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Lecture 2Phylogenetics of Fishes
1. Phylogenetic systematics
2. General fish evolution
3. Molecular systematics & Genetic approaches
Charles Darwin & Alfred Russel Wallace
1823 - 19131809 - 1882
All species are related through common descent
Willi Hennig (1913 – 1976)
• Hennig developed cladistical method to infer relatedness
• Goal is to correctly group ancestors and all their descendants
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
Cladistics (a.k.a Phylogenetic Systematics)
gillseyes
jaws
swim bladder
RockfishBichir
Sharks Lamprey Hagfish
Synapomorphy of rockfish, bichir, and sharks?
bony skeleton
Cladistics (a.k.a Phylogenetic Systematics)
gillseyes
jaws
swim bladder
RockfishBichir
Sharks Lamprey Hagfish
Sympleisomorphy of rockfish, bichir, and sharks?
bony skeleton
Cladistics (a.k.a Phylogenetic Systematics)
gillseyes
jaws
bony skeleton
swim bladder
RockfishBichir
Sharks Lamprey Hagfish
“Ancestral” and “derived” are relative to your focal group
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?
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?
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?
Problems with Traditional CladisticsHomoplasies• traits evolved due to convergence
- keel: stabilizes tail at high speeds
Statistically inconsistent• can lend more support for the wrong
answer
Problems with Traditional Cladistics
Bernal et al. 2001
Unequal rates• lineages can evolve at different rates
Problems with Traditional Cladistics
Cyprinidae
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
African Cichlids & the Great African Rift Lakes
Lake Malawi
Lake Victoria
Lake Tanganyika
~400-500 spp.
~180-250 spp.
~700-1000 spp.
Parallel or Convergent Evolution?
omnivore
vegetarian
piscivorous
carnivoregeneralist
omnivore
omnivore
vegetarian
piscivorous
carnivoregeneralist
omnivore
Parallel EvolutionLake Tanganyika Lake Malawi
3 common ancestors
Convergent evolutionLake Tanganyika Lake Malawi
1 common ancestor 1 common ancestor
Parallel or Convergent Evolution?
Take a few minutes to draw alternative phylogenetic hypotheses for parallel and convergent evolutionary scenarios (talk to your neighbors).
Predicted Result
Parallel Evolution
Predicted Result
Lake Tanganyika
Lake Malawi
Convergent evolution
0246
Victoria Haplochromines
Malawi HaplochrominesGroup A
Tanganyika JulidochromisTanganyika Lamprologus
Myrs
Malawi HaplochrominesGroup B
100
100
100
100Astatoreochromis
Molecular tree based on cytochrome b sequences
Molecular Clock Calibration in Sharks• Fossils and geologic
events
• Calibrate sequence divergence
• Establish molecular clock
• ~7-8x slower than mammals
Martin et al 1992
Evolution of Endothermy- monophyly or convergence?
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
Surfperches (Embiotocidae)
Bernardi & Bucciarelli 1999
Longo & Bernardi 2015Longo & Bernardi 2015
Surfperches (Embiotocidae)