STA 6166, Section 8489, Fall 2007, Homework #2, Due September 27, 2007 A) Please read Chapters 3 and 4. B) Please read the two papers, Palleroni and Hauser (2003) and Arnold et al. (2002), that are attached. For each paper answer the following questions: a. Is the study observational or experimental? b. What factors or explanatory variables are they interested in studying for their affects on the animals? c. What variables are they measuring on the animals? d. State in words all sets of hypotheses that the authors are interested in testing (note that the authors could be interested in more than one set of hypotheses!) e. Restate all sets of hypotheses in statistical terms, i.e. in terms of the population parameters that are believed to be affected by the treatments. C) I am providing a data set “Leaf Fractions.xls”. The researcher is interested in the effect of mixtures of different species on the decay rate of masses of leaves in streams. The scientist placed mesh bags filled with different combinations of species of leaves and removed them periodically to measure remaining mass. A subset of the data is provided. The data are the sample ID, percent of leaf mass remaining after 30 days of submersion (FRACTION), and the natural logarithm of percent remaining (L_FRACTION). Please use the three approaches we learned in class (histograms, Q-Q plots, and hypothesis testing) for determining if the sample data support the argument that the populations of FRACTION and L_FRACTION are Normally Distributed.ECOLOGYFluorescent Signaling in ParrotsKathryn E. Arnold,1* Ian P. F. Owens,2N. Justin Marshall3Fluorescent pigments appear to glow becauseultraviolet (UV) light is absorbed and reemit-ted at longer wavelengths. Humans use fluo-rescence as a highlighter, but it remains amystery whether naturally occurring fluores-cence functions as a signal or is a by-productof pigment structure. Here, we test for evi-dence of signaling using the fluorescentplumage of parrots (1).We performed mate choice experiments onwild-type budgerigars (Melopsittacus undula-tus), in which both sexes have fluorescent yel-low plumage on their crown and cheeks (Fig. 1,A and B) that is used in courtship displays.“Focal” individuals of each sex were given achoice between two “stimulus” birds of the op-posite sex, one retaining fluorescent plumage onits crown (F⫹treatment) and the other withexperimentally reduced fluorescence on itscrown (F⫺treatment) (2). We reduced fluores-cent emission by applying sunblock to thecrown. This decreased the amount of UV, whichis needed for excitation (Fig. 1C), reaching thefluorescent pigment. In the F⫹treatment, petro-leum jelly alone was applied. This does notspecifically absorb UV, so it does not preventfluorescent reemission. These treatment groupsdiffered substantially in terms of fluorescence,but not in UV reflectance because neither fluo-rescent nor manipulated crown feathers reflectUV. To confirm that preferences were sexualmate choice rather than social signaling, we alsoperformed trials in which the stimulus birdswere of the same sex as the focal birds.Our experiments revealed strong evidencefor fluorescent sexual signaling. When stimulusbirds were of the opposite sex to the focalindividual, both females (Fig. 2A) and males(Fig. 2B) showed a significant sexual prefer-ence for fluorescent stimulus birds. Mutualmate choice is expected in monomorphic, so-cially monogamous species, such as the bud-gerigar, in which both sexes provide parentalcare. Conversely, when stimulus birds were ofthe same sex as the focal birds, neither sex (Fig.2, C and D) showed a significant social prefer-ence for F⫹or F⫺birds. Given these results, wecalculated the effect of fluorescence on the“color” of their plumage as perceived by anoth-er budgerigar. By measuring the reflectancespectra of the feathers (3) and using the knownspectral sensitivities of budgerigar cone cells(4) (Fig. 1D), we cal-culated the signal dif-ference (in relativephotons) imparted byfluorescent yellowplumage (F⫹treat-ment) versus yellowplumage in which flu-orescence was pre-vented (F⫺treatment).Fluorescent plumageadds 14% extra “chro-matic signal” to thecrown region, as per-ceived by the visualsystem of another bud-gerigar (Fig. 1D).Moreover, the peak ofthe fluorescent contri-bution is not only ideal-ly placed for chromaticdetection by the bud-gerigar’s middle twovisual cones (or a com-bination of the two short cones versus the twolong cones) but also coincides with the sensitiv-ity peak of avian “double cones,” thought toplay a role in perceiving overall “brightness”(5).These findings show that the fluorescentplumage of parrots is an adapted sexual signal,rather than a by-product of plumage pigmenta-tion. Given the elaborate biochemical path-way by which fluorescent pigments are pro-duced (6), they may be costly and therebyhonest indicators of individual quality.References and Notes1. W. E. Boles, Birds Int. 3, 76 (1990).2. We used a two-way choice apparatus, with the focalbird in a central compartment separated from stim-ulus birds by Perspex transparent between 300 and700 nm. Illumination was provided by Daylight tubesand UV-rich light tubes to mimic natural conditions.Focal birds had 13 hours to acclimatize to the appa-ratus. Each trial lasted 4 hours. Stimulus birds wereswapped between end compartments half-waythrough. F⫺treatment was obtained by daubingfeathers with 40/60% (w/w) mixture of petroleumjelly and unscented, UV-absorbing chemicals (7). F⫹treatment was petroleum jelly alone.3. Under experimental light conditions, reflectance spectrawere measured normal to the crown with illuminationat 45° to the feather surface. Ten measures from eachof ten individuals were taken. There was no fluorescentsexual dimorphism. “Fluorescent contribution” was es-timated with spectral sensitivities of the budgerigar’s“short” (S) and “medium” (M) wavelength cones (4)combined with reflectance measurements of the F⫹and F⫺crown feathers. The percentage of fluorescentcontribution is then given by {[(M ⫻ F⫹⫺ S ⫻ F⫹) ⫺(M ⫻ F⫺⫺ S ⫻ F⫺)]/(M ⫻ F⫹⫺ S ⫻ F⫹)} ⫻ 100 (⫽14.3%).4. J. K. Bowmaker, L. A. Heath, S. E. Wilkie, D. M. Hunt,Vision Res. 37, 2183 (1997).5. D. Osorio, A. Miklo´si, Zs. Gonda, Evol. Ecol. 13, 673(2001).6. R. Stradi, E. Pini, G. Celentano, Comp. Biochem.Physiol. B. 130, 57 (2001).7. S. Andersson, T. Amundsen, Proc. R.
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