Figure 1.

Hypothetical mechanisms of differential allocation into male and female eggs (in the case where female eggs are bigger than male eggs). Scenario 1: (a) (i) differences in egg size exist prior to fertilization, and egg size per se determines the probability of an egg being fertilized (with a higher probability for larger eggs). (b) (i) Under this scenario, the range variation of egg size should be the same between mated and virgin mothers. (c) This scenario can be divided into two sub-scenarios: (i) there is no size threshold for fertilization, and the larger eggs of each female are preferentially fertilized. In this case, no relation is expected between mean egg size prior to mating and the proportion of fertilized eggs after mating. (ii) There is a size threshold for fertilization. In this case, the proportion of eggs above the threshold is expected to increase with mean egg size. Scenario 2: (a) (ii) the differential allocation is due to a differential provisioning of male and female eggs following fertilization, with fertilized eggs receiving more resources. (b) (ii) Under this scenario, the range variation of egg size should be larger among eggs from mated mothers, compared with eggs from virgin mothers. Indeed, if fertilized eggs draw more resources, fewer resources are available for unfertilized ones, leading to very large female eggs and very small male ones.