Ch. 23 Evolutionary Forces. What changes populations?

Transcription

1 Ch. 23 Evolutionary Forces What changes populations?

2 Forces of evolutionary change Natural selection traits that improve survival or reproduction will accumulate in the population adaptive change Genetic drift frequency of traits can change in a population due to chance events random change

3 Distribution of blood types Distribution of the O type blood allele in native populations of the world reflects original settlement

4 Distribution of blood types Distribution of the B type blood allele in native populations of the world reflects original migration

5 Out of Africa Likely migration paths of humans out of Africa 10-20,000ya 50,000ya 10-20,000ya Many patterns of human traits reflect this migration

6 Natural Selection Selection acts on any trait that affects survival or reproduction predation selection physiological selection sexual selection

7 Predation Selection Predation selection act on both predator & prey behaviors camouflage & mimicry speed defenses (physical & chemical)

8 Physiological Selection Acting on body functions disease resistance physiology efficiency (using oxygen, food, water) biochemical versatility protection from injury HOT STUFF! Some fish had the variation of producing anti-freeze protein 5.5 mya The Antarctic Ocean freezes over

9 Physiological selection Dogs pee on trees Why don t trees pee on dogs? NH 3 plant nutrient animal waste One critter s trash is another critter s treasure!

10 Sexual Selection Acting on reproductive success attractiveness to potential mate fertility of gametes successful rearing of offspring Survival doesn t matter if you don t reproduce!

11 What I feel do you that mean I NO. can do NO? better.

12 Sexual selection Sorry Guys, it s a FEMALE CHOICE! And hypergamy desires the genetic best.

13 The lion s mane Females are attracted to males with larger, dark manes Correlation with higher testosterone levels better nutrition & health more muscle & aggression better sperm count / fertility longer life But imposes a cost to male HOT! Is it worth it??

14 Sexual selection Acts in all sexually reproducing species the traits that get you mates sexual dimorphism influences both morphology & behavior can act in opposition to natural selection Jacanas Is there a testable hypothesis in there?

15 Sexual Dimorphism. Amongst vertebrates, the clearest dimorphism is between gamete (sex cell) size. This single physical difference explains why behavioural sex differences exist. Females gametes: large, nutrientfilled, expensive to produce, limited in number, and produced infrequently. If fertilised this will lead to high costs to the female. Male gametes: small, have no nutrients, cheap to produce, constantly made throughout life. Reproductive Capability: females are thus classed as the preserved sex and males the disposable sex. A population can sustain large-scale slaughter of its males and recover, but not large-scale slaughter of females. Females are the limiting factor in dimorphic animals species.

16 Reproductive Strategies Among Dimorphic Species Polygamy Hypergamy What drives this dynamic?

17 No. of offspring No. of offspring Bateman s Gradient. Bateman (1948) observed that the number of offspring fathered by male fruit flies increased in proportion to the number of females with which the male had mated. This results in selection of polygamic strategies in males. Female reproductive success did not increase as her number of partners increased. Because multiple mates does not increase reproduction, but may decrease it due to STDs. Polygamy is not selected for in females. This is 'Bateman's gradient' - the steeper the gradient the stronger is sexual selection. Differential Reproductive Success in Drosophila Based on Number of Mates No. of mates No. of mates males female s From Anderson & Iwasa (1996) p 54.

18 Parental Investment (PI). Trivers (1972) argued that a driving force behind sexual selection is the degree of parental investment each sex devotes to their offspring. Parental investment (PI) is defined as: any investment by the parent in an individual offspring that increases the offspring s chances of surviving (and hence reproducing) at the cost of the parent s ability to invest in other offspring. In most species, females invest heavily in their offspring while males do not.

19 Predictions Arising from Parental Investment Theory. 1. The sex that invests most heavily in an offspring will be more choosy about who they mate with (i.e females). 2. The sex that invests least in an offspring should compete more vigorously for access to the higher-investing sex (i.e males). 3. Male competition leads to physical dimorphism, and will be most marked in animals where there is little male parental investment (e.g. elephant seals). 4. Where male investment approaches that of females, competition will be reduced as will sexual dimorphism (e.g. swans). 5. Where male parental investment is higher, females will possess typically male characteristics (e.g. seahorses, the wattled jacana).

20 Bottleneck effect When large population is drastically reduced by a disaster famine, natural disaster, loss of habitat loss of variation by chance event alleles lost from gene pool not due to fitness narrows the gene pool

21 Cheetahs All cheetahs share a small number of alleles less than 1% diversity as if all cheetahs are identical twins 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

22 Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection founder effect small group splinters off & starts a new colony bottleneck some factor (disaster) reduces population to small number & then population recovers & expands again but from a limited gene pool

23 Founder effect When a new population is started by only a small group of individuals just by chance some rare alleles may be at high frequency; others may be missing skew the gene pool of new population human populations that started from small group of colonists example: colonization of New World albino deer Seneca Army Depot

24 Coevolution Two or more species reciprocally affect each other s evolution predator-prey disease & host competitive species mutualism pollinators & flowers

25 Cheetahs and Pronghorn antelope both evolved on the plains of North America. Cheetahs crossed over to Asia, but became extinct in North America during the Pleistocene Epoch. Consider this.if the cheetah gave the antelope their speed, what did the great cats give our Australopithecine ancestors? What? A present for me?

26 Effects of Selection Changes in the average trait of a population DIRECTIONAL SELECTION STABILIZING SELECTION DISRUPTIVE SELECTION giraffe neck horse size human birth weight rock pocket mice

27 The Ugly Truth--- Human Selection Factors I m not sure if I want to know about this, But, then yes I do...

28 Selection- fitness markers in human males Heart #1 Heart #2 Ladies, if you had to choose just one gentleman from behind the door, which door would it be? ence-environment

29 Selection- fitness markers in human males Symmetry-measure of genetic fitness, health and initiates attraction. Women can see it, hear it, and smell it! Dancing ability? Recent research indicates dancing skill is related to symmetry the better the dancer, the more symmetrical the male, the more attractive to females ence-environment Body Scents/Pheromones- associated with MHC [immune system markers] the more dissimilar to the female, the more attractive. It enhances immunity and resistance to parasites in offspring. Deeper, resonating voice- Again, one of those annoying correlations to testosterone and symmetry. Facial masculinity (angular features), height (6 ft+), wide shoulders, narrow waists (2:1 height-waist ratio or higher)- measures of testosterone. Dominance access to resources, physicality, high status in the tribe (read status and provisioning ability).

30 Selection- fitness markers in human females Heart #1 Heart #2 Gentlemen, if you had to choose just one lady from behind the door, which would you court? ence-environment

31 Fitness markers in human females Symmetry-measure of fitness and initiates attraction Two research viewpoints: A). Waist-Hip Ratio 60%-70% waist-size compared to hips (the hour-glass figure) B). BMI 19-20% Body Fat Considered a marker used by our hunter-gatherer forefathers to judge the health, genetic fitness and fertility of women

32 Two Scientific DebateTeams: - Hip to Waist Ratio Advocates - Body Mass Index Advocates Hip to Waist Ratio: Some researchers indicate that a woman is considered most attractive when her hip to waist ratio is 70%. Studies continue that interest is lost (nice way for the researchers to put it, huh?) when the ratio exceeds 80%. Beauty icons including Marilyn Monroe, Alessandra Ambrosio, Sophia Loren, Kate Moss, and even Venus de Milo all have ratios around 70%, but significantly different weights. Interestingly, some research indicates that fertility peaks near a HWR of 60%, which is very close to the golden mean ratio of waist circumference to hip circumference of 62%. J Pers Soc Psychol Aug;65(2): Adaptive significance of female physical attractiveness: role of waist-to-hip ratio.

33 Body Mass Index Advocates Other researchers found that male experiment participants perceptions of attractiveness matched body-mass ratios much more closely than the waist-hip ratios. These studies concluded that those judged most attractive had a BMI between 19-20%. Additionally it was found that attractiveness drops dramatically below 17% BMI and above 25%. Chart of findings below BMIs Anorexic women Fashion models Other models Typical women Bulimic women

34 Rudder s talk at the Empiricist League borrowed from the book s first chapter, covering the basics of whom we re attracted to and why. Accompanied by a slideshow, he brought up a chart 1 of how straight women rate the men on OKCupid based on their age. Women who are, say, 28 find guys who are also 28 about the most attractive, and so forth. Up until about 40, when that s getting too old. And then Rudder delivered the punchline. And the male version is

35

36

37

38 Any Questions??