Ecology Test 2 Chapter 5

Theory of Natural Selection

Charles Darwin - how organisms adapt to their environment

What are the 3 conditions required for Natural Selection?

characteristic variation, heritable variation, differences in survival and reproduction through environmental interactions

Fitness

the contribution bade by an individual to future generations relative to other individuals in the same population

ex: Bob Marley - 11 kids, Bruce Lee 2 kids — bob had more fitness

evolution

changes in genetics of a population of organisms over time

adaptation

any heritable behavioral, morphological, or physiological trait that evolved via natural selection

how is adaptation central to ecology?

it is key to understanding the distribution and abundance of species

example to show how adaptation is central to eco

some warm-blooded exothermic animals shapeshift and are getting large beaks, legs, tails, ears to better regulate body temperature as the earth heats up

genome

all of DNA in a cell’s nucleus

DNA

encodes genetic offspring that’s transmitted from parent to offspring

gene

encodes the info needed to produce an RNA molecule

mRNA

produced by protein-coding genes that encode the info and then the molecule encodes a sequence of amino acids that are assembled to produce a polypeptide

gene expression

different types of cells/different stages in the life cycle

alleles

alternate forms of the same gene

homozygous

2 same copies

heterozygous

2 different copies

genotype

alleles present at each gene within an organism’s gene

phenotype

appearance of an organism for a particular characteristic

target of selection

phenotype

homozygote phenotype

determined by one allele (RR/rr)

heterozygote phenotype

interaction of both alleles (Rr)

incomplete dominance

intermediation — neither allege is fully expressed (red + white = pink)

codominance

both alleles expressed (red + white = stripes of both)

qualitative trait

characteristic shows a small number of discrete phenotypic categories — encoded by 1 gene

quantitative trait

shows a continuous distribution of phenotypes — encoded by 2 or more genes like height, skin, eye, hair color, weight, body size

what environmental conditions show continuous variation

temperature, precipitation, sunlight, and predation level

what is an example when phenotype is determined by the environment

cat coloration - a mutated version of the gene coding for tyrosinase (temperature dependent), an enzyme (protein) that facilitates melanin production — the dark appendages are physically cooler than the rest of the body

phenotypic plasticity

the ability of one genotype to give rise to different phenotypes under different environmental conditions

norm of reaction

the set of phenotypes expressed by a single genotype across a range of environmental conditions — LEADS TO AN INCREASE IN FITNESS UNDER CURRENT ENVIRONMENTAL CONDITIONS

what can be understood from this graph?

there is a positive relationship

G1 is shallow while G2 has a steeper slope

G2 has more distribution so there is more phenotypic plasticity

Why is the body color of many insects affected by temperature during development?

“ultimate cause” the darker color helps them warm up in the sun while the lighter ones reflect the light

How is the body color of insects affected by temperature during development?

“proximate cause” during development, the expression level of genes is involved in incorporating the pigment melanin into the cuticle that is established

How do plants show phenotypic plasticity?

low light - 20% available PAR

• less biomass; more photosynthetic leaf area

• large, thin leaves; few branches

  • BASICALLY SMALL PLANTS, BIG LEAVES

high light - 100% PAR

• narrow leaves on many branches

developmental plasticity

phenotypic changes that CANNOT be reversed

acclimation

phenotypic plasticity in response to current environmental conditions that is reversible (changes depending on the on the environment

what is an example of acclimation?

seasonal changes in temperature tolerance in fish

transgenerational plasticity

phenotype of offspring influenced by parent’s environment (epigenetics)

when the parents experience temperature variation (transgenerational plasticity)

the eggs have prolonged egg development (developmental plasticity)

is a species composed on a single, continuous interbreeding population?

no, it is usually a group of subdivisions - local populations of inbreeding individuals and linked by movement of individuals

genetic variation is found

within and among subpopulations

genetic differentiation

large differences in frequencies of alleles; can result in speciation

gene pool

the sum of all genetic information called alleles across all individuals in a population

how is the gene pool measured

2 ways - allele frequency (A/a) and genotype frequency (AA, Aa, & aa)

phenotypic evolution

a change in the mean or variance of a trait across generations

what is an example of phenotypic evolution?

body height - change in mean and variance across generations

natural selection acts

directly on the phenotype

heritable variation

the variance of the breeding values among individuals

beak size

heritable variation

what criteria other than heritable variation is required for natural selection?

fitness - variation in fitness bc of variation in beak size

did heritability change?

no, there are similar slopes so high heritability in both years

what is the final criteria of phenotypic evolution?

fitness consequence of trait variation

birds with large beaks

feed on wider range of seed sizes - small, large, soft, hard

birds with smaller beaks

limited to feeding on smaller/softer seeds

what could have driven the selection towards larger beak sizes in 1978?

drought and population size

what happened and why

a. number of seeds dropped dramatically

b. the size and hardness of seeds increased

why? La Nina changed weather patterns so the average rainfall fell (drought) and the finch population dropped 85%

birds that survived had deeper beaks so what was the target of selection and selective agent?

target of selection - beak size

selective agent - change in seed size/abundance

what type of selection is the change in beak depth of the Galapagos medium ground finch?

directional selectionw

directional selection

the distribution of phenotypes shifts towards one end of the distribution

examples of directional selection

most adaptations - large antlers, drought resistance

stabilizing selection

the mean phenotype has higher fitness than the phenotypes at either end of the distribution

example of stabilizing selection

birth weight in human babies - babies that have a very high or very low birth weight have a lower change at survival — lower fitness

disruptive selection

phenotypes at both ends of the distribution have higher fitness than the mean phenotype — selective pressures different at each extreme

mutation

a heritable change in a gene or a chromosome

RANDOM

mutations can be beneficial, neutral, or harmful

harmful - removed via natural selection

beneficial - promoted via natural selection

genetic drift

a change in allele frequencies (may also change genotype frequencies) as a result of random chance — alleles can be lost via genetic drift

sexual reproduction

random recombination of alleles through crossing over, independent assortment, and fertilizationth

the larger the population

the greater the probability that most alleles will be represented in the next generation at around the same frequency

migration

the movement of individuals among local populations

gene flow

the movement of genetic information among populations

emigration

leaving

immigration

coming

assortative mating

nonrandom mating — choosing mates based on their own phenotype which reflects their genotype

random mating

change that an individual mates with another individual in equal to the frequency of the genotype of that individual in the population

nonrandom mating

changes genotype frequencies in the population but doesn’t change allele frequencies — you lose heterozygosity and can lead to inbreeding effects

example of nonrandom mating

humans - looks similar, same personality, same language…

inbreeding

a type of assortative mating that occurs when you mate with someone who is more closely related than expected by random chance

THIS INCREASES HOMOZYGOSITY IN ALL GENES

inbreeding depression

offspring are more likely to be homozygous for harmful recessive alleles — can lead to reductions in fertility, vigor, fitness, and death

Hardy-Weinberg Principle

undergoing evolution or nah. it assumes that there is random mating, no net change in mutation, a large pop., no migration, and no natural selection then it isn’t evolving

Allele frequency equation

p+q=1

p=A q=a

genotype frequency equation

p²+2pq+q²=1

p²=AA

pq=Aa

q²=aa

example question: The frequency of allele a is 0.4. What is the frequency of A? What is the expected frequencies of the 3 genotypes?

0.4 + x = 1 — x=0.6

(0.6)²+2(0.6)(0.4)+(0.4)²=1

AA 0.36, Aa 0.48, aa 0.16

natural selection

genetic changes among populations because of variation in local environmental conditions

variation in environmental conditions

phenotypic variation due to different selective pressures in different conditions — the father apart populations live, the more pronounced the variation can become

cline

a measurable difference in a phenotypic character(s) over a geographic region — size, color, body size…

continuous variation

results from gene flow between the populations along the gradient

example of cline

the Fence Lizard - wide range from eastern US through northern Mexico — the cline is the body size across its range

body size increases with latitude SO temperature changes body size

common garden experiment

individuals from different populations are grown in the same controlled conditions

example of the common garden experiment

plants with different phenotypes based on the expression of different genotypes

different populations genetically the same but exhibit phenotypic plasticity — result: plants with the same phenotype

plants from different populations are genetically distinct

different phenotypes based on the expression of different genotypes

plants from different populations genetically the same BUT exhibit phenotypic plasticity

plants with the same phenotype

clines can be discontinuous

step clines indicate abrupt changes in environment and in the phenotype and genotype

ecotypes

variants in different populations of a species

what can we infer from the figure related to phenotypic plasticity and genetic differentiation?

fitness influenced by environment (inland better) and genotype (ecotypes different in common garden)

area of hybridization between ecotypes occur

blurred lines

isolated populations can lead to

subspecies

selective breeding

artificial selection where humans are the selective agent

limitations to selective breeding

genetic diversity, inadvertently selects for multiple traits, limited by available alleles/gene pool — ex: fox to playful dog

genetic engineering

allows humans to alter organism’s genome

primary technique of genetic engineering

recombinant DNA

modified gene

transgene

organisms that carry the recombinant DNA

transgenic