JEZ-B-2019-11-0109

This is an interesting manuscript that provides new information about embryonic development and skin histogenesis in a species of gecko, Tarentola mauritanica.

The data are novel, and this research provides an obvious complement to a burgeoning interest in lizard embryogenesis.

Abstract
• P2, Line 5: Refers to a controversy related to lizard skin development, but it does not clarify what the issue actually is.
o Also, why are geckos “important models for learning about autopodium and digit development”?
• P2, Lines 17-20: Unclear. All taxa are unique and could be models for evo-devo. Perhaps emphasize the specific advantages of T. mauritanica?

Introduction
• P4, Line 15: Awkward. Studying species in ovo avoids killing adult females, but does kill embryos. Also, not really a justification for studying development.
• P4, Line 18: See recent work by Diaz (e.g., Diaz et al. 2019. Developmental Dynamics 248: 709-725) re: chameleon development
• P7, lines 13-22: I am a bit confused about the rationale. It seems to be split across multiple studying a species closely related to a previously studied taxon (T. annularis), investigating in ovo skin development, establishing a staging table, and investigating claw formation. Perhaps this is better summarized as establishing a staging table of in ovo development, which is then used to investigate skin and claw formation?

Materials and Methods
• P8: The number of female geckos (n=31) and the number of eggs collected (n=50) should be listed in this section.
o Also, details on housing (i.e., cage size), temperature, and animal protocol number(s) should be provided. Given the obvious parallels, was the incubation of T. mauritanica eggs similar or virtually identical to the methods employed for T. annularis (Khannoon, 2015)?
• P8, line 11: How many eggs were opened daily? How many embryos were collected at each stage (the text reports at least 3, but some stages had more?). This could be included as a column in Table 1.
• P8, line 19: Why was the staging table for T. annularis (by author Khannoon) not employed?
• P9, line 8: Where were the “…pieces of the dorsal and ventral skin” from? The body? The autopodia? Both?

Results
• P10: clutch size (almost certainly 2, but maybe some were 1)? Overall, were most stages of development similar to that of T. annularis? The authors note that T. mauritanica eggs are oviposited earlier, but are the morphologies otherwise parallel? It would be especially useful to note which features differ between the two taxa in the description.
• P10: In Khannoon (2015; a paper about the closely related species T. annularis), each stage description is regionally subdivided into subheading [head, limbs, and body] (similarly, subheading for various regions are included in Griffing et al., 2019 for the gecko Lepidodactylus). In the current manuscript about T. mauritanica, each stage description is a single, undivided paragraph. This makes direct comparisons between T. mauritanica and other species more challenging. Further, the reporting less consistent – for example, on P10, line 18, the description of pharyngeal arches comes after the description of the tail. In Khannoon (2015) pharyngeal arches are described along with the other cranial features.
• P10, line 17: That the tail was difficult to see was simply a function of how it was coiled, correct? This is a strange characteristic to note.
• P11, line 4: How was the tail “…more developed”? Was it longer?
• P14, line 6: What stages represent the first half of embryonic development related to skin formation? What stages represent the second half?
• P14: Related to the Skin (Results) and Claw Development (Results) sections, these descriptions would be more useful if reported in the Embryonic Table (Results) section (under separate subheadings: ‘skin’ and ‘claw development’).
• P15, lines 1-2: Please clarify what “…epidermis is in an advanced stage…” means.
• P15, line 4: Are the dome-like scales developing tubercular scales? Or another scale type?
• P15, line 7: Please clarify what “…hypertrophy at the outer scale surface with respect to the inner scale surface” means.

Discussion
• It would be easier to appreciate the current findings if the major embryonic events were presented in a table or other format that would allow for direct comparisons between T. mauritanica and other taxa (especially T. annularis). Is there evidence for differences in the timing of particular events?
• Parts of the Discussion seem to be quite speculative, and are not supported by or directly related to, the Results presented. For example, with respect to the paragraph on incubation time and temperature (see P20), it really seems to boil down there are species specific differences. The remainder of this paragraph doesn’t really add much. Similarly, the comments re: apoptosis (P19, lines 3-7) are not necessary, since this process was not being investigated in the current manuscript. Further, some of these discussions have already been advanced in Khannoon (2015).
• P17, line 7: referring to T. mauritanica as “the rough skinned gecko’ may generate confusion as to the common name of this species (which already includes Moorish gecko, crocodile gecko, and common wall gecko).

Figures
• In many of the figures, the embryos are strangely colored. For example, Fig 1 A,B and F are purple, Fig. 1E is green, and Fig. 1G is red. I’m not sure if this was intentional, but it should either be explained or eliminated.
• The white balance of the histological images is inconsistent, and not all the images are in focus (or perhaps the lens needs to be cleaned?). Also, scale bars should be included.