Flashcards
Chapter 24 Test (Short Answer)
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- 1There are many barriers that may reproductively isolate 2 individuals from different species and maintain the species as separate from one another. Consider the following scenario: There are 2 species of tropical lizards in the genus Anolis that both feed on insects. One Anolis lizard forages mainly on insects found in the treetops and the other species forages mainly on ground-dwelling insects. The 2 species are not known to interbreed in nature. However, when kept in captivity, the lizards do interbreed and produce viable, fertile offspring. What type of reproductive barrier is most likely keeping these species separate in nature? Review Chap 24.1 and Figure 24.3 and briefly explain your choice.Given the scenario, considering there is no physical barrier keeping these two species apart, this would be an example of sympatric speciation. Sympatric speciation is the formation of new species in populations that live in the same geographic area though they typically do not interbreed in nature.
- 2Summarize the key differences between allopatric and sympatric speciation. Give an example of each kind of speciation.Allopatric speciation: The formation of a new species in populations that are geographically isolated/separated from one another (isolated from its parent population) so genetics exchanges are not possible any longer. By living in different places, they have to face different environmental conditions (heat, salinity, pH…) and so to adapt differently. This causes the species to become slightly different from generation to generation.
" Example: water level in a lake may subside, resulting in two or more smaller lakes that are now home to separate population of animals that cannot cross it
Sympatric speciation: A speciation in which new species evolve from a single ancestral species; the formation of new species in populations that live in the same geographic area (new species formed without geographic separation).
" Example: divergence of resident and transient Orca in the northeast pacific. These two groups of Orca occur in the same habitat but are avoiding each other and they do not interbreed. They have different diets, vocal behavior and social structures - 3Plant species F has a diploid number of 8. Plant species G has a diploid number of 10. What would be the diploid number of an allopolyploid hybrid of species F and species G? (Write answer as a whole number).18
- 4(a) Which species concept(s) could you apply to both asexual and sexual species? (b) Which would be most useful for identifying species in the field? Explain.(a) All except the biological species concept can be applied to both asexual and sexual species because they define species on the basis of characteristics other than the ability to reproduce. In contrast, the biological species concept can be applied only to sexual species.
(b) The easiest species concept to apply in the field would be the morphological species concept because it is based only on the appearance of the organism. Additional information about its ecological habits or reproduction is not required. - 5What If? Suppose two bird species lived in a forest and are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and produce viable, fertile offspring. What type of reproductive barrier most likely keeps these species separate in nature? Explain.Because these birds live in fairly similar environments and can breed successfully in captivity, the reproductive barrier in nature is probably prezygotic; given the species' differences in habitat preference, this barrier could result from habitat isolation.
- 6Summarize key differences between allopatric and sympatric speciation. Which type of speciation is more common, and why?In allopatric speciation, a new species forms while in geographic isolation from its parent species; in sympatric speciation, a new species forms in the absence of geographic isolation. Geographic isolation greatly reduces gene flow between populations, whereas ongoing gene flow is more likely in sympatric populations. As a result, allopatric speciation is more common than sympatric speciation.
- 7Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur.Gene flow between subsets of a population that live in the same area can be reduced in a variety of ways. In some species-especially plants-changes in chromosome number can block gene flow and establish reproductive isolation in a single generation. Gene flow can also be reduced in sympatric populations by habitat differentiation (as seen in the apple maggot fly) and sexual selection (as seen in Lake Victoria cichlids).
- 8What If? Is allopatric speciation more likely to occur on an island close to a mainland or on a more isolated island of the same size? Explain your prediction.Allopatric speciation would be less likely to occur on an island near a mainland than on a more isolated island of the same size. We expect this result because continued gene flow between mainland populations and those on a nearby island reproduces the chance that enough genetic divergence will take place for allopatric speciation to occur.
- 9Making Connections. Describe how making an error during meiosis could lead to polyploidyIf all of the homologs failed to separate during anaphase I of meiosis, some gametes would end up with an extra set of chromosomes (and others would end up with no chromosomes). If a gamete with an extra set of chromosomes fused with a normal gamete, a triploid would result; if two gametes with an extra set of chromosomes fused with each other, a tetraploid would result.
- 10What are hybrid zones, and why can they be viewed as "natural laboratories" in which to study speciation?Hybrid zones are regions in which members of different species meet and mate, producing some offspring of mixed ancestry. Such regions can be viewed as "natural laboratories" in which to study speciation because scientists can directly observe factors that cause (or fail to cause) reproductive isolation.
- 1191. What If? Consider two species that diverged while geographically separated but resumed contact before reproductive isolation was complete. Predict the outcome over time if the two species mated indiscriminately and (a) hybrid offspring survived and reproduced more poorly than offspring from intraspecific matings or (b) hybrid offspring survived and reproduced as well as offspring from intraspecific matings.a) If hybrids consistently survived and reproduced poorly compared with the offspring of intraspecific matings, reinforcement could occur. If it did, natural selection would cause prezygotic barriers to reproduction between the parent species to strengthen over time, decreasing the production of unfit hybrids and leading to a completion of the speciation process.
b) If hybrid offspring survived and reproduced as well as the offspring of intraspecific matings, indiscriminate mating between the parent species would lead to the production of large numbers of hybrid offspring. As these hybrids mated with each other and with members of both parent species, the gene pools of the parent species could fuse over time, reversing the speciation process. - 12Speciation can occur rapidly between diverging populations, yet the time between speciation events is often more than a million years. Explain this apparent contradiction.The time between speciation events includes (1) the length of time that it takes for populations of a newly formed species to begin diverging reproductively from one another and (2) the time it takes for speciation to be complete once this divergence begins. Although speciation can occur rapidly once populations have begun to diverge form one another, it may take millions of years for that divergence to begin.
- 13Summarize evidence that the yup locus acts as a prezygotic barrier to reproduction in two species of monkey flowers. Do these results demonstrate that the yup locus alone controls barriers to the reproduction between these species? Explain.Investigators transferred alleles at the yup locus (which influences flower color) for each parent species to the other. M. Lewisii plants with an M. cardinalis yup allele receives many more visits from hummingbirds than usual; hummingbirds usually pollinate M. cardinalis but avoid M. lewisii. Similarly, M. Cardinalis plants with an M. lewisii yup allele receive many more visits from bumblebees than usual; bumblebees usually pollinate M. lewisii and M. cardinalis. Thus, alleles at the yup locus can influence pollinator choice, which in these species provides the primary barrier to interspecific mating. Nevertheless, the experiment does not prove that the yup locus alone controls barriers to reproduction between (for example, gametic isolation or a post zygotic barrier).
- 14Explain the role of gene flow in the biological species concept.According to the biological species concept, a species is a group of populations whose members interbreed and produce viable, fertile offspring; thus, gene flow occurs between populations of a species. In contrast, members of different species do not interbreed and hence non gene flow occurs between their populations. Overall, then, in the biological species concept, species can be viewed as designated by the absence of gene flow-making gene flow of central importance to the biological species concept.
- 15Can factors that cause sympatric speciation also cause allopatric speciation?Yes. Sympatric speciation can be promoted by factors such as polyploidy, sexual selection, and habitat shifts, all of which can reduce gene flow between the subpopulations of a larger population. But such factors can also occur in allopatric populations and hence can also promote allopatric speciation.
- 16What factors can support the long-term stability of a hybrid zone if the parent species live in different environments?If the hybrids are selected against, the hybrid zone could persist if individuals from the parent species regularly travel into the zone, where they mate to produce hybrid offspring. If hybrids are not selected against, there is no cost to the continued production of hybrids, and large numbers of hybrid offspring may be produced. However, natural selection for life in different environments may keep the gene pools of the two parent species distinct, thus preventing the loss (by fusion) of the parent species and once again causing the hybrid zone to be stable over time.
- 17Is speciation something that happened only in the distant past, or are new species continuing to arise today? Explain.As the goatsbeard plant, Bahamas mosquitofish, and apple maggot fly illustrate, speciation continues to happen today. A new species can begin to form whenever gene flow is reduced between populations of the parent species. Such reductions in gene flow can occur in many ways: A new, geographically isolated population may be founded by a few colonists; some members of the parent species may begin to utilize a new habitat; or sexual selection may isolate formerly connected populations or subpopulations. These and many other such events are happening today.
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- BCOR 12 Flashcards on Chapter 24 Test (Short Answer), created by Munro Richardson on 03/03/2018.
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