Chapter 14 The Origin of Species

Mosquito Mystery Speciation is the emergence of new species In England and North America Two species of mosquitoes exist and spread West Nile virus

14.1 The origin of species is the source of biological diversity Speciation, the origin of new species Is at the focal point of evolution Figure 14.1

Earth’s incredible biological diversity is the result of macroevolution Which begins with the origin of new species

CONCEPTS OF SPECIES 14.2 What is a species? Carolus Linnaeus, a Swedish physician and botanist Used physical characteristics to distinguish species Developed the binomial system of naming organisms Linnaeus’ system established the basis for taxonomy The branch of biology concerned with naming and classifying the diverse forms of life

Similarities between some species and variation within a species Can make defining species difficult Figure 14.2A Figure 14.2B

The Biological Species Concept The biological species concept defines a species as A population or group of populations whose members can interbreed and produce fertile offspring

Other Species Concepts The morphological species concept Classifies organisms based on observable phenotypic traits The ecological species concept Defines a species by its ecological role The phylogenetic species concept Defines a species as a set of organisms representing a specific evolutionary lineage

14.3 Reproductive barriers keep species separate Serve to isolate a species’ gene pool and prevent interbreeding Are categorized as prezygotic or postzygotic Table 14.3

Prezygotic Barriers Prezygotic barriers Prevent mating or fertilization between species

In temporal isolation Two species breed at different times Figure 14.3A

In behavioral isolation There is little or no sexual attraction between species, due to specific behaviors Figure 14.3B

In mechanical isolation Female and male sex organs or gametes are not compatible Figure 14.3C

Postzygotic Barriers Postzygotic barriers Operate after hybrid zygotes are formed

One postzygotic barrier is hybrid sterility Where hybrid offspring between two species are sterile and therefore cannot mate Figure 14.3D

MECHANISMS OF SPECIATION 14.4 Geographic isolation can lead to speciation In allopatric speciation A population is geographically divided, and new species often evolve A. harrisi A. leucurus Figure 14.4

population populations 14.5 Reproductive barriers may evolve as populations diverge Laboratory studies of fruit flies Have shown that changes in food sources can cause speciation Initial sample of fruit flies Starch medium Maltose medium Results of mating experiments Female Same Different population populations Female Starch Maltose 22 9 18 15 Male Maltose Starch Male Different Same 8 20 12 15 Mating frequencies in experimental group Mating frequencies in control group Figure 14.5A

Geographic isolation in Death Valley Has led to the evolution of new species of pupfish A pupfish Figure 14.5B

14.6 New species can also arise within the same geographic area as the parent species In sympatric speciation New species may arise without geographic isolation

Many plant species have evolved by polyploidy Multiplication of the chromosome number due to errors in cell division Parent species Zygote Offspring may be viable and self-fertile Meiotic error Self-fertilization 2n = 6 Diploid 4n = 12 Tetraploid O. lamarckiana Unreduced diploid gametes Figure 14.6A O. gigas Figure 14.6B

CONNECTION 14.7 Polyploid plants clothe and feed us Many plants, including food plants such as bread wheat Are the result of hybridization and polyploidy When a tetraploid plant pollinates a diploid plant of the parental species, what will be the ploidy of the resulting zygote?   Triploid AA BB  Wild Triticum (14 chromosomes) Triticum monococcum (14 chromosomes) AB Sterile hybrid (14 chromosomes) Meiotic error and self-fertilization AA BB  DD T.tauschii (wild) (14 chromosomes) T.turgidum Emmer wheat (28 chromosomes) ABD Sterile hybrid (21 chromosomes) Meiotic error and self-fertilization AA BB DD Figure 14.7A T.aestivum Bread wheat (42 chromosomes) Figure 14.7B

14.8 Adaptive radiation may occur in new or newly vacated habitats In adaptive radiation, the evolution of new species Occurs when mass extinctions or colonization provide organisms with new environments

Island chains Provide examples of adaptive radiation Cactus-seed-eater (cactus finch) 2 A 1 B B B 3 B C C 4 C C D C D 5 D Figure 14.8B Tool-using insect-eater (woodpecker finch) Seed-eater (medium ground finch) Figure 14.8A

14.9 Peter and Rosemary Grant study the evolution of Darwin’s finches TALKING ABOUT SCIENCE 14.9 Peter and Rosemary Grant study the evolution of Darwin’s finches Peter and Rosemary Grant Have documented natural selection acting on populations of Galápagos finches Figure 14.9

The occasional hybridization of finch species May also have been important in their adaptive radiation

14.10 The tempo of speciation can appear steady or jumpy According to the gradualism model New species evolve by the gradual accumulation of changes brought about by natural selection Time Figure 14.10A

The punctuated equilibrium model draws on the fossil record Where species change the most as they arise from an ancestral species and then change relatively little for the rest of their existence Time Figure 14.10B

Transparent protective MACROEVOLUTION 14.11 Evolutionary novelties may arise in several ways Many complex structures evolve in many stages From simpler versions having the same basic function Light-sensitive cells Light-sensitive cells Fluid-filled cavity Transparent protective tissue (cornea) Cornea Lens Layer of light-sensitive cells (retina) Eyecup Retina Nerve fibers Nerve fibers Optic nerve Optic nerve Optic nerve Patch of light- sensitive cells Simple pinhole camera-type eye Eye with primitive lens Complex camera-type eye Eyecup Limpet Abalone Nautilus Marine snail Squid Figure 14.11

Other novel structures result from exaptation a structure that evolved in one context is later adapted for another function.

14.12 Genes that control development are important in evolution Many striking evolutionary transformations are the result of a change in the rate or timing of developmental change. Paedomorphosis is the retention in the adult of features that were juvenile in ancestors Figure 14.12A

Changes in the timing and rate of growth Have also been important in human evolution Chimpanzee fetus Chimpanzee adult Human fetus Human adult Figure 14.12B

Stephen Jay Gould, an evolutionary biologist Contended that Mickey Mouse “evolved” Copyright Disney Enterprises, Inc. Figure 14.12C

14.13 Evolutionary trends do not mean that evolution is goal directed Evolutionary trends reflect species selection The unequal speciation or unequal survival of species on a branching evolutionary tree E RECENT Equus Hippidion and other genera PLEISTOCEN Nannippus Pliohippus Hipparion Neohipparion PLIOCENE Sinohippus Megahippus Callippus Archaeohippus MIOCENE Merychippus Anchitherium Hypohippus Parahippus Miohippus OLIGOCENE Mesohippus Paleotherium Epihippus Propalaeotherium Pachynolophus Orohippus EOCENE Grazers Browsers Figure 14.13 Hyracotherium