This document provides an overview of macroevolution, including how it differs from microevolution, the concept of species and speciation, mechanisms of reproductive isolation that lead to speciation (prezygotic and postzygotic barriers), examples of adaptive radiation and allopatric speciation, the role of fossils and geological time in understanding evolution, mechanisms of mass extinction (continental drift and meteorite impacts), and how molecular evidence from DNA is used to reconstruct phylogenetic relationships between organisms.

1. Lecture 6a: Macroevolution Macroevolution

2. Macroevolution Not really different than microevolution, but over a much larger scale Changes to species, not changes to populations

3. Species- what are they anyway? Biolgical Species Concept : members of the same species interbreed and have a shared gene pool, but are reproductively isolated from every other species Speciation : the evolution of new species

4. Species Two animals of the same species can reproduce and have fertile offspring One species can consist of one or many populations Appearance does not necessarily allow you to tell two species apart

5. Reproductive Barriers As speciation occurs, reproductive barriers arise that prevent breeding from occurring between the different species Barriers fall into two categories: prezygotic and postzygotic

6. Prezygotic Barriers Habitat Isolation: The different species inhabit different habitats Temporal Isolation: Breeding season is at different times of the year Behavioral Isolation: Pheromones, courtship rituals, songs or calls, etc are different Mechanical Isolation: Genitalia are incompatible Gamete Isolation: The gametes can not fuse to form a zygote

7. Behavioral isolation: Different dewlaps in Anolis lizards

8. Mechanical isolation: Watersnake hemipenes

9. Postzygotic Barriers Zygote mortality: A zygote is formed, but it does not survive Hybrid sterility: The zygote develops into an adult, but it is sterile F2 Fitness: The hybrids can reproduce, but the F2 generation can not

10. Hybrid Sterility: Both mules and zonkeys are sterile

11. Types of Speciation Allopatric Speciation Occurs when populations become geographically isolated, and move further and further apart genetically from the original species Ex. Ensatina salamanders, iguanas

12. Allopatric speciation in Galapagos finches

13. Types of Speciation Sympatric speciation Population develops into two or more groups without geographic isolation Polyploidy: increase in number of chromosomes to 3n or higher due to hybridization, sometimes followed by doubling of chromosomes- results in 3rd species

14. Types of Speciation Adaptive Radiation New species evolve from one ancestral species to fill different niches in the habitat Ex. Galapagos finches, Hawaiian honeycreepers

15. Adaptive radiation in cichlid fish, species have evolved to eat different food sources and to feed in different ways

16. Fossils To study extinct species, especially ones from millions of years ago, we look to fossils: The remains or traces of past life Can take several forms- amber, footprints, petrification, actual remains

17. Geologic Time See timeline Cambrian explosion: all major groups of animals appeared Number of species on Earth has continued to increase over time, even to the present day

19. Speciation We do not know how quickly species arise- there are two models: Gradualistic Model- slow steady change over a long period of time Punctuated Equilibrium: somewhat ‘sudden’ appearance of new species in fossil record The transitional fossils are unlikely due to geographic isolation and small numbers

20. Mass Extinctions Relatively sudden disappearances of large numbers of species Have been several, of course dinos the best known example Two main causes: Continental drift and meteorite impacts

21. Continental Drift The continents on Earth are moving Plate tectonics: The crust of Earth is floating on the molten mantle, the crust is in several pieces As the continents move, the climate changes

22. Pangaea: its formation 250 mya was probably the cause of the Permian Extinction

23. Meteorites Probably the cause of the dinosaur’s extinction Caused massive cloud of dust that blocked the sun, lowering temperatures worldwide Soot and iridium are found in Cretaceous clay, and a crater has been identified as well

24. Systematics DKPCOFGS As the category gets higher and higher, it gets more and more inclusive Ideally, organisms are classified according to their evolutionary relationships, so taxonomy is in constant flux as we learn more and more

25. Phylogenetic Trees Trees that show relatedness of different organisms Indicate common ancestor, and lines of descent Determined using comparative anatomy, embryology, molecular evidence

26. Phylogenetic Tree of chordates

27. Phylogenetic tree of canines

28. Anatomy Remember, it matters where the characteristic in question arose from, not what it does now Ex. Thorny devils vs. horny toads have Analagous structures Ex. Vertebrate forelimbs are Homologous structures

29. Thorny devil (Australia) Horned lizard (US) Analogous structures- horns on two lizards

30. Homologous structures- front limbs of several vertebrates

31. Using DNA to determine relationships Remember: evolution occurs when mutations in DNA occur-- it can not occur without those random changes Therefore, the more closely related animals are, the fewer differences there will be in their DNA This allows new information about DNA to be included in our understanding of how life on Earth evolved