CHAPTER 24 ORIGIN OF SPECIES “Macro-evolution”

“A place of genesis” Galapagos (Spanish for Tortoise) “Both in space and time, we seem to be brought somewhat near to that great fact – that mystery of mysteries – the first appearance 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 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 11 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 genetic mixing with other species Geographical isolation = Not intrinsic to the organisms themselves Reproductive isolation = Intrinsic, preventing populations belonging to 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 as Prezygotic or Postsygotic Prezygotic = prevent mating or hinder the fertilization of ova Postzygotic = prevent the hybrid zygote from 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 Squirrel South Rim White-tailed Antelope Squirrel North 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 interbreed with diploid plants Hugo de Vries (early 1900s)2 species of Evening Primrose

2 different species interbreed Sterile Propagate (asexually) Various mechanisms cause fertility (polyploid) Breed with each other, but not parental species Goatsbeard Wheat

Victoria Tanganyika 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 LightMonochromatic Orange Light Females exhibited Discriminate mating (coloration) Non-discriminate mating Laboratory Experiment 2 species of males Offspring viable/fertile Speciation = recent Sexual Selection

Two models for the tempo of speciation Matches fossil record Rapid change Slow/ Gradual Change Long periods of stasis (equilibrium) punctuated by episodes of speciation 1,000’s of years