1. Fish Taxonomy and Systematics Lecture 4: Cladograms & Speciation

2. Cladograms  Phylogenetic relationships expressed in cladograms - branching representation of the evolutionary relationships among taxa based on shared common traits and shared unique traits

3. Constructing a Cladogram  Listing of traits  Coding of each taxon by presence/absence of each trait  Assemble groupings based on trait conditions  Use the simplest branching structure possible: principle of parsimony Which states that “cladogram (tree) having the fewest number of “steps” (evolutionary changes) is the one accepted”

4. TAXA Lancelet (outgroup) Lamprey Salamander Leopard Turtle Tuna Vertebral column (backbone) Hinged jaws Four walking legs Amniotic (shelled) egg CHARACTERS Hair (a) Character table Hair Hinged jaws Vertebral column Four walking legs Amniotic egg (b) Phylogenetic tree Salamander Leopard Turtle Lamprey Tuna Lancelet (outgroup) 0 00 0 0 0 00 0 0 00 000 1 11 1 1 1 1 11 1 1 11 11 Sequentially group taxa by shared derived character states (apomorphies)

5. More on traits... Meritic-count it! Morphometric-measurable shape fin lengtheye shapehead length ratios between such measures... anatomical characteristics molecular characteristics

6. Which traits do I use?

7. Relationship  Recency of common ancestry i.e., taxa sharing a common ancestor more recent in time are more closely related than those sharing common ancestors more distant in time.

8. Ingroup – group studied Outgroup – group not part of ingroup, used to “root” tree  The out-group serves as a base line for comparisons with the other organisms being evaluated, the in-group

9. Sister taxa ANCESTRAL LINEAGE Taxon A Polytomy Common ancestor of taxa A–F Branch point (node) Taxon B Taxon C Taxon D Taxon E Taxon F

10. Apomorphy (derived trait)  = a new, derived feature e.g., for this evolutionary transformation scales --------> feathers (ancestral feature) (derived feature)  Presence of feathers is an apomorphy for birds.

11. Taxa are grouped by apomorphies  Apomorphies are the result of evolution.  Taxa sharing apomorphies underwent same evolutionary history should be grouped together.

12. Example: Are fish more closely related to sharks or to humans?

15. Constructing a Cladogram This example shows the evolutionary relationships among plants. 1. In the table below, the traits in the row for the out-group are marked with a zero.  When a plant has a trait not found in the out- group, the trait is considered a derived trait and is marked with a one.  Next the numbers of shared derived traits are totaled.

16. Constructing a Cladogram Derived Traits OrganismsVascular tissueSeedsFlowers Mosses (Out-group)000 Pine trees110 Flowering plants111 Ferns100 Total321

17. Constructing a Cladogram 2. Starting with a diagonal line, as shown on the next slide, the out-group (mosses) is placed on the first branch of the cladogram.  Just past this first branch, the most common derived trait is listed—vascular tissue.  Vascular tissue is a series of tubes and vessels within a plant.

18. Constructing a Cladogram 3. Next the second most common derived trait is determined, which in this case is seeds.  The ferns lack seeds and so are placed in the second branch of the cladogram. 4. The third most common derived trait is flowers.  Conifers do not have flowers and so are placed in the third branch above the second branch on the cladogram.  The flowering plants are placed at the end of the cladogram.

19. Constructing a Cladogram Mosses Ferns Pine trees Flowering plants Vascular tissue Seeds Flowers

20. Speciation Q. How do populations become distinct species?  Speciation - process by which a new species originates.  Involves the creation of a population of organisms that are novel enough to be classified in their own group.  The process whereby gene flow is reduced sufficiently between sister populations to allow each to become different evolutionary lineages  Allopatric (with geographic isolation): speciation resulting from divergent evolution of populations that are geographically isolated from each other.  Non-allopatric (without geographic isolation)

21. Speciation  Allopatric (with geographic isolation) speciation:  Vicariant - large populations geographically isolated (little inbreeding) (United States)  Founder - small population becomes geographically isolated and then reproductively isolated via inbreeding, selection, drift (Gilligan’s Island)  Reinforcement - early isolation followed by sympatry, but selection against hybrids

22. Speciation  Non-allopatric (without geographic isolation)  Sympatric - sister species evolve within the dispersal range of each other, but adapt to different habitats - habitat-dependent assortive mating (tribes)  Parapatric - sister species evolve in segregated habitats across a narrow contact zone - little mixing in spite of proximity

24. Speciation Based on Gene Flow (a) Allopatric speciation (b) Sympatric speciation

25. Allopatric  In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations  The definition of barrier depends on the ability of a population to disperse  Separate populations may evolve independently through mutation, natural selection, and genetic drift

26. Allopatric speciation in the Grand Canyon A. harrisi A. leucurus Examples of Allopatric speciation: Allopatric speciation of squirrels in the Grand Canyon. Animals like birds do not show speciation like those animals that are barred from breeding by the canyon.

27. Key question about allopatric species is whether they are indeed different enough that viable, fertile offspring would not be produced by mating. This can be tested sometimes as in…

28. Allopatric speciation  Reproductive isolation between populations generally increases as the distance between them increases  Barriers to reproduction are intrinsic; separation itself is not a biological barrier

29. Mantellinae (Madagascar only): 100 species Rhacophorinae (India/Southeast Asia): 310 species Other Indian/ Southeast Asian frogs Millions of years ago (mya) 1 23 1 2 3 100 80 60 40 20 0 88 mya65 mya56 mya India Madagascar

30. Sympatric Speciation  Sympatric means “same country”  Speciation takes place in geographically overlapping populations  Occurs because of  Polyploidism  Habitat differentiation  Sexual selection

31. Polyploidism  Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division 1.Autopolyploidy 2.Allopolyploidy

32. Autopolyploidy in plants 2n=6 4n=12 Failure of cell division after chromosome duplication gives rise to tetrapliod cells which may be viable and self-fertile

33. Allopolyploid  An allopolyploid is a species with multiple sets of chromosomes derived from different species  Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

34. Ancestral species: Triticum monococcum (2n = 14) AABB Wild Triticum (2n = 14) Product: AA BB DD T. aestivum (bread wheat) (2n = 42) Wild T. tauschii (2n = 14) DD

35. Habitat differentiation  Sympatric speciation can also result from the appearance of new ecological niches  North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees, so food preference may isolate the two populations

36. Sexual selection  Sexual selection can drive sympatric speciation  Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria  Example: Lake Victoria has 200 closely related species of Cichlids (fish) which probably all arose from one ancestor with the driving force for speciation being:  Competition for a limited resource (food) within the lake, and adaptation to new food sources. This gave rise to different species that are kept from breeding with each other by distinctive coloration pattern.