Hatching on a budget: The economized energy expenditure of beetle embryos*

Oviparous animals are a biological example of a thermodynamically quasi-isolated system. Additional to the genetic code, most energy and matter necessary for embryo development is stored inside the egg from the time point of fertilization up to the time point of hatching. It remains controversial how energy is stored and transferred, especially in quiescent periods between large-scale deformations. Here, we study extra-embryonic tissue dynamics in two key processes during embryo development, gastrulation and dorsal closure, in the serosa membrane of the red flour beetle Tribolium castaneum. We argue that energy in the serosa tissue is close-to-fully conserved between serosa window closure during gastrulation and dorsal closure. We identify active and passive processes with sub-cellular resolution using 3D non-invasive velocity and stress estimation techniques. We localize the point of origin of forces driving serosa tissue rupture and retraction. We believe that this study of extra-embryonic tissue dynamics signifies the importance of studying both mechanics and thermodynamics in embryogenesis.