Gosner stage is a generalized system of describing stages of embryonal and larval development in anurans (frogs and toads). The Gosner system includes 46 numbered stages, from fertilized

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

(stage 1) to the completion of metamorphosis (stage 46). It was introduced by Kenneth Gosner in 1960. The system is widely used in

herpetology Herpetology (from Greek ἑρπετόν ''herpetón'', meaning " reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and r ...

to describe

tadpole A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found ...

s. Gosner stages are based on certain morphological landmarks that allow comparing development in different species that may greatly differ in age or size.

Developmental stages

The Gosner system includes 46 stages, from fertilized embryo (stage 1) to the completion of metamorphosis (stage 46). In the original publication, only two major developmental stages were distinguished, embryonic or prefeeding stages (1–25) and larval stages (26–46). McDiarmid and Altig (1999) distinguish four major developmental stages, as detailed in the table below. In ecological literature, the term "hatchling" may refer to stages 24–26. However, for direct-developing species, hatching occurs in the end of the development.

Limitations

As a generalized system, Gosner stages may not be adequate for describing development of some anuran tadpoles. For example, in the torrent-dwelling tadpoles of ''

Ansonia longidigita ''Ansonia longidigita'' (common names: long-fingered slender toad, long-fingered stream toad) is a species of toad in the family Bufonidae. It is endemic to northern and western Borneo in Sabah and Sarawak (Malaysia) and in Brunei. Description T ...

'' and ''

Meristogenys orphnocnemis ''Meristogenys orphnocnemis'' is a species of frog in the family Ranidae, sometimes known as Sabah Borneo frog or dusky-footed torrent frog. It is endemic to Borneo and found in the mountains of Sabah (Malaysia), Brunei, and East Kalimantan (In ...

'', the usual Gosner stages become inappropriate beyond the stage 41 because the tadpoles retain their oral disc longer than the system depicts. This is interpreted as an adaptation that allows the tadpoles to cling to the rocks until the tail is almost fully resorbed. In '' Limnonectes limborgi'', the tadpoles are free-living but non-feeding ("nidicolous") and retain their

yolk sac The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is fa ...

until stage 37, at least. Direct-developing frogs hatch directly as froglets, without free-living larval stage.

References

{{Reflist, 30em, refs= {{cite journal , last5=Zachariah , first5=Anil , last4=Rao , first4=Ramprasad , last3=Raju , first3=David Valiaparampil , last2=Mathew , first2=Jobin Kuruvilla , last1=Abraham , first1=Robin Kurian , name-list-style=amp , title=Reproduction and metamorphosis in the Myristica Swamp tree frog, ''Mercurana myristicapalustris'' (Anura: Rhacophoridae) , journal=PeerJ , date=2018 , volume=6 , pages=e5934 , doi=10.7717/peerj.5934 , pmid=30498632 , pmc=6252067 {{cite book , last=Beebee , first=Trevor J. C. , year=1996 , title=Ecology and conservation of amphibians , publisher=Chapman and Hall , location=London , pages=16–17 , isbn=978-0-412-62410-0 {{cite journal , last1=Gosner , first1=Kenneth L. , title=A simplified table for staging anuran embryos and larvae with notes on identification , journal=Herpetologica , date=1960 , volume=16 , issue=3 , pages=183–190 , jstor=3890061 {{cite journal , last8=Wang , first8=Bin , last7=Liu , first7=Jing , last6=Jiang , first6=Jianping , last5=Fei , first5=Liang , last4=Cui , first4=Jianguo , last3=Xu , first3=Ning , last2=Wei , first2=Gang , last1=Li , first1=Shize , name-list-style=amp , title=A new species of the Asian music frog genus ''Nidirana'' (Amphibia, Anura, Ranidae) from Southwestern China , journal=PeerJ , date=2019 , volume=7 , pages=e7157 , doi=10.7717/peerj.7157 , doi-access=free {{cite book , last1=McDiarmid , first1=Roy W. , last2=Altig , first2=Ronald , name-list-style=amp , title=Tadpoles: The Biology of Anuran Larvae , url=https://books.google.com/books?id=77fPT1qk_9AC&pg=PA8 , year=1999 , publisher=University of Chicago Press , isbn=978-0-226-55762-5 , pages=8–11 {{cite journal , last1=Nodzenski , first1=Edwardine , last2=Inger , first2=Robert F. , name-list-style=amp , title=Uncoupling of related structural changes in metamorphosing torrent-dwelling tadpoles , journal=Copeia , date=1990 , volume=1990 , issue=4 , pages=1047–1054 , doi=10.2307/1446488 , jstor=1446488 {{Cite journal , authorlink1=Jodi Rowley , last1=Rowley , first1=Jodi J. L. , last2=Altig , first2=Ronald , name-list-style=amp , doi=10.1163/156853812X626179 , title=Nidicolous development in ''Limnonectes limborgi'' (Anura, Dicroglossidae) , journal=Amphibia-Reptilia , volume=33 , pages=145–149 , year=2012 {{cite web , url=http://www.virginiaherpetologicalsociety.com/amphibians/amphibian-development/amphibian-development.htm , title=Amphibian Development Charts , publisher=Virginia Herpetological Society , accessdate=16 July 2019 {{cite book , title=Herpetology: An Introductory Biology of Amphibians and Reptiles , edition=4th , first1=Laurie J. , last1=Vitt , first2=Janalee P. , last2=Caldwell , name-list-style=amp , publisher=Academic Press , year=2014 , pages=43–44

External links

Amphibian Development Charts
by the Virginia Herpetological Society—illustrated chart of Gosner stages. Frogs Vertebrate developmental biology