Evolution Test 3

Neutral Theory of Molecular Evolution

the majority of mutations are neutral and may fix in populations through genetic drift

Probability of fixation

Likelihood of an allele becoming fixed in a population

q = ½ N

Rate of fixation

(2N)(u)(1/2N)=u

probability of fixation ½ N

mutation rate u

number of genes 2N 

polymorphism

The coexistence of two or more distinct forms in the same population

molecular clock

Model that uses DNA comparisons to estimate the length of time that two species have been evolving independently

Variation in the expression of behavior traits

Vp = Vg + Ve

Vg - genetics (hard wired)

Ve - environment (soft wired) 

Hard wired behavior

Automatic responses ingrained in behavior

Soft wired behavior

Traits influenced by experiences and environment 

Sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates

Intrasexual selection

A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex

Contest between males 

Intersexual selection

Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex

Female choice 

Why do females get to choose?

Females invest a lot of energy to produce few eggs

Females invest more in caring for the zygotes after fertilization 

Sperm competition strategies

Producing more sperm

Sperm precedence 

Direct benefits of mate choice

Females choose males that will improve their immediate chances of survival and reproduction

Ex: superior territory 

Indirect benefits of mate choice

Choosing a good mate increases fitness of offspring

Females look for characteristics that indicate the ability to secure resources, high quality diet and health, less likely to carry disease, good genes 

Runaway sexual selection - sexy son hypothesis

when selection for preference of a sexual trait and selection for that trait continue to reinforce each other because the sons of females that have preference for a trait inherit the trait from their fathers so they experience high mating success

Good genes hypothesis

the hypothesis that an individual chooses a mate that possesses a superior genotype because they are indicators of high fitness (good genes)

Manipulation

a donor may dispense aid to a recipient because the donor is being manipulated

Individual advantage - mutualism

every participant individually benefits from cooperation

Reciprocation

individuals take turns being the donor and the recipient of altruistic behaviors

Kin selection

individual is benefiting from a genetic relationship

Inclusive fitness

individual fitness through relative

Hamilton's Rule

The principle that for natural selection to favor an altruistic act, the benefit to the recipient, devalued by the coefficient of relatedness, must exceed the cost to the altruist.

donor

actor of altruistic act

Recipient

who is being helped

b

benefit of recipient

r

coefficient of relatedness

shared genes 

c

cost

= 1 

Asexual 

no production of gametes

Sexual

produce gametes

Parthogenesis

reproduction that consists of only females that produce more females from unfertilized eggs

Hermaphrodite

an organism that has both male and female reproductive organs

Outcrossing

gametes from different individuals combine to form offspring

Sexual reproduction pros

increases genetic variability

greater adaptability to changing environments

Sexual reproduction cons

Few offspring in a long time

need to make gametes and find a mate (uses energy)

Asexual reproduction pros

Don't need a partner

unchanging environment 

fast 

identical

Asexual reproduction cons

Identical

no variation 

deleterious mutations accumulate 

environment could change which could require a trait that’s not established

Cost of producing sons

In sexual reproduction on 1/2 of the genes are passed down

Cost of meiosis

breaks up favorable genotypes

Cost of mating

finding mates, risky, time consuming, producing offspring with low fitness if mating with the wrong mate

Sib-competition model

genetically variable sibs may partition resources better

Mueller's rachet

process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner

The Red Queen Hypothesis

sexual selection allows hosts to evolve at a rate that counters the rapid evolution of parasites

Inbreeding

Continued breeding of individuals with similar characteristics

Outbreeding

the process of mating less closely related individuals when compared to the average of the population

Culling

process of eliminating less productive or less desirable cattle from the herd

Isogamy

gametes are equal in size

Anisogamy

Refers to a difference in gamete size in males and females. Eggs large and costly, sperm small and cheap

Sex ratio

the ratio of males to females in a population

Fisher's Principle

Natural selection favors production of the rarer sex so that the sex ratio is kept balanced at 1:1

Speciation

Formation of new species

Anagenesis

species formation without branching of the evolutionary line of descent.

Speciation event

A point in evolutionary history at which a given population splits into independent evolutionary lineages.

Cladogenesis

the formation of a new group of organisms or higher taxon by evolutionary divergence from an ancestral form.

Carl Linnaeus

"Father of Taxonomy"; established his classification of living things; famous for animal naming system of binomial nomenclature

Plato

All imperfect variations of ideal form

Essentialism

a line of thought that explains social phenomena in terms of natural ones

Common descent

principle that all living things were derived from common ancestors

Earnst Mayr

developed the biological species concept

Theodosious Dobzhansky

"Nothing in biology makes sense except in the light of evolution"

Biological species concept

Species is a group of populations whose members have the potential to produce fertile offspring.

Evolutionary species concept

every species has its own evolutionary history, which is partly documented in the fossil record

Phylogenetic species concept

A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.

Problems with BSC

Hybrids happen

asexual reproducers

fossil organisms

Hybrid

Offspring of crosses between parents with different traits

Parapatric population

adjacent to each other

Semispecies

populations of a species that are completely isolated from one another but have not yet become truly separate species

Superspecies

a collection of semispecies

Sympatric populations

populations occupying the same geographic area and capable of encountering one another

Ring species

populations that can interbreed with neighboring populations but not with populations separated by larger geographical distances

Polytypic species

species that consist of a number of separate breeding populations, each varying in some genetic trait

Allopatric populations

closely related species that are geographically separate

Prezygotic barriers

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted

Temporal isolation

form of reproductive isolation in which two populations reproduce at different times

Habitat isolation

populations live in different habitats and do not meet

Behavioral isolation

Form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding

Mechanical isolation

Morphological differences prevent fertilization

Gametic isolation

Sperm of one species may not be able to fertilize eggs of another species

Post-zygotic barriers

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

Hybrid mortality

Hybrid offspring develop but then die

Hybrid inviability

A postzygotic barrier in which hybrid zygotes fail to develop or to reach sexual maturity

Hybrid sterility

hybrid offspring mature but are sterile as adults

Hybrid breakdown

Hybrid is fertile, but when they breed the next generation is sterile.

Haldane's Rule

If in the offspring of two different animal species one sex is absent, rare, or sterile, that sex is the heterogametic sex

Hybrid zone

a geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry

Cline

a graded change in a character along a geographic axis

Step cline

Stepwise variations between populations with each step being a race; occurs in parapatric speciation, narrow hybrid zones, and semispecies, natural selection

Broad cline

Occurs in sympatric speciation, broad hybrid zone, migration

No hybrid zone

Occurs in allopatric speciation, no hybrid zones, and polytypic species, races, and subspecies

Primary hybrid zone

overlap/hybridization area that occurs during initial speciation event

Secondary hybrid zone

Formed when two allopatric populations (genetically differentiated) come together and interbreed at secondary contact zone

Allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

Vicariance

the physical splitting of a habitat

Founder effect speciation

Isolating event in which a small population becomes separated from its "parent" population. Over time, reproductive isolation may evolve

Polyploidy

condition in which an organism has extra sets of chromosomes due to non-disjunction at meiosis

Autopolyploidy

an individual that has more than two chromosome sets that are all derived from a single species

Allopolyploidy

polyploidy resulting from contribution of chromosomes from two or more species