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Introduction to Speciation Microevolution is the change in the gene pool of a population from one generation to the next. Speciation is the process by which one species splits into two or more species. Every time speciation occurs, the diversity of life increases. The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.

How Can We Define A Species? The word species is from the Latin for “kind” or “appearance.” Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions. How similar are members of the same species? What keeps one species distinct from others?

Discussion Question ARE THESE BIRDS THE SAME SPECIES??

There are Different Ways to Define a Species The Biological Species Concept The Morphological Species Concept The Ecological Species Concept The Phylogenetic Species Concept

Biological Species Concept Defines a species as A group of populations That are made up of organisms that have the potential to interbreed and When they interbreed they produce vital and fertile offspring Therefore, members of the same species look similar because they interbreed.

Problems Using This Concept Some pairs of clearly distinct species occasionally interbreed and produce hybrids. Ex. grizzly and polar bears make grolar bear Hard to determine if organisms can interbreed if they do not come in contact with one another. Cannot determine if fossils could interbreed. Some organisms reproduce asexually

The Morphological Species Concept Classifies species based on physical traits Can be applied to asexual organisms and fossils Does not work if convergent evolution has occurred in two different species. Eastern Meadowlark Western

Ecological Species Concept Defines a species based on its ecological niche, or “job” Focuses on unique adaptations to particular roles in a biological community. For example, two species may be similar in appearance but distinguishable based on what they eat or where they live.

Phylogenetic Species Concept Defines a species as the smallest group of individuals that share a common ancestor and thus forms a branch on the tree of life. Scientists use evolutionary history based on Morphology DNA Problem is deciding how much difference makes it a different species

Order Family Genus Species Felis catus (domestic cat) Felidae Felis Figure 15.15B Order Family Genus Species Felis catus (domestic cat) Felidae Felis Mustela frenata (long-tailed weasel) Mustela Mustelidae Carnivora Lutra lutra (European otter) Lutra Figure 15.15B Relating classification to phylogeny Canis latrans (coyote) Canidae Canis Canis lupus (wolf) 13

Discussion Question Is there one concept that is better than the others? Why is it better or why is there not a better one?

Reproductive Barriers Keep Species Separate serve to isolate the gene pools of species and prevent interbreeding. Depending on whether they function before or after zygotes form, reproductive barriers are categorized as prezygotic or Postzygotic.

Individuals of different species Prezygotic Barriers Figure 14.3A Individuals of different species Prezygotic Barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Fertilization Postzygotic Barriers Figure 14.3A Reproductive barriers between species Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Viable, fertile offspring 16

Prezygotic Barriers Five types of prezygotic barriers prevent mating or fertilization between species. In habitat isolation, two species live in the same general area but not in the same kind of place. In temporal isolation, two species breed at different times (seasons, times of day, years).

Prezygotic Barriers Continued In behavioral isolation, there is little or no mate recognition between females and males of different species. In mechanical isolation, female and male sex organs are not compatible. In gametic isolation, female and male gametes are not compatible.

Postzygotic Barriers Three types of postzygotic barriers operate after hybrid zygotes have formed. In reduced hybrid viability, most hybrid offspring do not survive. In reduced hybrid fertility, hybrid offspring are vigorous but sterile. In hybrid breakdown, the first-generation hybrids are viable and fertile but the offspring of the hybrids are feeble or sterile.

STERILE Horse Donkey Mule Figure 14.3G Figure 14.3G Reduced hybrid fertility STERILE Mule 22

Mechanism of Speciation Speciation is the process by which one species splits into two or more species. Two Mechanisms of Speciation Allopatric Sympatric

Allopatric Speciation In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools. Isolated populations will no longer share changes in allele frequencies caused by natural selection, genetic drift, and/or mutation.

Allopatric Speciation For example the Grand Canyon and Colorado River separate two species of antelope squirrels South rim A. harrisii North rim A. leucurus

Allopatric Speciation The geographic barriers cause the populations to change and adapt to different environments. Adaptations to different environments could cause reproductive barriers to form. Creating two separate species.

Example: Pangea Breaking Apart According to the theory of plate tectonics, the Earth’s crust is divided into giant, irregularly shaped plates that essentially float on the underlying mantle. In a process called continental drift, movements in the mantle cause the plates to move. As Pangea broke apart, habitats changed and existing species had to adapt Causing Macroevolution to occur

Laurasia 135 Gondwana Mesozoic Millions of years ago Pangaea 251 Present Cenozoic Mesozoic Millions of years ago Paleozoic 251 135 65.5 1 2 Pangaea 3 4 Gondwana Laurasia Antarctica Eurasia Africa India South America Australia North America Madagascar Mesozoic Millions of years ago Paleozoic 251 135 2 Pangaea Gondwana Laurasia 1 Figure 15.7C Continental drift during the Phanerozoic eon 28

Present Cenozoic Millions of years ago 65.5 Mesozoic Laurasia 135 Paleozoic 251 135 65.5 1 2 Pangaea 3 4 Gondwana Laurasia Antarctica Eurasia Africa India South America Australia North America Madagascar Present Cenozoic Mesozoic Millions of years ago 135 65.5 4 Gondwana Laurasia Antarctica Eurasia Africa India South America Australia North America Madagascar 3 2 Figure 15.7C Continental drift during the Phanerozoic eon 29

Zones of violent tectonic activity Direction of movement North Figure 15.7B Zones of violent tectonic activity Direction of movement North American Plate Eurasian Plate Juan de Fuca Plate Caribbean Plate Philippine Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Figure 15.7B Earth’s tectonic plates Scotia Plate Antarctic Plate 30

Sympatric Speciation Sympatric speciation occurs when a new species arises within the same geographic area as a parent species. How can reproductive isolation develop when members of sympatric populations remain in contact with each other? Gene flow between populations may be reduced by polyploidy, habitat differentiation, or sexual selection.

Polyploidy Many plant species have evolved by polyploidy in which cells have more than two complete sets of chromosomes. Sympatric speciation can result from polyploidy within a species (by self-fertilization) or between two species (by hybridization).

Islands Can Showcase Speciation Most of the species on Earth are thought to have originated by allopatric speciation. Isolated island chains offer some of the best evidence of this type of speciation. Multiple speciation events are more likely to occur in island chains that have physically diverse habitats, islands far enough apart to permit populations to evolve in isolation, and islands close enough to each other to allow occasional dispersions between them.

Video Speciation Video- Cornell Lab of Ornithology (Resources Page) https://www.youtube.com/watch?v=8yvEDqrc3XE

Darwin’s Finches Show Adaptive Radiation The evolution of many diverse species from a common ancestor is adaptive radiation. There are 14 species of Darwin’s Finches These finches share many finchlike traits, differ in their feeding habits and their beaks, specialized for what they eat, and arose through adaptive radiation. Cactus-seed-eater (cactus finch) Tool-using insect-eater (woodpecker finch) Seed-eater (medium ground finch)

Darwin’s Finches Show Adaptive Radiation

Hybrid Zones Hybrid zones are regions in which members of different species meet and mate to produce at least some hybrid offspring. In order to be two separate species, the hybrid zone must be Hybrids occur in low frequencies Small/narrow and stable in size, or Hybrids must have lower fitness than parental species.

Adaptive Radiation Also Occurs After Mass Extinctions Over the last 500 million years, five mass extinctions have occurred, and in each event, more than 50% of the Earth’s species went extinct. One major mass extinction was the extinction of the dinosaurs. The fossil record shows that the vast majority of species that have ever lived are now extinct.

Extinction of dinosaurs Ancestral mammal Monotremes (5 species) Figure 15.10 Extinction of dinosaurs Ancestral mammal Monotremes (5 species) Reptilian ancestor Marsupials (324 species) Eutherians (placental mammals; 5,010 species) Figure 15.10 Adaptive radiation of mammals (width of line reflects numbers of species) 250 200 150 100 65 50 Time (millions of years ago) 39

How Long Does Speciation Take to Occur? Speciation can occur rapidly or slowly. In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years. Two models: Species that gradually evolve Species change in a punctuated equilibria where most change occurs as they arise from ancestral species.

Punctuated pattern Gradual pattern Time Figure 14.11 Figure 14.11 Two models for the tempo of speciation Time 41

Exit Ticket Identify and explain the two types of speciation. Propose one solution to determining when speciation has occurred (when two species are different species) and identify one pro and one con to this method.