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Q34 - Assembling a Bird Phylogenetic Tree from Fragments

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Phylogenetic Trees & Cladistics

Biosystematics

In this task you get a few parts of a phylogenetic tree of birds, and you should assemble the full tree based on them.

Four small cladogram fragments, each showing 5 of the 10 named bird species clustered in a different partial arrangement, illustrating overlapping subsets of the true relationships: (top-left) A. crecca separate, then P. cristatus+S. borin paired, joined with T. totanus+P. carbo paired; (top-right) A. cinerea separate, then C. monedula joined with a T. pilaris+(P. cristatus+S. borin) group; (bottom-left) C. monedula separate, then A. cinerea+P. carbo paired, joined with C. crex+L. argentatus paired; (bottom-right) T. pilaris+S. borin paired, joined with C. crex+(T. totanus+L. argentatus). Fig.1.

The species to place in the full phylogenetic tree, indicated by letters:

  • A – A. cinerea
  • B – A. crecca
  • C – C. crex
  • D – C. monedula
  • E – L. argentatus
  • F – P. carbo
  • G – P. cristatus
  • H – S. borin
  • I – T. pilaris
  • J – T. totanus

You should find the place of each species in the tree below. Match the letter of the species (A-J) with the Roman numerals (I.-VII.) of the positions in the tree. One numeral can belong to more than one letter.

A skeleton phylogenetic tree with seven labeled terminal/grouped positions (I. through VII.) arranged hierarchically: a shallow pair of “I.” tips, joined with “II.”, joined with a pair of “III.” tips (deeper split), forming the upper major clade; separately, “IV.” joins with “V.”, which joins with a pair of “VI.” tips, forming the lower major clade; “VII.” branches off earliest, separate from both major clades. Fig.2. Target skeleton tree with positions I–VII to be filled in with species letters A–J.

Indicate your answer by putting an X in the appropriate box on the answer sheet.

Q34.1. Given four overlapping partial phylogenetic trees (each showing 5 of 10 bird species: A-A. cinerea, B-A. crecca, C-C. crex, D-C. monedula, E-L. argentatus, F-P. carbo, G-P. cristatus, H-S. borin, I-T. pilaris, J-T. totanus), assemble the full consensus tree and match each species letter to its position (Roman numeral I-VII) in the skeleton tree. Where does species A (A. cinerea) belong?
Q34.2. Where does species B (A. crecca) belong?
Q34.3. Where does species C (C. crex) belong?
Q34.4. Where does species D (C. monedula) belong?
Q34.5. Where does species E (L. argentatus) belong?
Q34.6. Where does species F (P. carbo) belong?
Q34.7. Where does species G (P. cristatus) belong?
Q34.8. Where does species H (S. borin) belong?
Q34.9. Where does species I (T. pilaris) belong?
Q34.10. Where does species J (T. totanus) belong?
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Question reproduced from IBO 2019, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key