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Blog 2: Evidence for Evolution

 The anole lizards of the Caribbean islands embody two of Darwin's predictions: that species change over time (microevolution) and that lineages diverge (speciation). 

Within the forests of the Caribbean islands, niches are distributed vertically, from the ground to the tree canopy. As the anoles colonize a new island, they fill those niches and as a result begin to develop certain traits better suited to those niches. The anoles who stay on the ground have longer limbs for faster running, while the anoles who live among the tree's branches have shorter legs to hold onto thin twigs. Leafy canopy anoles have large sticky toepads to help them cling onto broad leaves and not fall to the forest floor. This microevolution happens rapidly, across relatively few generations, because natural selection is so strong.  Scientists have actually been able to observe this process happening in real time, which is evidence for Darwin's prediction that species change over time. 


Anoles also go through the process of speciation. According to the biological species concept, a species is defined as a group of organisms that are able to interbreed and produce viable offspring. Reproductive isolation is one way for closely related lineages to diverge, when populations lose the ability to interbreed with one another. This happened to the anoles through changes in a reproductive trait. Male anoles have a flap of skin on their neck called a dewlap that they use in mating displays. Over time, the dewlaps of the males in each niche change in color - enough to where females of other niches won't mate with them. As each anole population becomes totally reproductively isolated, they are classified as separate species. 



This is a great video that describes some of the research done on anole evolution in the Caribbean:

https://www.biointeractive.org/classroom-resources/origin-species-lizards-evolutionary-tree

Image Sources:

Losos, Johnothan. "Lizard Genome Promises Great Advances in Understanding Evolution." National Geographic. 31 Aug. 2011. Web. 22 May 2015.

https://www.the-scientist.com/daily-news/rapid-evolution-in-real-time-36550

Comments

  1. Madison NSeptember 28, 2021 at 10:04 AM

    Really good summary, Victoria! You hit the super important concepts without muddying the waters with jargon or over-explanations. AND, you hit on the most fascinating part of Darwin's whole theory (at least, to me): the connection between minor changes and speciation. What do you think sparked the change in color of dewlaps between niche-separated males? Was it completely random mutation, or did natural selection have a hand? And speaking of selection, why did females change their color preferences to match the dewlaps of males in their niche? Or do you think the color preference change can first?

    Of course, a lot of these questions are stuff we haven't discussed in class yet. So, uh, no sweat if you're staring at your computer in panic. Just think about it! And we'll get there eventually :]

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