Data from: Variation in offspring size with birth order in placental fish: a role for asymmetric sibling competition?

Such competition occurs in species with postnatal parental care and may also occur when mothers provision embryos between fertilization and birth (matrotrophy). We hypothesized that the combination of matrotrophy and the simultaneous provisioning of embryos in different stages of development (superfetation) leads to asymmetric competition between sibling embryos.

Moreover, we expect the intensity of this competition to increase with the level of superfetation as high levels of superfetation result in greater temporal overlap between broods. This hypothesis predicts that offspring from early broods, which predominantly compete with less developed siblings, will be larger at birth than offspring from later broods, which experience competition from more and less developed siblings.