Editing Anaconda (section)

==Mating system==
[[File:Eunectes murinus - Flickr - Dick Culbert.jpg|thumb|upright=1.2|''Eunectes murinus''{{dubious|date=March 2024}} in Colombia]]

The mating seasons in ''Eunectes'' varies both between species and within species depending on locality, although the trend appears to be the dry season.<ref name="ReedRodda">{{cite book|last1=Reed|first1=Robert N.|last2=Rodda|first2=Gordon H.|title=Giant constrictors: Biological and management profiles and an establishment risk assessment for nine large species of pythons, anacondas, and the boa constrictor|series=U.S. Geological Survey Open-File Report 2009-1202|publisher=U.S. Geological Survey|location=Reston, Virginia|year=2009|url=https://www.researchgate.net/publication/259932038}}</ref><ref name=Pizzatto>{{Cite journal |last1=Pizzatto |first1=Lígia |last2=Marques |first2=Otavio A. V. |date=2007 |title=Reproductive ecology of Boine snakes with emphasis on Brazilian species and a comparison to Pythons |journal=South American Journal of Herpetology |volume=2 |issue=2 |pages=107–122 |doi=10.2994/1808-9798(2007)2[107:reobsw]2.0.co;2|s2cid=86033920 }}</ref> The green anaconda ''([[Green anaconda|E. murinus]])'' is the most well-studied species of ''Eunectes'' in terms of their mating system, followed by the yellow anaconda ''([[Yellow anaconda|E. notaeus]])''; unfortunately ''[[Eunectes deschauenseei|E. deschauenseei]]'' and ''[[Eunectes beniensis|E. beniensis]]'' are much less common, making the specific details of their mating systems less well understood.<ref name="ReedRodda" />

===Sexual dimorphism===
[[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 ''([[Eunectes murinus|E. murinus]])'' have one of the most extreme size differences, where females average roughly {{convert|32|kg|lb|-1|abbr=on}} and males average only around {{convert|7|kg|lb|abbr=on}}.<ref name="Pizzatto" /><ref name="Rivas_etal_2007">{{cite book|last1=Rivas|first1=Jesús A.|last2=Muñoz|first2=M. C.|last3=Burghardt|first3=G. M.|last4=Thorbjarnarson|first4=J. B.|chapter=Sexual size dimorphism and the mating system of the green anaconda (''Eunectes murinus'')|pages=461–473|title=Biology of the Boas and Pythons|year=2007|editor-last1=Henderson|editor-first1=Robert W.|editor-last2=Powell|editor-first2=Robert|location=Eagle Mountain, Utah|publisher=Eagle Mountain Publishing|isbn=978-0-9720154-3-1}}</ref> 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.<ref name="Rivas2001">{{Cite journal |last1=Rivas |first1=Jesús A. |last2=Burghardt |first2=Gordon M. |date=2001 |title=Understanding sexual size dimorphism in snakes: wearing the snake's shoes |journal=Animal Behaviour |volume=62 |issue=3 |pages=F1–F6 |doi=10.1006/anbe.2001.1755|s2cid=5374924 }}</ref> 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.<ref name="Rivas2001" /> 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.<ref name="Rivas2001" />

===Breeding balls===
During the mating season female anacondas release pheromones to attract males for breeding, which can result in [[Polyandry in nature|polyandrous]] breeding balls; these breeding balls have been observed in ''[[Green anaconda|E. murinus]]'', ''[[Yellow anaconda|E. notaeus]]'', and ''[[Eunectes deschauenseei|E. deschauenseei]]'', and likely also occur in ''[[Eunectes beniensis|E. beniensis]]''.<ref name="Rivas_etal_2007" /><ref name="Rivas2001" /><ref name="Waller2007">{{cite book|last1=Waller|first1=T.|last2=Micucci|first2=P. A.|last3=Alvarenga|first3=E.|chapter=Conservation biology of the yellow anaconda (''Eunectes notaeus'') in Northeastern Argentina|pages=340–362|title=Biology of the Boas and Pythons|year=2007|editor-last1=Henderson|editor-first1=Robert W.|editor-last2=Powell|editor-first2=Robert|location=Eagle Mountain, Utah|publisher=Eagle Mountain Publishing|isbn=978-0-9720154-3-1}}</ref><ref name="Rivas2005">{{Cite journal |last1=Rivas |first1=Jesús A. |last2=Burghardt |first2=Gordon M. |date=2005 |title=Snake mating systems, behavior, and evolution: The revisionary implications of recent findings |journal=Journal of Comparative Psychology |volume=119 |issue=4 |pages=447–454 |doi=10.1037/0735-7036.119.4.447 |pmid=16366778}}</ref> 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.<ref name="Rivas_etal_2007" /> 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 spur]]s to "tickle" and encourage her to allow penetration.<ref name="Rivas_etal_2007" /> 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.<ref name="Rivas_etal_2007" /><ref name="Rivas2001" />

===Sexual cannibalism===
[[File:Anaconda and Squamata skeletons.jpg|thumb|{{convert|14|ft|m|round=0.5|adj=on|order=flip}} green anaconda skeleton on display at [[Museum of Osteology]] with other [[Squamata|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 ''[[Green anaconda|E. murinus]]''.<ref name="Quintana">{{cite journal | last1 = De la Quintana | first1 = Paola | last2 = Pacheco | first2 = Luis | last3 = Rivas | first3 = Jesús | title = ''Eunectes beniensis'' (Beni Anaconda). Diet: Cannibalism |date=January 2011 | url = https://www.researchgate.net/publication/274698904 | journal = Herpetological Review | volume = 42 | issue = 4| page = 614 }}</ref> 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 ''[[Eunectes deschauenseei|E. deschauenseei]]'', although it is likely that it occurs in all ''Eunectes'' species.<ref name="ReedRodda" /><ref name="Quintana" />

===Asexual reproduction===
Although sexual reproduction is by far the most common in ''Eunectes'', ''[[Green anaconda|E. murinus]]'' has been observed to undergo [[Parthenogenesis in squamata|facultative parthenogenesis]].<ref name="ReedRodda" /><ref name="Shibata">{{Cite journal |last1=Shibata |first1=Hiroki |last2=Sakata |first2=Shuichi |last3=Hirano |first3=Yuzo |last4=Nitasaka |first4=Eiji |last5=Sakabe |first5=Ai |date=2017 |title=Facultative parthenogenesis validated by DNA analyses in the green anaconda (''Eunectes murinus'') |journal=PLOS ONE |volume=12 |issue=12 |pages=e0189654 |doi=10.1371/journal.pone.0189654 |pmc=5728508 |pmid=29236745|bibcode=2017PLoSO..1289654S |doi-access=free }}</ref> 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]].