NIS - BIOLOGY

1. NIS - BIOLOGY Lecture 81 – Lecture 82 – Lecture 83 Modern Classification OzgurUnal

2. Do these two organisms belong • to the same species? • How about these? Determining Species

3. It isn’t always easy to define species. • There are different definitions of species. • As knowledge increases, definitions change. • Organisms that are different species by one definition might be the same species by another definition. • Typological species concept • Biological species concept • Phylogenetic species concept Determining Species

4. Typological species concept: • Aristotle and Linnaeus thought of each species as a distinct different group of organisms based on physical similarities  typological species concept • It is based on the idea that species are unchanging, distinct and natural types. Determining Species • The type specimen was an individual of the species that best displayed the characteristics of that species. • When another specimen was found that varied significantly from the type specimen, it was classified as a different species. • Check out Figure 17.6!!

5. Biological species concept: • Two evolutionary biologists, Theodosius Dobzhansky and Ernst Mayr, redefined the term species in the 1930s and 1940s. • Species a groups of organisms that is able to interbreed and produce fertile offsprings in a natural setting. • Examples?? Determining Species • There are limitations to this definition. • Example: Wolves and dogs • This definition does NOT account for extinct species or species that reproduce asexually. • However, this definition still works in most everyday experiences of classification.

6. Phylogenetic species concept: • In the 1940s, evolutionary species concept was proposed as a companion to the biological species concept. • The evolutionary species concept defines species in terms of populations and ancestry. • According to this concept, two or more groups that evolve independently from an ancestral population are classified as different species. Determining Species • More recently, this concept has developed into the phylogenetic species concept. • Phylogeny is the evolutionary history of species.

7. Phylogenetic species concept: • The phylogenetic species concept defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent. • When a phylogenic species branches, it becomes two different phylogenetic species. • Example: Recall allopatric speciation • This definition can account for the extinct species and species that reproduce asexually. • Check out Table 17.2!! Determining Species

8. How can you distinguish the following veggies? • These veggies belong to the same species • called Brassica oleracea. Characters

9. To classify a species, scientists often construct patterns of descent, or phylogenies, by using characters. • Characters can be morphological or biochemical. • Shared morphological characters suggest that species are related closely and evolved from a recent common ancestor. Characters

10. Remember that analogous characters do not indicate a close evolutionary relationship. • Homologous characters might perform different functions, but show an anatomical similarity inherited from a common ancestor. • Example: birds and dinosaurs • Similar features: large hollow spaces • Some fossil dinosaur bones had feathers. • The evidence provided by these • morphological characters indicates that • modern birds are related more closely • to theropod dinosaurs than they are • related to other reptiles. Morphological Characters

11. Scientists use biochemical characters, such as aminoacids and nucleotides, to help them determine evolutionary relationships among species  Figure 15.9!! • Chromosome structure and number is also powerful clue  Mustard family (Cruciferae) members have almost identical chromosome structure  common ancestor • Check out Figure 17.8!! Biochemical Characters

12. DNA and RNA analyses are also powerful tools for reconstructing phylogenies. • The greater the number of shared DNA sequences between species, the greater the number of shared genes  the greater the evidence that the species share a recent common ancestor Biochemical Characters

13. Compare the elephants shown in Figure 17.9!! • Asiatic elephant  Elephas maximus • African elephant (savannah)  Loxodonta africana • Afican elephant (forest)  Loxodonta cyclotis • Recent DNA studies show that African elephants diverged from a common ancestor about 2.5 million years ago. • 2.5 million years ago... How do we know that? Biochemical Characters

14. Molecular clocks: • Mutations occur randomly in DNA. • Mutations can be harmful, beneficial • or neutral. • As time passes mutations accumulate in the chromosomes. • Systematists can use these mutations to help them determine the degree of relationship among species. Biochemical Characters • A molecular clock is a model that is used to compare DNA sequences from two different species to estimate how long the species have been evolving since they diverged from a common ancestor. • Check out Figure 17.10!!

15. Molecular clocks: • The differences between DNA sequences in the genes of different species indicate the presence of mutations. • The more mutations  the more time has passed since divergence • How about the rate of mutations? Biochemical Characters • The speed by which mutations occur is not always the same in a single gene  difficult to read the molecular clock! • Many factors affect the rate of mutation.. • Researchers try to compare genes • that accumulate mutations at a • relatively constant rate  such as the • gene for cytochrome c

16. Remember pedigrees? Phylogenetic Resconstruction

17. The most common systems of classification today are based on a method of analysis called cladistics. • Cladistics is a method that classifies organisms according to the order that they diverged from a common ancestor. Phylogenetic Resconstruction • Character types: • Scientists consider two main types of characters when doing cladistics analysis: Ancestral trait and Derived trait • Example: Birds and mammals • Ancestral trait: backbone • Derived trait: feathers (for birds) and • hair (for mammals)

18. Cladograms: • Systematists use shared derived characters to make a cladogram. • A cladogram is a branching diagram that represents the proposed phylogeny or evolutionary history of a species or group. • A cladogram is a model similar to pedigrees. How? • The groups used in cladograms • are called clades. • A clade is one branch of • the cladogram. Phylogenetic Resconstruction

19. The outgroup is the species or group of species on a cladogram that has more ancestral characters with respect to the other organisms being compared. • The cladogram is constructed by sequencing the order in which derived characters evolved with repsect to the outgroup. • The closeness of clades in the clagodram indicate the number of characters shared. • The nodes where the branches originate represent a common ancestor. • The greater the number of derived characters shared by groups, the more recently the groups share a common ancestor. • A cladogram is also called a phylogenetic tree. • Check out Figure 17.12!! Phylogenetic Resconstruction

20. Phylogenetic Resconstruction

21. Phylogenetic Resconstruction