The Origin of Species Chapter 24 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Biological Species Cynotilapia afra, introduced at West Thumbi Island in Lake Malawi in the 1960s, has split into two genetically distinct populations, located at the north and south ends of the island. How can scientists determine whether these populations are now different species? See whether the two populations are morphologically different from each other: coloring, bone structure, and so on. Determine whether captured individuals from the two different populations will mate and produce offspring in a laboratory fishtank. Determine whether gene flow occurs naturally between the two different populations. Determine whether individuals from one population will interbreed with individuals from the other population when introduced into each other’s native habitats. Answer: d Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Mechanism of Reproductive Isolation If the two populations of C Mechanism of Reproductive Isolation If the two populations of C. afra at West Thumbi Island have different striping patterns, what might be a likely mechanism contributing to speciation? polyploidy female mating preferences differing habitat preferences temporal isolation mechanical isolation Answer: b Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Species Concepts Which species concept(s) may be used to classify prokaryotes? biological species concept only phylogenetic and morphological species concepts ecological and phylogenetic species concepts phylogenetic species concept only ecological, morphological, and phylogenetic species concepts Answer: e Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Adaptive Radiation Cichlids in Lake Victoria are thought to have diversified from a relatively few individuals to several hundred species in about 12,000 years (the last time the lake dried up). How could this hypothesis be tested? Examine the fossil record in lake sediments. Look for morphological characteristics shared among Lake Victoria species that are distinct from the species present in other lakes. Look for genetic characteristics shared among Lake Victoria species that are distinct from species present in other lakes. This is not a testable hypothesis. Answer: c A phylogenetic analysis should provide the most conclusive answer: The Lake Victoria species should form one or a few clades distinct from the clades in other African great lakes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Mechanisms of Adaptation In vertebrate radiation, exemplified by African cichlids, modification of jaws occurs during adaptation to different food sources. Such rapid modifications could result from which of the following? changing the expression of genes that control the growth of different jaw bones during development evolving new genes that generate new jaw bones acquiring genes by hybridizing with other species that exploit the same food source individuals exercising their jaw muscles in different ways, causing the jaws to grow accordingly Answer: a Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Allopatric Speciation What characteristics of organisms would make them more likely to undergo allopatric speciation? large range limited mobility being a generalist rather than a specialist all of the above none of the above Answer: d Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Speciation and Physical Environment In what types of environments should a scientist look for examples of ongoing speciation? areas that have a large range of altitudes, such as mountains and deep valleys areas such as large plains that facilitate migration of animals extreme physical environments that are marginal for supporting life areas that are already species-rich areas that have undergone recent environmental disturbance or change Answer: e Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Reproductive Isolation Mechanisms Sea urchins are broadcast spawners: They release their gametes into the water column. What reproductive isolation mechanism(s) might operate for sea urchin species? behavioral isolation mechanical isolation gametic isolation temporal isolation postzygotic mechanisms Answers: c and d Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Human Brain Evolution A comparison of the human and chimpanzee genomes shows that they are 99% identical, with very few differences in protein coding genes. What mechanisms may be responsible for evolution of the human brain? One or a few novel genes organized new brain structures. The timing of the expression of brain development genes altered. Brain development genes acquired mutations that made them more active in promoting brain growth. Genes that had other functions acquired new functions in brain development (exaptation). Answer: b The most likely explanation is b, but the other options cannot be ruled out at this point. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.