Embryonic Staging Table for a Direct‐Developing Salamander, Plethodon cinereus (Plethodontidae)

Abstract

This work presents a refined staging table for the direct-developing red-backed salamander Plethodon cinereus, which is based on the incomplete staging system of James Norman Dent (J Morphol 1942; 71:577-601). This common species from eastern North America is a member of the species-rich lungless salamander family Plethodontidae. The staging table presented here covers several stages omitted by Dent and reveals novel developmental features of P. cinereus embryos. These include putative Leydig cells and open gill clefts, which are found in larvae of metamorphosing species but were previously reported as absent in direct-developing Plethodon. Other features found in larvae of metamorphosing salamander species, such as the palatopterygoid bone and lateral line neuromasts, were not observed in this material. The occurrence of larval and metamorphic features in these embryos has direct bearing on the patterns of life history evolution within the plethodontidae family. This study emphasizes the degree to which typically larval structures are retained in this direct-developing species and provides a staging table for further investigations into the development and evolution of plethodontid salamanders.

Hatching plasticity is associated with a more advanced stage at hatching in an Ambystoma with terrestrial eggs

“…In the absence of water, it is conceivable that embryos could develop through metamorphosis, provided they have enough yolk (Callery et al., 2001 ). Indeed, although the developmental progression through embryonic stages varies across direct‐developing species (discussed in Callery et al., 2001 ), direct‐developing frogs and salamanders both progress through a tadpole (frog) or gilled larva (salamander) form before they hatch (Callery et al., 2001 ; Kerney, 2011 ; Marks & Collazo, 1998 ). In this way, extended development is, in fact, a characteristic of direct development.…”

PAX6 protein in neuromasts of the lateral line system of salamanders (Eurycea)

“…Interestingly, the underlying afferent lateral line neurons can still be observed within some species of dusky salamanders (genus Desmognathus ), for example, seepage salamanders ( D. aeneus ) and pygmy salamanders ( D. wrighti ) in the absence of neuromasts [14]. The retention of afferent lateral line neurons has been interpreted as neuro-anatomical paedomorphy [15,16]. It would be interesting to explore whether neuromasts of metamorphosing salamanders that maintain a lateral line similarly evince PAX6 in their neuromasts.…”

Expression of a novel surfactant protein gene is associated with sites of extrapulmonary respiration in a lungless salamander

“…Ambystoma mexicanum were staged according to Bordzilovskaya et al [46] and Nye et al [47]. Desmognathus fuscus embryos were staged using a staging table derived for P. cinereus, as their developmental timing and morphology are grossly similar [48].…”