Reproductive metabolism scaling across ectotherms

Abstract

Life history theory typically considers the costs of reproduction in terms of energy content to released offspring (often measured as clutch mass at birth), yet direct reproductive costs are actually accrued by the mother during the offspring production and provisioning phase. While female body size is well recognised as a strong predictor of clutch mass, remarkably, there is no consensus on how the total energetic costs of reproduction should relate to adult size, nor whether the type of offspring produced (egg or live-young) can modify these relationships. We compiled estimates of body size and metabolism (i.e., reproductive costs) across gravid and non-gravid females, as well as species-specific estimates of clutch mass, for ~80 ectotherm species spanning ~10 orders of magnitude in body size, from rotifer to python. Reproductive cost scaling was hypoallometric – larger species had less reproductive costs relative to their body size than smaller species. Furthermore, species that produced heavier clutches also had relatively less costs than species that produced lighter clutches. Surprisingly, these patterns were congruent across reproductive modes implying that metabolic demands of viviparous and oviparous offspring may change dramatically once released from the mother.