The parasitic bacterium Pasteuria ramosa castrates and later kills its host, the crustacean Daphnia magna. The length of time between infection and host death affects the number of spores eventually produced and released by the parasite, as the following scatter plot reveals. The x-axis measures age at death for 32 infected host individuals, and the response variable is the square-root-transformed number of spores produced by the infecting parasite (Jensen et al. 2006).

a. Describe the shape of the relationship between the number of spores and host longevity.

b. What equation would be best to try first if you wanted to carry out a nonlinear regression of Y on X?

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Square root (no. spores + 0.5) 3000- 2500 2000- 1500 1000 500 0 30 40 50 60 70 Host longevity (days) 80