Eunectes
Temporal range: Miocene–recent[1]
Green anaconda (E. murinus)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Boidae
Subfamily: Boinae
Genus: Eunectes
Wagler, 1830[2]
Type species
Boa murina
Range of Eunectes
Synonyms

Eunectes is a genus of boas found in tropical South America commonly called anacondas. They are a semiaquatic group of snakes and include one of the largest snakes in the world, E. murinus, the green anaconda. Four species are currently recognized.[3][4]

Origin

The recent fossil record of Eunectes is relatively sparse compared to other vertebrates and other genera of snakes. The fossil record of this group is effected by an artifact called the Pull of the Recent.[5] Fossils of recent ancestors are not known, so the living species 'pull' the historical range of the genus to the present.

Etymology

The name Eunectes is derived from Ancient Greek: εὐνήκτης, romanized: eunēktēs, lit. 'good swimmer'.

Distribution and habitat

Found in tropical South America from Ecuador, Brazil, Colombia and Venezuela south to Argentina.[2]

Feeding

All four species are aquatic snakes that prey on other aquatic animals, including fish, river fowl, and caiman. Videos exist of anacondas preying on domestic animals such as goats and sometimes even jaguars[6] that venture too close to the water.

Relationship with humans

While encounters between people and anacondas may be dangerous, they do not regularly hunt humans. Nevertheless, threat from anacondas is a familiar trope in comics, movies, and adventure stories (often published in pulp magazines or adventure magazines) set in the Amazon jungle. Local communities and some European explorers have given accounts of giant anacondas, legendary snakes of much greater proportion than any confirmed specimen.

Although charismatic, there is little known on the biology of wild anacondas. Most of our knowledge comes from the work of Dr. Jesús A. Rivas and his team working in the Venezuelan Llanos.[7]

Species

Species Taxon author Common name Geographic range Image
E. beniensis Dirksen, 2002[8] Bolivian anaconda South America in the Departments of Beni and Pando in Bolivia
E. deschauenseei Dunn and Conant, 1936[3] Dark-spotted anaconda South America in northeastern Brazil and coastal French Guiana[2]
E. murinus (Linnaeus, 1758)[3] Green anaconda South America in countries east of the Andes, including Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil and on the island of Trinidad[2]
E. notaeus Cope, 1862[3] Yellow anaconda South America in eastern Bolivia, southern Brazil, Paraguay and northeastern Argentina[2]
†E. stirtoni Hoffstetter and Rage, 1977[9] This species is extinct; its fossils have been found in the La Venta fauna (Miocene) in Colombia. Its validity, however, is questionable.

Mating system

The mating seasons in Eunectes varies both between species and within species depending on locality, although the trend appears to be the dry season.[10][11] The green anaconda (E. murinus) is the most well-studied species of Eunectes in terms of their mating system, followed by the yellow anaconda (E. notaeus); unfortunately E. deschauenseei and E. beniensis are much less common, making the specific details of their mating systems less well understood.[10]

Sexual dimorphism

Sexual size dimorphism in Eunectes is the opposite of most other vertebrates. Females are larger than males in most snakes, and green anacondas (E. murinus) have one of the most extreme size differences, where females average roughly 32 kg (70 lb) and males average only around 7 kg (15 lb).[11][12] This size difference has several benefits for both sexes. Large size in females leads to higher fecundity and larger offspring; as a result male mate choice favours larger females.[13] Large size is also favoured in males because larger males tend to be more successful at reproducing, both because of their size advantage in endurance rivalry and their advantage in sperm competition because larger males are able to produce more sperm.[13] One reason that males are so much smaller in Eunectes is that large males can be confused for females, which interferes with their ability to mate when smaller males mistakenly coil them in breeding balls; as a result, there is an optimum size for males where they are large enough to successfully compete, but not large enough to risk other males trying to mate with them.[13]

Breeding balls

During the mating season female anacondas release pheromones to attract males for breeding, which can result in polyandrous breeding balls; these breeding balls have been observed in E. murinus, E. notaeus, and E. deschauenseei, and likely also occur in E. beniensis.[12][13][14][15] In the green anaconda (E. murinus), up to 13 males have been observed in a breeding ball, which have been recorded to last two weeks on average.[12] In anaconda breeding balls, several males coil around one female and attempt to position themselves as close to her cloaca as possible where they use their pelvic spurs to "tickle" and encourage her to allow penetration.[12] Since there are often many males present and only one male can mate with the female at a time, the success of a male often depends on his persistence and endurance, because physical combat is not a part of the Eunectes mating ritual, apart from firmly pushing against other males in an attempt to secure the best position on the female.[12][13]

Sexual cannibalism

4.5-metre (14 ft) green anaconda skeleton on display at Museum of Osteology with other squamates and reptiles.

Cannibalism is quite easy in anacondas since females are so much larger than males, but sexual cannibalism has only been confirmed in E. murinus.[16] Females gain the direct benefit of a post-copulatory high-protein meal when they consume their mates, along with the indirect benefit of additional resources to use for the formation of offspring; cannibalism in general (outside of the breeding season) has been confirmed in all but E. deschauenseei, although it is likely that it occurs in all Eunectes species.[10][16]

Asexual reproduction

Although sexual reproduction is by far the most common in Eunectes, E. murinus has been observed to undergo facultative parthenogenesis.[10][17] In both cases, the females had lived in isolation from other anacondas for over eight years, and DNA analysis showed that the few fully formed offspring were genetically identical to the mothers; although this is not commonly observed, it is likely possible in all species of Eunectes and several other species of Boidae.

Indigenous mythology

According to the founding myth of the Huni Kuin, a man named Yube fell in love with an anaconda woman and was turned into an anaconda as well. He began to live with her in the deep world of waters. In this world, Yube discovered a hallucinogenic drink with healing powers and access to knowledge. One day, without telling his anaconda wife, Yube decided to return to the land of men and resume his old human form. The myth also explains the origin of cipó or ayahuasca — a hallucinogenic drink taken ritualistically by the Huni Kuin.[18][19][20]

References

  1. ↑ Hsiou, Annie S.; Albino, Adriana M. (1 December 2009). "Presence of the genus Eunectes (Serpentes, Boidae) in the Neogene of Southwestern Amazonia, Brazil". Journal of Herpetology. 43 (4): 612–619. doi:10.1670/08-295.1. S2CID 55097666.
  2. 1 2 3 4 5 6 McDiarmid, R. W.; Campbell, J. A.; Toure, T. (1999). Snake Species of the World: A Taxonomic and Geographic Reference. Vol. 1. Washington, District of Columbia: Herpetologists' League. ISBN 1-893777-01-4.
  3. 1 2 3 4 "Eunectes". Integrated Taxonomic Information System. Retrieved 18 July 2008.
  4. ↑ Eunectes beniensis at the Reptarium.cz Reptile Database. Accessed 12 December 2008.
  5. ↑ Sahney, Sarda; Benton, Michael (2017). "The impact of the Pull of the Recent on the fossil record of tetrapods" (PDF). Evolutionary Ecology Research. 18: 7–23.
  6. ↑ Rivas, Jesús. "Frequently Asked Questions". Archived from the original on 21 December 2016. Retrieved 30 July 2012.
  7. ↑ Rivas, Jesús. "Life history and conservation of the green anaconda (Eunectes murinus)". Archived from the original on 6 March 2018. Retrieved 30 July 2012.
  8. ↑ Dirksen, Lutz (2002). Anakondas. Monographische Revision der Gattung Eunectes (Wagler, 1830) (in German). Münster: Natur und Tier-Verlag. ISBN 3-931587-43-6.
  9. ↑ Hoffstetter, R.; Rage, J. C. (1977). "Le gisement de vertébrés miocènes de La Venta (Colombie) et sa faune de serpents". Annales de Paléontologie (Vertébrés) (in French). 63: 161–190.
  10. 1 2 3 4 Reed, Robert N.; Rodda, Gordon H. (2009). Giant constrictors: Biological and management profiles and an establishment risk assessment for nine large species of pythons, anacondas, and the boa constrictor. U.S. Geological Survey Open-File Report 2009-1202. Reston, Virginia: U.S. Geological Survey.
  11. 1 2 Pizzatto, Lígia; Marques, Otavio A. V. (2007). "Reproductive ecology of Boine snakes with emphasis on Brazilian species and a comparison to Pythons". South American Journal of Herpetology. 2 (2): 107–122. doi:10.2994/1808-9798(2007)2[107:reobsw]2.0.co;2. S2CID 86033920.
  12. 1 2 3 4 5 Rivas, Jesús A.; Muñoz, M. C.; Burghardt, G. M.; Thorbjarnarson, J. B. (2007). "Sexual size dimorphism and the mating system of the green anaconda (Eunectes murinus)". In Henderson, Robert W.; Powell, Robert (eds.). Biology of the Boas and Pythons. Eagle Mountain, Utah: Eagle Mountain Publishing. pp. 461–473. ISBN 978-0-9720154-3-1.
  13. 1 2 3 4 5 Rivas, Jesús A.; Burghardt, Gordon M. (2001). "Understanding sexual size dimorphism in snakes: wearing the snake's shoes". Animal Behaviour. 62 (3): F1–F6. doi:10.1006/anbe.2001.1755. S2CID 5374924.
  14. ↑ Waller, T.; Micucci, P. A.; Alvarenga, E. (2007). "Conservation biology of the yellow anaconda (Eunectes notaeus) in Northeastern Argentina". In Henderson, Robert W.; Powell, Robert (eds.). Biology of the Boas and Pythons. Eagle Mountain, Utah: Eagle Mountain Publishing. pp. 340–362. ISBN 978-0-9720154-3-1.
  15. ↑ Rivas, Jesús A.; Burghardt, Gordon M. (2005). "Snake mating systems, behavior, and evolution: The revisionary implications of recent findings". Journal of Comparative Psychology. 119 (4): 447–454. doi:10.1037/0735-7036.119.4.447. PMID 16366778.
  16. 1 2 De la Quintana, Paola; Pacheco, Luis; Rivas, Jesús (January 2011). "Eunectes beniensis (Beni Anaconda). Diet: Cannibalism". Herpetological Review. 42 (4): 614.
  17. ↑ Shibata, Hiroki; Sakata, Shuichi; Hirano, Yuzo; Nitasaka, Eiji; Sakabe, Ai (2017). "Facultative parthenogenesis validated by DNA analyses in the green anaconda (Eunectes murinus)". PLOS ONE. 12 (12): e0189654. Bibcode:2017PLoSO..1289654S. doi:10.1371/journal.pone.0189654. PMC 5728508. PMID 29236745.
  18. ↑ As visões da anaconda: a narrativa escrita indígena no Brasil. Por Lynn Mario T. Menezes de Souza. Revista Semear n°7
  19. ↑ O que nos diz a arte Kaxinawa sobre a relação entre identidade e alteridade? Por Elsje Maria Lagrou. Mana vol. 8 n°1 Rio de Janeiro abril de 2002 ISSN 0104-9313.
  20. ↑ Eliane Camargo (1999). "Yube, o homem-sucuriju: Relato caxinauá" (PDF). Amerindia (in Portuguese). No. 24. Archived from the original (PDF) on 31 January 2005. Retrieved 17 June 2018.

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