Goals: Be able to. Sexual Dimorphism

Transcription

1 Goals: Be able to Connect sexual dimorphism and sexual selection. Use parental investment arguments to describe why sexual selection occurs. Explain why long male peacock tails are an indicator of good genetic quality. Differentiate between monogamy and polygamy. Sexual Dimorphism Secondary sexual characteristics: Differ between males and females. Not directly related to reproduction Why are there differences between males and females? 1

2 Natural selection: Differential survival and reproductive success. Sexual selection: Differential success getting mates. Sexual selection is a form of natural selection! Traits best for attracting mates sometimes not best for survival In most mammals, which parent typically invests more resources in the young? 1. Male 2. Female Differences between sexes are due to differences in:? Parental investment!! Both: Improve chances of leaving successful offspring. Male: Improve chances of mating. Female: Limited by # of offspring they can produce = high quality. Investment is typically higher on the part of the female so They mostly get to choose! 2

3 Mating systems Monogamy: 1 mate Offspring need 2 parent care to survive. Examples: Humans, birds Why do females prefer certain displays over others? Displays / ornaments are indicators of genetic quality, health, access to resources Polygamy: More than 1 mate simultaneously Uniparental care, typically by female Examples: Most animals Group # offspring 2 nd brood Control % Small reduction % Large reduction % 1. What are 2 things that these results indicate about reproductive success and tail spot size? 2. Which of the following would make spot size a valid indicator of male quality? #1 reason why Reduced spot size by coloring in with marker a. Lice preferentially eat white tail spots. b. Black feather pigmentation is more expensive to maintain than white. In the South American jacana, a single female will mate and lay eggs with many males (who alone take care of the chicks). From this information, you might guess that a. Female lilyhoppers have more excessive ornamentation than males. b. Sexual selection does not occur in lilyhoppers. c. There is a lack of sexual dimorphism in lilyhoppers. d. Males compete with each other for access to females. Goals: Be able to Describe the biological species concept (BSC), and problems with it. Describe different forms of reproductive isolation. Explain how speciation occurs. Differentiate between the biological and genealogical species concepts. Define a biological race, and relate it to the genealogical species concept. 3

4 Which of these pairs is the same species? What makes a successful group? Unique from other groups. Coherent within the group (species). Happy face spiders Biological Species Concept (BSC) Interbreed to produce fertile offspring in nature Does not interbreed with other species What keeps species from interbreeding? Barriers: Pre-fertilization and post-fertilization. Pre-fertilization Isolation : Spatial (ranges don t overlap) Pre-fertilization Isolation : Behavioral (mating dance / song) Pre-fertilization Isolation : Mechanical (different equipment) Damselfly penises Fig 11.1 blue-footed boobies Lyre bird 4

5 Pre-fertilization Isolation : Temporal (reproductive timing) Pre-fertilization Isolation : Gametic (sperm-egg incompatibility) Fig 11.2 Species A and species B often mate with each other, but no zygotes are ever produced. This is most likely 1. Temporal isolation 2. Spatial isolation 3. Mechanical isolation 4. Gametic isolation Post-fertilization Isolation: Hybrid infertility or inviability Mules can t make balanced gametes Fig 11.3 What causes speciation? Reduced gene flow (isolation) Evolutionary change reproductive isolation Mutation Speciation involves the development of reproductive isolation. 1. How could a single mutation in beetle color alone cause speciation? 2. Would a mutation in ANY gene lead to speciation? Geographic isolation Mutation Fig

6 Allopatric: Speciation due to geographic isolation; Geography reduces gene flow. Sympatric: Speciation in the SAME geographic location Apple maggot flies Apples fruit early Hawthorns fruit late Fig 11.7 Fig 11.8 What type of reproductive isolation is occurring in the apple-maggot flies? Geographical isolation + evolution speciation 1. Temporal 2. Mechanical 3. Gametic 4. Post-fertilization Rapid speciation: Colonization of empty habitats by founders Fig 11.5 Oregon Is the BSC foolproof? 1. Ring species When does the BSC not apply? Yellow-eyed Sierra Nevada Yellow-blotched Monterey Large-blotched 2. Fertile hybrids exist 6

7 Problems with the BSC: 3. Extinct species Morphological species concept: Species based upon unique physical characteristics 4. Some populations are genetically distinct, but still interbreed. Biological race: Populations of a species whose gene pools have diverged significantly Genealogical species concept: distinct gene pools Fig Fig True/False: 2 different genealogical species could still interbreed. 1. True 2. False Why is the BSC a good way to identify species? It A. Describes the species as an evolutionary unit. B. Works most of the time. C. Is based upon mechanisms of speciation. D. Provides a litmus test. E. The BSC is not a good way to identify species. Goals: Be able to Explain why human races based upon skin color are NOT biologically sound. Describe why human populations have not generated into distinct biological races. Explain the difference between natural selection and genetic drift, and how both have contributed to human evolution. Are traditionally-defined human races (based upon skin color) biologically defensible? Asian Black or African American American Indian or Alaska Native Native Hawaiian or Other Pacific Islander White Some other race Fig

8 The history of Homo sapiens multiregional out of Africa assimilation The Out-of-Africa hypothesis suggests that different human populations 1. Have been diverging in geographic isolation for millions of years. 2. Arose from pre-human ancestors independently. 3. Have not interbred with each other until the past 3,000 years. 4. None of the above. Fig Prediction 1: There should be alleles unique to different races. If groupings based upon skin color had a biological basis, what would you expect about the genetic similarity of those groups? Scientists have not found any examples of alleles unique to a race. Test: sickle-cell allele distribution Fig Prediction 2: Allele frequency should be the same within a race. PTC allele globin allele sequence D Eurasian SE Asian There is more genetic diversity between different African peoples than between some Africans and Europeans African Fig

9 Why would you expect there to be more genetic diversity amongst different groups of African people? Longer history more time for mutation & divergence Are traditionally-defined human races (based upon skin color) biologically defensible? No! Why not? Humans are always on the move Migration of the I B allele through Europe Fig Why not? Humans are a young species Are traditional human race definitions biologically tenable? 1. No, because there is more genetic variation within than between different human races. 2. Yes, because skin color is geneticallyinfluenced. 3. No, because speciation has occurred without reproductive isolation. 4. Yes, because they are the result of natural selection. There is 3x as much genetic diversity between 2 emperor penguins as between 2 humans! 9

10 Due to natural selection: Fitness of traits differs in different environments Human populations do differ Due to Natural selection (adaptive) Genetic drift (random) Fig Natural selection for nose type Fig Natural selection for skin color Fig Convergent evolution Natural selection for skin color Fig Natural selection for skin color Fig Folate = healthy baby UV light destroys folate Dark skin blocks UV UV light helps make Vit D Light skin allows UV light in Not enough folate Not enough Vit D 10

11 Some people have lighter skin than others, because they need to 1. Produce more folate. 2. Let more UV light in to make vitamin D. 3. Block harmful UV light from destroying vitamin D. 4. Protect folate from destruction due to UV light. Human populations do differ Due to Natural selection (adaptive) Genetic drift (random) Genetic drift: evolution due to chance Founder effect: new pop has different allele frequency due to chance of founders. Red allele rare Fig Bottleneck: Event reduces population size. Allele freq changes due to chance survivors. Red allele rare Red allele freq New Location!! Small pop leaves: more red lizards Is the red allele adaptive? Red allele freq Old Location Gray lizards die by chance Is the red allele adaptive? Fig Genetic drift plays a large role in small populations Red allele rare Red allele gone Old Location Chance event Negative impact: reduces genetic diversity You separate guppies into 3 different tanks with identical environments. After 100 guppy generations, you put all 3 populations back together. Populations A and B can still mate with each other, but population C can only mate with itself. What most likely happened? 1. Speciation due to natural selection. 2. Speciation due to genetic drift. 3. Evolution has occurred, but not speciation. Fig

12 Is it appropriate to continue using the human race concept in today s society? 12