1. Chapter 24: The Origin of Species 1.What is a species? -A population whose members can interbreed in nature and produce viable, fertile offspring -aka….reproductive isolation 2.What kinds of barriers keep different species isolated so they cannot mate? -Figure 24.4 -Pre–zygotic barriers – before mating &/or zygote is formed -Post–zygotic barriers – after zygote is formed

2. Figure 24.4 Reproductive Barriers Prezygotic barriers impede mating or hinder fertilization if mating does occur Individuals of different species Mating attempt Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation HABITAT ISOLATION TEMPORAL ISOLATIONBEHAVIORAL ISOLATION MECHANICAL ISOLATION (b) (a) (c) (d) (e) (f) (g)

3. Viable fertile offspring Reduce hybrid viability Reduce hybrid fertility Hybrid breakdown Fertilization Gametic isolation GAMETIC ISOLATION REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN (h) (i) (j) (k) (l) (m)

4. Chapter 24: The Origin of Species 1.What is a species? 2.What kinds of barriers keep different species isolated so they cannot mate? 3.How are new species created? -Allopatric speciation -when a geographic barrier isolates a population blocks gene flow -Sympatric speciation -intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow

5. Figure 24.5 Two main modes of speciation (a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. (b) Sympatric speciation. A small population becomes a new species without geographic separation.

6. Chapter 24: The Origin of Species 1.What is a species? 2.What kinds of barriers keep different species isolated so they cannot mate? 3.How are new species created? -Allopatric speciation – -when a geographic barrier isolates a population blocks gene flow -ex. mountain range emerging, new river dividing a field, island -Adaptive radiation -evolution of many diversely adapted species from a common ancestor -Seen on islands -Sympatric speciation -intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow

7. Figure 24.12 Adaptive radiation 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

8. Chapter 24: The Origin of Species 1.What is a species? 2.What kinds of barriers keep different species isolated so they cannot mate? 3.How are new species created? -Allopatric speciation – -when a geographic barrier isolates a population blocks gene flow -Adaptive radiation -evolution of many diversely adapted species from a common ancestor -Seen on islands -Sympatric speciation -intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow -Autopolyploidy -An individual has more than 2 chromosome sets derived from a single species from an error in meiosis

9. Figure 24.8 Sympatric speciation by autopolyploidy in plants 2n = 6 4n = 12 2n2n 4n4n 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 branch will be diploid. Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.

10. Chapter 24: The Origin of Species 1.What is a species? 2.What kinds of barriers keep different species isolated so they cannot mate? 3.How are new species created? -Allopatric speciation – -when a geographic barrier isolates a population blocks gene flow -ex. mountain range emerging, new river dividing a field, island -Adaptive radiation -evolution of many diversely adapted species from a common ancestor -Seen on islands -Sympatric speciation -intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow -Autopolyploidy -An individual has more than 2 chromosome sets derived from a single species from an error in meiosis -Allopolyploidy -2 different species produce the polyploid hybrid

11. Figure 24.9 One mechanism for allopolyploid speciation in plants 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

12. Sympatric speciation: non-random mating Figure 24.10 Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orange light, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank. EXPERIMENT P. nyererei Normal light Monochromatic orange light P. pundamilia Under normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile. RESULTS The researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently. CONCLUSION

13. Chapter 24: The Origin of Species 1.What is a species? 2.What kinds of barriers keep different species isolated so they cannot mate? 3.How are new species created? 4.What is the difference between gradualism & punctuated equlibrium?

14. Figure 24.13 Two models for the tempo of speciation Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations. Time (a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence. (b)

15. Figure 24.14 A–E Pigmented cells (photoreceptors) Epithelium Nerve fibers Pigmented cells Nerve fibers Patch of pigmented cells. The limpet Patella has a simple patch of photoreceptors. Eyecup. The slit shell mollusc Pleurotomaria has an eyecup. Fluid-filled cavity Epithelium Cellular fluid (lens) Cornea Optic nerve Pigmented layer (retina) Optic nerve Pinhole camera-type eye. The Nautilus eye functions like a pinhole camera (an early type of camera lacking a lens). Cornea Lens Retina Optic nerve Complex camera-type eye. The squid Loligo has a complex eye whose features (cornea, lens, and retina), though similar to those of vertebrate eyes, evolved independently. (a) (b) (d) (c) (e) Eye with primitive lens. The marine snail Murex has a primitive lens consisting of a mass of crystal-like cells. The cornea is a transparent region of epithelium (outer skin) that protects the eye and helps focus light.

16. Chapter 24: The Origin of Species 5. What other mechanisms can influence evolution/speciation? A) Differences in allometric growth (proportional growth of body structures) Figure 24.15 B Chimpanzee fetus Chimpanzee adult Human fetus Human adult (b) Comparison of chimpanzee and human skull growth. The fetal skulls of humans and chimpanzees are similar in shape. Allometric growth transforms the rounded skull and vertical face of a newborn chimpanzee into the elongated skull and sloping face characteristic of adult apes. The same allometric pattern of growth occurs in humans, but with a less accelerated elongation of the jaw relative to the rest of the skull. DEVELOPMENTAL FACTORS…

17. 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) Figure 24.16 A, B

18. 5. What other mechanisms can influence evolution/speciation? Chapter 24: The Origin of Species A) Differences in allometric growth (proportional growth of body structures) B) The expression of homeotic genes (which determine the “body plan” of an organism) may change through mutation. Chicken leg bud Region of Hox gene expression Zebrafish fin bud Figure 24.18 DEVELOPMENTAL FACTORS…