Speciation

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify chronological patterns of change and communicate that biological evolution is supported by multiple lines of empirical evidence that identify similarities inherited from a common ancestor (homologies).

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Source, 2022-03

Speciation

(Okay, you're making up words now!)

Speciation is the formation of a new species. It is the process by which a population evolves to become different, distinct species.

What could be a cause of speciation? What could cause one species to become two different species?

There are a variety of things which can cause speciation, but reproductive isolation in a population is one major cause of speciation.

Reproductive isolation is the inability of a species to breed and successfully produce offspring. This is a major cause of speciation because without reproduction, a species cannot survive. Instead of extinction of one species, this causes the creation of two new species that are able to successfully reproduce.

There are 5 major types of reproductive isolation.

Behavioral Isolation

Behavioral isolation occurs when populations of the same species develop differences in courtship rituals or other types of behaviors.

Geographic Isolation

Geographic isolation occurs when populations of the same species become separated by geographic barriers such as rivers, mountains, bodies of water, etc.

This is also referred to as allopatric speciation.

Temporal Isolation

Temporal isolation occurs when populations of the same species develop differences in the time or season that they breed.

Mechanical or Chemical Isolation

Mechanical or chemical isolation occurs when the reproductive structures or chemical barriers of species do not allow organisms to interbreed.

Ecological or Habitat Isolation

Ecological or habitat isolation occurs when species that could interbreed do not because they live in different areas, even if they are within the same general ecosystem.

Two birds living in different environments will never meet, so they will not be able to reproduce.

Genetic Equilibrium and the Hardy Weinberg Principle

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify chronological patterns of change and communicate that biological evolution is supported by multiple lines of empirical evidence that identify similarities inherited from a common ancestor (homologies).

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Genetic Equilibrium and the Hardy Weinberg Principle 

(This guy sounds like some stand-up comedian. Just saying…)

Genetic equilibrium is the situation in which allele frequencies remain constant through time. REMEMBER: Allele frequencies are the frequencies of alleles in a population, often expressed as a fraction, percentage, or decimal.

So… In a population of 100 turtles if…

64 turtles are “BB”

12 turtles are “Bb”

24 turtles are “bb”

Then we can figure out the frequency of B and b (which is the allele frequency). How many B's are there? How many b's are there?

Math… then, we can say that the B allele frequency is 70% and the b allele frequency is 30%.

The Hardy-Weinberg Principle states that allele frequencies in a population will remain constant under 5 conditions:

1. No natural selection occurs in a population.
2. No migration into or out of a population (no gene flow).
3. No mutations happen in the gene pool of a population.
4. Random mating throughout the population.
5. Large populations of organisms to keep frequencies constant.

That is to say that… 

…in a large, random-mating population that is not affected by the evolutionary processes of mutation, migration, or natural selection, allele frequencies (and genotype frequencies) will remain constant throughout time. 

Psst… THIS IS NOT COMMON IN REAL LIFE.

Source, 2022-03

This can be thought of as all of the parts adding up to one. All of the fractions of alleles will add up to one.  Sometimes it is shown like this:

Hardy-Weinberg Equations for Genetic Equilibrium

Where "frequency" is expressed as a decimal representing how many there are compared to the total number and where… 

 

p = frequency of dominant allele (A)

q = frequency of recessive allele (a)  

 

then… 

p + q = 1 

 

and further…

  p² + 2pq + q² = 1

will also be true so that…

2pq = frequency of heterozygous organisms (Aa)

p² = frequency of homozygous dominant organisms (AA)

q² = frequency of homozygous recessive organisms (aa) 

 

 

______________________

Example:

You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Find the allele frequency and the genotype frequency for the population.

Given that 36% are homozygous recessive…

That means that 

q² = 36% = .36

Which means that q = .6

We can then solve for p…

p + q = 1

p + .6 = 1

p = 1 = .6

p = .4

So… if p = .4 then…

p² = .16

Now, we can find the heterozygous frequency; it is equal to 2pq

2pq = 2 • .4 • .6

2pq = .48

We can check that… 

p² + 2pq + q² = 1 

.16 +  .48 + 36 = 1

Now, we can put that into words… 

The frequency of the "a" allele is .6.

The frequency of the "A" allele  .4.

(These add to 1)

The frequency of the genotype "aa" is .36. <-- this was given

The frequencies of the genotype "AA" .16.

The frequencies of the genotype "Aa" is .48.

(These add to 1)

______________________

Why Does This Matter?

• This principle provides a baseline to compare actual populations to.
  
  
•  Step 1: Find allele frequencies in year 1
  
  
•  Step 2: Find allele frequencies in year 5
  
  
• If a population is in genetic equilibrium, then the allele frequencies from Year 1 would equal Year 5. If Year 5 shows different allele frequencies, then we know that genetic drift is happening, and we can find out how much a population has changed.
  
  
• With this information, we can see how quickly a population is changing.

In essence, this process allows a means to demonstrate genetic drift within a given population, which indicates that something is changing. Microevolution can be, therefore, measured and described in terms of changes in the present allele frequencies.

Chronological Patterns of Change

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify chronological patterns of change and communicate that biological evolution is supported by multiple lines of empirical evidence that identify similarities inherited from a common ancestor (homologies).

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Chronological Patterns of Change

(We should put some time into this!)

When a mutation leads to a favorable gene that gives one an advantage, it is called an adaptation. When adaptations survive and reproduce in a population, it is referred to as natural selection. Natural selection can drastically change the phenotypes of an animal given enough time.

Remember that a phenotype is the physical expression of the genetic code. The phenotype is what is seen, whereas the genotype is the genes that are present.

There are 3 main ways phenotypes can change via natural selection. They are all caused by environmental pressures that would make a certain phenotype unfavorable.

Favorable Traits

Before we look at these types, we need to get an understanding of a biology concept: being favored.

A favorable trait or behavior is one that increases an organism's fitness; it helps the organism live, thrive, survive, and reproduce. Favored traits are the ones that most readily lead to the survival of an organism.

Stabilizing Selection

Stabilizing selection is a type of natural selection where the population average favors intermediate values for a trait.

Directional Selection

Directional selection is a type of natural selection where the population average favors one extreme value over another for a trait.

Disruptive Selection

Disruptive selection is a type of natural selection where the population average favors both extreme values for a trait.

Summary

So, any of the three patterns can be present and they all can lead to certain phenotypes being preferred—that is to say that the environmental pressure will prevent some specific phenotypes from being passed on while other phenotypes will be removed from the population.

Those three patterns are one way that phenotypes can shift over time. 

If a gene is changed, the allele frequencies of that population also change. Allele frequency is a measure of how often a certain allele appears in a population.

How many alleles do you have for each gene? You will recall that everyone has two allele for any give trait, and they can be the same or different. 

When both genes are the same, the trait is said to be homozygous. When they are different, then it is heterozygous.

If all rabbits in a population are heterozygous, the “G” allele frequency is 50% and the “g” allele frequency is 50%.

If a mutation causes a gene to change, then alleles will also change randomly.

A random change in allele frequency is called genetic drift.

This is much easier to see in smaller populations.

Genetic Drift

There are two types of genetic drift events:

• Founder Effect
• Bottleneck Effect

Founder Effect

The Founder Effect is a situation where allele frequencies change due to the migration of a small subgroup into a population.

Bottleneck Effect

The Bottleneck Effect is a situation where there is some sort of disaster that reduces a population to a very small amount.

This typically reduces genetic variation.

Introducing Evolution of Populations and Biodiversity

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify chronological patterns of change and communicate that biological evolution is supported by multiple lines of empirical evidence that identify similarities inherited from a common ancestor (homologies).

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Introducing Evolution of Populations and Biodiversity 

(This could be different!)

If you look around, even within an urban environment, you will see a huge number of different plants, and animals. Insects, alone account for bazillions of different species… But… well… you probably know that already.

This article will look at theories that provide some insight into how so much diversity might have come to be. It will look at patterns of change over time and attempt to put that into a biological framework.

Leading into the discussion, it would be helpful to introduce a few concepts. 

Species

First is the species. A species, in biology, is a classification comprising related organisms that share common characteristics and are capable of interbreeding (Source 2020-03). Genetically, they share DNA configuration and can reproduce.

It is notable that some interspecies breeding is possible (hybridization), but usually results in offspring that are not capable of breeding. However, there are exceptions (e.g. ligers).

 

Population

Additionally, it is helpful to understand the idea of a biological population. In simple terms, population refers to a particular group within a species that can be easily identified apart from other members of the same species. Sparrows that live in Minnesota might (because of climate) be considered a different population as compared to sparrows that live in Florida.

Specimen

Within any population are the individual members. It is not uncommon to talk about a particular specimen within a population. Specimen refers to any single member of a population. 

Sample

While we are at it, let's just get this out of the way, too!

A sample is a selection of some number of specimen from a population. A naturalist might take a sample of 10 specimen from that population of sparrows that live in Florida and compare them to a sample of 10 specimen from that population of sparrows that live in Minnesota!

Two Types of Evolution: Macro and Micro

Evolution (of species) can be viewed through two distinct lenses. The first is microevolution.

Microevolution is characterized by small-scale changes in a population that lead to favorable traits being reproduced. This is similar to the effect of favorable adaptations. Microevolution can take place over the course of a few years in organisms that reproduce quickly.

There are many examples of microevolution such as:

• Antibiotic-resistant bacteria 
• New strains of viruses (e.g. Flu, COVID)
• Larger bodies of male sparrows in colder climates (Source, 2022-03).
• Pesticide resistant insects (Source, 2022-03).

Microevolution refers to evolutionary changes within a species (or a single population of a species) over a relatively short period of time. The changes often only affect a single trait in the population, or a small group of genes (Source, 2022-03).

In many cases, the species will adapt to changes around it. Natural selection plays a role in this; the traits and behaviors that lead to higher levels of fitness are passed on. Traits and behaviors that decrease fitness eventually are far less prevalent if they exist in the population at all.

It is important to understand that microevolution refers to changes of traits and behaviors within a species that remains the same species. 

Macroevolution, on the other hand is the large-scale evolutionary changes that happen over a long period of time, and often results in either creating or destroying a species.

The end result of macroevolution is that a particular species of something either ceases to exist (extinction) or shifts genetically into one or more new, different species. If macroevolution occurs, it results in there being different species.

Both types of evolution occur amongst populations of organisms.

Patterns in Macroevolution

There are 6 patterns of macroevolution.

1. Extinction
2. Adaptive radiation
3. Convergent evolution
4. Coevolution
5. Punctuated equilibrium
6. Changes in developmental genes

Extinction

Extinction is the state of a species being completely gone.

Many species in the 21st Century are on the verge of extinction due to factors such as loss of habitat or human harvesting. These species are considered to be endangered.

Endangered species are those that are at risk of becoming extinct.

History has witnessed the extinction of numerous species including the wooly mammoth and the dodo bird.

Adaptive radiation

Adaptive radiation is the process of a single species evolving into several new species that live in different ways. This is what Darwin claimed happened among finches on the Galapagos Islands.

This is typically a result of minor adaptations.

Convergent evolution

Convergent evolution is the process by which unrelated organisms come to resemble one another.

This commonly happens through adaptations that appear in response to environmental conditions (analogous structures).

Converge means to come together. In dolphin and sharks, both adapted to have slender bodies so they could glide through the water easily.

Contra to convergent evolution is a concept called divergent evolution.

Divergent evolution is the process where  related species from a common ancestor gain differences resulting in a new species.

Diverge means to spread apart.

Divergent evolution and adaptive radiation are very similar.

Adaptive radiation is a smaller-scale model of macroevolution that revolves around adaptations. Even though the result is new species, those new species are still relatively similar (Darwin’s finches).

Divergent evolution is a larger-scale model of macroevolution that happens over hundreds of years. The result is several new species that really aren’t very similar (tiger, cow, giraffe)

Coevolution

Coevolution is the process where two species evolve in response to changes in each other.

Most predator/prey relationships result in coevolution.

Example of coevolution…

Punctuated equilibrium

This is more of a model of macroevolution that attempts to describe how it happens.

Punctuated equilibrium is the idea that evolution has isolated episodes of rapid speciation between long periods of little or no change.

Graduated equilibrium is the idea that evolution proceeds through slow, gradual changes.

Changes in developmental genes

Changes in developmental genes happen when genes that control the development of an organism are altered. All of the genes in one population are part of their gene pool. If the gene pool changes, then some genes must have changed. Genes are made up of specific sequences of DNA. In order for genes to change, the DNA must change first.

Mutations are changes in the DNA sequence and are a common source of genetic variation.

Darwin's Evidence for Evolution

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify chronological patterns of change and communicate that biological evolution is supported by multiple lines of empirical evidence that identify similarities inherited from a common ancestor (homologies).

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Darwin's Evidence for Evolution

(Off we go!)

Charles Darwin was a naturalist in the middle of the 1800s who became known as the Father of Evolution.

Darwin published his most interesting notes in his book titled On the Origin of Species. This book detailed key terms for natural selection and contained his “evidence” for evolution.

One of the principles he proposed was called descent with modification. 

Descent with modification is an idea that describes how species descend from each other and inherit changes. It theorizes that all species that can be observed presently descended from previous species. If two or more species are thought to have come from the same previous species, the earlier species is called a common ancestor.

According to Darwin, all living things originated from a common ancestor.

This idea was integral to Darwin's theory. Darwin offered four main components for his evidence of evolution.

Darwin's Evidence for Evolution

1. Fossils document how life on Earth has changed/evolved over time.

Regarding fossil evidence, 95% of fossils are from marine animals.

2. Homologous structures (structures that appear with similarities in different species) suggest that similar organs/limbs of different organisms are connected to each other by way of a common ancestor.

Homologous structures (above) are structures that are similar in related organisms, suggesting a common ancestor; they do not have to have the same function.

Analogous structures (below) are structures that are similar in unrelated organisms; these structures simply evolved in sometimes-different ways to do the same job.

Though both bats and birds have wings and can fly, they structure of the wings is very different. The bone patterns suggest different ancestors.

Homologous structures:

Suggest a common ancestor

Do not have to have the same function

Analogous structures:

Do not suggest a common ancestor

These are structures in unrelated organisms that have evolved to have the same function

Typically in response to environmental similarities

3. Similarities in embryology suggests all living things have developed from a common ancestor.

 

4. Geographic distribution of living species says that unique groups of animals only exist on islands, suggesting these animals have evolved from others on the mainland after to the supercontinent breakup.

To Darwin, all four of these pieces suggested that all living things came from a common ancestor.