Figure 2: Normal population-level and induced variation is consistent with predictions of an inhibitory cascade.
From: Shared rules of development predict patterns of evolution in vertebrate segmentation
(a) Proximal-distal tradeoffs in experimental groups are statistically indistinguishable from wildtype/controls (likelihood ratio=3.391, df=2, P=0.184), and together they are consistent with IC model predictions (yellow line: sn+2=−0.97 × sn+0.69, r2=0.813, P=0.000; r=−0.063, df=199, P=0.375). (b) An impermeable barrier between developing the s0–sn joint leads to a significant increase in proximal phalangeal proportions (sn) and decrease in distal segment (sn+2) proportions, while middle segment (sn+1) proportions remain unchanged (ANCOVA, P<0.001). (c) The rock dove (Columba livia) and domesticated/feral pigeons follow the same proximal-distal tradeoff (yellow), paralleling the predicted IC model trajectory (red dashed) (r=0.060, df=34, P=0.729). (d) The ‘Racing Homer’ domesticated pigeon breed has significantly shifted proximal-distal (s1–s3) wing element proportions, but no difference was found in zeugopod (s2) proportion (ANCOVA, P<0.001, N=54). Note that digits were not included in this analysis, thus s2 proportions are inflated, but otherwise does not impact the s1–s3 tradeoff prediction. (e,f) When decomposed into local three-segment series, somites and their skeletal derivatives (principally vertebral centra) exhibit a PD trajectory consistent with the IC model predictions (sn+1=0.331±0.001; sn+2=−1.01 × s1+0.67, r2=0.83, P<0.001; [sn+/2]/[sn] = 2.02 × [s2/s1]−1.01, r2=0.74, P<0.001).
