Biology

Geckos rapidly evolve bigger heads in response to human activity

Geckos rapidly evolve bigger h...
The gecko species Gymnodactylus amarali has been found to be evolving larger heads in response to human activity
The gecko species Gymnodactylus amarali has been found to be evolving larger heads in response to human activity
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The gecko species Gymnodactylus amarali has been found to be evolving larger heads in response to human activity
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The gecko species Gymnodactylus amarali has been found to be evolving larger heads in response to human activity

Life is adept at adapting to changes in the environment – and the environment is changing faster than ever, thanks to us. Evolution is normally thought of on the scale of millions of years, but a new study has observed how human activity has directly driven separate populations of geckos to evolve new attributes in the space of just 15 years.

The human activity in question began in 1996, with the building of the Serra da Mesa Hydroelectric Plant in Brazil. An artificial reservoir was created by flooding 656 sq mi (1,700 sq km), and in the process almost 300 new islands were now cut off from the "mainland."

Researchers from the University of Brasilia and the University of California, Davis studied the newly-separated populations of animals on these islands, focusing on the most common gecko species in the area, Gymnodactylus amarali. The team found that over 15 years, G. amarali on the islands had grown bigger heads on average than those of the same species found on the mainland.

Before the dam was built, the geckos in the area had lived mostly off termites, with larger lizard species eating the bigger bugs and leaving the smaller ones to G. amarali. But it turns out that flooding the valley had wiped out those larger lizards, and with less inter-species competition for food, G. amarali adapted to fill the niche they left behind. The geckos grew larger mouths and heads to help them chow down on the newfound bounty of bigger termites.

It's a great "Petri dish" example of natural selection at work. Essentially, those G. amarali with bigger heads had access to more food, leading to them being more successful at survival and reproduction. Over time, the big-head genes were passed down to later generations in higher numbers, until it became a common characteristic of the island-dwelling geckos. Those still on the mainland, meanwhile, still faced competition from the larger lizards and so saw no change in head size, making them a perfect control group.

While their heads grew, the lizards' bodies stayed more or less the same size. The researchers say this is most likely a matter of efficiency: bigger bodies require more energy to run, which would offset the advantage of a larger head. And as further evidence that a bigger head relative to body size was the most efficient evolutionary path, the researchers found that the trait independently became common among populations on five islands isolated from each other.

The story of G. amarali isn't necessarily a sad one, but it does highlight just how much influence human behavior has on the environment, both directly and indirectly.

The research was published in the journal PNAS.

Source: Keele University via The Conversation

7 comments
highlandboy
The selective environmental breeding has resulted in the gene for small heads being bred out. It would be interesting to see how many generations of lizard is required to make the entire population homozygous for large heads resulting in a population that would therefore be less adaptable. As many domesticated animals breeders have discovered, breeding animals with homozygous attributes often results in a weaker strain that lacks hybred vigour.
Don Duncan
To the extent that other animals use tools or modify their environment it is considered "natural". When humans do it, it is "unnatural". Why? Give another species more intelligence and it will adapt its world to survive. That's logical and natural. But some humans claim our species has no right to do so if it "endangers" other species. Why are other species sacred? Why is humanity held hostage to the needs of other species? Why is humanity put last? Is this "species self loathing"? It wouldn't matter in a free world. But we are not free. We are controlled by an elite given that privilege by the masses. And that "privilege" strongly attracts the least worthy to control. Those who seek political power deserve it least. This makes the present political paradigm of institutionalized violence dangerous to life. In a free world, a world where reason, individual choice is the paradigm, the irrational self loathing members would be bred out of the gene pool.
Kpar
Too bad it doesn't work in reverse- humans could use bigger heads (provided they were filled with more brains...).
sk8dad
Don Duncan, I'm not sure your arguments on equating the effort to preserve biodiversity and reduce the effects of human industrial development with self-loathing. Sure it's inconvenient some times when a rare lizard prevents the development of vacation condos, and alternative energy means that coal towns go belly up, but you have to view the survival of the human species as a whole. Many known environmental interaction affect our survival, and many more unknown ones as well. We humans came about in a world with a certain level of biodiversity, so it stands to reason that any change, however large or small, could have an effect on our long-term survival. If you view every species, not as an individual, but as nodes in a global mesh of interactions, you can imagine that there is a certain level of redundancy to compensate if a small number of species disappear or change. If, however, a large number of species disappear or change, you are likely to have a cascade effect that causes even disruption to the mesh. The more nodes disappear or rearrange, the more the probability that some node crucial to our survival will alter in a deleterious way. That would be bad. An excellent example is the decline of honey bees, the rapid decline of major fisheries, and the rapid increase in antibiotic-resistance in bacteria. We humans are not particularly special other than the fact that we are the only species on the planet with the ability to create technology in a global scale that can significantly affect biodiversity. I would argue that the need to preserve bio-diversity and reduce industrial effects on the environment equates to self-preservation of our species -- not self-loathing as you put it.
Buellrider
I must be one of those self loathing humans that hate seeing what we humans are doing to lessen the garden of Eden we started with. I guess that a dystopian future holds no fear to those that most probably think all our man made noise, pollution and overcrowding is just fine so long as there is something good to watch on tv.
PG
So...there ARE humans with bigger heads than others. Does that mean they "evolved" that bigger head in order to cope with the environment. I don't suppose there already were lizards with bigger heads and we just hadn't seen them yet. Oh look! A lizard with a bigger head than the rest! It MUST have evolved . In 15 years.... Give me a BREAK!
sk8dad
PG, evolution works on a population not an individual as popular pseudo-science and science fiction will have you believe. A scientific study is distinctly different in process and intent than a comic book.