24.3 Hybrid zones reveal factors that cause reproductive isolation Flashcards
29) The phenomenon of fusion is likely to occur when, after a period of geographic isolation, two populations meet again and
A) their chromosomes are no longer homologous enough to permit meiosis.
B) a constant number of viable, fertile hybrids is produced over the course of generations.
C) the hybrid zone is inhospitable to hybrid survival.
D) an increasing number of viable, fertile hybrids is produced over the course of generations
E) a decreasing number of viable, fertile hybrids is produced over the course of generations.
D) an increasing number of viable, fertile hybrids is produced over the course of generations
30) The constantly changing nature of the Appalachian ground crickets ( Allonemobius fasciatus and Allonemobius socius) hybrid zone favors
A) no gene flow between the two gene pools.
B) little gene flow between the two gene pools.
C) increased levels of gene flow between the two gene pools.
D) extinction of both species as the hybrids persist.
D) extinction of both species as the hybrids persist.
31) A hybrid zone is properly defined as
A) an area where two closely related speciesʹ ranges overlap.
B) an area where mating occurs between members of two closely related species, producing viable offspring.
C) a zone that features a gradual change in species composition where two neighboring ecosystems border each other.
D) a zone that includes the intermediate portion of a cline.
E) an area where members of two closely related species intermingle, but experience no gene flow.
B) an area where mating occurs between members of two closely related species, producing viable offspring.
32) Which of these should decline in hybrid zones where reinforcement is occurring?
A) gene flow between distinct gene pools
B) speciation
C) the genetic distinctness of two gene pools
D) mutation rate
E) hybrid sterility
A) gene flow between distinct gene pools
33) The most likely explanation for the high rate of sympatric speciation that apparently existed among the cichlids of Lake Victoria in the past is
A) sexual selection.
B) habitat differentiation.
C) polyploidy.
D) pollution.
E) introduction of a new predator.
A) sexual selection.
34) The most likely explanation for the recent decline in cichlid species diversity in Lake Victoria is
A) reinforcement.
B) fusion.
C) stability.
D) geographic isolation.
E) polyploidy.
B) fusion.
35) In the narrow hybrid zone that separates the toad species Bombina bombina and Bombina variegata, what is true of those alleles that are unique to the parental species?
A) Such alleles should be absent.
B) Their allele frequency should be nearly the same as the allele frequencies in toad populations distant from the hybrid zone.
C) The allelesʹ heterozygosity should be higher among the hybrid toads there.
D) Their allele frequency on one edge of the hybrid zone should roughly equal their frequency on the opposite edge of the hybrid zone.
C) The allelesʹ heterozygosity should be higher among the hybrid toads there.
On the volcanic, equatorial West African island of Sao Tomé, two species of fruit fly exist. Drosophila yakuba inhabits the islandʹs lowlands, and is also found on the African mainland, located about 200 miles away. At higher elevations, and found only on Sao Tomé, is found the very closely related Drosophila santomea. The two species can hybridize, though male hybrids are sterile. A hybrid zone exists at middle elevations, though hybrids there are greatly outnumbered by D. santomea. Studies of the two speciesʹ nuclear genomes reveal that D. yakuba on the island is more closely related to mainland D. yakuba than to D. santomea (2n=4 in both species). Sao Tomé rose from the Atlantic Ocean about 14 million years ago.
37) The observation that island D. yakuba are more closely related to mainland D. yakuba than island D. yakuba are to D. santomea is best explained by proposing that D. santomea
A) descended from a now-extinct, non-African fruit fly.
B) arose de novo; that is, had no ancestors.
C) descended from a single colony of D. yakuba, which had been introduced from elsewhere, with no subsequent colonization events.
D) descended from an original colony of D. yakuba, of which there are no surviving members. The current island D. yakuba represent a second colonization event from elsewhere.
D) descended from an original colony of D. yakuba, of which there are no surviving members. The current island D. yakuba represent a second colonization event from elsewhere.
41) If the low number of hybrid flies in the hybrid zone, relative to the number of D. santomea flies there, is due to the fact that hybrids are poorly adapted to conditions in the hybrid zone, and if fewer hybrid flies are produced with the passage of time, this is most likely to lead to
A) fusion.
B) reinforcement.
C) stability.
D) further speciation events.
B) reinforcement.
