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

Speciation

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

Speciation in Fruit Flies

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 Starch medium Maltose medium Initial sample of fruit flies Results of mating experiments Female Starch Maltose Same Different population populations Maltose Starch Male Different Same Mating frequencies in experimental group in control group 22 9 20 8 12 18 15 Figure 14.5A

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

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 Figure 14.6B Parent species Meiotic error Self-fertilization Offspring may be viable and self-fertile Zygote Unreduced diploid gametes 2n = 6 Diploid 4n = 12 Tetraploid O. gigas O. lamarckiana Figure 14.6A

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 AA BB AB AA BB DD ABD AA BB DD  Wild Triticum (14 chromosomes) Triticum monococcum (14 chromosomes) Sterile hybrid (14 chromosomes) Meiotic error and self-fertilization  T.tauschii (wild) (14 chromosomes) T.turgidum Emmer wheat (28 chromosomes) Sterile hybrid (21 chromosomes) Meiotic error and self-fertilization Figure 14.7A T.aestivum Bread wheat (42 chromosomes) Figure 14.7B

Real Examples of Possible Speciation Rhagoletis pomonella is a fly that is native to North America. Its normal host is the hawthorn tree. Sometime during the nineteenth century it began to infest apple trees. Since then it has begun to infest cherries, roses, pears and possibly other members of the rosaceae. Quite a bit of work has been done on the differences between flies infesting hawthorn and flies infesting apple. There appear to be differences in host preferences among populations. Offspring of females collected from on of these two hosts are more likely to select that host for oviposition (Prokopy et al. 1988). Genetic differences between flies on these two hosts have been found at 6 out of 13 allozyme loci (Feder et al. 1988, see also McPheron et al. 1988). Laboratory studies have shown an asynchrony in emergence time of adults between these two host races (Smith 1988). Flies from apple trees take about 40 days to mature, whereas flies from hawthorn trees take 54-60 days to mature. This makes sense when we consider that hawthorn fruit tends to mature later in the season that apples. Hybridization studies show that host preferences are inherited, but give no evidence of barriers to mating. This is a very exciting case. It may represent the early stages of a sympatric speciation event (considering the dispersal of R. pomonella to other plants it may even represent the beginning of an adaptive radiation). It is important to note that some of the leading researchers on this question are urging caution in interpreting it. Feder and Bush (1989) stated

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

Prezygotic Barriers Prezygotic barriers Prevent mating or fertilization between species Figure 14.3A In temporal isolation Two species breed at different times

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

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

Provide examples of adaptive radiation Island chains Provide examples of adaptive radiation Cactus-seed-eater (cactus finch) Seed-eater (medium ground finch) Tool-using insect-eater (woodpecker finch) 1 2 3 4 5 A B C D Figure 14.8B 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 Figure 14.11 Light-sensitive cells Fluid-filled cavity Transparent protective tissue (cornea) Cornea Layer of light-sensitive cells (retina) Nerve fibers Optic nerve Eyecup Retina Lens Patch of light- sensitive cells Simple pinhole camera-type eye Eye with primitive lens Complex Limpet Abalone Nautilus Marine snail Squid

Other novel structures result from exaptation The gradual adaptation of existing structures to new functions

14.12 Genes that control development are important in evolution “Evo-devo” Is a field that combines evolutionary and developmental biology

Many striking evolutionary transformations Are the result of a change in the rate or timing of developmental changes Figure 14.12A

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

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

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 Hippidion and other genera Nannippus Neohipparion Hipparion Sinohippus Megahippus Archaeohippus Callippus Hypohippus Anchitherium Miohippus Parahippus Paleotherium Propalaeotherium Pachynolophus Orohippus Epihippus Equus Pliohippus Merychippus Mesohippus Hyracotherium Grazers Browsers EOCENE OLIGOCENE MIOCENE PLIOCENE E RECENT PLEISTOCEN Figure 14.13