Clutch size in Daphnia: even versus odd?

It has recently been hypothesized for Daphnia that even numbers of eggs per clutch are more common than odd numbers, because of the paired nature of the ovaries. This effect has important consequences for the production of optimal egg sizes. To test the hypothesis, we have analysed data sets containing information for a total of 12,504 clutches, from two inter-specific hybrids and six species of Daphnia. We did not find strong patterns in the data. Even-sized clutches were more common in some of the data sets, and not in others. We therefore conclude that trends towards the production of eggs in pairs are weak, and unlikely to have a significant effect on optimal clutch and offspring size