Eco Chapter 5: Adaptation and Natural Selection

Natural selection

differential success (survival and reproduction) of individuals within a population, acts directly on phenotype

Requirements for natural selection leading to evolution:

1. variation in traits must be heritable (passed down to future gen)
2. variation leads to differences in survival and fitness (reproduction) among individuals in a population

fitness

the proportionate contribution made by an individual to future generations relative to other individuals (how many offspring rat A has compared to the population of rats)

Adaptation

any heritable behavioral, morphological, or physiological trait that has evolved through the process of natural selection (traits that increase survival/fitness in a given set of environmental conditions)

gene

basic unit of heredity, a section od DNA that contains the code needed to build or regulate proteins

genome

all the DNA within a cell

gene expression

the process by which the information coded in a gene is turned into a function (ex: hair color, nose shape, insulin production, responses to environmental conditions such as producing more melanin in response to solar radiation)

alleles

alternative forms of the same gene (such as A or a) humans are diploid meaning we have two copies of the same gene and thus 2 alleles (one from each parent)

homozygous traits

two alleles are the same (dominant: AA or recessive: aa)

heterozygous traits

two alleles are different (Aa)

genotype

alleles present at each gene within an organism’s genome (the alleles themselves, ex: AA, Aa, or aa)

phenotype

the physical expression of a genotype (AA is expressed as red flower petals while aa is white petals)

complete dominance

both AA and Aa are phenotypically expressed as the dominant variation (flowers with AA and Aa both have red petals)

incomplete dominance

only AA are expressed as the dominant variation (red petals) and Aa is expressed as an in-between variation of AA (red) and aa (white) thus Aa would be expressed as pink petals

subpopulations

local populations of interbreeding individuals linked by movement of individuals

gene pool

sum of all genetic information across all individuals in a population

genetic differentiation

genetic variation found among subpopulations

developmental plasticity

phenotypic changes that CANNOT be reversed (ex: plants grown in low light conditions have stunted growth that cannot be changed by moving them to higher light conditions)

acclimation

phenotypic plasticity in response to current environmental conditions that CAN be reversed (tanning: producing more melanin in response to more solar radiation exposure)

phenotypic evolution

a change in the mean/variance of the phenotype of a trait across generations (can be caused by the differences in fitness among traits)

target of selection

phenotypic trait that selection acts directly upon (melonated butterflies vs white butterflies, melonated frequency increased during industrial revolution)

selective agent

environmental cause of fitness differences among phenotypes (industrial revolution increased the smoke/soot in the air, it got on tree bark which made it darker, the melonated butterflies could now blend in better than the white ones and were less hunted)

directional selection

fitness favors phenotypes at one end of the distribution

disruptive selection

fitness favors phenotypes at both ends of the distribution but not the mean

stabilizing selection

fitness favors phenotypes at the mean of the distribution

The only process that leads directly to adaption…

natural selection

mutation

creates genetic variation by randomly introducing new alleles (can be beneficial, harmful, or neutral)

genetic drift

a change in allele frequencies as a result of random chance (not fitness based)

bottleneck effect

type of genetic drift, occurs when population experiences a drastic reduction in size (ex: disease outbreak kills 2/3 of a population and now the allele frequency has randomly shifted to what the surviving population has

founded effect

type of genetic drift, occurs when a small group breaks off of the population and establishes a new one (Galapagos finches made new populations on different islands, the allele frequencies of the new populations were based on the random alleles of the populators)

gene flow

the movement of genetic information among populations, reduces genetic variation among populations as allele frequencies become more similar

sexual reproduction: (list 2 characteristics)

1. fertilization: offspring have a subset of the alleles that their parents carry

2. random recombination of alleles through crossing over and independent assortment during meiosis

assortative mating

a form of nonrandom mating, individuals in a population choose mates based on their phenotype which reflects their genotype

positive assortative mating

mates are usually phenotypically similar, nonrandom, increases homozygosity (large males attracted to large females)

negative assortative mating

mates are usually phenotypically less similar, nonrandom, increases heterozygosity (large males attracted to smaller females)

inbreeding

individuals mate with members of the population that are more closely related to them than expected by random chance (incest, increases homozygosity at all genes)

inbreeding depression

offspring of inbreeding are more likely to have harmful recessive alleles that can lead to reduced fertility, vigor, fitness, and death

cline

a measurable change in a phenotypic character of characters over a geographic region or a gradient in genotypic frequency (ex: genetic skin color gradient is darkest at the equator and becomes lighter the farther away from the equator a population is)

Phenotypic Plasticity vs Clines

step clines

abrupt changes in local environments and in the phenotype/genotype of organisms (industrial revolution brought about an abrupt change in the melanin frequency among butterflies)

ecotypes

population adapts to its unique local conditions, areas of hybridization between ecotypes may occur

geographic isolates

geographic barriers may greatly impact the gene flow between populations, this could create subspecies

adaptive radiation

multiple species within the same lineage that exploit different features of the environment (Galapagos finches and their beaks which are specialized for different aspects of the environments they live in)