Chapter 17: The Origin of Species

A drug called colchicine prevents cell division after the chromosomes have doubled at the start of meiosis. Describe how you would use colchicine to produce a new polyploid plants species.

Apply colchicine to the developing flowers and pollinate them. Pollen and ovules should contain diploid sperm and eggs that will fuse in fertilization to produce a polyploid embryo.

Review the material on the possibility of sympatric speciation in Rhagoletis flies. What types of genotypic, phenotypic or behavioral data would convince you that the two forms have become separate species?

Convincing data to support the conclusion that the two forms of fruit flies are separate species would be evidence that individuals of the two types do not mate under natural conditions of that matings between the two types do not produce viable offspring.

Many of the oak tree species in Central and Eastern North America hybridize (interbreed). Are they "true species"?

If we use strict reading of the biological species concept as our species definition, then naturally hybridizing populations are not technically separate species. But if hybridization is sufficiently rare that there is little gene flow between the two populations, most biologists would say that the two populations represent separate species.

What are the two major types of reproductive isolating mechanisms? Give examples of each type and describe how they work.

Premating isolating mechanisms include geographic isolation (a physical barrier between species), ecological isolation (species occupy different habitats), temporal isolation (species breed at different times), behavioral isolation (species have mating behaviors), and mechanical incompatibility (physical difference prevents mating between species). Postmating isolating mechanisms include gametic incompatibility (sperm and eggs of different species cannot fuse), hybrid inviability (hybrid offspring do not survive), and hybrid infertility (hybrid offspring are sterile).

Define the following terms: species, speciation, allopatric speciation, and sympatric speciation. Explain how allopatric and sympatric speciation might work and give a hypothetical example of each.

Species are all the populations of organisms that are capable of interbreeding under natural conditions and that are reproductively isolated from members of other populations. Speciation is the formation of new species through evolution. Allopatric speciation is speciation that occurs when two populations are geographically separated from each other. This may occur if the two isolated populations diverge genetically due to different selective pressures are genetic drift and are no longer able to interbreed. Sympatric speciation is speciation that occurs when two populations share the same geographic area. Speciation environmental change to genetic Divergence of organisms living in each, resulting in reproductive isolation.

All instances of speciation require a. genetic isolation and divergence b. genetic drift c. geographic subdivision of a population d. adaptive radiation

a

Analysis of Rhagoletis fly populations in North America provides evidence that id some members of an insect population shift to a new host species, a. sympatric speciation may eventually result b. adaptive radiation is likely c. little or no subsequent genetic divergence is likely d. sympatric speciation is probably impossible in insects

a

The biological species concept is difficult or impossible to apply to a. asexually reproducing organisms b. large organisms c. rapidly evolving organisms d. plants

a

The process by which many new species arise in a relatively short period of time is known as __________. This process often occurs when a species arrives in a previously unoccupied ___________.

adaptive radiation; habitat (or environment)

Which of the following does not describe a premating isolating mechanism? a. the courtship display of a bird of paradise b. the sterility of the offspring of a horse and a donkey c. the difference between the flowering periods of the Monterey pine and the Bishop pine d. the tendency of each species of fig wasps to breed only in the fruits of a particular species of fig

b

Fill in the following with the appropriate isolating mechanisms: Occurs when members of two populations have different courtship behaviors: _________ Occurs when hybrid offspring fail to survive to reproduce: __________ Occurs when members of two populations have different breeding seasons: _________ Occurs when sperm from one species fails to fertilize the eggs of another species: __________ Occurs when the sexual organs of two species are incompatible: __________

behavioral isolation, hybrid inviability, temporal isolation, gametic incompatibility, mechanical incompatibility

In the initial phase of allopatric speciation, gene flow between parts of a population is inhibited by a. competition b. hybrid inviability c. geographic isolation d. ecological isolation

c

Formation of a new species occurs when two populations of existing species first become and then _________. The process in which geographic separation of parts of a population leads to the formation of new species called _________. Isolated populations may diverge through the action of _________ or ________.

genetically isolated, diverge; allopatric speciation; genetic drift, natural selection

A species is a group of ________ that evolves _________. The biological species concept identifies species on the basis of their ________. The biological species concept cannot be applied to species that reproduce __________.

populations, independently; reproductive isolation; asexually

A species may be at higher risk of extinction if tis geographic range includes a _________ area, or if its food or habitat requirements are _________. The leading direct. cause of extinction is _________.

small, specialized; habitat destruction