The functional significance of residual yolk in hatchling lizards Amphibolurus muricatus (Agamidae)

1. Although post-hatching parental care is uncommon in reptiles, reproducing females may none the less contribute to the nutritional state of their offspring by depositing more yolk into the egg than is needed for embryogenesis. This ‘extra’ yolk (i.e. residual yolk) is drawn into the offspring’s body prior to hatching and is widely assumed to serve as an energy resource for early life activities. However, empirical data on the functional significance of residual yolk are rare. 2. We surgically removed residual yolk from hatchling lizards Amphibolurus muricatus to evaluate its effects on offspring growth and survival over 4 weeks under two environmental conditions: low or high food abundance. 3. Unsurprisingly, higher food abundance enhanced growth rates of the young lizards. However, experimental removal of residual yolk did not affect any of the traits that we measured in either nutritionally harsh or benign post-hatching environments. 4. Overall, our results challenge the common assumption that residual yolk is an important source of energy during early life in lizards, and suggest instead that residual yolk is of trivial nutritional significance (especially, relative to prey availability). Residual yolk in A. muricutus may instead have a different (non-nutritive) function, or be a nonfunctional relict retained through phylogenetic conservatism from ancestral taxa.