LECTURE 06. Today: Follow up on minute papers Modes of selection Non random mating Sexual selection Guest speaker: Dr. Daniel Fergus Summary 2/17/2014

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1 Spring 2014: Mondays 10:15am 12:05pm (Fox Hall, Room 204) Instructor: D. Magdalena Sorger Website: theantlife.com/teaching/bio295-islands-evolution LECTURE 06 Today: Follow up on minute papers Modes of selection Non random mating Sexual selection Guest speaker: Dr. Daniel Fergus Summary 1

2 FOLLOW-UP MINUTE PPERS Follow up on minute papers Microsatellites evolutionary role, how to isolate nt supercolonies why not more common? How ants communicate New species absence of morph. differences, subspecies, Ethiopia species named? 2

3 MECHNISMS OF EVOLUTION Mechanisms of evolution Gene flow (Migration) Mutation Selection Natural selection Sexual selection (prerequisite: Nonrandom mating) Genetic drift 3

4 Mechanisms of evolution Gene flow (Migration) Mutation Selection Natural selection Sexual selection (prerequisite: Nonrandom mating) Genetic drift MODES OF SELECTION 4

5 Modes of selection Relationship between phenotype and fitness Directional Disruptive Stabilizing Modes of selection 5

6 Directional selection one extreme phenotype is fittest Directional selection Grant

7 Stabilizing selection = normalizing selection if intermediate phenotype is fittest, genetic variation reduced Stabilizing selection 7

8 Disruptive selection = diversifying selection two or more phenotypes are fitter than intermediate, maintains genetic variation, can lead to rapid speciation Disruptive selection EVOLUTION OF NISOGMY 8

9 Disruptive selection Total resource Divided resource must be 4x better at survival EVOLUTION OF NISOGMY Disruptive selection Selection acts more strongly on small gametes Egg DN Penalty for failing to resist a small gamete: not so bad Sperm Sperm Sperm Sperm Sperm DN DN DN Penalty for not finding a large partner: severe More variability in the gene pool EVOLUTION OF NISOGMY 9

10 Disruptive selection Egg Defend food! Sperm lot of stored food Steal food! Not so much stored food EVOLUTION OF NISOGMY Disruptive selection Big, lots of food resources Small, good at parasitizing food resources Inbetween: not good at either 10

11 Disruptive selection or Heterozygote advantage/superiority (overdominance) Heterozygotes have higher fitness than either homozygote Deleterious mutations tend to be recessive If dominant: keep organism from reproducing Polymorphism is maintained 11

12 Heterozygote advantage: Sickle cell anaemia allele Hb S causes sickle cell anemia when homozygous (Hb S /Hb S ) heterozygotes more resistant to malaria (Hb /Hb S ) homozygotes more susceptible to malaria (Hb /Hb ) Homozygote advantage (underdominance) Homozygotes have higher fitness that heterozygotes selection against the mean Causes disruptive selection 12

13 Frequency dependent selection Fitness of a genotype depends on the genotype frequency in the population EXMPLE: Cichlid fish (Perissodus microlepis) Lake Tanganyika 13

14 Frequency dependent selection negative frequency dependent selection: favors rarer morph in each generation Oscillating selection Different from frequency dependent selection: fitness of phenotype does not depend on frequency Similar to Frequency dependent: selection changes through time EXMPLE: Darwin s finches 14

15 Density dependent selection density dependent processes occur when population growth rates are regulated by the density of a population EXMPLE: Optimal clutch size Density dependent selection OPTIML CLUTCH SIZE Number of surviving offspring Clutch size 15

16 CSE STUDY HWIIN HPPY FCED SPIDERS Biology Theridion grallator Builds small, flimsy webs on undersides of leaves Night active, hang below leaf from silk threads Capture insects on underside of leaf, feed in situ Distribution: Oahu, Molokai, Maui, Hawaii HWIIN HPPY FCED SPIDERS 16

17 HWIIN HPPY FCED SPIDERS HWIIN HPPY FCED SPIDERS 17

18 HWIIN HPPY FCED SPIDERS Oxfort & Gillespie 2001 Color polymorphism Highly variable for color 70 % yellow, 30 % patterned Hawaii populations contain morphs superficially almost identical to those found on Maui (occur at similar frequencies) underlying genetic control differs HWIIN HPPY FCED SPIDERS Oxfort & Gillespie

19 How can the substantial differences in the genetics of color between Maui and Hawaii be explained? HWIIN HPPY FCED SPIDERS Oxfort & Gillespie 2001 Simplest hypothesis for the genetic difference: Hawaii population was initiated by very small number of immigrants from Maui HWIIN HPPY FCED SPIDERS Oxfort & Gillespie

20 Molecular evidence indeed suggests colonization of island chain from Oahu (the oldest island) to Maui and Molokai, and then to Hawaii HWIIN HPPY FCED SPIDERS Oxfort & Gillespie 2001 HWIIN HPPY FCED SPIDERS Oxfort & Gillespie

21 What happened? tiny founder population initial population expanded to fill suitable habitats new genetic architecture underlying color variation spread across island HWIIN HPPY FCED SPIDERS Oxfort & Gillespie 2001 Natural selection 70:30 ratio is quite constant Not clear what selection Possibly frequency dependent selection Rare morph preferred HWIIN HPPY FCED SPIDERS Oxfort & Gillespie

22 Results: biogeography negligible gene flow among islands recent decline in effective population size (bottleneck) colonization from older to younger islands and strong founder effect supported interaction of drift and balancing selection HWIIN HPPY FCED SPIDERS Croucher et al NON-RNDOM MTING 22

23 Non random (assortative) mating No change in allele frequencies Positive assortative mating Negative assortative mating Inbreeding Positive assortative mating mates are phenotypically (not genetically) MORE similar than by random chance homozygotes heterozygotes 23

24 Positive assortative mating a a a a a a a a a a a a NO CHNGE TO LLELE FREQUENCIES Negative assortative mating mates are phenotypically (not genetically) LESS similar than by random chance homozygotes heterozygotes 24

25 Negative assortative mating a a a a a a a a a a a a NO CHNGE TO LLELE FREQUENCIES Inbreeding mating between individuals that are more closely related than expected by chance homozygotes heterozygotes 25

26 Inbreeding a a a a a a a a a a a a NO CHNGE TO LLELE FREQUENCIES Non random mating is a prerequisite for sexual selection 26

27 SEXUL SELECTION NTURL SELECTION is any consistent difference in fitness among phenotypically different classes of biological entities. Endler

28 SEXUL SELECTION Selection based on traits that affect an individual s ability to reproduce. G. fortis SEXUL SELECTION NTURL SELECTION 28

29 Sexual dimorphism = difference between males and females Why does sexual dimorphism occur in such a great variety? If sexual selection explains differences between sex must act on different sex differently 29

30 Sexual dimorphism: birds of paradise Parental investment There is a link between resources for gametes and other forms of care ND SEXUL COMPETITION Trivers (1972) 30

31 Parental investment Male can potentially fertilize eggs at much faster rate than female can produce them Female can best increase reproductive success by increasing rate of converting resources into eggs and offspring Male can best increase reproductive success by finding and fertilizing many different females Reproductive success: Parental investment limited by access to females limited by resources 31

32 Parental investment Why do females invest more in offspring than males? parental care less beneficial (uncertain paternity) Opportunity cost of care greater Parental investment: testicle size & mating system Dorus et al

33 Parental investment: testicle size & mating system Dorus et al Parental investment: testicle size & mating system Soulsberry

34 Why male usually competes for female differences in gamete size produce large, immobile, food rich gametes produce tiny, mobile pieces of self propelled DN 2 kinds of sexual struggle same sex (usually males) to drive away or kill rivals: male male competition (intrasexual competition) same sex but to charm opposite sex: female choice & male choice (intersexual competition) 34

35 Sexual selection Male male competition Combat Sperm competition Infanticide lternative strategies Female choice Resources Sexy son (runaway selection) Good genes Male choice Male male competition Often occurs when individuals can monopolize access to females Combat (pre mating) Sperm competition (post mating) Infanticide (post conception) lternative strategies 35

36 Male male competition Combat Male male combat over access to mates Selects for: large body size, weaponry, armor, but also tactical cleverness EXMPLE: Marine iguanas Parental investment by females larger than by males Female digs nest, buries eggs, guards nest Female puts 20 % of body mass into egg production, male contributes ejaculate (minimal) Sperm competition Male male competition Mating success determined not by achieving copulation but by fertilizing eggs EXMPLE: Damselflies females possess spermatheca, mate with multiple males Males have adapted penis to remove rival sperm 36

37 Sperm competition Male male competition Mating success determined not by achieving copulation but by fertilizing eggs EXMPLE: Dunnocks female polyandrous in order to secure help with parental care Males try to ensure paternity by forcing her to eject rival sperm from previous matings Infanticide Male male competition Competition after conception EXMPLE: Langurs live in groups with single dominant male if another male takes over group, kills all infants ensure paternity (parental investment), females become sexually receptive sooner 37

38 Infanticide: Langurs Male male competition lternative strategies: Sneaker males EXMPLE: Cuttlefish smaller males can t compete with larger males sneak a mating while larger males are busy 38

39 Female choice Resources Sensory bias Genetic benefits Resources Female choice Male trait cue to resources that improve female s reproductive success (fight for territory) EXMPLE: Helicopter damselflies 39

40 Resources Female choice Female chooses male based on ability to provide food (nuptial gift) EXMPLE: Hanging flies Evolution of empty nuptial gifts: dance flies (Empididae) 40

41 Sensory bias Female choice Certain traits intrinsically stimulating and evoke greater response because of organization of sensory system (supernormal stimuli) EXMPLE: Sword tail fish Genetic benefits Female choice Sexy son hypothesis or runaway selection (females gain attractive sons which in turn will again succeed getting females) EXMPLE: peacock 41

42 Genetic benefits Female choice Good genes or handicap model (elaborate displays handicap in day to day survival, males must be extra good if manage to survive despite handicap) EXMPLE: long tailed widowbird But why doesn t overall variation decline over generations? 42

43 Bowerbirds SEXUL SWELLINGS IN BBOONS Females compete for matings with dominant male Compete to mate with several males in group Sufficient paternity chance: protect against infanticide Male choice 43

44 LPINE CCENTOR (Prunella collaris) Male only helps female with brood if chance of paternity Mating with several males more help with brood care Females display &sing Male choice If both sexes invest heavy, pays for both to be choosy! EXMPLE: Great Crested Grebes 44

45 Lek mating ggregation of males who display for females, females visit leks EXMPLE: stalk eyed flies Cryptic female choice Females can store sperm from multiple males and manipulate paternity by choosing which sperm fertilizes eggs EXMPLE: cannibalistic orb web spider 45

46 GUEST SPEKER Dr. Daniel Fergus 46

47 Question 1 What would happen over evolutionary time to a population of Laupala if the females in that population evolved an "openended" preference for fast song pulse rate, meaning faster song pulse rates are always preferred? Question 2 Why do females prefer specific pulse rates? What, if any, advantages are there to mating with a male that sings at a specific rate? DISCUSSION Recap Modes of selection Non random mating Sexual selection Crickets 47

48 SUMMRY 1. What was the most important thing you learned during this class? 2. What important question regarding what you learned remains unanswered for you? (What would you like to know about next?) SUMMRY NME & DTE 48

49 For next week: The Beak of the Finch: Read Chapter 9 Read paper (will be posted) 49

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