Rhinatrema bivittatum (Guérin-Méneville, 1838)
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Brazil, French Guiana, Guyana, Suriname
This species was featured in News of the Week November 27, 2023:
Amphibians are famous (or perhaps infamous) for their outsized genomes. Indeed, some salamanders have genomes up to 120 billion base pairs (120 GB) and, for comparison, the human genome is only 3 GB. Because large genomes are challenging to sequence, scientists have been slow to generate high-resolution genomes for amphibians. Recently Ovchinnikov et al. (2023) provided the second and third published high-resolution genomes for caecilians, specifically for Geotrypetes seraphini and Microcaecilia unicolor. By comparing the newly sequenced genomes with the first published caecilian genome (Rhinatrema bivittatum) and other vertebrate species, they made a number of interesting discoveries and observations. For example, the large genomes of caecilians are, not surprisingly, chock full of repeat sequences, which is typical of other taxa with extra-large genomes. However, whereas supersized salamander genomes are dominated by long terminal repeat (LTR) elements, those of caecilians are dominated by long interspersed elements (LINES), indicating that while both caecilians and salamanders have large genomes because of transposal elements (TEs) “gone wild”, this is not the result of failure to control a specific type of TE. Another finding is that the caecilian genomes have a large number of novel gene families (at least 1150) enriched for functions in olfaction and chemical signaling likely tied to their unique chemosensory tentacles as primary olfactory organs. Finally, the authors could find no evidence in caecilians of a developmental gene enhancer called ZRS that regulates the famous limb morphogenesis gene “Sonic Hedgehog”. Notably, snakes have been shown to have a mutant form of ZRS that, when inserted into mice, results in a limbless serpentized phenotype. The complete absence of the ZRS enhancer in caecilians implicates this gene in the convergent evolution of limblessness in caecilians and snakes. (Written by J McGuire)
Rhie A, McCarthy SA, Fedrigo O. et al. (2021). "Towards complete and error-free genome assemblies of all vertebrate species." Nature, 592, 737–746. [link]
Edited by: Michelle S. Koo (2023-11-26)
Species Account Citation: AmphibiaWeb 2023 Rhinatrema bivittatum <https://amphibiaweb.org/species/2016> University of California, Berkeley, CA, USA. Accessed Dec 2, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 2 Dec 2023.
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