Eunectes

Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Infraclassis: Lepidosauromorpha
Superordo: Lepidosauria
Ordo: Squamata
Subordo: Serpentes
Superfamilia: Booidea

Familia: Boidae
Subfamilia: Boinae
Genus: Eunectes
Species (4): E. beniensis - E. deschauenseei - E. murinus - E. notaeus

Name

Eunectes Wagler, 1830
Synonymy

Maxhoserboa Hoser, 2012

References

Hsiou, A.S.; Albino, A.M. 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 Reference page.

Links

Eunectes at the New Reptile Database. Accessed on 8 Mar 2008.

Vernacular names
Deutsch: Anakondas
English: Anacondas
español: Anaconda
suomi: Anakondat
français: Anaconda
italiano: Anaconda
日本語: アナコンダ属
македонски: Анаконди
Nederlands: Anaconda
norsk: Anakonda
português: Anaconda
svenska: Anakonda
ไทย: งูอนาคอนดา
中文: 水蚺屬

Eunectes is a genus of boas found in tropical South America. 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]

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, caimans, and capybaras. Some accounts exist of anacondas preying on domestic animals such as goats and sometimes even jaguars[5] 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 set in the Amazon jungle. Anacondas have also figured prominently in South American folklore, where they are sometimes depicted as shapeshifting mythical creatures called encantados. 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.[6]
Species
Yellow anaconda
The green anaconda (Eunectes murinus) has been used for many commercially successful films as a deadly creature.
Bolivian anaconda
Species Taxon author Subspecies

other than nominate[3]
Common name Geographic range
E. beniensisEunectes beniensis, Rio Beni, Puerto Salinas, El Beni, Bolivia.jpg Dirksen, 2002[7] 0 Bolivian anaconda South America in the Departments of Beni and Pando in Bolivia.
E. deschauenseei Dunn and Conant, 1936[3] 0 Dark-spotted anaconda South America in northeastern Brazil and coastal French Guiana.[2]
E. murinusEunectes murinus2.jpg (Linnaeus, 1758)[3] 1 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. notaeusAnaconda jaune 34.JPG Cope, 1862[3] 0 Yellow anaconda South America in eastern Bolivia, southern Brazil, Paraguay and northeastern Argentina.[2]
†E. stirtoni Hoffstetter and Rage, 1977[8] 0 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.[9][10] 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 much less well understood.[9]
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).[10][11] 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.[12] 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.[12] 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.[12]
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.[11][12][13][14] 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.[11] 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.[11] 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.[11][12]
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.[15] 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.[9][15]
Asexual reproduction

Although sexual reproduction is by far the most common in Eunectes, E. murinus has been observed to undergo facultative parthenogenesis.[9][16] 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.
References

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.
McDiarmid, R. W.; Campbell, J. A.; Toure, T. (1999). Snake Species of the World: A Taxonomic and Geographic Reference. 1. Washington, District of Columbia: Herpetologists' League. ISBN 1893777014.
"Eunectes". Integrated Taxonomic Information System. Retrieved 18 July 2008.
Eunectes beniensis at the Reptarium.cz Reptile Database. Accessed 12 December 2008.
Rivas, Jesús. "Frequently Asked Questions". Archived from the original on 21 December 2016. Retrieved 30 July 2012.
Rivas, Jesús. "Life history and conservation of the green anaconda (Eunectes murinus)". Archived from the original on 6 March 2018. Retrieved 30 July 2012.
Dirksen, Lutz (2002). Anakondas. Monographische Revision der Gattung Eunectes (Wagler, 1830) (in German). Münster: Natur und Tier-Verlag. ISBN 3-931587-43-6.
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.
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.
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.
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 978-0972015431.
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.
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 978-0972015431.
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.
De la Quintana, Paola; Pacheco, Luis; Rivas, Jesús (January 2011). "Eunectes beniensis (Beni Anaconda). Diet: Cannibalism". Herpetological Review. 42 (4): 614.

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.