Introductory Questions #1 (fifth overall) 1)How would you define a species? What are two key factors you must consider? 2)What is the key as to how a new species forms? 3)Explain the difference between a prezygotic barrier and a postzygotic barrier. 4)How is allopatric speciation different from sympatric speciation? 5)Name the two models that have been proposed to explain evolution observed in the fossil record.

Introductory Questions #2 1)Give two examples of a prezygotic and postzygotic barrier. 2)Why is sympatric speciation more common in plants vs. animals? 3)Which model (gradualism or puntuated equilibrium) is more reflective of the fossil record? Briefly explain why? 4)How do new body designs and evolutionary novelties form? 5)What is allometric growth and paedomorphosis? 6)When was the last mass extinction event? How many have occurred in the last 600 million years?

Macroevolution & Speciation Chapter 24 Define a Species Isolation Extinction Events Geological Timetable Phylogenetics

Overview of the Existence of Species Estimated number of million different species Only 1.75 million have been scientifically named The breakdown: -250,000 Plants -42,000Vertebrates -750,000Insects How would you define a species?

What is a species? Biological species concept (Mayr): a population or group of populations whose members have the potential to interbreed produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

Considered separate species if they cannot interbreed (or are reproductively isolated)Considered separate species if they cannot interbreed (or are reproductively isolated) What is a Species?

How Does a new Species Emerge? There has to be some ISOLATION event that separates a population of individuals Separation has to be maintained with barriers Applies to sexually reproducing organisms Asexual reproducers: species concept is difficult to apply -classified by structural & biochemical differences

Modes of Reproductive Isolation

Prezygotic Barriers Prezygotic barriers: impede mating between species or hinder the fertilization of the ova Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling & courtship) Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors)

Postzygotic Barriers Postzygotic Barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability frogs; zygotes fail to develop or reach sexual maturity Reduced hybrid fertility mule; horse x donkey; cannot backbreed Hybrid breakdown cotton; 2nd generation hybrids are sterile

What if they breed, but don’t produce viable offspring? (mules)

Problem With “Species” Definition: If they never have the opportunity to interbreed, how do you know if they can?

We Can Separate Species Based On % Of Shared Dna How Much of a difference is needed to call 2 organisms separate species?

Modes of speciation (based on how gene flow is interrupted) Allopatric: populations segregated by a geographical barrier ; can result in adaptive radiation (island species) Sympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome); -polyploidy in plants -cichlid fishes

Punctuated Equilibrium Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record

The fossil of the earliest known bird, Archeaopteryx, was discovered in 1861 Fossils of dinosaurs with feathers may support the bird- dinosaur theory

Microevolution Small genetic changes in a population Small genetic changes in a population Change in frequency of a single allele due to selection Change in frequency of a single allele due to selection

Macroevolution Large-scale changes in organisms Large-scale changes in organisms Involves new genera Involves new genera

Macroevolution consists of the major changes in the history of life –The fossil record chronicles these changes, which have helped to devise the geologic time scale Macroevolution

Macroevolution: the origin of new taxonomic groups Speciation: the origin of new species 1- Anagenesis (phyletic evolution): accumulation of heritable changes 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

Adaptive Radiation

By forming new islands, volcanoes can create opportunities for organisms –Example: Galápagos But volcanic activity can also destroy life –Example: Krakatau Figure 15.4B, C

The elimination a species from the earthThe elimination a species from the earth Background Extinction Rate - relatively constant rate of extinction in the fossil recordBackground Extinction Rate - relatively constant rate of extinction in the fossil record Mass Extinction - major loss of species: climate change, humans, catastrophiesMass Extinction - major loss of species: climate change, humans, catastrophiesExtinction

Figure million years ago Cretaceous extinctions 60 ?

- These mass extinctions may have been a result of an asteroid impact or volcanic activity –Every mass extinction reduced the diversity of life –But each was followed by a rebound in diversity Ex. Mammals filled the void left by the dinosaurs Six Mass Extinction Events in the last 600 million years (2) of the major extinctions are: -Permian (90% of all marine species went extinct) -Cretaceous (Killed the dinosaurs) Mass Extinctions

Figure 15.1

Every mass extinction reduced the diversity of life

CRITICAL QUESTION: How Do Humans Affect Extinction Rates?

Simplify ecosystemsSimplify ecosystems –(monocultures/disturbed habitats) Strengthen pest populationsStrengthen pest populations Eliminate predators (can create new pests)Eliminate predators (can create new pests) How Do Humans Affect Extinction Rates?

Introduce new species (starlings)Introduce new species (starlings) OverharvestOverharvest Interfer with chemical cycling and energy flow (UV/ozone, heat pollution)Interfer with chemical cycling and energy flow (UV/ozone, heat pollution) How Do Humans Affect Extinction Rates?

Did birds evolve from dinosaurs? Evolutionary biologists investigate this question by looking at the fossil record Are Birds Really Dinosaurs with Feathers?

The sequence of fossils in rock strata indicates the relative ages of different species Radiometric dating can gauge the actual ages of fossils The actual ages of rocks and fossils mark geologic time

Continental drift is the slow, incessant movement of Earth’s crustal plates on the hot mantle Continental drift has played a major role in macroevolution Figure 15.3A Pacific Plate North American Plate Nazca Plate South American Plate African Plate Eurasian Plate Split developing Indo-Australian Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) Antarctic Plate

This movement has influenced the distribution of organisms and greatly affected the history of life –Continental mergers triggered extinctions –Separation of continents caused the isolation and diversification of organisms –Rate : 1-2 cm/year Figure 15.3B Millions of years ago Eurasia CENOZOIC MESOZOIC PALEOZOIC North America Africa India South America Antarctica Australia Laurasia Gondwana Pangaea

Continental Drift/Plate Tectonics Pangea (Paleozoic)  LaurasiaGondwana (Mesozoic)  Europe -S. America Greeland -Australia N. America -Africa(Cenozoic) ** First Proposed by Alfred Wegner (1912) **Later Reproposed in the 1960’s after WWII and sonar mapping of the ocean floor

Continental drift explains the distribution of lungfishes –Lungfishes evolved when Pangaea was intact Figure 15.3C

Figure 15.3D NORTH AMERICA SOUTH AMERICA EUROPE AFRICA ASIA AUSTRALIA = Living lungfishes = Fossilized lungfishes

Plate tectonics, the movements of Earth’s crustal plates, are also associated with volcanoes and earthquakes –California’s San Andreas fault is a boundary between two crustal plates Connection: Tectonic trauma imperils local life Figure 15.4A San Andreas fault San Francisco Santa Cruz Los Angeles