Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 24 The Origin of Species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Speciation, the origin of new species, is at the focal point of evolutionary theory Evolutionary theory must explain how new species originate and how populations evolve Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Limitations of the Biological Species Concept The biological species concept does not apply to – Asexual organisms – Fossils – Organisms about which little is known regarding their reproduction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Definitions of Species Morphological: defines a species by structural features Paleontological: focuses on morphologically discrete species known only from the fossil record Ecological: views a species in terms of its ecological niche Phylogenetic: defines a species as a set of organisms with a unique genetic history

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways: – Allopatric speciation – Sympatric speciation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Allopatric (“Other Country”) Speciation In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations One or both populations may undergo evolutionary change during the period of separation

LE 24-7a Initial population of fruit flies (Drosophila pseudoobscura) Mating experiments after several generations Some flies raised on maltose medium Some flies raised on starch medium

LE 24-7b Female Starch Maltose Starch Maltose Male Same population Different populations Male 20 8 Mating frequencies in experimental group Mating frequencies in control group Same population Different populations 9 22

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polyploidy Polyploidy is presence of extra sets of chromosomes due to accidents during cell division It has caused the evolution of some plant species An autopolyploid is an individual with more than two chromosome sets, derived from one species

LE 24-8 Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue. Gametes produced by flowers on this tetraploid branch are diploid. Offspring with tetraploid karyo- types may be viable and fertile— a new biological species. 2n = 6 4n = 12 4n4n 2n2n

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An allopolyploid is a species with multiple sets of chromosomes derived from different species

LE 24-9 Species B 2n = 6 Species A 2n = 4 Normal gamete n = 3 Normal gamete n = 3 2n = 10 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Viable fertile hybrid (allopolyploid) Meiotic error; chromosome number not reduced from 2n to n

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Allopatric and Sympatric Speciation: A Summary In allopatric speciation, a new species forms while geographically isolated from its parent population In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Adaptive Radiation Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Tempo of Speciation The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

LE Time Gradualism model Punctuated equilibrium model

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution Is Not Goal Oriented The fossil record often shows apparent trends in evolution that may arise because of adaptation to a changing environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings According to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics The appearance of an evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype