23. Speciation

Species

What is a Species? Crash Course Zoology #13

Add labels to the figure that follows, which illustrates the three steps required for speciation to occur. <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/6667068017f4a26d-1677236694715.jpg" style="width: 300px;">

Neanderthals disappeared about 40,000 years ago when the modern human population increased. This is an example of what outcome(s) of secondary contact (see Table 24.4)? Predict one way this result might have come about. <IMAGE>

For two populations of organisms to be considered separate biological species, they must be                   .
a. reproductively isolated from each other;
b. unable to produce living offspring;
c. physically very different from each other;
d. A and C are correct;
e. A, B, and C are correct

Speciation: Of Ligers & Men - Crash Course Biology #15

What does the term punctuated equilibria describe?

What distinguishes a morphospecies?
a. It has distinctive characteristics, such as size, shape, or coloration.
b. It represents a distinct branch in a phylogeny of populations.
c. It is reproductively isolated from other species.
d. It is a fossil from a distinct time in Earth history.

A revolution in the study of human evolution is under way thanks to the invention of techniques that enable DNA sequencing of not only modern humans, but also ancient humans.

Modern humans (Homo sapiens) and archaic humans called Neanderthals (H. neanderthalensis) shared a common ancestor in Africa but diverged in different geographic areas. When modern humans migrated out of Africa and dispersed around the world starting about 100,000 years ago, they overlapped with Neanderthals in Europe. This scenario is best described as
a. species living in sympatry following allopatric speciation

b. species living in sympatry following sympatric speciation

c. species living in allopatry following allopatric speciation

d. species living in allopatry following sympatric speciation

Sexual selection favors individuals with traits that increase their ability to obtain mates, such as mating calls in crickets. Using this example, propose a scenario where sexual selection could contribute to divergence in sympatric speciation.

Cultivated American cotton plants have a total of 52 chromosomes (2n = 52). In each cell, there are 13 pairs of large chromosomes and 13 pairs of smaller chromosomes. Old World cotton plants have 26 chromosomes (2n = 26), all large. Wild American cotton plants have 26 chromosomes, all small. Propose a testable hypothesis to explain how cultivated American cotton probably originated.

Bird guides once listed the myrtle warbler and Audubon’s warbler as distinct species that lived side by side in parts of their ranges. However, recent books show them as eastern and western forms of a single species, the yellow-rumped warbler. Most likely, it has been found that these two kinds of warblers
a. live in similar habitats and eat similar foods.
b. interbreed often in nature, and the offspring are viable and fertile.
c. are almost identical in appearance.
d. have many genes in common.

A revolution in the study of human evolution is under way thanks to the invention of techniques that enable DNA sequencing of not only modern humans, but also ancient humans.

Human populations today are not considered separate species under the biological species, morphospecies, and phylogenetic concepts. Explain what kind of evidence supports this statement.

Name the two types of speciation represented by this diagram. For each type, describe how reproductive barriers may develop between the new species.

Speciation

Murky, polluted water is causing reduced hybrid viability.

No. Reduced hybrid viability would contribute to reinforcement of reproductive barriers rather than fusion of species.

Overfishing is causing the species to fuse due to a lack of potential same-species mates for many fish.

No. There is no evidence that overfishing is contributing to fusion of species.

Extinctions are being caused by the Nile perch, an introduced predator.

No. Although the introduction of the Nile perch has led to the extinction of some cichlid species, it does not appear to be contributing to the observed fusion.

The viability of cichlid eggs is being reduced by water pollution.

No. Unless the pollution was directly selecting for or against hybrid eggs, such a situation would have no bearing on fusion of species in the lake.

Females have a difficult time visually selecting males of the same species in the murky, polluted water.

How can changes in the environment promote or discourage speciation?

In the Lake Victoria cichlids, what appears to be contributing to fusion of different species?

No. A single gene has been shown to cause a mechanical barrier to reproduction, but there is a better answer.

No. At least 26 chromosomal segments have been implicated in the speciation of certain sunflowers, but there is a better answer.

No. At least four gene loci are involved in a fruit fly speciation event, but there is a better answer.

No. Undoubtedly a speciation event has occurred based on changes in 14 genes, but there is a better answer.

There is no set number of genes or loci that produces a new species. Genetic and environmental factors interact.

Think about how many different causes of reproductive isolation there might be.

How many genes must change in order to form a new species?

When the ranges of two different species meet, a stable “hybrid zone” occupied by hybrid individuals may form. How is this possible?
a. Two diverged populations are capable of mating and producing viable and fertile offspring.
b. Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species.
c. Hybrid individuals may have reduced fitness and thus be strongly selected against.
d. One species has a selective advantage, so as hybridization continues, the other species will go extinct.

The red wolf, Canis rufus, which was once widespread in the southeastern and south central United States, was declared extinct in the wild by 1980. Saved by a captive breeding program, the red wolf has been reintroduced in areas of eastern North Carolina. The current wild population is estimated to be about 100 individuals. It is presently being threatened with extinction due to hybridization with coyotes, Canis latrans, which have become more numerous in the area. Red wolves and coyotes differ in terms of morphology, DNA, and behavior, although these differences may disappear if interbreeding continues. Although the red wolf has been designated as an endangered species under the Endangered Species Act, some people think that its endangered status should be withdrawn and resources should not be spent to protect what is not a “pure” species. Do you agree? Why or why not?

Short Video: Prezygotic Barriers

No. This prezygotic mechanism involves incompatible gametes.

No. This is an anatomical incompatibility that prevents mating.

No. Fertilization occurs in hybrid breakdown, but the second-generation hybrid is not viable.

No. This involves hybrid individuals producing fewer viable offspring.

The answer is a type of prezygotic barrier.

Two species of water lilies in the same pond do not interbreed because one blooms at night and the other during the day. The reproductive barrier between them is an example of __________.

True or false? Speciation is a slow process. Justify your answer.

No. Living in the same area does not make them the same species.

No. Although very similar, they are different enough in appearance that they were once classified as two species.

No. There is no evidence pointing to that possibility.

No. They should never have been considered two species because they can interbreed and produce fertile offspring.

successfully interbreed and produce fertile offspring

Consider the different species concepts.

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species that lived side by side in parts of their ranges. However, recent books show them as eastern and western forms of a single species, the yellow-rumped warbler. Apparently, the myrtle warbler and Audubon's warbler __________.

Biologists have found more than 500 species of fruit flies on the various Hawaiian Islands, all apparently descended from a single ancestor species. This example illustrates
a. polyploidy.
b. temporal isolation.
c. adaptive radiation.
d. sympatric speciation.

No. If they are geographically isolated from each other, it is unlikely that they arose by sympatric speciation.

No. Gene flow would be more likely to prevent speciation.

No. Polyploidy among animals is extremely rare. Also, molecular studies done on the Gal&#225;pagos finches have not indicated that polyploidy was a factor in their speciation.

No. Hybridization tends to increase gene flow between previously isolated populations.

How does geographic isolation lead to speciation?

The Gal&#225;pagos finches collected by Darwin are thought to have descended from a very small parent population. Different species of finches that are confined to only one or two islands most likely arose by __________.

No. The two gametes would be n = 2 and n = 4. They would combine for a total of 6, which after doubling would be 12.

Think about the gametes that will be produced by each of the parental species.

If a new species of plant is to be produced by means of allopolyploidy from two parental species that are 2n = 4 and 2n = 8, how many chromosomes would you expect in the somatic cells of the new species?

What prevents horses and donkeys from hybridizing to form a new species?
a. limited hybrid fertility
b. limited hybrid viability
c. hybrid breakdown
d. gametic isolation

Which concept of species would be most useful to a field biologist identifying new plant species in a tropical forest?
a. biological
b. ecological
c. morphological
d. phylogenetic

Neanderthals disappeared about 40,000 years ago when the modern human population increased. This is an example of what outcome(s) of secondary contact (see Table 24.4)? Predict one way this result might have come about. <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/0572b61f110c86e6-1677310669064.jpg" style="width: 300px;">

Define Species

No. This is isolation due to the inability of gametes to unite.

No. This is due to structural differences preventing mating or pollen transfer.

No. In this case, many hybrid zygotes fail to develop.

No. A geographic barrier is a physical barrier preventing interbreeding.

Review the forms of reproductive isolation.

There are two groups of pine trees that appear to be very similar phenotypically and genotypically. However, one releases pollen in January, when the female structures of that group are receptive, and one in March. What kind of reproductive barrier is this?

Explain why allopatric speciation would be less likely on an island close to a mainland than on a more isolated island.

Bird guides once listed the myrtle warbler and Audubon’s warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?
a. The two forms interbreed often in nature, and their offspring survive and reproduce well.
b. The two forms live in similar habitats and have similar food requirements.
c. The two forms have many genes in common.
d. The two forms are very similar in appearance.

Types of Speciation: Allopatric, Sympatric, Peripatric, and Parapatric

One species of frog mates in April, but another mates in May.

No. Because mating does not take place, this is a prezygotic barrier, specifically, temporal isolation.

The sperm of a marine worm can only fertilize eggs of the same species.

No. Because a zygote is not produced, this is a prezygotic barrier, specifically, gametic incompatibility.

One species of flower grows in forested areas, another in meadows.

No. This is a prezygotic barrier, specifically, ecological (spatial) isolation, and thus no mating takes place.

Two pheasant species perform different courtship dances.

No. This is an example of behavioral isolation, which is a prezygotic barrier.

Two fruit flies of different species produce sterile offspring.

Consider which of these requires the formation of a zygote but one that doesn't work all that well. Review the forms of reproductive isolation.

Which of the following is an example of a postzygotic reproductive barrier?

isolated species changing over a few thousand generations represent graduated equilibrium, not punctuated equilibrium

No. A few thousand generations is a very short period in geological time, so this could appear as a punctuated equilibrium.

polyploidy is not a mechanism of punctuated equilibrium

No. Polyploidy represents one of the main mechanisms of punctuated equilibrium, especially in plants.

fossils of organisms that existed during periods of stasis should be as abundant as those of organisms that existed during periods of rapid change

No. In the model of punctuated equilibrium, periods of stasis are much more common than are periods of rapid change.

the tempo of evolution consists of abrupt episodes of speciation among long periods of equilibrium

Think about the patterns observed in the fossil record.

According to the punctuated equilibrium model of evolution, __________.

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent?
a. habitat isolation
b. temporal isolation
c. behavioral isolation
d. gametic isolation

A revolution in the study of human evolution is under way thanks to the invention of techniques that enable DNA sequencing of not only modern humans, but also ancient humans.

Before the application of DNA sequencing to fossils, which species concept was most useful for distinguishing human fossils? What is one disadvantage of this approach?

A catastrophic event must cause geographic separation of two populations.

No. Geographic separation is not always necessary for speciation (remember sympatric speciation), and it may be gradual, not catastrophic.

No. A hybrid zone could not be established until gene flow had already been interrupted for some length of time. In addition, a hybrid zone might tend to slow or stop speciation.

The populations must become reproductively isolated.

No. Although reproductive isolation is necessary for speciation according to the biological species model, reproductive isolation is unlikely to occur until gene flow is interrupted and the populations have diverged genetically to some extent.

One of the populations must become polyploid.

No. Though polyploidy can stop gene flow almost instantaneously, it is not very common, nor is it necessary for speciation to occur.

Gene flow between populations must be interrupted.

What is the basic element that holds the gene pool of a species together?

What is the first thing that must happen in order for speciation to occur?

According to the most accepted scientific hypothesis about the origin of two new species from a single common ancestor, most new species arise when                   .
a. many mutations occur;
b. populations of the ancestral species are isolated from one another;
c. there is no natural selection;
d. a supernatural creator decides that two new species would be preferable to the old one;
e. the ancestral species decides to evolve

If you sequenced the DNA of all your classmates, you would probably observe that the percentage of Neanderthal genes in their genomes varies from 0–4%. How would you know whether there is a significant difference in percentage between students with blue eyes and students with brown eyes?

Which of the following describes vicariance?

a. Small populations coalesce into one large population.
b. A population is fragmented into isolated subpopulations.
c. Individuals colonize a novel habitat.
d. Individuals disperse and found a new population.

The island birds all have red feathers, but the mainland birds have green feathers.

No. Populations with different appearances are not necessarily different species.

The preferred food of the island birds is quite different from the diet of mainland birds.

No. Though two such populations might be considered different species under the ecological species concept, the biological species concept requires reproductive isolation.

Individuals from the different populations frequently direct courtship behavior toward members of the other population.

No. This suggests that speciation did not occur.

Hybrid offspring of matings between individuals from the two populations do not look like either parent.

Individuals from the different populations sometimes mate with each other, but all of the resulting eggs are sterile.

Consider the definition of the biological species concept.

Imagine that part of a population of South American finches is blown by a storm onto an island far offshore and manages to survive and reproduce there for a period of 10,000 years. After that period, a climate change results in lower sea levels and the reconnection of the island with the mainland. Members of the formerly isolated island finch population can now interact freely with members of the original mainland population. Which of the following observations would, by itself, lead you to conclude unequivocally that the island finch population had evolved into a distinct species, according to the biological species concept?

What is a species?

Explain how each of the following makes it difficult to clearly define a species: variation within a species, geographically isolated populations, asexual species, fossil organisms.

No. Genetic drift can result in reproductive isolation of allopatric populations, increasing the likelihood of speciation.

No. Because mutations are random, when they occur in isolated allopatric populations they increase the likelihood of speciation occurring.

No. Natural selection can result in reproductive isolation of allopatric populations, increasing the likelihood of speciation.

No. One of the mechanisms reduces the likelihood of speciation.

How does speciation occur?

Which of the following evolutionary mechanisms does not contribute to the process of allopatric speciation?

All of the following statements support the hypothesis that humans cannot be classified into biological races except:
a. There is more genetic diversity within a racial group than average differences between racial groups;
b. Alleles that are common in one population in a racial group may be uncommon in other populations of the same race;
c. Geneticists can use particular SNP alleles to identify the ancestral group(s) of any individual human;
d. There are no alleles found in all members of a given racial group;
e. There is genetic evidence of mixing among human populations occurring thousands of years ago until the present.

No. With reduced hybrid viability, fertilization occurs, but the resulting hybrid is weak and unlikely to survive to reproduce.

No. With hybrid sterility, fertilization occurs, but the resulting hybrid is sterile.

No. With gametic isolation, mating occurs, but fertilization does not occur because the gametes are not compatible.

No. With hybrid breakdown, fertilization occurs, but the second-generation hybrid is not viable.

Consider which of these is a barrier that prevents gametes from meeting each other. Review the forms of reproductive isolation.

Which of the following reproductive barriers actually prevents individuals of closely related species from copulating successfully?

Three-spine sticklebacks are small fish that originated in the ocean and continue to exist there, but then some took up residence in hundreds of streams and freshwater lakes in the Northern Hemisphere. Predict whether you would expect to find different species in lakes today.

According to the biological species concept, species are defined by their
a. particular roles in a biological community.
b. ability to interbreed and produce viable, fertile offspring.
c. reproductive isolation from nearby populations.
d. common ancestry.

Which of the following is an example of a prefertilization barrier to reproduction?
a. A female mammal is unable to carry a hybrid offspring to term;
b. Hybrid plants produce only sterile pollen;
c. A hybrid between two bird species cannot perform a mating display;
d. A male fly of one species performs a “wing-waving” display that does not convince a female of another species to mate with him;
e. A hybrid embryo is not able to complete development

Allopatric & Sympatric Speciation | A-level Biology | OCR, AQA, Edexcel

Biological Species

No. It usually takes many generations for speciation to occur by geographic isolation.

in a very large population spread over a large area

No. It normally takes many generations for sexually reproducing organisms to speciate.

No. Allopatric speciation occurs by geographic isolation, and it takes several generations for speciation to occur in this manner.

No. This most likely will not lead to new species arising in a single generation.

if a change in chromosome number creates a reproductive barrier

Think about some of the mechanisms of sympatric speciation.

A new species can arise in a single generation __________.

Allopatric and sympatric speciation | Biology | Khan Academy

When hybrids produced in a hybrid zone can breed with each other and with both parent species, and they survive and reproduce as well as members of the parent species, one would predict that
a. the hybrid zone would be stable.
b. sympatric speciation would occur.
c. reinforcement of reproductive barriers would keep the parent species separate.
d. reproductive barriers would lessen and the two parent species would fuse.

All over the world, natural habitats are being fragmented into tiny islands by suburbs, ranches, farms, and roads. If asked to join a science panel to speak to Congress, could you explain how this fragmentation process could lead to extinction? How it could lead to speciation?

Sympatric Speciation and Hybrid Zones

Animation: Polyploid Plants

Hybrid Zones & Speciation

Select True or False to indicate which of the following groups could be identified using the biological species concept.
T/F lizard species living today
T/F sunflower species living today
T/F extinct dinosaurs
T/F bacteria living today

No. Hybridization would mark the beginning of gene flow between two formerly isolated populations.

No. Sexual reproduction is one reproductive strategy. The cessation of gene flow might indicate a barrier of some kind to sexual reproduction.

No. Sexual selection can occur only among members of a population where gene flow is occurring.

No. Fusion refers to two or more populations reestablishing gene flow and forming one species.

How does gene flow hold a population together?

When gene flow between two populations ceases, the potential for __________ exists.

SCIENTIFIC THINKING Explain how the murky waters of Lake Victoria may be contributing to the decline in cichlid species. How might these polluted waters affect the formation of new species?

No. This is a specific pattern of speciation, not a condition that leads to it.

No. However, rapid speciation often follows mass extinctions.

Interbreeding among neighboring populations

Consider the biological species concept.

Which of the following conditions is necessary for speciation to occur?

prevent a hybrid zygote from developing into a viable, fertile adult

No. This would be an action of a postzygotic barrier.

are necessary in order for speciation to occur

No. Prezygotic barriers are a component of reproductive isolation, which is only one aspect of speciation under the biological species concept.  However, reproductive isolation can also occur due to postzygotic barriers.

No. Donkeys and horses are capable of mating, but their offspring (mules and hinnies) are almost always sterile.

prevent fertilization of gametes from members of closely related species

Review the different forms of reproductive isolation and think about the prefix "pre-."

Prezygotic barriers __________.

Fill in the blanks in the following concept map.
a. 
b. 
c. 
d. 
e. 
f.

What Makes a Species a Species?

Which of the following factors would not contribute to allopatric speciation?
a. A population becomes geographically isolated from the parent population.
b. The separated population is small, and genetic drift occurs.
c. The isolated population is exposed to different selection pressures than the parent population.
d. Gene flow between the two populations continues to occur.

Yes. After several generations, the reproductive barrier (behavioral isolation) between the starch- and maltose-fed populations was complete.

No. Some mating between the starch flies and maltose flies did occur.

Yes. After several generations, the reproductive barrier (mechanical isolation) between the starch- and maltose-fed populations was complete.

No. Some mating between the starch flies and maltose flies did occur. Also, this experiment was an example of behavioral isolation.

No. After several generations, the formation of a reproductive barrier (mechanical isolation) was evident but not absolute.

No. This experiment was an example of behavioral isolation.

No. Even after several generations, there was no evidence of a reproductive barrier forming between the populations.

No. The starch flies were more apt to mate with other starch flies, and the maltose flies were more apt to mate with other maltose flies, although some interbreeding still did occur.

No. After several generations, the formation of a reproductive barrier (behavioral isolation) was evident but not absolute.

Review Dodd's fruit fly experiments on divergence of allopatric populations.

According to the experiment of Diane Dodd, can adaptive divergence of allopatric fruit fly populations lead to reproductive isolation?

Which of the following factors would not contribute to allopatric speciation?
a. The separated population is small, and genetic drift occurs.
b. The isolated population is exposed to different selection pressures than the ancestral population.
c. Different mutations begin to distinguish the gene pools of the separated populations.
d. Gene flow between the two populations is extensive.

No. There is an easier way to arrive at a conclusion. In addition, many of the speciation events in Lake Victoria are too recent to have left fossil evidence.

Compare DNA sequences because the DNA of members of the same species should be identical.

No. There is a more direct way to arrive at a conclusion.

Do studies on comparative anatomy, especially looking for homologous structures.

No. There is an easier way to arrive at a conclusion.

No. One of the other choices will suffice.

Observe the fish in their natural environment for possible instances of interbreeding leading to several generations of fertile offspring.

Review the definition of a biological species.

Lake Victoria, in Africa, is home to a group of related fishes known as cichlids. Many of these fishes are similar in appearance but have different feeding habits. What is the best method for scientists to determine conclusively whether the fish are members of a population that has a lot of variation or members of entirely different species?

Speciation: An Illustrated Introduction

No. Although reduced hybrid viability would tend to strengthen reproductive barriers, there is a better answer.

No. Although hybrid breakdown would tend to strengthen reproductive barriers, there is a better answer.