Credit: Science (2024)
A new study in Science, Vol. 384 No. 6697, “Metabolic loads and the costs of metazoan reproduction,” shows that the energy cost of reproduction is much greater than previously believed. Per the Editor’s summary, “Reproduction is one of the biggest energy investments that an animal will make. It has also been well studied over many years, leading to much knowledge about how much energy is directly invested in the production of offspring. However, the other half of this investment, the cost of caring for offspring, was not clear. Ginther et al. developed a framework for estimating the overall costs of reproduction across taxa and teased apart the factors that contribute to the total. They found that caring for offspring is as much as 10 times more energy expensive than producing them, and this higher expense is the case not just in mammals (in which costs are the highest), but in other taxa as well.”
The abstract follows.
Abstract
Reproduction includes two energy investments—the energy in the offspring and the energy expended to make them. The former is well understood, whereas the latter is unquantified but often assumed to be small. Without understanding both investments, the true energy costs of reproduction are unknown. We present a framework for estimating the total energy costs of reproduction by combining data on the energy content of offspring (direct costs) and the metabolic load of bearing them (indirect costs). We find that direct costs typically represent the smaller fraction of the energy expended on reproduction. Mammals pay the highest reproductive costs (excluding lactation), ~90% of which are indirect. Ectotherms expend less on reproduction overall, and live-bearing ectotherms pay higher indirect costs compared with egg-layers. We show that the energy demands of reproduction exceed standard assumptions.
