Homework #2 Evolution and Ecology

BioS 230 Homework 2 Student Name: __________________________ Please write/type out your answers using different color (e.g. blue/red) in this document or in a separate paper. Make sure TA is able to read your handwriting! 1. (7 pts) Hercules beetle (Dynastes hercules) is sexually dimorphic, with males producing horns to compete for mates. Assuming that you conducted a breeding experiment to impose artificial selection to reduce the horn size of male Hercules beetles. You measured 50 Hercules beetles and obtained a mean horn size of 5.8 cm. You selected 10 Hercules beetles with shortest horns as breeders. The mean horn size of the breeders is 4.3 cm. After mating, male offspring of the Hercules beetle breeders have a mean horn size of 4.7 cm. What is the heritability of horn size in this male Hercules beetle population? Show your work and round numbers to 2 decimal places. Note: Selection differential (S) will be negative value if selection favors lower values of a trait, which would result in negative response to selection (R). 1 Midoffspring height (inches) 2. (8 pts) Below is a scatter plot of offspring height as a function of parent height in a hypothetical animal population. Show your work and round numbers to 2 decimal places. 76 74 72 70 68 y = 0.883x + 16.406 66 64 62 62 64 66 68 70 72 Midparent height (inches) 74 76 a) From the regression line of the scatter plot in Q2(a), estimate the heritability (h2) of height. Round numbers to 2 decimal places. (2 pts) b) Five pairs of the tallest parents were selected as breeders. The mean height of the initial population was 68.3 inches. The mean height of the breeders was 74.5 inches. Calculate the selection differential (S). (2 pts) c) Predict the response to selection (R). Round numbers to 2 decimal places. (2 pts) d) Predict the average height of the population in the next generation (2 pts). Show your work and round numbers to 2 decimal places. 2 3. (11 pts) Construct a cladogram to demonstrate the evolutionary relationships of five species based on the characteristics presented in the table below. The column that has “X” indicates the organism has that particular characteristic. Label the derived traits on the cladogram. Character Amniotic Egg Feathers Fur Lungs Warm-blooded Vertebrae Reptile X X X Bird X X X X X Mammal Amphibian X X X X X Bony fish X X X 3 4. (24 pts) You are a paleontologist attempted to reconstruct a phylogeny for 8 species (A-H) based on the fossil skull specimens. You have collected and measured morphological characteristics for each skull specimen, summarized in the table below. Data do not reflect the evolution of currently living organisms. Species 1 (teeth) 2 (canine) 3 (brow) A B C D E F G H (Outgroup) 16 18 18 18 18 18 22 22 N N N N N N P W N N N Y Y Y Y Y 4 5 (diastema) (mandible) Y Y N N N N N N R R R R R O O O 6 (nose) N N N N Y Y N Y 7 (eye) C C C C C C C E 8 (crest) N N N N N Y Y Y Descriptions for each morphological characteristic: Character #1 = Number of teeth on the maxilla (upper jaw) Character #2 = Presence of canine (W = well developed, P = partially developed, or N = no) Character #3 = Presence of brow ridge (Y = yes, or N = no) Character #4 = Presence of diastema (Y = yes, or N = no) Character #5 = Mandible shape (O = oval shape, R = rectangle shape) Character #6 = Presence of nasal conchae (Y = yes, or N = no) Character #7 = Eye sockets (E = open eye sockets, C = closed eye sockets) Character #8 = Presence of medial cranial crest (Y = yes, or N = no) Here are mammal skull images that display some of the characters listed in the table. Note: The images provided are to help you envision how morphological data were collected. You do not have to know the locations of the structures to construct the phylogeny. 4 Phylogeny Reconstruction Use the cladogram below, label the species (A-H) at the appropriate terminal nodes (tips). Identify the synapomorphies (shared derived characters) and autapomorphies (unique derived characters to a given taxon), Characters# 1-8, on the cladogram. The locations of the derived characters have been designated with the “tick marks”. The placement of the outgroup species H and the first synapomorphy (Character #7) have been provided for you. Instructions for Phylogeny Reconstruction 1. Look at the morphological data listed in the table. Start with Character #7. Species A-G have closed eye sockets (C). Species H has open eye socket (E), suggesting that open eye socket is an ancestral trait. Label 7(C) at the first “tick mark” to indicate all the descendant taxa after this point have closed eye sockets. From there, the placement of the species H can be determined. The placements of species H and the first syapomorphy 7(C) have been provided to you. 5 2. Look at Character #2. Species A-F do not have canine. Species G has a partially developed canine. Species G has a morphological character more similar to the outgroup species H than other taxa. With this information, label derived characters 2(N) and 2(P) at the corresponding tick marks on the cladogram. 3. You should be able to place species G on the terminal node (tip), and label another autapomorphy that separates species G from species H. When there are two derived characters on the same branch, since we do not have sufficient information to determine which trait evolved first, you don’t have to worry about the order of the derived characters. 4. Next, look at Character #5 and #8. Label synapomorphy 5(R) and 8(N) on the branch and determine the proper placement for species F. 5. Proceed with Characters #6, #3, #4, and #1 (in this order). Place the derived characters on the cladogram following the morphological character descriptions in the table, e.g. 6(N) or 6(Y). Identify the terminal nodes (tips) for other species. 6. At this point, you should have all the species (A-H) and derived characters (Characters #1-8) properly placed on the cladogram. Do a final check on your phylogeny to make sure you obtain the derived characters listed in the table for each species. 7. You have successfully reconstructed a phylogeny! 6