BIOL 221 - Unit 1

Why do zebras have stripes?

* Biting flies
* Aposematic deterrence of hyenas

evolution

a change in allele frequencies overtime

allele

different forms of the same gene

phenotypes

observable traits

population

a group of individuals of the same species that live in the same area at the same time

fitness

the ability of an individual to produce viable offspring relative to others of the same species

four process of evolution

* natural selection
* genetic drift
* gene flow
* mutation

mutation

ultimate source of genetic variation, modifies allele frequencies by introducing new alleles, random changes in DNA sequences

natural slection

process by which individuals with certain heritable traits tend to produce more surviving offspring than individuals without those traits

sexual selection

a trait that helps an organism obtain a mate

modes of natural selection

* directional selection
* stabilizing selection
* disruptive selection
* balancing selection

directional selection

favors one extreme phenotype

stabilizing selection

favors phenotypes near the middle of the range of phenotypic variation

disruptive selection

favors extreme phenotypic variation

balancing selection

no single phenotype is favored at all times

genetic drift

any change in allele frequencies in a population that is random, caused by random sampling process that takes place during fertilization

special cases of genetic drift

* founder effect
* genetic bottleneck

founder effect

change in allele frequencies that occur when a new population is established

genetic bottleneck

a sudden reduction in the diversity of alleles in a population

gene flow

the movement of alleles between populations

homologies

similarities that exist in species due to common ancestry, recognized and studied at three levels: developmental, genetic, and structural

transitional features

trait in a fossil species that is intermediate between those of older and younger species

vestigial traits

a reduced or incompletely developed structure that has no function or reduced function, but is clearly similar to functioning organs or structures in ancestral species or closely related species

adaptation

a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait

criteria for natural selection

* variation exists among individual organisms that make up a population
* traits are passed on to offspring
* more offspring are produced than can survive and reproduce
* individuals with certain heritable traits are more likely to survive and reproduce

species

an evolutionarily independent population or group of populations

What concepts are used to identify species?

* biological species
* morphospecies
* phylogenetic species

prezygotic isolation

prevents individuals of different species from mating successfully

postzygotic isolation

hybrid offspring of matings between members of different species either do not survive or do not reproduce

mechanisms of reproductive isolation

* temporal
* habitat
* behavioral
* mechanical
* gametic barrier
* hybrid inviability
* hybrid sterility

speciation

splitting event that forms two or more distinct species from a single ancestral species

What must happen for speciation to occur?

* genetic isolation
* genetic divergence

genetic isolation

elimination of gene flow between populations

genetic divergence

populations begin to evolve independently of each other

Under what conditions can reproductive isolation and divergence occur?

* allopatry
* sympatry

fossil record

the only record that provides direct evidence of what organisms in the past looked like, where they lived and when they existed

How does the diversity of life undergo big changes?

* Adaptive radiation
* mass extinction

fossil

a piece of physical evidence from an organism that lived in the past

adaptive radiation

a single lineage rapidly produces many descendant species with a wide range of adaptive forms

mass extinction

the rapid extinction of a large number of organisms around the world

limitations of the fossil record

* habitat bias
* taxonomic & tissue bias
* abundance bias
* temporal bias

habitat bias

fossils are more likely to form in areas where sediment are actively being deposited

taxonomic & tissue bias

harder parts of organisms decompose more slowly

temporal bias

older fossils have been exposed to potentially destructive forces for a longer time and are more likely to be pushed farther into the Earth’s interior

abundance bias

abundant, widespread, and longer-existing organisms are more likely to leave physical evidence than rare, local, or ephemeral species

niche

range of conditions that a species can tolerate and the range of resources that it can use

examples of mass extinction

* anoxic conditions
* asteroid impact
* extensive/severe acid rain
* human impacts
* large tsunami
* rapid climate change
* rapid sea-level change
* volcanic eruption
* widespread fires

examples of background extinction

* competition
* emerging disease
* gradual environment change
* predation pressure

biological species concept

main criteria is reproductive isolation and no gene flow between populations

morphospecies concept

main criteria is differences in shape, size, or other morphological features

phylogenetic species concept

main criteria is evolutionary history of populations

allopatry speciation

populations geographically seperated

sympatry speciation

populations live in the same geographical area

How does allopatric speciation occure?

* dispersal
* vicariance

vicariance

the physical splitting of a habitat

How does sympatric speciation occur?

External factors

* disruptive selection based on different ecological niches and/or mate preference

Internal factors

* chromosomal mutations

mechanisms that can trigger adaptive radiation

extrinsic factors

* existing genetic variation

intrinsic factors

* genetic changes (ex. mutation, gene duplication)

advantages of the biological species concept

* reproductive isolation = evolutionary independence

disadvantages of the biological species concept

* not applicable to asexually reproducing or extinct species
* difficult to assess if populations do not overlap geographically

advantages of the morphospecies concept

* widely applicable

disadvantages of the morphospecies concept

* subjective
* misidentifies polymorphic species
* misses cryptic species

advantages of the phylogenetic species concept

* widely applicable
* based on testable criteria

disadvantages of the phylogenetic species concept

* relatively few well-estimated phylogenies are currently available