Extreme body size variability in the golden silk spider (Nephila edulis) does not extend to genitalia

Nephila edulis is a spider with large body size variability in males and fe males. Genital characters show negative allometric values compared to somat ic characters. In males, the embolus (the most important structure for sper m transfer) had a significantly lower coefficient of variation than body si ze. This suggests that male genitalia are under stabilizing selection favou ring intermediate size. Female N. edulis showed a trend similar to males re garding allometric values in genitalia. In females, however, the variation coefficient in a specific genital character crucial for successful copulati on did not differ from that of indicators for overall body size. This sugge sts that in Nephila the genitalia of the females experience less stabilizin g selection than those of the males. In male and female genitalia, the mode of selection seems to cause developmental instability not in degrees of fl uctuating asymmetry but in the degree of data scatter which indicates a low er coefficient of determination.