Nymphalis antiopa Pupa Mass Data

We collected the mass data of our mourning cloak (Nymphalis antiopa) pupae.

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​After collecting and sexing all of our antiopa pupae and sorting them into two containers for each sex (see Sexing Nymphalis antiopa Pupae), we proceeded to weigh them to collect mass data. We were most interested in seeing the difference in mean mass between the sexes.

After collecting the data, we did some basic statistics. Below are the summary stats and histograms, one stacked for both sexes plus one for each sex.

Summary Satistics for Nymphalis antiopa Pupa Mass Data
                      Mean                    Std Dev                  Median       Min      Max      N  
Male           0.7880952381      0.06476047044     0.8               0.6          0.9       84
Female       0.8957746479     0.08006536565      0.9               0.7          1.1         71
All               0.8374193548      0.08983996384      0.8               0.6          1.1        155

Looking at the graphs first, the stacked male and female graph appears to be mostly unimodal and symmetric but slightly skewed right, with no outliers. The female graph is unimodal and very symmetric, almost a perfect normal curve. The male graph, on the other hand, is a little bit unusual, being slightly skewed left with a very high concentration in the center, o.8.  

The female masses are indeed higher the male's, having a mean of 0.896 g to the male's 0.788 g, over a decigram higher. A confidence interval for the difference in means is 0.085 to 0.131 (C=0.95), so clearly the difference is real. A two-sample t-test for the difference in means between the sexes also shows that the female mean mass is statistically significantly higher than the males (t = 9.2555; df = 153; p<0.0001). 


We also can't help but notice how shockingly little variation there is for the mass of both sexes, especially the male's, with standard deviations of just 0.0648 and 0.080 for males and females respectively. From what we've seen with most other larvae we have reared, the size variation is almost always very high, probably due to a plethora of random factors other than genetics while rearing - some larvae will just grow and grow while others hardly do at all, resulting in large and tiny pupae from the same rearings. It is usually only when larvae are thinned out to low densities, or if they are highly gregarious that pupae size tend to be more consistent.

​With the antiopas here, the pupae are very consistent in size and as larvae, they were extremely gregarious all the way up to pupation (they pupated in rows on the same branches), and they all grew at the same rate, all molting to the successive larval instars in near perfect synchrony. This suggests that competition between solitary larvae is a considerably large factor in their performance when reared in high densities. 

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Authors
Alan Liang

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