23. Speciation

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

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 __________.

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?

At which point in the adaptation of a population is it clear that speciation has occurred?

Three species of frogs, Rana pipiens, Rana clamitans, and Rana sylvatica, all mate in the same ponds, but they pair off correctly because they have different calls. This is a specific example of a __________ barrier, called __________.

Prezygotic barriers __________.

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

Which of the following is an example of a postzygotic reproductive 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 __________.

The time interval between speciation events is typically __________.

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

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?

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?

Sometimes two phenotypically different populations interbreed to a limited extent, so that it is difficult to determine whether they are clearly separate species. This is not a concern to scientists because this __________.

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

In which of the following pairs of populations is allopatric speciation most likely to occur?

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

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

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?

A new species can arise in a single generation __________.

The Galápagos 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 __________.

In the case of the Lake Victoria cichlids, sympatric speciation has been shown to be driven by __________.

In a hybrid zone, which of the following would tend to lead to reinforcement?

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

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

Comparison of human fossils with living humans seems to show that there have been no significant physical changes in Homo sapiens in 30,000 to 50,000 years. What might an advocate of punctuated equilibrium say about this?

According to the punctuated equilibrium model of evolution, __________.

Define 'biological species.'

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

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

Add labels to the figure that follows, which illustrates the three steps required for speciation to occur.

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

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

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.

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

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.

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

Which of the following is an example of a postzygotic reproductive barrier? a. One Ceanothus shrub lives on acid soil, another on alkaline soil. b. Mallard and pintail ducks mate at different times of year. c. Two species of leopard frogs have different mating calls. d. Hybrid offspring of two species of jimsonweeds always die before reproducing.

The biological definition of 'race' corresponds to all of the following except: a. the genealogical species concept; b. the idea that subgroups within the same species can be distinguished from each other by ancestry; c. there is a natural hierarchy of groups within a species from 'lowest' to 'highest' forms; d. it should be possible to identify races on the basis of shared allele frequencies among populations; e. races within a species are not reproductively isolated from each other.

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.

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.

In the field of nanotechnology, DNA is used like Velcro to assemble tiny particles into structures that are < 0.0001 mm in size. Draw a model to illustrate how two particles (a circle and a square) could be brought together by linking them to short single-stranded DNA molecules. If the DNA sequence linked to the circle is GGATC, then provide the sequence linked to the square and identify the 5′ and 3′ ends of each strand.

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

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.

Distinguish between microevolution and macroevolution.

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.

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.

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

What does the term punctuated equilibria describe?

Can factors that cause sympatric speciation also cause allopatric speciation? Explain.

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.

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?

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?