Figure 1: Dimensional changes in the elongating germband of Tribolium.

(a–c) Quantitative trends in germband dimensions plotted as a function of developmental stage (measured by number of EN stripes, all statistics describe linear regressions). (a) As segments are added in Tribolium, the germband increases in length (black, R²=0.89, P<0.0001, n=166) more rapidly than the overall increase in germband area (red, R²=0.34, P<0.0001, n=166). During this time, the growth zone (defined as the region behind the last EN stripe) shrinks both in area (b, red; R²=0.77, P<0.0001, n=163) and anterior/posterior length (c, red, R²=0.81, P<0.0001, n=170). The area of the most recently added segment also decreases during germband elongation (b, black, R²=0.54, P<0.0001, n=163), although its length remains relatively constant (c, black, R²=0.02, not significant). These data are also plotted by developmental stage (Supplementary Fig. 1). (d) The average growth zone area of animals prior to elongation (one EN stripe, black, n=8) needs to be only 18% larger to account for the area at the time of birth of all the segments added during germband extension (red; sum of multiple averages). (e) Tribolium germbands removed from egg and mounted flat. Top embryo shows measures used in this study (defined in methods); beneath are selected stages stained with EN to show changes in embryo size and shape during germband extension. Scale bar, 100 μm.