Figure 3. The degree of NPX exposure corresponds to the severity of morphological effects observed in late-stage axolotl embryos.

(A-D) In stage 28 embryos, NPX appears to have no effect on development demonstrated by the lack of observable defects. (E-H) In stage 45 embryos, increasing concentration of NPX corresponds with the development of progressively more severe morphological defects. Dashed bars demonstrate how morphologic measurements were performed. (I-L) All 3 treatment concentrations produce statistically significant decreases in head length, dorsal fin height, eye diameter, and pre-optic length in stage 45 embryos. Sample sizes for morphologic analysis were n=8, n=40, n=22, and n=19 for the control, 5 μg/mL NPX, 10 μg/mL NPX, and 20 μg/mL NPX treatment groups, respectively. Embryos that did not have grossly appreciable development of their eyes or gills were excluded from the eye diameter, pre-optic length, and head length measurements. Non-parametric, unpaired Mann-Whitney t-tests were performed to analyze these results. p-value= *, **, ***, **** = p-value < 0.05, < 0.01, < 0.001, and <0.0001, respectively.