Evolution and Natural Selection

Define evolution

change in the heritable characteristics of a population down through natural selection

Evidence for evolution

• new variants of coronavirus

• comparing base sequences from same gene/protein in different species (cladogram)

• gene families from diverse groups

• selective breeding done by humans (plants/animals)

Homologous structures as evidence for evolution

• human, mole, porpoise and bat all have same bones in forelimbs but with diff functions

• homologous structures suggest they evolved from common ancestor

• differences came from divergent evolution

vestigial structures

• rudimentary organs that serve no current function

• left over from ancestors

• ex: tailbone and appendix

Analogous structures

• preform similar functions but have different origins (we know from cladistics)

• ex: fish and whale tails are similar but from different ancestors

• ex: human and octopus eyes are similar

Speciation by separation

• 2 pops become separated and cant interbreed

• evolve in different ways

• if cant interbreed when reintroduced then they are different species

• ex: zosterop birds have 100+ species

geographical separation

• populations separated and cant interbreed

• separated by mountain range, rivers, islands, etc.

• most common barrier to gene flow

• ex: bonobos and chimpanzees and congo river

• can lead to differential selection

Differential selection

• when natural selection acts differently in 2 pops

• diffs can be enough that they become diff species

• caused by different climates, resource competition, predation

• Ex: lava lizards in the galapagos

Allopatric speciation

• different homeland

• geographical isolation

sympatric speciation

• same homeland

• speciation occurs when organisms are in same place

• includes behavioral and temporal speciation

behavioral isolation

• lifestyles or habuts used to identify members of a species

• ex: bird songsand mating rituals in birds of paradise or chichlids in different depths of same lake

Temporal speciation

• when animals and plants mate/produce flowers or pollen at different times

• timing of reproduction is different = reproductive isolation

• diurnal vs nocturnal

• ex: winter pine processionary moth

  • originally larvae hatched in fall, new pop hatches in summer

  • they cant interbreed so are different species

Adaptation

characteristics that make an org suited to their environment/lifestyle

adaptive radiation

• species extend range when group migrates to new area

• become founders of new pop

• availability of niches can lead to adaptive radiation (spreading out)

• minimizes competition between species

• ex: galapagos finches

adaptive radiation in broncchinias

• ancestor cam to Guiana shield 20 million years ago and have been diversifying for the last 13 million

• nutrient deficient soils have caused many strategies for adaptation

  • rely on roots alone

  • curved vertical leaves forming a tank to trap insects

  • expanded leaf bases make chambers for ants to live

  • more water tanks

  • some are epiphytic and live with nitrogen fixing bacteria

Barriers to hybridization

• since hybrids cant produce offspring they are a waste of resources

• species have evolved barriers to prevent hybrids

• ex: courtship rituals in birds of paradise (only breed with same species)

Mating flight in honey bees

• queens produce pheromones

• male drones from diff colonies follow her

• queen mates with up to 20 drones

• gathers enough to fertilize several years worth of eggs

what is polyploidy and why does it happen?

• ogrs with >2 sets of chromosomes

• can be consequence of replication of chromosomes that is NOT followed by cell division

• can result from cross-breeding between species

consequences of polyploidy

• can make diploid and haploid gamete fuse to make triploid

• if cell insterile the hybrid replicates without dividing which makes allotetraploid cells

  • these cells COULD undergo meiosis and make successful gametes

natural selection

• process by which orgs are better adapted to their environment are able to survive and produce more fertile offspring

• mechanism by which evolution occurs

3 conditions required for natural selection

• variation within a population

• overproduction of offspring

• differential survival

how is variation created?

• mutation - makes new alleles, which makes new phenotype

• meiosis - crossing over and independent assortment make new allele combos

• sexual reproduction - creates more allelic combos in offspring

Adaptation

some characteristic make an individual better suited to their environment

examples of adaptation

• prickly pear cactus - tall with spines to resist predation from iguanas

• red footed boobys - large feet to perch on trees

• male lava lizardz - have red heads and do push ups to attract mates

overproduction

• most species produce more offspring than the environment can support

• leads to competition for resources →differential survival

Differential survival

• survival of the fittest

• better adapted individuals tend to survive and produce more offspring

• “good” characteristics depend on the environment

• adaptations increase overall “fittness” of the population

density (in)dependent factors effect on natural selection

• Increased density = increased resource competition

• effect of cold on temp is density independent and abiotic

• food and water are density dependent

sexual selection

• individuals must reproduce to contribute to evolution

• sexual selection includes behaviors to attract mates

  • males fighting to mate

  • males dancing/singing

  • exaggerated traits (peacock)

• indicate overall health and vigor

• can also attract predators

what is a gene pool and why does it change?

• all genes and alleles in a population

• individuals who reproduce contribute to the gene pool of the next generation

• gene pool expanded when new orgs arrive

• when reproductively isolated, gene pool decreases

allele frequencies

• different pops have different allele frequencies for genes

• use AlFred database to search for allele frequencies

• allele frequencies change due to natural selection

• evolution = change in allele frequency

stabalizing pattern of selection

• moderate traits preferred

• medium tail

disruptive selection

• for both extremes

• short OR long tail preferred

directional selection

• moves from one extreme towards the other

• short tail → long tail

conditions required for harvey-weinberg experiment

• no mutations (no new alleles)

• no preferential selection (random mating)

• no immigration/emigration

• large population (so allele frequencies don't change = genetic drift)

• no natural selection (equal chance of survival)