Figure 2

Retinal development in E. coqui and D. pictus. (A, B) Morphometric analysis of retinal development (modified from [29]). Cross-sectional area of the central retina (light blue) or of its cellular layer (dark blue) is plotted against developmental age. In addition, a proliferative index indicating the PCNA positive proportion of the cellular layer is shown in green. Each symbol represents a measurement from a single individual (there are less data points for the proliferative index than for area measurements because PCNA staining was not apparent in each individual). Curves are drawn through mean values in case more than one individual per stage was analyzed. For each species, timing of first outgrowth of axons from retinal ganglion cells (RGC), the first retinofugal fibers in the optic chiasm, the formation of inner and outer plexiform layers (IPL and OPL, respectively) and of a distinct layer of photoreceptor (PR) outer segments in the retina are indicated in red. For D. pictus the approximate duration of larval and metamorphic phases are emphasized, while for E. coqui, which lacks a free-living larva, the time of hatching is shown (at hatching, E. coqui corresponds to frogs at the end of metamorphosis with respect to many characters). In each graph, one scale unit of the abscissa represents 1 day of development at 24°C, except for larval stages of D. pictus, which are of variable duration and are represented here in an extremely telescoped way. TS 15+6, TS 15+10 and Go 45+8 refer to stages at 6 and 10 days posthatching (E. coqui) or 8 days postmetamorphosis (D. pictus), respectively. (C) Overview of retinal development in E. coqui and D. pictus based on camera lucida drawings of sections through the central retina of different developmental stages. Hatched lines indicate plexiform layers, the inner nuclear layer is sandwiched in between. Stippling indicates PCNA-positive regions.