Evolutionary Forces at work What changes populations? Natural Selection: Evolutionary Forces at work What changes populations? 2007-2008

Forces of evolutionary change 1. Natural selection traits that improve survival or reproduction will accumulate in the population Referred to as: adaptive change 2. Genetic drift frequency (how often they occur) of traits can change in a population due to chance events The changes are random

1. Natural Selection Selection acts on any trait that affects survival or reproduction a. predation selection b. physiological selection c. sexual selection

Predation Selection a. Predation selection acts on both predator & prey Behaviors camouflage & mimicry speed defenses (physical & chemical)

b. 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

Physiological selection Dogs pee on trees…Why don’t trees pee on dogs? NH3 plant nutrient animal waste One critter’s trash is another critter’s treasure!

Survival doesn’t matter if you don’t reproduce! c. 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!

Example of Sexual selection: Lion’s mane It’s FEMALE CHOICE, baby!

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?? YES! This implies greater ‘fitness’ in the male Even though it’s very hot to have a large mane the benefit of attracting mates and successfully producing & rearing young since you have that large mane outweighs the costs. Females who chose these males were more “successful” (more, healthier young) and therefore had a greater opportunity to pass on the trait of being attracted to longer darker manes to their daughters and the trait of having longer, darker manes to their sons.

In people…being ‘Sexy’ = fitness markers

Fertility figures through the ages!

Is there a testable hypothesis in there? Sexual selection Acts in all sexually reproducing species the traits that get you mates sexual dimorphism (male and female are very different : ( di = two / morph = body) influences both morphology & behavior can act in opposition to natural selection Jacanas Is there a testable hypothesis in there?

2. 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

albino deer Seneca Army Depot 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: Amish (1700’s/400 people) Small founder group, less genetic diversity than Africans All white people around the world are descended from a small group of ancestors 100,000 years ago (Chinese are white people!) albino deer Seneca Army Depot

Out of Africa Likely migration paths of humans out of Africa 10-20,000ya 10-20,000ya Migration Paths According to the "Out of Africa" theory, modern humans appeared as a single African species nearly 100,000 years ago, then spread throughout the world (K.Wong, Is Out of Africa Going Out the Door?, Scientific American 281(2), August 1999). 50,000ya Many patterns of human traits reflect this migration

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

Cheetahs All cheetahs share a small number of alleles 2 bottlenecks 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

Can lead to‘fixation’ All individuals in the population are homozygous for an allele Example in book: Northern Elephant seal – on brink of extinction with 20 left Laws change, now 170,000 in pop Every seal is homozygous for all genes tested (no diversity!) Why might this be a ‘bad’ thing?

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

In Class assignment… Go to page 282-285 In Class assignment… Go to page 282-285. Read about: directional stabilizing disruptive selection…. Explain the picture on the next slide…begin by defining the term. We will discuss in 15 minutes…!

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

Any Questions??