Do female Platyfish prefer male Platyfish with yellow swordtails? A.L. Basolo proposed and tested a selection model in which females have a pre-existing bias for a male trait even before the males possess it. Six pairs of males were surgically given artificial, plastic swordtails—one pair received a bright yellow sword, the other a transparent sword. Females were given the opportunity to engage in courtship activity with either of the males. Of the total time spent by each female engaged in courtship during a 20 minute observation period, the percentages of time spent with the yellow-sword male were recorded.
A data frame with 84 observations on the following 3 variables.
The proportion of courtship time spent by 84 females with the yellow-sword males
Factor variable with 6 levels—
"Pair 5" and
Body size of the males
Ramsey, F.L. and Schafer, D.W. (2002). The Statistical Sleuth: A Course in Methods of Data Analysis (2nd ed), Duxbury.
Basolo, A.L. (1990). Female Preference Predates the Evolution of the Sword in Swordtail Fish, Science 250: 808–810.
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str(case0602) boxplot(Proportion~Pair, case0602, ylab="Proportion") #as in Display 6.5 summary(aov(Proportion~Pair, case0602)) n.fish <- with(case0602, tapply(Proportion, Pair, length)) av.fish <- with(case0602, tapply(Proportion, Pair, mean)) sd.fish <- with(case0602, tapply(Proportion, Pair, sd)) male.body.size <- with(case0602, tapply(Length, Pair, unique)) mean.body <- mean(male.body.size) table.fish <- data.frame(n.fish, round(av.fish*100,2), round(sd.fish*100,2), male.body.size, 2*(male.body.size-mean.body)) names(table.fish) <- c("n", "average", "sd", "male.body.size", "coefficient") s.pooled <- with(table.fish, round(sqrt(sum(sd^2*(n-1))/sum(n-1)),2)) g <- with(table.fish, sum(average*coefficient)) se.g <- with(table.fish, round(s.pooled*sqrt(sum(coefficient^2/n)),2)) g/se.g
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