Natural Selection in anoles

Apply your understanding of natural selection to explain how heat tolerance has evolved in crested anole lizards in urban habitats in Puerto Rico.

Heat tolerance evolved in Puerto Rican crested anoles through natural selection in urban habitats, which are warmer due to the urban heat island effect.

Lizards with higher natural heat tolerance survive and reproduce better in these hot urban environments, passing their advantageous genes and traits to offspring.

This leads to an increase in heat-tolerant individuals over generations, driven by the selective pressure of elevated temperatures.

How are the anoles an example of directional selection. 

Anoles provide several classic examples of directional selection, where an environmental pressure, such as urbanization, pushes a population's traits toward a new extreme.

• Urban anoles have evolved longer limbs compared to their forest counterparts. This trait is selectively advantageous in cities, where lizards need to sprint across open, flat surfaces like concrete, sidewalks, and walls to escape predators.

• Urban anoles have also evolved larger, stickier toe pads with more lamellae. These larger toe pads allow them to cling to the smooth, artificial surfaces found in cities, such as glass windows and painted concrete. 

Explain why anoles in puerto rico are an example of natural selection, but not genetic drift.

They result from a predictable selective pressure that favors specific adaptive traits. In contrast, they are not a result of genetic drift, which is a random, non-adaptive process that disproportionately affects small populations. The changes are a clear cause-and-effect relationship. 

Urban areas are hotter than forests

Urban areas:

• surface absorbs more heat

• less cooling from evaporation and plant transpiration

• less ground storage of rainfall

Rural:

• surface absorbs less heat

• greater cooling from evaporation and plant transpiration

• greater ground storage of rainfall

Differing genotype frequencies

C/C genotypes, which relate to a higher critical thermal max, are more common in urban than forest populations

C/G genotypes, which relate to a lower heat tolerance, are less common in urban populations, indicating that they will have a lower heat tolerance

Examples of popular press:

Buzzfeed, forbes, national geographic, popular science, CNN, Fox News

examples of primary literature

original research articles in peer-reviewed journals, technical reports, conference proceedings, dissertations, and theses

primary article main points

• The RARS gene codes for arginyl-tRNA synthetase, which is an enzyme that attaches the amino acid arginine to its corresponding tRNA, which is used during translation to build proteins. 

• Urban lizards have a version of the RARS gene that is associated with heat tolerance plasticity, meaning they tolerate higher temperatures; higher fitness than lizards without this gene.

• Lizards with this mutation were selected for in urban environments, and the allele become more common in the population over time.