ESS 345 Ichthyology. Systematic Ichthyology Part II Not in Book

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1 ESS 345 Ichthyology Systematic Ichthyology Part II Not in Book Thought for today: Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that! -Lewis Carroll, mathematician and writer ( )

2 Classification and phylogenetic systematics mononphetic groupings that reflect natural relationships in nature Species terminus of the line A B C D E F G H I J Genera?? Sister groups What is a clade? Which clade is most primitive? Which node is most recent common ancestor to GH and DEF? Which terminal taxon is B more closely related to? ( A or C) Hierarchical but anything above species is arbitrary

3 How to determine evolutionary relationships A B C D E F G H I J Schools of thought Guess Phenetics / numerical taxonomy Phylogenetic systematics = cladistics

4 Phenetics Problems with similarity in determining genealogy Similarity can result from 3 things 1. Convergent evolution 2. Shared evolutionary history 3. Shared evolutionary history (recent shared ancestors)

5 Cladistics Preferred method to reconstruct phylogenies Based on concept of primitive vs. advanced characters Apomorphy Plesiomorphy Study the distribution of characters among taxa (species) Represent species relationship on a cladogram Use Synapomorphies to establish relationships (recent common ancestry) Gather more evidence Revise hypotheses with new evidence

6 Example: applying cladistics X A B C

7 Example: applying cladistics 4 taxa, assume monophyly Outgroup + other 3 taxa (in group) X A B C Print

8 X Possible Relationships A B C B X A C X C A B A B C X Print

9 Characters Morphometrics Meristics Anatomy Color Genetics Anything else quantifiable

10 Other Characters Used Pigment, bars, spots, color Sexually dimorphic structures Photophores (in certain groups) Behavioral and physiological Genetic (electrophoretic, mitochondrial or nuclear DNA)

11 Character Matrix Character X Species A Species B Species C 1 scale type gas bladder type caudal fin type Weberian app jugular pelvic fin jaws Assume outgroup is plesiomorphic Print

12 Character 1 and 6 X A B C 1 1, 6 Print Nothing resolved We can just ignore 1 and 6 for now

13 Character 2 A B C X 2 2 Print

14 Character 3 and 4 A B C X 3, 4 3,4 Synapomorphy = common possession of a derived homologous character Print

15 Character 3 and 4 X A 2 B 2 C 3, 4 3, 4 2 had to evolve twice independently if we are to satisfy the cladogram for characters 3 and 4 (convergent evolution - analogous traits in the terminal taxa) Print Is that likely?

16 Reconstructed Evolutionary History A B 2 C X 2 5 3, 4 2,3,4,5 5 steps A B 3, 4 C Count all the steps that had to have happened X 2 3, steps 2,3,4,5 Print

17 Reconstructed Evolutionary History X B A C , 5 B A C 2,3,4,5 7 steps X , 5 2 Print 2,3,4,5 7 steps

18 Principle of Parsimony Bird and bat wings X A 2 B 2 5 C 3, 4 2,3,4,5 So 2 evolved independently twice Autapomorphy: derived character restricted to a single species 5 steps PAUP* (Phylogenetic Analysis Using Parsimony) Ockham s Razor (avoid redundancy i.e., homoplasy)

19 Conclusions Character 2 is homoplasy in taxa A and B The cladogram representing evolutionary relationships is represented in the classification A, B, C is a monophyletic group A is a genus B and C are a genus Cannot classify A and B together using a similar trait

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21 So, What really is a species? Many definitions: at least 20 yes two zero!

22 What is a species? That previous discussion of evolution and presenting evolutionary relationships might help you conceptualize what a species really is.

23 Morphological Species Concept Based on appearance (morphospecies) C. Tate Regan-(early 1900s) a group of organisms with a distinctive enough morphological characters that are sufficiently definite to entitle them to a specific name Doesn t work

24 Biological Species Concept Based on reproductive isolation Ernst Mayr (1942) RIMs Reproductive Isolating Mechanisms Two kinds Pre-zygotic (pre-mating) Post-zygotic (post mating)

25 Problems with the BSC Identifying reproductive isolation Does one hybrid invalidate the definition? RIMS evolve gradually; species distinctions in adjacent forms Natural or artificial Asexual species Genetic differences may not necessarily indicate reproductive isolation OR morphological divergence How do fossil species fit in? What about chronospecies?

26 Evolutionary Species Concept a single lineage of ancestordescendant population which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate (Wiley 1981)

27 Implications of the ESC New species arise as a species-level taxa, not as higher categories. The first appearance of a new type is not a class New species arise only by splitting of other forms. Change within lineages does not create a new species! Species behave like individuals Chronospecies not really not different species Subspecies?

28 Other species concepts Autapomorphic species concept the least inclusive monophyletic group definable by at least one autapomorphy Monophyletic species concept (phylospecies)

29 Speciation Anagenesis/Chronospecies Cladogenesis Allopatric (Vicariance) Sympatric / Syntopic Ecological Morphological Sexual Founder (peripatric) Parapatric Stasipatric

30 Common models of speciation

31 Use the character information and animalcules to reconstruct the phylogenetic history of the group. Synapomorphies are important in determining monophyletic groupings. Consider animal A to be the out group and animals B,C,D to be the in-group. Complete the following: 1. Create a character matrix 2. Draw the most parsimonious tree 3. List any homoplasious characters 4. List any autapomorphies Characters and character states 1. Eyes (present) 2. Eye spots (present or absent) 3. Spines (present or absent) 4. Eye type (basal or stalked) 5. Feet (present or absent) 6. Antenna (present or absent)