Module #16

Speciation and the Pace of Evolution

Module Introduction:

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• Over time, speciation has given rise to the millions of species present on Earth today.
• Beyond determining how many species exist, environmental scientists are also interested in understanding how quickly new species can evolve and how quickly species can go extinct.
• In this section, we will examine the processes that produce new species and the factors that determine how rapidly species can evolve in response to changes in the environment.

Module #16: Speciation and the Pace of Evolution

Essential Knowledge

2.6 Adaptations (Module 16)

• Organisms adapt to their environment over time, both in short- and long-term scales, via incremental changes at the genetic level.
• Environmental changes, either sudden or gradual, may threaten a species’ survival, requiring individuals to alter behaviors, move, or perish.

Speciation

• Speciation is the evolutionary development of new species.

New species commonly evolve through two processes:

• Allopatric speciation: The process of speciation that occurs with geographic isolation.
• Sympatric speciation: The evolution of one species into two, without geographic isolation.

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Regardless of the manner (allopatric or sympatric) speciation ALWAYS requires reproductive isolation of populations. This allows each group to evolve independently and ultimately become a unique species.

Allopatric Speciation

• Allopatric speciation requires organisms be isolated from each other geographically (allopatric literally translates to “other fatherland”).
• In this case, geographic isolation results in reproductive isolation, allowing two distinct populations to develop and eventually evolve into unique species.
• Geographic isolation: Physical separation of a group of individuals from others of the same species.
• Reproductive isolation: The result of two populations within a species evolving separately to the point that they can no longer interbreed and produce viable offspring.

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Example of Allopatric Speciation

• Geographic barriers can split populations.
• Natural selection may favor different traits in as each isolated population adapts to its specific, non-identical habitat, resulting in unique genotypes and phenotypes .
• Over time, the two populations may become so genetically distinct that they are no longer capable of interbreeding. At this point, they are said to be reproductively isolated, resulting in two independent populations → novel species.

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Sympatric Speciation

• Flowering plants such as wheat commonly form new species through the process of polyploidy, an increase in the number of sets of chromosomes beyond the normal two sets.
• (a) The ancestral einkorn wheat (Triticum boeoticum) has two sets of chromosomes and produces small seeds.
• (b) Durum wheat (Triticum durum), which is used to make pasta, was bred to have four sets of chromosomes and produces medium-sized seeds.
• (c) Common wheat (Triticum aestivum), which is used mostly for bread, was bred to have six sets of chromosomes and produces the largest seeds.

Sympatric speciation occurs within the same environment in the absence of geographic isolation, usually through polyploidy.

Polyploidy is very common nature, which is believed to be the result of “hybrid vigor” in which the polyploid offspring is healthier than either parent.

Darwin’s Finches

• In the Galapagos Islands, speciation has led to a large variety of finch species, all descended from a single species that colonized the islands from the South American mainland.
• This is known as adaptive radiation, a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms when new resources become available.
• Adaptive radiation can be an example of allopatric or sympatric speciation depending on the specific scenario. Here is it sympatric, since the finches live together, but occupy different niches.

The Rate of Evolution

The pace of evolution depends on several factors:

• A species can survive an environmental change if it can quickly evolve adaptations to new conditions. 
• Slow rates of evolution occur when a population has long generation times or contains low genetic variation. 
• Evolution by artificial selection can be very rapid such as with the Atlantic cod that have been experiencing heavy commercial fishing.
• Recent advances in biotechnologies like CRISPR have allowed for the direct manipulation of genes and DNA (as seen with GMOs), maximizing the rate of evolution.

Genetically modified organism (GMO): An organism produced by copying genes from a species with a desirable trait and inserting them into another species.

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Genetic Engineering

• Genetic engineering (also called genetic modification) is a process that uses laboratory-based technologies to alter the DNA makeup of an organism.
• Genetic engineering can be used for a variety of purposes including modifying crops to become pest, drought, etc. resistant, improving the growth rate of livestock or accelerating carbon sequestration in trees.
• Genetic engineering can be accomplished in a variety of ways such as CRISPR.

Helpful Videos on Genetic Modification:

1. Genetic Engineering Will Change Everything Forever – CRISPR
2. Are GMOs good or bad?
3. Genetic Engineering and Diseases

Fishery Artificial Selection

• When species experience harvest (e.g. fishing), certain individuals are selectively removed from the population by people.
• Generally speaking, larger fish are targeted, resulting in artificial selection for smaller individuals. This has implications for the entire species.

Module Review:

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• In this module, we learned that species evolve through the mechanisms of allopatric and sympatric speciation.
• We also saw that there are a number of factors that can affect the pace of evolution including how quickly the environment changes, how much genetic variation exists in the population, the size of the population and the generation time of the species.