The question
Name: ______________________ Date: ____________ Build a cladogram from a trait table (4 points)
Data table
Characters of five fish species
Researchers studied four closely related fish species from a lake system, P, Q, R and S, and a species from a nearby river, O, which other evidence shows lies outside the group formed by the four lake species. They scored five characters as present (1) or absent (0).
| Species | Dark bars on the body | Enlarged lower jaw | First and second back fins joined | Pelvic fins absent | Blue throat in males |
|---|---|---|---|---|---|
| O | 0 | 0 | 0 | 0 | 0 |
| P | 1 | 0 | 0 | 0 | 0 |
| Q | 1 | 1 | 0 | 0 | 0 |
| R | 1 | 1 | 1 | 0 | 1 |
| S | 1 | 1 | 1 | 1 | 0 |
(a) Identify the outgroup, and describe how it is used to decide which state of each character is derived. [1 point]
(b) Construct a cladogram of the five species that is consistent with the data. Mark where each of the five characters arose. You may draw it or write it with nested parentheses and list where each character arose. [1 point]
(c) For the clade made up of R and S, identify one shared derived character and one shared ancestral character, and explain the difference between them. [1 point]
(d) New DNA sequence data show that Q and R share many mutations that S lacks, so Q and R are sister taxa, with S joining them next. Predict how the cladogram changes, and explain what the new tree implies about the history of the joined back fins. [1 point]