The motility of the chicken embryo: Energetic cost and effects of
hypoxia
4.4. Conclusions
Motility permeates animal life at all levels of organization. Postnatally, body movements are primarily related to locomotion, for food gathering, escaping predators and finding mates, or to postural adjustments, as with the behavioral responses to ambient temperature. Prenatally, motility serves very different purposes and is both passive and active. The passive embryo's movements, like those caused by the periodic rotation of the egg by the incubating parent, are important in limiting the problem of adherence of the embryo to the surrounding membranes. Active movements can serve some heat control and communication with the incubating parent (Gräns and Altimiras, 2007 and Du et al., 2011). However, the most essential role of active embryonic motility must be its contribution to muscle-skeletal development, which relies on the mechanical loads encountered by the spontaneous muscle contractions (Pitsillides, 2006 and Nechaeva et al., 2010). Absence of active motility, as in experimental paralysis, unavoidably leads to poor cartilage formation and skeletal deformities. The current data have indicated that the embryo's active body movements are energetically very economical. This conclusion is in keeping with the general principle that life-indispensable functions cannot have evolved to be energetically expensive.
Because embryonic motility is rather inexpensive, it is possible for the embryo to continue to move in hypoxia, when body growth is curtailed. It also follows that cessation of motility during hypoxia would be of little benefit to the embryo, since it cannot be an important mechanism of energy saving.