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

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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