Chapter 24: The Origin of Chapter 24: The Origin of SpeciesSpecies

MacroevolutionMacroevolutionCumulative effects of speciation over vast Cumulative effects of speciation over vast amounts of timeamounts of time

Anagenesis/phyletic evolutionAnagenesis/phyletic evolutionGradual accumulation of changesGradual accumulation of changes transform transform a single species a single species

Cladogenesis/branching evolutionCladogenesis/branching evolutionSplitting of a gene poolSplitting of a gene pool*single species morphs & diverges into 2 or *single species morphs & diverges into 2 or more speciesmore speciesCLADOGENESIS INCREASES BIODIVERSITYCLADOGENESIS INCREASES BIODIVERSITY

Defining a speciesDefining a species Morphological species conceptMorphological species concept

Based on body shape, size, & featuresBased on body shape, size, & features Paleontological species conceptPaleontological species concept

Focuses on morphologically discrete Focuses on morphologically discrete species known only in the fossil recordspecies known only in the fossil record

Ecological species conceptEcological species concept Views species in terms of its nicheViews species in terms of its niche

Phylogenetic species conceptPhylogenetic species concept Species is defined by its unique genetic Species is defined by its unique genetic

history on the tree of lifehistory on the tree of life Compares physical & molecular Compares physical & molecular

sequencessequences

SpeciationSpeciation New species adds to biological New species adds to biological

diversitydiversity SpeciesSpecies

Biological species conceptBiological species concept Populations whose members are Populations whose members are

reproductively compatible and offspring reproductively compatible and offspring viable and fertileviable and fertile

Limitations: prokaryotes, fossil species, & Limitations: prokaryotes, fossil species, & relatively unknown speciesrelatively unknown species

Reproductive isolationReproductive isolation biological factors (barriers) that biological factors (barriers) that

impede 2 populations from producing impede 2 populations from producing viable, fertile hybridsviable, fertile hybrids

Pre-zygotic barriersPre-zygotic barriers Impede mating or hinder fertilizationImpede mating or hinder fertilization Includes habitat, temporal, behavioral, Includes habitat, temporal, behavioral,

mechanical, & gametic isolationmechanical, & gametic isolation Postzygotic barriersPostzygotic barriers

Non-viable or sterile hybridNon-viable or sterile hybrid

Allopatric speciationAllopatric speciation Geography divides a population & its Geography divides a population & its

gene poolgene pool Isolated populations evolve by Isolated populations evolve by

natural selection & genetic drift, natural selection & genetic drift, resulting in reproductive isolationresulting in reproductive isolation

Sympatric speciationSympatric speciation(species exist in same geographically overlapping region)(species exist in same geographically overlapping region)

Speciation occurs as a result of Speciation occurs as a result of chromosomal changes chromosomal changes

PolyploidyPolyploidy Autopolyploid- more than 2 chromosome sets Autopolyploid- more than 2 chromosome sets

from one speciesfrom one species Allopolyploid- more than 2 chromosome sets from Allopolyploid- more than 2 chromosome sets from

more than one speciesmore than one species Often used to create new desirable cropsOften used to create new desirable crops

non-random matingnon-random mating Female selects male based on appearanceFemale selects male based on appearance

Evolutionary trendsEvolutionary trends GradualismGradualism

Species descend from a common ancestorSpecies descend from a common ancestor Gradually diverge as changes accumulate & Gradually diverge as changes accumulate &

unique adaptations are acquiredunique adaptations are acquired Punctuated equilibriumPunctuated equilibrium

Long periods of no apparent change in species Long periods of no apparent change in species followed by abrupt changefollowed by abrupt change

***Change may not be as dramatic as fossil ***Change may not be as dramatic as fossil record suggests record suggests

Adaptive radiationAdaptive radiation Common ancestor exists for many diversely Common ancestor exists for many diversely

adapted species adapted species Diversity occurs when groups are introduced Diversity occurs when groups are introduced

into new environments when:into new environments when: A few organisms migrateA few organisms migrate Environment changes opening up new nichesEnvironment changes opening up new niches

Evolutionary changeEvolutionary change Evolution of complex traits may Evolution of complex traits may

occur incrementally occur incrementally Each step on path to complexity Each step on path to complexity

must be of benefit to organismmust be of benefit to organism Exaptation- structures that take on a Exaptation- structures that take on a

new role in addition to initial role in new role in addition to initial role in ancestor specieancestor specie

Evolutionary changeEvolutionary change HeterochronyHeterochrony

Evolutionary change in the rate or Evolutionary change in the rate or timing of developmental events timing of developmental events Allometric growthAllometric growth

Proportioning that gives a body specific Proportioning that gives a body specific formform

Change in timing of development has Change in timing of development has significant morphological impactsignificant morphological impact

Ex. Salamander feet (ground vs. tree Ex. Salamander feet (ground vs. tree dwelling)dwelling)

PaedomorphosisPaedomorphosis Reproductive development accelerates vs. Reproductive development accelerates vs.

somatic development; sexually mature somatic development; sexually mature adult retains juvenile features of ancestoradult retains juvenile features of ancestor

Evolutionary changeEvolutionary change Change in Homeotic genesChange in Homeotic genes

Results in substantial evolutionary Results in substantial evolutionary change in placement & spatial change in placement & spatial organization of body partsorganization of body parts

**Large changes in appearance may **Large changes in appearance may result from small genetic change!!result from small genetic change!!

Species selectionSpecies selection Species that endure the longest appear Species that endure the longest appear

to give direction to evolutionary “trend” to give direction to evolutionary “trend” even though other features existed even though other features existed

Ex. Evolution of horsesEx. Evolution of horses