Figure 3: Segment addition throughout germband elongation in Tribolium is not linear.
From: Changing cell behaviours during beetle embryogenesis correlates with slowing of segmentation
To determine the rate of segment addition, we measured segment number at 2-h time intervals from 12 to 22 h AEL (embryos labelled, for example, 12 h could be 11 to 12 h since each egg lay was 1-h long). A linear regression through a scatter plot of all time points gave a segmentation rate of 1.3 segments per hour (see Supplementary Fig. 3). However, analysing the variance between time intervals demonstrates that segment addition is not linear but is better characterized as having intervals of distinct periodicity (a, numbers in parentheses indicate group sample size; letters denote statistical significance; analysis of variance: R2=0.91, F=278; for replicates see Supplementary Fig. 4). In particular, segment addition slows between 16 and 18 h, a time that roughly corresponds to the transition from adding thoracic to abdominal segments (b). This is followed by a rapid period of segment addition between 18 and 20 h. The direct comparison of rate of segment addition (c) clearly demonstrates that the period is not constant during germband elongation. Bars represent difference between averages of successive time points. Scale bar, 100 μm.
