Ch. 24 The Origin of Species Objective: Show the different ways in which speciation can occur.

Overview Speciation is the process of the creation of a new species. – Explains differences and similarities among species. Anagenesis: 1 species changes into another Cladogenesis: 1 species changes into 2 – Connects micro- to macroevolution (evolution above species level) (b) Cladogenesis (a) Anagenesis

© 2011 Pearson Education, Inc. Animation: Macroevolution Right-click slide / select “Play”

24.1 Reproductive Isolation Biological Species Concept A species is individuals that can mate and have viable offspring – Reproductively isolated (no gene flow) Barriers: – Prezygotic: prevents fertilization – Postzygotic: zygote won’t be fertile

Prezygotic Barriers Habitat Isolation 2 species that occupy different habitats within the same area may only encounter each other rarely if ever.

Temporal Isolation Species that breed during different times of the day, seasons, or year. Leopard Frogs

Behavioral Isolation Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barrier.

© 2011 Pearson Education, Inc. Video: Albatross Courtship Ritual

© 2011 Pearson Education, Inc. Video: Giraffe Courtship Ritual

© 2011 Pearson Education, Inc. Video: Blue-footed Boobies Courtship Ritual

Mechanical Isolation Morphological differences Gametic Isolation Gametes can’t fertilize each other.

Postzygotic Isolations Reduced Hybrid Viability The genes of different parent species may interact and impair the hybrid’s development.

Reduced Hybrid Fertility Hybrids created but, they may be sterile. If chromosomes of the parents differ in number or structure, meiosis in the hybrids won’t produce normal gametes. Hybrid Breakdown Some first-generation hybrids are viable and fertile, but when they mate with each other the next offspring are feeble or sterile.

24.2 Speciation Can Take Place With or Without Geographic Separation Allopatric (“Other Country”) Speciation Physical separation of 1 population into >1. Founder’s Effect: Galapagos finches Separation leads to reproductive isolation by: – Different mutations – Sexual selection differs – Genetic drift

Sympatric (“Same Country”) Speciation Speciation in overlapping populations due to reduced gene flow. Polyploidy – Autopolyploidy: individual with more than two sets of chromosomes. – Plants would be able to self pollinate to make correct gametes creating isolation from other plants nearby. 2n = 6 4n = 12 2n2n 4n4n

Polyploidy – Allopolyploid: different species make a hybrid offspring which should be sterile except for asexually reproducing organisms. Ex: type of weeds brought from Europe, oats, cotton, potatoes, tobacco, and wheat. Figure 24.9 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Viable fertile hybrid (allopolyploid) Normal gamete n = 3 Normal gamete n = 3 Species A 2n = 4 Species B 2n = 6 2n = 10

Habitat Differentiation and Sexual Selection – Apple flies: original fed on hawthorn trees but started using apples, which mature more quickly. (temporal) – Nonrandom mating: cichlids coloration in Africa differs. (behavioral) P. nyererei Normal light Monochromatic orange light P. pundamilia

24.3 Hybrid Zones Reveal Factors That Causes Reproductive Isolation Hybrid zones are regions in which members of nearly different species meet and mate creating a hybrid. EUROPE Yellow-bellied toad, Bombina variegata Fire-bellied toad range Hybrid zone Yellow-bellied toad range Fire-bellied toad, Bombina bombina Frequency of B. variegata-specific allele Yellow-bellied toad range Hybrid zone Fire-bellied toad range Distance from hybrid zone center (km)

24.4 Speciation Can Occur Rapidly or Slowly and Can Result From Changes in Few or Many Genes The Tempo of Speciation Punctuated Equilibrium – Periods of no change followed by sudden change according to fossil record. Gradualism – Organisms are constantly changing (but not necessarily in bone structure or a way that shows up in fossils). Once initiated, speciation completes quickly Time

Studying the Genetics of Speciation Speciation can be traced at the genetic level. – Ex: flower plants differ in their pollinators by having different genes for flower color and type of nectar.

Evolution of Genes That Control Development Heterochrony: change in rate of development – Allometric growth: how body parts grow for differing time frames Chimpanzee fetus Chimpanzee adult Human fetus Human adult Ground-dwelling salamander. A longer time peroid for foot growth results in longer digits and less webbing. Tree-dwelling salamander. Foot growth ends sooner. This evolutionary timing change accounts for the shorter digits and more extensive webbing, which help the salamander climb vertically on tree branches. (a) (b)

Changes in Spatial Pattern Hox genes (a type of homeotic gene) tell cells what structure to develop into. Chicken leg bud Region of Hox gene expression Zebrafish fin bud

Evolution is NOT Goal Oriented Organisms don’t think “I need wings” and are then able to make wings over generations. Organisms use what they have that helps them currently.

Adaptive Radiation Many species adapted from 1 due to many new environmental challenges. – Extinction of dinosaurs  mammal flourished – Hawaiian Islands  newly created and bare for organisms to diversify on. Dubautia laxa Dubautia waialealae KAUA'I 5.1 million years O'AHU 3.7 million years LANAI MOLOKA'I 1.3 million years MAUI HAWAI'I 0.4 million years Argyroxiphium sandwicense Dubautia scabra Dubautia linearis N MOVED TO CH. 25

24.3 Macroevolution Evolutionary Novelties – Human Eye: a complex organ … how did it evolve? Improve on given structure based on current function Start simple – photoreceptors that tell light from dark Cup photoreptors in round shape. Filter light through a pupil Focus light with a lens Protect eye with cornea Pigmented cells (photoreceptors) Epithelium Nerve fibers Pigmented cells Nerve fibers Fluid-filled cavity Epithelium Cellular fluid (lens) Cornea Optic nerve Pigmented layer (retina) Optic nerve Cornea Lens Retina Optic nerve (a) (b) (d) (c) (e)