A temperature-adjusted developmental timer for precise embryonic staging

Developmental biology research depends on careful staging of developing embryos, but the rate of development is extremely sensitive to the temperature at which embryos are raised. It is not always practical to grow embryos at a precisely controlled temperature, so here we describe a simple, inexpensive device based on an Arduino-compatible microprocessor and temperature sensor that provides a metric of developmental time that compensates for changes in temperature. The underlying assumption is that the rate of development will be linear with respect to temperature over an organism's thermal tolerance range. The device measures the ambient temperature and integrates effective degree-minutes over time. For convenience, this is displayed to the user as a temperature-adjusted standard developmental time. In initial testing we have found the device to be extremely helpful for fixing Ciona embryos during precise developmental windows.