Chapter 24: The Origin of Species Macroevolution Macroevolution Cumulative effects of speciation over vast amounts of time Cumulative effects of speciation over vast amounts of time Anagenesis/phyletic evolution Anagenesis/phyletic evolution Gradual accumulation of changes  transform a single species Gradual accumulation of changes  transform a single species Cladogenesis/branching evolution Cladogenesis/branching evolution Splitting of a gene pool Splitting of a gene pool *single species morphs & diverges into 2 or more species *single species morphs & diverges into 2 or more species CLADOGENESIS INCREASES BIODIVERSITY CLADOGENESIS INCREASES BIODIVERSITY

Defining a species Morphological species concept Morphological species concept Based on body shape, size, & features Based on body shape, size, & features Paleontological species concept Paleontological species concept Focuses on morphologically discrete species known only in the fossil record Focuses on morphologically discrete species known only in the fossil record Ecological species concept Ecological species concept Views species in terms of its niche Views species in terms of its niche Phylogenetic species concept Phylogenetic species concept Species is defined by its unique genetic history on the tree of life Species is defined by its unique genetic history on the tree of life Compares physical & molecular sequences Compares physical & molecular sequences

Speciation New species adds to biological diversity New species adds to biological diversity Species Species Biological species concept Biological species concept Populations whose members are reproductively compatible and offspring viable and fertile Populations whose members are reproductively compatible and offspring viable and fertile Limitations: prokaryotes, fossil species, & relatively unknown species Limitations: prokaryotes, fossil species, & relatively unknown species

Reproductive isolation biological factors (barriers) that impede 2 populations from producing viable, fertile hybrids biological factors (barriers) that impede 2 populations from producing viable, fertile hybrids Pre-zygotic barriers Pre-zygotic barriers Impede mating or hinder fertilization Impede mating or hinder fertilization Includes habitat, temporal, behavioral, mechanical, & gametic isolation Includes habitat, temporal, behavioral, mechanical, & gametic isolation Postzygotic barriers Postzygotic barriers Non-viable or sterile hybrid Non-viable or sterile hybrid

Allopatric speciation Geography divides a population & its gene pool Geography divides a population & its gene pool Isolated populations evolve by natural selection & genetic drift, resulting in reproductive isolation Isolated populations evolve by natural selection & genetic drift, resulting in reproductive isolation

Sympatric speciation (species exist in same geographically overlapping region) Speciation occurs as a result of Speciation occurs as a result of chromosomal changes chromosomal changes Polyploidy Polyploidy Autopolyploid- more than 2 chromosome sets from one species Autopolyploid- more than 2 chromosome sets from one species Allopolyploid- more than 2 chromosome sets from more than one species Allopolyploid- more than 2 chromosome sets from more than one species Often used to create new desirable crops Often used to create new desirable crops non-random mating non-random mating Female selects male based on appearance Female selects male based on appearance

Evolutionary trends Gradualism Gradualism Species descend from a common ancestor Species descend from a common ancestor Gradually diverge as changes accumulate & unique adaptations are acquired Gradually diverge as changes accumulate & unique adaptations are acquired Punctuated equilibrium Punctuated equilibrium Long periods of no apparent change in species followed by abrupt change Long periods of no apparent change in species followed by abrupt change ***Change may not be as dramatic as fossil record suggests ***Change may not be as dramatic as fossil record suggests Adaptive radiation Adaptive radiation Common ancestor exists for many diversely adapted species Common ancestor exists for many diversely adapted species Diversity occurs when groups are introduced into new environments when: Diversity occurs when groups are introduced into new environments when: A few organisms migrate A few organisms migrate Environment changes opening up new niches Environment changes opening up new niches

Evolutionary change Evolution of complex traits may occur incrementally Evolution of complex traits may occur incrementally Each step on path to complexity must be of benefit to organism Each step on path to complexity must be of benefit to organism Exaptation- structures that take on a new role in addition to initial role in ancestor specie Exaptation- structures that take on a new role in addition to initial role in ancestor specie

Evolutionary change Heterochrony Heterochrony Evolutionary change in the rate or timing of developmental events Allometric growth Evolutionary change in the rate or timing of developmental events Allometric growth Proportioning that gives a body specific form Proportioning that gives a body specific form Change in timing of development has significant morphological impact Change in timing of development has significant morphological impact Ex. Salamander feet (ground vs. tree dwelling) Ex. Salamander feet (ground vs. tree dwelling) Paedomorphosis Paedomorphosis Reproductive development accelerates vs. somatic development; sexually mature adult retains juvenile features of ancestor Reproductive development accelerates vs. somatic development; sexually mature adult retains juvenile features of ancestor

Evolutionary change Change in Homeotic genes Change in Homeotic genes Results in substantial evolutionary change in placement & spatial organization of body parts Results in substantial evolutionary change in placement & spatial organization of body parts **Large changes in appearance may result from small genetic change!! **Large changes in appearance may result from small genetic change!! Species selection Species selection Species that endure the longest appear to give direction to evolutionary “trend” even though other features existed Species that endure the longest appear to give direction to evolutionary “trend” even though other features existed Ex. Evolution of horses Ex. Evolution of horses