment. Additonally, small genetic changes can and do often lead to huge phenotypic changes through changing development (developmental gain is the term I favor).

So an eagle species being introduced into an environment which has abundant prey leading to a dramatically increased size isn't really all that surprising. It isn't even really "macro-evolution", since it isn't a big step in "mutation space".

[squozebrain]

Measured rates range from a few tenths of a darwin in some very stable fossil lineages to hundreds of thousands of darwins in radiative evolution in cichlids.

What exactly is a "darwin"?

[Flint]

http://www.unc.edu/~rowlett/units/dictD.html

darwin

a logarithmic unit measuring the rate of evolution in characteristics of organisms. If the measurement of a characteristic (such as length, for example) changes from a to b in y million years, then the rate of evolution is (ln b - ln a)/y darwins. (Technically, since the difference in natural logarithms is dimensionless, the darwin is a specialized name for the inverse megayear Ma-1). The unit is named for Charles Darwin (1809-1882), the English biologist who founded the theory of evolution.

[Writer@Large]

<YEC>

Be that as it may, it was STILL an eagle. It didn't turn into a rhinocerous.

</YEC>

:Cheeky:

--W@L

[Monad]

<YEC>

Be that as it may, it was STILL an eagle. It didn't turn into a rhinocerous.

</YEC>

:Cheeky:

--W@L

Yeah - just as we are still apes :D

[Urvogel Reverie]

Using genetic analysis scientists have proved that the giant eagle that used to prey on moa's in New Zealand was not descended from the larger wedge tail, as had been assumed, but from the much smaller little eagle. Further more it was so close genetically that their common ancestor would have been less than a million years ago meaning that Haast's eagle underwent massive evolutionary change to adapt to the new predation opportunities in the NZ ecosystem in a very short space of time.

http://news.bbc.co.uk/1/hi/sci/tech/4138147.stm

Intersting, but not entirely unexpected. We know that other insular birds often evolve very rapidly (e.g., rails losing flight) from some ancestral state to the derived state in which they are currently (or were currently) found.

Urvogel Reverie

[mountain_hare]

I can just hear the Creationists bleating out a reply "That doesn't fit the definition of 'real' speciation".

[Oolon Colluphid]

I can just hear the Creationists bleating out a reply "That doesn't fit the definition of 'real' speciation".
Yup. Definitive proof that Einstein was wrong. Something can move faster than light: a creationist's goalposts.

[Hopeful Monsters]

Yup. Definitive proof that Einstein was wrong. Something can move faster than light: a creationist's goalposts.You ought to use that one somewhere on your site :cool: :D

[braces_for_impact]

Thanks for the info guys! Always good reading to be had here.