SYSTEMATICS/ TAXONOMY

1. SYSTEMATICS/TAXONOMY CHAPTER 13 BIOL 1120

2. SPECIES • MACROEVOLUTION—large, complex changes in life • Changes accumulate in populations slowly over time • TIME!!!!! • Evolution—produced diversity of life • Organisms grouped into species—distinct types of organisms • The meaning of the term “species” has evolved over time

3. Linnaeus (1707-1778) • Species—all examples of creatures that were alike in minute detail of body structure • Two-word naming—binomial nomenclature • First name—genus • Second name—species • Hierarchical system for classification: grouped similar genera into orders, classes, kingdoms • His system did not consider evolutionary relationships (each species was created separately and could not change)---meaning species could not appear/disappear, not related to one another

4. Darwin (1809-1882) • Connected species diversity to evolution • As natural selection became accepted, scientists no longer viewed classification as a way to just organize life • Classification became thought of as hypotheses about the evolutionary history of life

5. Ernest Mayr (1940s) • Amended Linneaus’s and Darwin’s work by considering reproduction and genetics. • Biological species—a population, or group of populations, whose members can interbreed and produce fertile offspring • Speciation (formation new species) occurs when members of a population can no longer successful interbreed

6. Speciation

7. Mayr • Species—does not rely on physical appearance (less subjective than Linnaeus’s observations) • Linneaus-2 similar looking butterflies cannot belong to different species • Mayr—if two groups can produce fertile offspring, share a gene pool, same species

8. Species--Conflicts • Mayr’s concept of species—cannot relate to asexual reproducers • Cannot apply to extinct organisms (fossil) • Some organisms can interbreed in captivity, but do not in nature • Reproductive isolation is not absolute—closely related plants can produce fertile offspring together • Species concept cannot always be used to decide if organisms are the same/different species • DNA analysis is helpful (if >97% identical, same species) • DNA drawback—cannot determine if organisms currently share a gene pool • ISOLATION is mot common criterion used to define species

9. Reproductive Barriers/Speciation • Interruption in courtship, fertilization, embryo formation, or offspring development. • 2 broad groups: prezygotic and prostzygotic • Prezygotic occur before formation of zygote • Postzygotic: reduce the fitness of a hybrid offspring (offspring from two different species)

10. Prezygotic BarriersAffect the ability of two species to combine gametes and form a zygote • Barriers include: • Ecological (habitat) isolation: difference in habitat preference in same geographic area • Temporal isolation: Mating will not occur if two species are active at different times of day or reach reproductive maturity at different times of year • Behavioral isolation: behavioral differences (distinct calls of different species of tree frogs to attract mates • Mechanical isolation: any change in the shape of gamete delivering or receiving structures can prevent interbreeding • Gametic isolation: sperm cannot fertilize egg; aquatic organisms release sperm, gametes have distinct surface molecules to recognize gametes

11. Postzygotic Barriers (hybrid incompatibility) • Barriers include: • Hybrid inviability: hybrid embryo dies before reaching reproductive maturity; genes of parents incompatible • Hybrid infertility (sterility): mule; infertile because horse egg has 1> chromosome than donkey, meiosis does not occur because chromosomes are not homologous • Hybrid breakdown: a hybrid that can reproduce, but their offspring may have abnormalities that reduce their fitness Successful hybridization rare in animals; occurs frequently in plants

12. Allopatric Speciation Speciation/Spatial Patterns • allo-other; patric-fatherland • Geographic barrier • River, desert, glacier, changes in sea level, formation or destruction of mountains, bodies of water • No interaction=no gene flow • Microevol. act independently in each group • Most common mechanism; abundant evidence

13. Sympatric Speciation Speciation/Spatial Patterns • Sym-together • Populations diverge genetically while living in the same area • Habitats-consist of microenvironments; species specialize in different zones • Plants: polyploidy, increases the # of sets of chromosomes • Occurs when gametes of 2 diff species fuse; also when meiosis fails • ½ flowering plants are polyploids; 95% ferns • Rare in animals (extra chromosomes are often fatal)

15. ParapatricSpeciation Speciation/Spatial Patterns • Para-alongside • Part of a population enters a new habitat bordering range of parent species • Gene flow can occur among individuals that venture into shared border zone • Can be a result of disruptive selection: ind. w/ intermediate forms have lower fitness than at either extreme; selection would counteract gene flow by eliminating ind. not well suited for either habitat

17. Darwin One species gradually transforms into another through a series of intermediate stages TIME!!! Speciation-Gradualism

18. Gould and Eldredge Brief bursts of rapid evolution interrupting long period of little change (transitional forms don’t exist—explains lack in fossil record) Fits w/allopatric speciation – geographic isolation Speciation—Punctuated equilibrium

19. Speciation and Adaptive Radiation • Occurs in rapid bursts • Gives rise to multiple specialized forms in a short time • Heterogeneous environment (multiple food sources)

20. Extinction • Death of an entire species • Factors: • Failure to adapt to environmental change • Lack of alleles in gene pool to produce fertile offspring • Habitat loss • Predators • Disease • Smaller populations likely to endure a major change • Low genetic diversity • Inbreeding (lethal recessive alleles, reduce reproduction/survivabilty) • HUMANS!!!!

21. Extinction • Background extinction rate • Gradual loss of species as populations shrink when facing new challenges • Mass extinction • A great number of species disappear over short period of time (impact theory)

23. Taxonomic Hierarchy • Taxonomists—classify based on similarities • 3 Domains (Archaea, Bacteria, Eukarya) • Kingdom King • Phylum Phillip • Class Called • Order On • Family Five • Genus Great • Species Soldiers • Taxa: a group at any rank • The more features two organisms share, the more taxonomic levels they share

24. Phylogenetics • Evolutionary tree (also called phylogeny) • Illustrate specie’s relationships based on decent from common ancestors • Evidence used to construct: • Anatomical features of fossils and existing organisms • Behaviors • Physiological adaptations • Molecular sequences • May be misleading • Cladistics solves this problem

25. Cladistics • Phylogenetic system • Groups by distinguishing between ancestral and derived characters • Ancestral character: inherited traits that resemble ancestors • Derived character: features that are different that the ancestor

26. Cladistics • Builds on concept of homology (homologous structures-common ancestor) • Shared, derived characters are used to define groups • A clade (monophyletic group) group of organisms consisting of a common ancestor and all its descendants

27. Cladogram • Treelike diagram depicting shared, derived characteristics (based on historical relationships/ not similarities) • Tips of branches = taxa (existing species) • node = indicates where two groups arose from a common ancestor • Branching pattern = populations that diverge genetically, split off, form new species Common ancestor Common ancestor