Taste organ growth and development in the direct developing frog Eleutherodactylus coqui (Lissamphibia: Eleutherodactylidae)

Abstract

Previous research on amphibian taste organs concerned amphibians with a biphasic life history, that is, with larval period and metamorphosis. Direct developing frog species, such as Eleutherodactylus coqui, undergo a cryptic metamorphosis before hatching, and many larval‐specific features are vestigial or have been lost entirely from their ontogeny. Taste buds are present in larval stages of biphasically developing anurans and are replaced by taste discs during metamorphosis. One goal of this study was to characterize the ontogeny of taste buds and/or discs in E. coqui. The other goal was to examine correlations between body size and taste organ density and size in different regions of oral epithelium. The research reveals the presence of only one type of taste organ, characteristic of metamorphs of biphasic amphibians, namely taste disc. In addition, taste disc density and the area of the taste disc sensory zone change dramatically during growth.

Tongue and taste organ development in the ontogeny of direct‐developing salamander Plethodon cinereus (Lissamphibia: Plethodontidae)

“…Only one generation of taste organs was found during P. cinereus ontogenesis. This observation is similar to the other direct developing amphibians studied so far (see Wake and Schwenk, ; Junqueira et al, ; Budzik et al, ,b). TDs occur in post‐metamorphic individuals of anurans and urodeles with free‐living larva (Graziadei and De Han, ; Jasiński, ; Nomura et al, ; Żuwała and Jakubowski, ; Żuwała et al, ).…”

“…Similar growth occurs in P. cinereus, where the adult TD-sensory zone diameter is twice that of the hatchlings. The difference in TD-size indicates growth of the organ scales with organismal growth ( _ Zuwała et al, 2002;Budzik et al, 2015a). However, relative post hatching TD-growth differs between the tongue and palate in P. cinereus.…”

“…TDs occur in post-metamorphic individuals of anurans and urodeles with free-living larva (Graziadei and De Han, 1971;Jasi nski, 1979;Nomura et al, 1979;_ Zuwała andJakubowski, 2001, 2007;_ Zuwała et al, 2002). The convergent lack of "larval" TBs is common to P. cinereus and E. coqui (Budzik et al, 2015a), and possibly other groups of batrachian direct developers, or even species with endotrophic larvae. In endotrophic amphibians parental (maternal) resources, mainly in the form of egg yolk, are the only source of energy necessary for development to the adult stages (Altig and Johnston, 1989;Thibaudeau and Altig, 1999).…”

“…Despite the prevalence of terrestrial direct development in salamanders, there are no studies that have examined the development of taste organs in direct‐developing plethodontids. Budzik et al () recently revealed the presence of only TD‐type taste organs during the ontogeny of the direct developing anuran Eleutherodactylus coqui (Budzik et al, ). However, in all studied direct developing caecilians (Gymnophiona), only TB‐type taste organs were distinguished (Wake and Schwenk, ; Junqueira et al, ; Budzik et al, ).…”

“…Metamorph TDs are constructed similarly, except that there are three types of supporting cells: mucous cells, wing cells and glial-like cells. These differences are apparent in the shape of the organ (Budzik et al, 2015b) and appearance of apical projections from the surface of the oral epithelium, named the "taste sensory zone" (e.g., _ Zuwała and Jakubowski, 2001). The TB-sensory zone consists of apical surfaces of supporting cells covered by microvilli (which externally appear homogeneous) and two types of microvilli emerging from the taste receptor cells: a single thick microvillus and a tuft of thin microvilli (e.g., _ Zuwała and Jakubowski, 1991).…”