'Armored' fish study helps strengthen Darwin's natural selection theory

Aug 28, 2008

Shedding some genetically induced excess baggage may have helped a tiny fish thrive in freshwater and outsize its marine ancestors, according to a UBC study published today in Science Express.

Measuring three to 10 centimetres long, stickleback fish originated in the ocean but began populating freshwater lakes and streams following the last ice age. Over the past 20,000 years - a relatively short time span in evolutionary terms - freshwater sticklebacks have lost their bony lateral plates, or "armour," in these new environments.

"Scientists have identified a mutant form of a gene, or allele, that prohibits the growth of armour," says UBC Zoology PhD candidate Rowan Barrett. Found in fewer than one per cent of marine sticklebacks, this allele is very common in freshwater populations.

Barrett and co-authors UBC post-doctoral fellow Sean Rogers and Prof. Dolph Schluter set out to investigate whether the armour gene may have helped sticklebacks "invade" freshwater environments. They relocated 200 marine sticklebacks with the rare armour reduction allele to freshwater experimental ponds.

"By documenting the physical traits and genetic makeup of the offspring produced by these marine sticklebacks in freshwater, we were able to track how natural selection operates on this gene," says Rogers.

"We found a significant increase in the frequency of this allele in their offspring, evidence that natural selection favours reduced armour in freshwater," says Barrett.

Barrett and Rogers also found that offspring carrying the allele are significantly larger in size. "It leads us to believe that the genetic expression is also tied to increased growth rate," says Barrett.

"If the fish aren't expending resources growing bones - which may be significantly more difficult in freshwater due to its lack of ions - they can devote more energy to increasing biomass," says Barrett. "This in turn allows them to breed earlier and improves over-winter survival rate."

Celebrating its 150th anniversary this week, Darwin's first publication of his natural selection theory proposed that challenging environments would lead
to a struggle for existence, or "survival of the fittest." Since then, scientists have advanced the theory by contributing an understanding of how genes affect evolution.

"This study provides further evidence for Darwin's theory of natural selection by showing that environmental conditions can directly impact genes controlling physical traits that affect the survival of species," says Barrett.

Source: University of British Columbia

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User comments : 8

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D666
5 / 5 (3) Aug 28, 2008
A slight refinement of old news.
TBBucs
5 / 5 (2) Aug 28, 2008
I was _really_ hoping for a picture.
jeffsaunders
4.5 / 5 (2) Aug 28, 2008
Every half-way decent study in evolution strengthens Darwin's theory.

However, I believe a lot of mistakes were made in this study - which makes it pretty useless as an endorsement.
seanpu
2 / 5 (2) Aug 29, 2008
natural selection is great to explain what it was originally intended to explain: "that environmental conditions can ... impact ... physical traits that affect the survival of species" by regulating the population to regulating genes more favored to an environment, but that which ALREADY exist. it is a refinement mechanism. Its been proved time and time again in real life, in experiment and computer simulations.

HOWEVER, natural selection cannot by definition "directly impact genes controlling physical traits". it can only impact the behaviors of individual species thereby impact individuals ability to mate, thereby affecting the gene pool in proceeding generations, and only bu that method impacting genes (not so direct hu?).

Its a common misconception that Darwin [fill-gap-with-any-theory] changes genes in anything but a disruptive way (mutations). Very VERY rarely do mutations create benefit for organisms. And not one single study, experiment or computer simulation has shown that by strictly Darwinian theory useful, constructive, innovative genes have been produced.

How new genetic information is create? I have no idea. But within the context of an individual organism or species it is proved, in the real world, by study and by experiment, that new genes are ACQUIRED by some form of horizontal gene transfer. Its only once these new genes have been successfully integrated into the new host, that Darwin's Natural Selection can determine how good those genes are for the host and the host species.

gmurphy
5 / 5 (2) Aug 29, 2008
seanpu, natural selection cannot directly mutate genes, true. But our genetic code is huge and we only use a tiny portion of it. Natural populations tend to have a large spread of antagonistic genes activated (bony v.s non-bony stickleback), these mutants are the primary source of variance in the populations response to changing circumstances. The mutants successfully spead their dna, evolution in motion. The point is that the population has a great deal of variance inherent in it anyway, negating the need for potentially catastrophic mutation events to provide the population with the variance it needs.
CaptSpaulding
5 / 5 (1) Aug 29, 2008
seanpu, regardless if only 0.01% of new mutations are actually useful and it occurs in a population of several billion, it becomes buried in the population as a whole and can become significantly expressed if pressures permit.
D666
not rated yet Aug 29, 2008
natural selection is great to explain what it was originally intended to explain: "that environmental conditions can ... impact ...


Senpu, it really sounds to me like you have a very basic fundamental misunderstanding of the nature of genes. Your posting makes it sound like you think there's a gene for "arm" or "leg" and an organism can't just "develop" this gene.

That isn't how mutations work, that isn't how genetics work. As someone (Gell-Mann?) once said, you're so far off that you're not only not right, you're not even wrong. (I'm sure I've butchered the quote).

Your point about horizontal gene transfer is a good one -- we're discovering more and more how much viruses are involved in genetic changes. But understand this: EVERY SPECIES ON EARTH has the genetic information necessary to make a feather, or an arm, or a tentacle. Just not in the correct order to do so. In the end, it's just GATC.
lengould100
not rated yet Sep 02, 2008
I would also point out, in support of D666, that EVERY SPECIES ON EARTH (including trees, fungi, blue whales and crocodiles) has a basically identical basis of life, eg. a cellular structure whose design and operation is controlled by a set of genes coded in some DNA or RNA.

All are so obviously similar at the core fundamentals that its more logical than not to conclude they all began from a single ancestor.