Evolution

1. Evolution The Origin of Species

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

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

4. CONCEPTS OF SPECIES • 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

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

6. Table 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

7. Prezygotic Barriers • Prezygotic barriers • Prevent mating or fertilization between species • Temporal Isolation • Habitat Isolation • Behavioral Isolation • Mechanical Isolation • Gametic Isolation

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

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

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

11. Postzygotic Barriers • Postzygotic barriers • Operate after hybrid zygotes are formed • Hybrid sterility • Hybrid inviability • Hybrid breakbown

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

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

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

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

16. Sympatric Speciation

17. Sympatric speciation

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

19. 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 • e.g. the Cambrian explosion; the rise of placental mammals after the dinosaur extinction

20. Adaptive Radiation • Four of the 13 finch species found on the Galápagos Archipelago, are thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources.

22. Convergent evolution • Describes how organisms acquire the same biological traits despite being unrelated. • Traits are described as analogous structures (similar function but no common origin)

23. Convergent Evolution Astrophytumasterias E obesasymmetricaies

24. Convergent Evolution

25. The pace of speciation can appear steady or jumpy • Gradualism model • Punctuated equilibrium model

26. Time • According to the gradualism model • New species evolve by the gradual accumulation of changes brought about by natural selection Figure 14.10A

27. 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

28. Transparent protective tissue (cornea) Cornea Light-sensitive cells Light-sensitive cells Fluid-filled cavity Lens Layer of light-sensitive cells (retina) Retina Eyecup 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 MACROEVOLUTION • Evolutionary novelties may arise in several ways • Many complex structures evolve in many stages • From simpler versions having the same basic function

29. Other novel structures result from exaptation • The gradual adaptation of existing structures to new functions • Example: http://evolution.berkeley.edu/evolibrary/news/061001_trapjaw

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