Figure 1

δ¹³C‰ and δ¹⁵N‰ values of spermathecae from the control experiments, treatment 1. The four symbols indicate samples from the 4 replicates. Threshold values were defined as 2–3 standard deviations (s.d.) above the mean value of virgin spermathecae samples, and are indicated for δ¹⁵N‰ (2 s.d. solid line) and δ¹³C‰ (3 s.d. broken line). Experimental samples could thus be defined as ¹³C labelled (top left quadrant), ¹⁵N labelled (bottom right quadrant), labelled with both isotopes (Both, top right quadrant) or no label was detected (Neither, bottom left quadrant).