Egg size is a good predictor of parental care behaviour among bony fishes

Parental care is a major feature in the evolution of life-history traits and appears highly associated with the trade-off between egg number and size. It has been a controversial issue in studies about reproductive strategy and is deemed to have evolved multiple times, both in aquatic and terrestrial taxa. To explore relationships between parental care and egg size, we examined 313 species of bony fishes, including 152 species with parental care and 161 species without parental care. We mapped parental care onto a maximum likelihood (ML) unrooted phylogeny and analysed egg size and numbers data set using a logistic regression. The phylogenetically controlled analyses revealed that parental care is dispersed along with the retrieved phylogeny and that at least four distinct lineages parallel evolved from non-parental care lineages to parental care ones. The results of the logistic regression highlighted that egg size can be used as a good predictor of parental care and that there is a strong and consistent threshold in egg size transition between parental and non-parental care fishes. We conclude that egg size predicts parental care in bony fish and that egg size distribution is polymodal within parental care species probably reflecting the variation in the amount of energy used for care. To advance the knowledge about the hypotheses raised in this study, it would be important to gather information about more species and their respective number and size of eggs and the presence/absence of parental care.