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Chapter 11 Review - Coggle Diagram
Chapter 11 Review
11.6 Patterns in Evolution
Evolution through natural selection is not random
The environment controls the direction of natural selection. When the environment changes, different traits may become advantageous. The response of species to environmental challenges and opportunities is not random.
Convergent Evollution
Evolution toward similar characteristics in unrelated species is called convergent evolution.
Analogous structures, such as wings on birds and insects, are common examples of convergent evolution.
Divergent Evolution
Divergent evolution is when closely related species evolve in different directions
The evolution of the red fox and kit fox is an example of this trend. Though closely related, the two species have different appearances that are the results of adapting to different environments.
Species can shape each other over time.
Beneficial Relationships Through Coevolution
Coevolution is the process in which two or more species evolve in response to changes in each other.
The bull-thorn acacia is a plant species with branches covered in hollow thorns.Although the thorns protect the plant from being eaten by large animals, small herbivores such as caterpillars can fit between them. To the rescue comes Pseudomyrmex ferrugineus, a species of stinging ants.these ants live inside the thorns and feed on the plant’s nectar. The ants protect the plant by stinging animals that try to eat the leaves.
The hollow thorns and nectar-producing leaves of the acacia and the stinging of the ants have evolved due to the relationship between the two species.
Evolutionary Arms Races
Coevolution can also occur in competitive relationships.
For example, the thick shells and spines of murex snails are an adaptive response to predation by crabs. In turn, crabs have evolved powerful claws strong enough to crack the snails’ shells.
Species can become extinct.
The elimination of a species from Earth is called extinction. Extinction often occurs when a species as a whole is unable to adapt to a change in its environment.
Background extinction: Extinctions that occur continuously but at a very low rate
Unlike catastrophic mass extinctions, background extinction events usually affect only one or a few species in a relatively small area, such as a rain forest or a mountain range.
They can be caused by local changes in the environment, such as the introduction of a new predator species or a decrease in food supply.
Mass Extinctions: These events often occur at the global level. Therefore, they destroy many species—even entire orders or families.
Mass extinctions are thought to occur suddenly in geologic time, usually because of a catastrophic event such as an ice age or asteroid impact.
Speciation often occurs in patterns.
The theory of punctuated equilibrium, which states that episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolution- ary change.
The diversification of one ancestral species into many descendent species is called adaptive radiation.
One example of adaptive radiation is the radiation of mammals following the mass extinction at the end of the Cretaceous period 65 million years ago.
11.4 Hardy Weinberg equation
Hardy Weinberg equilibrium describes population that are not evolving.
in 1908, Hardy and Weinberg showed that genotype frequencies in a population stay the same over time as long as certain conditions are met.
Very large population, no genetic drift can occur
No emigration or immigration, no gene flow can occur
No mutations, no new alleles can be added to the gene pool
Random mating, no sexual selection
No natural selection, all traits must equally aid in survival
The Hardy Weinberg equation is used to predict genotype frequencies in a population
If p equals the frequency of the dominant allele and q equals the
frequency of the recessive allele, the equation can be written as
Five factors lead to evolution
Genetic drift: allele frequencies can change due to chance alone
Gene flow: the movement of alleles from one population to another changes the allele frequencies in each population
Mutation: New alleles can form through mutation, mutation create the genetic variation needed for evolution
Sexual selection: Certain traits may improve mating success, alleles for these traits increase in frequency.
Natural selection: Certain traits may be an advantage for survival. Alleles for these traits may increase in frequency.
11.1 Genetic variation within population
Genetic variation in a population increases the chance that some individuals will survive
A phenotype is a trait produced by one or more genes. In a population, there will be a wide range of phenotypes, for example, some penguins would be short and rounded, others could be tall and slim.
A population with a lot of genetic variation likely has a wide range of population; the greater the variation in phenotypes, the more likely it is that some individuals can survive in changing environment.
For example, in an unusually cold winter, short, rounded penguins might be better able to stay warm than tall, slim penguins. But if there is a shortage of food, tall, slim penguins might be better divers, allowing them to catch more fish.
Genetic variation is stored in population's gene pool, the combined alleles of all the individuals in a population.
Different combinations of alleles in a gene pool can be formed when organisms mate and have offspring. Each allele exists at a certain rate, or frequency.
An allele frequency is a measure of how common a certain allele is in the population.
you can calculate allele frequencies: first count the number of times an allele occurs in a gene pool. Then divide by the total number of alleles for that gene in the gene pool.
Gene variation comes from several sources
Mutation
A mutation is a random change in the DNA of a gene. This change can form a new allele.
Mutations in reproductive cells can be passed on to offspring. This increases genetic variation in the gene pool.
Because there are many genes in each individual and many individuals in a population, new mutations form frequently in gene pools.
Recombination
New allele combination form in offspring through a process called recombination -- Most recombination occurs during meiosis, the type of cell division needed for sexual reproduction.
When gametes are made, each parents' alleles are arranged in new ways. This shuffling of alleles results in many different genetic combinations.
Hybridization
Some biologists are considering hybridization as another source of genetic variation.
Hybridization is the crossing of two different species that share common genes.
Research suggests that this process occurs within many groups of animals, including birds and mammals, when similar species live in same area and individuals cannot easily find mates of their own species.
11.2 Natural Selection in Population
Natural selection acts on distribution of traits.
This type of distribution, in which the frequency is highest near the mean value and decreases toward each extreme end of the range, is called a normal distribution.
For some traits, all phenotype provides and equal chance of survival. The distribution of these traits generally shows a normal distribution. Phenotypes near the middle of the range tend to be more common, while the extremes are less common.
However, environmental condition can change, and a certain phenotype can be an advantage. Nature favors individuals with this phenotype. These individuals are able to survive and reproduce at higher rates than individuals with less favorable phenotypes. Therefore, alleles associated with favorable phenotypes increase in frequency.
Natural selection can change the distribution of a trait in one of three ways.
Microevolution is the observable change in the allele frequencies of a population over time. Microevolution occurs on a small scale—within a single population. One process that can lead to microevolution is natural selection.Natural selection can change the distribution of a trait along one of three paths: directional, stabilizing, or disruptive selection. Such changes can have major effects on how a population looks and behaves.
Directional selection:
A type of selection that favors phenotypes at one extreme of a trait’s range is called directional selection. Directional selection causes a shift in a population’s phenotypic distribution. An extreme phenotype that was once rare in
a population becomes more common.
The rise of drug-resistant bacteria provides a classic example of this type of selection. Before antibiotics were developed in the 1940s, a trait for varying levels of drug resistance existed among bacteria. At the time, there was no advantage to having drug resistance. But once antibiotics came into use, the resistant bacteria had a great advantage.The early success of antibiotics in controlling infectious diseases led to overuse of these drugs. This overuse favored even more resistant phenotypes. New drugs were then developed to fight the resistant bacteria. This resulted in the evolution of “superbugs” that are highly resistant to many drugs. Today, over 200 types of bacteria show some degree of antibiotic resistance.
Stabilizing Selection:
During stabilizing selection, the intermediate phenotype is favored and becomes more common in the population.That is, the distribution becomes stable at the intermediate phenotype rather than shifting toward one of the extremes.
Gall flies lay their eggs in developing shoots of the tall goldenrod plant. The fly larvae produce a chemical that causes the plant tissue to swell around them. The gall serves as a home where the larvae can develop. There is a range of phenotypes for body size in gall-fly larvae. Each body size causes a certain size gall to form, and each of the two main predators of gall flies specializes on a specific gall size. If the gall is too big, downy woodpeckers will feed on the larvae inside.If the gall is too small, the parasitic wasp lays its own eggs inside small galls, and after the wasp larvae emerge from eggs, they eat the gall fly larvae.
In this situation, selective pressure from predators works against fly phenotypes that produce galls at both extremes, large and small. As a result, flies that produce middle-sized galls become more common.
Disruptive selection: Disruptive selection occurs when both extreme phenotypes are favored, while individuals with intermediate phenotypes are selected against by something in nature.
Young male lazuli buntings vary widely in the brightness of their feathers, ranging from dull brown to bright blue. Dominant adult males are those with the brightest blue feathers on their heads and backs. These birds have their pick of the best territories. They also are most successful at attracting females. However, for young bun- tings, the brightest blue and dullest brown males are more likely to win mates than males with bluish brown feathers are.
Research suggests that dominant adult males are aggressive toward young buntings that they see as a threat, including bright blue and bluish brown males. The dullest brown birds can there- fore win a mate because the adult males leave them alone. Meanwhile, the bright blue birds attract mates simply because of their color.
Both extreme phenotypes are favored in this situation, while intermediate forms are selected against. The bluish brown males are not as well adapted to compete for mates because they are too blue to be left alone by adult males, but not blue enough to win a mate based on color alone. By favoring both extreme phenotypes, disruptive selection can lead to the formation of new species.
11.3 Other Mechanisms of Evolution
Gene flow is the movement of alleles between populations
When an organism joins a new population and reproduces, its alleles become part of that population's gene pool. At the same time, these alleles are removed from the gene pool of its former population
Gene flow is the movement of alleles from one population to another. For many animals, gene flow occurs when individuals move between populations. Gene flow can occur in fungi and plant populations when spores or seeds are spread to new areas.
Gene flow increases the genetic variation of the receiving population. Gene flow between neighboring populations keeps their gene pools similar. However, the less gene flow that occurs between two populations, the more genetically different the two populations can become. A lack of gene flow also increases the chance that the two populations will evolve into different species.
Genetic drift is a change in allele frequencies due to chance.
Genetic drift causes a loss of genetic diversity in a population.
Bottleneck effect: Genetic drift occurs after an event greatly reduces the size of a population
One example of the bottleneck effect is the overhunting of northern elephant seals during the 1800s. By the 1890s, the population was reduced to about 20 individuals. These 20 seals did not represent the genetic diversity of the original population. Since hunting has ended, the population has grown to over 100,000 individuals. However, it has very little genetic variation.
Through genetic drift, certain alleles have become fixed, while others have been lost completely from the gene pool.
Founder effect: Genetic drift happens after a small number of population colonize an area.
The gene pool of these populations are often very different from those ones of the larger populations.
The founder effect can be studied in human populations, such as Old Order Amish communities. These communities were founded in North America by small number of migrants from Europe. For example, the Amish of Lancaster country, Pennsylvenia, have a high rate of Ellis - van Creveld syndrome. Although this form of dwarfism is the rare in other human populations, it has become common in Amish population through genetic drift.
Effects of Genetic drift
Genetic drift can cause several problems for population. One problem is that the population loses genetic variation. With little genetic variation, a population is less likely to have some individuals that will be able to adapt to a changing environment.
Alleles that are lethal in homozygous individuals may be carried by heterozygous individuals and hence, become more common in the gene pool by chance alone.
Sexual selection occurs when certain traits increase mating success.
Intrasexual selection involves competition among males, the winner of the competition mates with female.
Intersexual selection occurs when males display certain traits that attract the female, such as peacocks fanning out their tails.
11.5 Speciation through isolation
If gene flow between two population stops for any reason, the populations are said to be isolated. As these populations adapt to their environments, their gene pool may change. Random processes such as mutation and genetic drift can also change gene pools. All of these changes add up over many generations.
With time, the two isolated populations become more and more genetically different. Individuals in one population may also begin to look and behave differently from individuals in the other population.
Reproductive isolation occurs when members of different populations can no longer mate successfully.
Reproductive isolation between populations is the final step of becoming separate species. The rise of two or more species from one existing species is called speciation.
Population can become isolated in several ways.
Behavioral barrier
Behavioral isolation is isolation caused by differences in courtship or mating behaviors.
Over 2000 species of fireflies are isolated in this way. Male and female fireflies produce patterns of flashes that attract mates of their own species. For example, Photuris frontalis emits one flash every second, P. hebes emits one flash every 2 seconds, and P. fairchildi produces a double flash every 5.5 seconds.
Geographic Barriers
Geographic isolation involves physical barriers that divide a population into two or more groups.
These barriers can include rivers, mountains, and dried lakebeds.the formation of the Isthmus of Panama created a barrier for many marine species. Marine organisms could no longer easily cross between the Atlantic and Pacific oceans. Over time, the isolated populations became genetically different.
Temporal Barrier
Temporal isolation exists when timing prevents reproduction between populations
For example, two tree species that grow on the Monterey peninsula in California are very closely related.However, they have different pollination periods. The Monterey pine sheds its pollen in February, while the Bishop pine sheds its pollen in April. These pine species have likely evolved through temporal isolation.
