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Figure 1 | Frontiers in Zoology

Figure 1

From: Development of the retinotectal system in the direct-developing frog Eleutherodactylus coqui in comparison with other anurans

Figure 1

Heterochrony plot comparing the timing of retinotectal and brain development (colored symbols, suites of characters I-IV) with development of the spinal cord (grey symbols, suites of characters V-VIII) and other characters (black symbols, suites of characters IX-XII) in E. coqui and D. pictus (modified, corrected, and supplemented from [28]). X and Y axes represent time axes, along which stages of development are indicated. To facilitate comparisons, the approximate correspondence of stages of D. pictus [86, 87] with stages of X. laevis [88]) are also indicated. The duration of the larval period (dashed part of Y axis) in D. pictus and X. laevis is variable and is represented here in a very telescoped fashion. All symbols in the plot except the asterisks represent developmental events (e.g., outgrowth of retinofugal fibers), whose timing in E. coqui is plotted against timing in D. pictus (for detailed list see below). The asterisks compare timing of NeuroD expression between X. laevis and E. coqui. Timing of events is based on data reported in this paper as well as [18, 19, 21, 28, 29]; a few data on limb development are taken from [9] and from [93] on D. sardus. For a detailed list of developmental events see Tables 1 and 2 (colored symbols) and references [21, 28] (black and grey symbols). Whereas suites of developmental events conserved between two species compared in a heterochrony plot are expected to plot along a diagonal line, temporal dissociations (heterochronic shifts) are indicated by deviations from such a pattern [21]. The distribution of events in this heterochrony plot reveals multiple heterochronic shifts of developmental events between E. coqui and D. pictus. While retinotectal differentiation (blue triangles; suite II) remains temporally coordinated with early development of the CNS (pink triangles; suite I), early differentiation of the spinal cord (grey squares; suite V), and early embryonic development of many cranial structures (black symbols; suite IX) in E. coqui, the formation of lateral motor columns and innervation of the limbs (grey triangles; suite VII) is predisplaced into early embryonic stages paralleling precocious onset of limb development (black symbols; suite X) in E. coqui. The formation of dorsal root ganglia also occurs earlier in E. coqui (grey triangles; suite VI). Growth of the retina (red circles; suite III), the tectum (green circles; suite IV), and the spinal cord (grey circles; suite VIII) all occur relatively early in E. coqui. Metamorphic remodeling of cranial structures (black symbols; suites XI and XII) occurs immediately after embryonic cranial development (black symbols; suite IX) in E. coqui.

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