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CHAPTER 24ORIGIN OF SPECIES
“Macro-evolution”
“A place of genesis”
Galapagos (Spanish for Tortoise)
“Both in space and time, we seem to be brought somewhatnear to that great fact – that mystery of mysteries – the firstappearance of new beings on this Earth.” - Darwin
Macroevolution =
The origin of new taxonomic groups (Kingdoms Species)
Speciation =
The origin of new species
The keystone process in the origination of diversity of higher taxon
“Phylogeny”
Linnaeus
Kingdom
Phylum
Class
Order
Family
Genus
Species
Canis lupus
Canis lupus
Canis familiaris
Canis familiaris
“Descent with modification”
Two patterns of speciation (fossil record)
Anagenesis (up/origin) = the accumulation of changes associated with the transformation of one species into another
Cladogenesis (branching/origin) =the budding of one or more new species from a parent species
Cladogenesis promotes biological diversity by increasing the number of species
1 1 2
Biological species concept 1942 Ernst Mayr
A species is a population or group of populations whose members have the potential to interbreed with each other in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species
Based on interfertility rather than physical similarity
A biological species is the largest set of populations in which genetic exchange is possible and that is genetically isolated from other populations
This concept hinges on reproductive isolation, with each species isolated by factors (barriers) that prevent interbreeding, thereby blocking geneticmixing with other species
Geographical isolation =Not intrinsic to the organisms themselves
Reproductive isolation =Intrinsic, preventing populations belongingto different species from interbreeding, even if their ranges overlap
Any factor that impedes two species from producing viable, fertile hybrids contributes to reproductive isolation
The various reproductive barriers that isolate gene pools of species can be categorized asPrezygotic or Postsygotic
Prezygotic = prevent mating or hinderthe fertilization of ova
Postzygotic = prevent the hybrid zygotefrom developing into a viable, fertile adult
Two modes of speciation
distinguished by the way gene flow among populations is initially interrupted
Speciation takes place in populations with geographically separate ranges.
Gene flow is initially interrupted or reduced between two populations because they are separated by space
Harris’s Antelope SquirrelSouth Rim
White-tailed Antelope SquirrelNorth Rim
Allopatric Speciation
A model for adaptive radiation on island chains
Sympatric Speciation
Speciation occurs in geographically overlapping populations when biological factors, such as chromosomal changes and nonrandom mating, reduce gene flow
Let’s look and plants and animals
In plants, sympatric speciation can result from accidents during cell division that result in extra sets of chromosomes, a mutant condition known as polyploidy
More than 2 chromosome sets
Cannot interbreedwith diploid plants
Hugo de Vries (early 1900s) 2 species of Evening Primrose
2 different species interbreed
SterilePropagate (asexually)
Various mechanisms cause fertility (polyploid)
Breed with each other,but not parental species
Goatsbeard
Wheat
VictoriaTanganyika
Malawi
The Great Rift Valley
Hot Spots for “Speciation”
Lake Victoria< 200 years old
Sympatric Speciation in Animals
Polyploid speciation less common in animals (does occur)
Other mechanisms that lead to sympatric speciation in animals
200+ species of closely related species of Cichlids (family)
Adaptive radiation (exploiting food resources) lead to speciation = allopatric
Nonrandom mate selection (females select males/coloration) = sympatric
Natural Light Monochromatic Orange Light
Females exhibitedDiscriminate mating (coloration)
Non-discriminate mating
Laboratory Experiment2 speciesof males
Offspring viable/fertileSpeciation = recent
Sexual Selection
Two models for the tempo of speciation
Matches fossil record
Rapid changeSlow/ Gradual Change
Long periods of stasis (equilibrium)punctuated by episodes of speciation
1,000’s of years