Figure 1.
Male and female Gnatocerus cornutus.
Reported body length is the average straight line distance from head to tip of elytra measured from dorsal and ventral views. Horn length is the average of right and left horns measured by a curved line along the middle of the horn viewed from the dorsal side.
Figure 2.
Effect of parasite exposure on male morphology.
The relationships between horn size and (A) body length or (B) body mass plotted for exposed (open circles, dashed line) and control (closed circles, solid line) beetles. Below each plot we report the results of the GLM with p-values for significant model terms in bold. Both body size measures are significant predictors of horn size. Significant, negative treatment effects indicate that parasite infection reduces horn size. Non-significant interactions indicate no change in the slope of the body size to horn size allometry for length or mass.
Table 1.
Effect of parasite exposure on beetle morphology and activation of the melanin-synthesis cascade.
Table 2.
Main effects of parasite exposure treatment, body size and horn size on PPO and PO activity.
Figure 3.
PPO activity is positively related to body length and horn length in control beetles.
(A) Body length and (B) horn length are significant predictors of PPO activity in control beetles. Horn size is not significant after accounting for the contribution of body size (see text).
Table 3.
Results of male-male competition experiments.
Figure 4.
Differences in time spent with the female as a function of difference in (A) body length, and (B) horn length.
Solid lines mark zero difference in time and size. In the upper right quadrant larger males spend more time with females (as expected), and in the lower left, smaller males spend more time (counter to expectation). Dashed lines mark the difference between the average size of uninfected and infected males (Table 1). Males are expected to win only 3.4% of the time (1 of 29) when their body length disadvantage exceeds the average reduction due to infection - or 6.9% (2 of 29) for average infection induced horn length reduction (open circles).