Processes of Evolution Chapter 12 Part 1

12.1 Impacts/Issues Rise of the Super Rats When humans tried to eradicate rats with warfarin, natural selection favored individuals with a mutation for warfarin resistance Warfarin 一開始是註冊. 為老鼠藥（現名為殺鼠靈 ) Warfarin 為Wisconsin Alumni Research Foundation（贊助 Warfarin 合成的基金會）和 Coumarin（表示 Warfarin 是 coumarin 的衍生物）的縮寫。在上個世紀，大家慢慢注意「血栓」在西方國家是一個重要的死亡因子。「血栓」的產生會堵塞血管進而可能造成人體組織缺乏氧氣及養分。血栓的預防及治療極為重要，這也造成了口服抗凝血劑的廣泛運用。1940年從發霉的飼料中找到的劇毒生化物質，動物服用後數天後就會慢性出血而死亡，註冊為毒鼠藥使用。

Video: Rise of the super rats

12.2 Making Waves in the Gene Pool Individuals in a population share the same traits (phenotype) because they share the same genes (genotype) Gene pool All of the genes in a population

Alleles and Traits Alleles of the same genes are the main source of variation in a population Traits with two distinct forms are dimorphic Traits with several distinct forms are polymorphic Traits with continuous variation may have interactions of several genes or be influence by environment Mutation is the source of new alleles

Sources of Variation in Traits

Phenotypic Variation in Humans

Mutation Revisited Mutations are the original source of alleles, but many are lethal or neutral Lethal mutation Mutation that drastically alters phenotype; usually causes death Neutral mutation A mutation that has no effect on survival or reproduction

Allele Frequencies Microevolution (change in allele frequencies) is always occurring in natural populations Microevolution Small-scale change in allele frequencies of a population or species Allele frequency Abundance of a particular allele among members of a population

Genetic Equilibrium Genetic equilibrium Theoretical state in which a population is not evolving (allele frequencies do not change) Only occurs if five conditions are met: Mutations never occur, population is infinitely large, population is isolated from gene flow, mating is random, all individuals survive and reproduce equally

Processes of Microevolution Genetic equilibrium does not occur in nature because processes that drive microevolution are always in play Mutation Natural selection Genetic drift Gene flow

Animation: Adaptation to what?

Animation: How to find out if a population is evolving

Animation: Sources of genotype variation

12.3 Natural Selection Revisited Natural selection occurs in different patterns depending on species and selection pressures Directional selection Stabilizing selection Disruptive selection

Directional Selection Mode of natural selection in which phenotypes at one end of a range of variation are favored Allele frequencies shift in a consistent direction in response to selection pressure Examples: peppered moths, rock pocket mice, antibiotic-resistant bacteria

Directional Selection

Number of individuals in population Time 1 Number of individuals in population Figure 12.3: Animated! Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored. Range of values for the trait Fig. 12-3a, p. 219

Figure 12.3: Animated! Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored. Fig. 12-3b, p. 219

Time 2 Figure 12.3: Animated! Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored. Fig. 12-3b, p. 219

Time 3 Figure 12.3: Animated! Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored. Fig. 12-3c, p. 219

Animation: Directional selection

Directional Selection in Peppered Moths Predation pressure favors moths that are best camouflaged when the environment changes

Figure 12.4 Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color. Fig. 12-4, p. 219

Figure 12.4 Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color. Fig. 12-4a, p. 219

Figure 12.4 Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color. Fig. 12-4b, p. 219

Figure 12.4 Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color. Fig. 12-4c, p. 219

Figure 12.4 Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color. Fig. 12-4d, p. 219

Directional Selection in Rock Pocket Mice Mice with coat colors that do not match their surroundings are more easily seen by predators Rock Pocket Mice 黑腹絨鼠

Stabilizing Selection Mode of natural selection in which intermediate phenotypes are favored and extreme forms are eliminated Example: sociable weavers

Stabilizing Selection

Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6, p. 221

Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6a, p. 221

Number of individuals in population Time 1 Number of individuals in population Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Range of values for the trait Fig. 12-6a, p. 221

Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6b, p. 221

Time 2 Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6b, p. 221

Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6c, p. 221

Time 3 Figure 12.6: Animated! Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7. Fig. 12-6c, p. 221

Animation: Stabilizing selection

Stabilizing Selection in Sociable Weavers Body weight in sociable weavers is a trade off between starvation and predation Sociable Weavers 織布鳥

Figure 12. 7 Stabilizing selection in sociable weavers (top) Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season. Figure It Out: What is the optimal weight of a sociable weaver bird? Answer: About 29 grams. Fig. 12-7, p. 221

Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season. Figure It Out: What is the optimal weight of a sociable weaver bird? Answer: About 29 grams. Fig. 12-7a, p. 221

Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season. Figure It Out: What is the optimal weight of a sociable weaver bird? Answer: About 29 grams. Fig. 12-7b, p. 221

300 200 Number of survivors 100 Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season. Figure It Out: What is the optimal weight of a sociable weaver bird? Answer: About 29 grams. 25.5 27.5 29.5 31.5 33.5 35.5 23.5 Body mass (grams) Fig. 12-7b, p. 221

Disruptive Selection Disruptive selection Mode of natural selection that favors extreme phenotypes in a range of variation Intermediate forms are selected against Example: African seedcrackers

Disruptive Selection

Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8, p. 222

Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8a, p. 222

Number of individuals in population Time 1 Number of individuals in population Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Range of values for the trait Fig. 12-8a, p. 222

Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8b, p. 222

Time 2 Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8b, p. 222

Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8c, p. 222

Time 3 Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 12-8c, p. 222

Animation: Disruptive selection

Disruptive Selection in African Seedcrackers African seedcrackers tend to have either a large bill or a small one – but no sizes between

Figure 12. 9 Disruptive selection in African seedcrackers Figure 12.9 Disruptive selection in African seedcrackers. Birds with bills that are about 12 or 15 millimeters wide are favored. The difference is a result of competition for scarce food during dry seasons. lower bill 12 mm wide Fig. 12-9a, p. 222

Figure 12. 9 Disruptive selection in African seedcrackers Figure 12.9 Disruptive selection in African seedcrackers. Birds with bills that are about 12 or 15 millimeters wide are favored. The difference is a result of competition for scarce food during dry seasons. lower bill 15 mm wide Fig. 12-9b, p. 222

Animation: Change in moth population

Animation: Disruptive selection among African finches