Butterflies have a Z/W mechanism of sex determination. In thissystem, females are the heterogametic sex, so females are ZW andmales are ZZ. Papilio glaucus, the Eastern Tiger Swallowtail, isfound throughout the eastern United States. Papilio canadensis, theCanadian Tiger Swallowtail, is found throughout Southern Canada andthe Northern United States. The two species are known to hybridizewhere their ranges overlap near the Great Lakes.
For butterflies living in seasonal environments, it is importantto correctly time the diapause â a state of physiological dormancythat allows them to survive the winter. P. canadensis lives incolder climates and therefore has only one generation per year andan obligate diapause; all pupae of this species diapause from latefall until the next spring, when they resume development. In P.glaucus, most pupae diapause only in response to cold temperatures;as long as weather remains warm, they continue to develop. However,some P. glaucus pupae show obligate diapause similar to P.canadensis. The gene that controls diapause in Papilio is locatedon the Z chromosome, and obligate diapause is specified by therecessive allele ob.
A population of P. glaucus near Lake Michigan is atHardy-Weinberg equilibrium. You have found that 9% of the malepupae show obligate diapause.
(1 point) What is the percentage of female pupae that showobligate diapause? (Show how you calculated this).
(1 point) What is the frequency of the ob allele in males and infemales?
(1 point) What will be the frequency of obligate diapause pupaein the next generation in the absence of selection, in eachsex?
Males:
Females:
(8 points) Winter came early and suddenly this year. Pupae thatwere in diapause because of the ob allele were safe, with arelative fitness of 1. Pupae that had not diapaused were much moresusceptible to the cold and most of them died leaving them with arelative fitness of 0.2. All adults and other larvae died. What isthe new frequency of the ob allele in the next generation? Inmales:
In females:
You now bring P. canadensis and P. glaucus back to the lab tocarry out some controlled crosses. The P. canadensis populationthat you chose is fixed for the ob allele. The P. glaucuspopulation that you chose is fixed for the alternative dominantallele at this locus that allows for environmental determination ofdiapause. From the following matings, what is the frequency ofdiapausing pupae that you would expect? (Show how you calculatedthis).
(2 points) Male canadensis x Female glaucus
Males:
Females:
(2 points) Male glaucus x Female canadensis
Males:
Females:
P.glaucus is highly palatable to predators. Females come in twoforms: a yellow form that looks identical to males and has somelevel of crypsis and a dark form, which mimics the unpalatablebutterfly Battus philenor. This trait is specific to females andthe locus that determines the phenotype is biallelic and located onthe W-chromosome.
(1 point) What form of mimicry is this?
(3 points) You are comparing two populations of P.glaucus foundin different regions. What factors do you think might influence therelative fitness of the two morphs?
(1 point) What type of selection would you expect to act on thegene responsible for color morph determination? (check one)
Negative Frequency Dependent Selection
Positive Frequency Dependent Selection
Balancing Selection
Directional Selection
