Rogge found that even very young, neural-tube-stage embryos, before developing gills, blood, or the ability for muscular movement, kept their developing head in the oxygen sweet spot. "Once we started with the behavior research, it sort of snowballed and we suddenly got to the point where I spun the one-day-old embryos. We figured they would turn back, because they had ciliary rotation, but watching them ever so slowly return to the front, almost like clock-work, was amazing."
Rogge also induced embryos to lose their gills in the egg -- and was thus able to directly measure and compare the oxygen uptake ability of animals with and without gills, in eggs and in the water. "Embryos normally keep their external gills as long as they stay in the egg, but when they hatch they re-route the blood flow and the gills shrivel up in a matter of minutes" said Warkentin. "Now this makes sense. The external gills aren't much use to tadpoles, but they seem to be critical for embryos if they are to get enough oxygen."
People don't typically think of eggs as "doing" much. However, early development is a crucial time when death is a common occurance, and natural selection will favor any ability the embryo may have that increases its chances of survival.
|Contact: Beth King|
Smithsonian Tropical Research Institute