Lecture 2 Phylogenetics of Fishes. 1. Phylogenetic systematics. 2. General fish evolution. 3. Molecular systematics & Genetic approaches

Transcription

1 Lecture 2 Phylogenetics of Fishes 1. Phylogenetic systematics 2. General fish evolution 3. Molecular systematics & Genetic approaches

2 Charles Darwin & Alfred Russel Wallace All species are related through common descent

3 Willi Hennig ( ) Hennig developed cladistical method to infer relatedness Goal is to correctly group ancestors and all their descendants

4 Cladistics (a.k.a Phylogenetic Systematics) Fundamental approach divide characters into two groups Apomorphies: more recently derived characteristics Pleisomorhpies: more ancestral, primitive characteristics Identify Synapomorphies (shared derived characteristics) group clades by synapomorphies

5 Cladistics (a.k.a Phylogenetic Systematics) Synapomorphy of rockfish, bichir, and sharks? jaws eyes gills bony skeleton swim bladder Rockfish Bichir Sharks Lamprey Hagfish

6 Cladistics (a.k.a Phylogenetic Systematics) Sympleisomorphy of rockfish, bichir, and sharks? jaws eyes gills bony skeleton swim bladder Rockfish Bichir Sharks Lamprey Hagfish

7 Cladistics (a.k.a Phylogenetic Systematics) Ancestral and derived are relative to your focal group jaws eyes gills bony skeleton swim bladder Rockfish Bichir Sharks Lamprey Hagfish

8 Cladistics (a.k.a Phylogenetic Systematics) Monophyletic (aka clade): all taxa are descended from a common ancestor that is not the ancestor of any other group (every taxa descended from that ancestor is included) examples?

9 Cladistics (a.k.a Phylogenetic Systematics) Paraphyletic: the group does not contain all species descended from the most recent common ancestor of its members examples?

10 Cladistics (a.k.a Phylogenetic Systematics) Polyphyletic: taxa are descended from several ancestors that are also the ancestors of taxa classified into other groups examples?

11 Problems with Traditional Cladistics Homoplasies traits evolved due to convergence - keel: stabilizes tail at high speeds

12 Problems with Traditional Cladistics Statistically inconsistent can lend more support for the wrong answer Bernal et al. 2001

13 Problems with Traditional Cladistics Unequal rates lineages can evolve at different rates Cyprinidae

14 Molecular Systematics & Genetic Approaches Compares similarities and differences in DNA sequences identify informative sequences (aka synapomorphies) Different parts of the genome evolve at different rates choose appropriate sequences to compare Address questions about biogeography & evolutionary history that traditional systematics can not

15 African Cichlids & the Great African Rift Lakes Lake Victoria ~ spp. Lake Tanganyika ~ spp. Lake Malawi ~ spp.

16 Parallel or Convergent Evolution? omnivore omnivore vegetarian vegetarian piscivorous piscivorous carnivore generalist carnivore generalist omnivore omnivore

17 Lake Tanganyika Parallel Evolution Lake Malawi 3 common ancestors

18 Lake Tanganyika Convergent evolution Lake Malawi 1 common ancestor 1 common ancestor

19 Parallel or Convergent Evolution? Take a few minutes to draw alternative phylogenetic hypotheses for parallel and convergent evolutionary scenarios (talk to your neighbors).

20 Predicted Result Parallel Evolution

21 Convergent evolution Predicted Result Lake Tanganyika Lake Malawi

22 Molecular tree based on cytochrome b sequences 100 Victoria Haplochromines Malawi Haplochromines Group A Malawi Haplochromines Group B 100 Astatoreochromis Tanganyika Julidochromis Tanganyika Lamprologus Myrs

23 Molecular Clock Calibration in Sharks Fossils and geologic events Calibrate sequence divergence Establish molecular clock ~7-8x slower than mammals Martin et al 1992

24 Evolution of Endothermy - monophyly or convergence?

25 Molecular Systematics & Genetic Approaches Gene trees vs. species trees gene trees don t necessarily reflect the species tree The more gene trees you sample, the more likely you converge on the species tree red = gene tree blue = species tree

26 Surfperches (Embiotocidae) Bernardi & Bucciarelli 1999

27 Longo Longo && Bernardi Bernardi Surfperches (Embiotocidae)