GAMETE TRAITS
Egg size did not differ significantly between females from high and low density sites (mean egg size: Female(high) = 64.36 μm ± 0.359 versus Female(low) = 64.35 μm ± 0.244 , GLMM: F1, 29 = 0.01, P = 0.939). However, we did detect a significant difference in egg size among locations (mean egg size: Williamstown = 64.27 μm; ± 0.233 Geelong = 65.65 μm ± 0.179; Portarlington = 63.43 μm ± 0.308, GLMM: F2, 29 = 18.39, P < 0.0001). Our analysis of sperm length revealed a significant difference between high- and low-density sites (GLMM: F1, 29 = 5.01, P = 0.035), with sperm from low density sites being longer compared with sperm from high density sites (mean sperm length: low density = 51.13 μm ± 0.547 cf. high density = 49.86 μm ± 0.387). There was no significant difference in sperm length among locations (GLMM: F2, 29 = 0.11, P = 0.893).
There was no effect of population density (F1,24.159 = 0.4036, P = 0.531) or sperm density (F1,25.2 = 0.520, P = 0.478) on sperm motility PC1 scores, or their interaction (F1,25.1 = 0.04, P = 0.845). Similarly, PC2 scores were not affected by population density (F1,28.5 = 0.25, P = 0.620), sperm density (F1,29.8 = 0.24, P = 0.627) or their interactions (F1,29.6 = 0.07, P = 0.797). Male condition also did not affect sperm motility PC1 (F1,37.6 = 0.13, P = 0.909) or PC2 (F1,43.9 = 0.63, P = 0.431) scores. The percentage of motile sperm was not affected by population density (F1,27.6 = 0.04, P = 0.841), but it was affected by sperm density (F1,27.1 = 0.45, P < 0.001). We also detected no significant effects of the interaction between population and sperm density (F1,26.9 = 0.014, P = 0.907) or the effect or male condition (F1,37.1 = 1.80, P = 0.882) on the percentage of motile sperm. Sperm were on average more motile at the 1 × 108 concentration (31.82% ± 2.22) compared to the 1 × 106 concentration (14.42% ± 2.85).