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Nosy knowtrias

Also known as the nutria, the coypu (Myocastor coypus [Molina, 1782]), is a large amphibious rodent from about 5 to 7 kg (Woods et al. 1992). Native to South America, its range includes Argentina, Chile, Paraguay, Uruguay, as well as the southern parts of Bolivia and Brazil. It is associated with aquatic habitats and primarily feeds on vegetation along the river banks (Woods et al. 1992). Coypu shares some ecological adaptations with another amphibious species, the beaver (e.g., it can remain submerged for about 10 min!). The two species however are phylogenetically distant. The main external morphological difference between the beavers and the coypu is probably the tail that is flat in the formers.

Underwater picture of a wild coypu (Myocastor coypus) taken with an underwater camera trap. Photo by Quentin Martinez and Cécile Molinier.

In the late 19th and early 20th centuries, coypus have been exported for fur production to Europe, North America, Asia, and Africa. Due to accidental escapes and voluntary releases, the species is now considered as one of 100 of the world's worst invasive alien species (GISD 2021). At high densities, their burrows present along the river banks may impact the overall wetland ecosystems. The expansion of the coypu seems to be limited by the extreme temperature of cold winters. However with the overall global warming, some models predict a massive worldwide expansion of the species (Jarnevich et al. 2017).

We are still discovering new things about this species. As an example, recent evidence shows that the coypu may have reduced olfactory capabilities in comparison to its close terrestrial relatives (Martinez et al. 2020). Indeed, it was found that the relative size of their olfactory organs is reduced, including the loss of two olfactory turbinals, a nasal structure involved in olfaction. In order to investigate the olfactory question from a genomics perspective and test if there is a relation between the morphology and the genome (Martinez et al. 2023), today we release the chromosome-length assembly for the coypu Myocastor coypus.

The new genome assembly via Hi-C upgrade of a draft generated by combining Nanopore long reads with Illumina short reads, made by Marie-Ka Tilak, Quentin Martinez, Rémi Allio, Pierre-Henri Fabre and team from Institut des Sciences de l'Évolution de Montpellier (ISEM) and Université de Montpellier (UM).

This project was funded by l‘Agence Nationale de la Recherche (Défi des autres savoirs, Grant DS10, ANR-17-CE02-0005 RHINOGRAD 2017 granted to Pierre-Henri Fabre). We thank the other collaborators of this project: Cécile Molinier, Benoit de Thoisy and Vincent Goanec.

In accordance with the local program for pest management and in collaboration with Régis Gibert and Nathalie Vazzoler-Antoine the original sample comes from a wild Myocastor coypus (34130, Lansargues, France). The sample (QM1153) used fot assembly is now part of the ISEM collection. Browse the 20 chromosome-length scaffolds of the new assembly using the interactive map below!


GISD. Of the World's Worst Invasive Alien Species. Global Invasive Species Database. 100, (2021).

Jarnevich, C. S., Young, N. E., Sheffels, T. R., Carter, J., Sytsma, M. D., & Talbert, C. (2017). Evaluating simplistic methods to understand current distributions and forecast distribution changes under climate change scenarios: an example with coypu (Myocastor coypus). NeoBiota, 32(1), 107.

Martinez, Q., Clavel, J., Esselstyn, J. A., Achmadi, A. S., Grohé, C., Pirot, N., & Fabre, P. H. (2020). Convergent evolution of olfactory and thermoregulatory capacities in small amphibious mammals. Proceedings of the National Academy of Sciences, 117(16), 8958-8965.

Martinez Q, Courcelle M, Douzery E, Fabre PH. When morphology does not fit the genomes: the case of rodent olfaction. Biol Lett. 2023 Apr;19(4):20230080. doi: 10.1098/rsbl.2023.0080. Epub 2023 Apr 12. PMID: 37042683; PMCID: PMC10092080.


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