Eunectes, Wagler, 1830
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publication ID |
https://doi.org/ 10.3390/d16020127 |
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publication LSID |
lsid:zoobank.org:pub:A58A262E-2E07-48D3-B712-209CCDFFD038 |
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DOI |
https://doi.org/10.5281/zenodo.10684307 |
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persistent identifier |
https://treatment.plazi.org/id/F75ABC77-7570-B306-FE2E-2B71FCB8A6E1 |
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treatment provided by |
Diego |
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scientific name |
Eunectes |
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3.1.1. Eunectes View in CoL View at ENA Overview
The three-gene matrix counted 2939 bp, charset ND4 = 1–848; charset ND2 = 849–1863; and charset Cytb = 1864–2939, including 1015 bp of ND2, 848 bp of ND4, and 1076 bp of cytochrome Bfor 71 individuals (including outgroups Boa , Corallus , Epicrates ; Table S1 View Table 1 ). The concatenated alignment had 24.5% missing data, reflecting the inclusion of published sequence data for some but not all genes in favor of increasing phylogenetic accuracy by increasing taxonomic coverage [ 90] (coverage by taxon and gene summarized in Table S1 View Table 1 ). The BI consensus tree and ML tree had very similar topologies and therefore the BI tree is presented here ( Figure 2 View Figure 2 ; ML tree is presented in Figure S1 View Figure 1 ). Both methods confirm a sister-clade relationship between Green Anacondas, and a clade composed of the other three anaconda species as proposed by Dirksen [ 24].
3.1.2. Yellow Anaconda Phylogenetics and Taxonomy
Our analyses indicate a poorly defined phylogenetic structure in the clade composed of E. notaeus , E. deschauenseei , and E. beniensis . Although specimens identified as E. deschauenseei or E. beniensis are found in well-supported clades, those identified as E. notaeus are not, and instead represent a paraphyletic clade with E. deschauenseei and E. beniensis ( Figure 2 View Figure 2 ).
Comparisons were made to relate morphology to genetic placement. One of the snakes captured in the Bolivian Beni (B54) has markings that best fit the description of E. deschauenseei , as indicated by the height of the lateral flecks, which do not reach half the height of the snake, and the dorsal blotches separated by two or three scales ( Figure 3 View Figure 3 ). This specimen is recovered with other E. deschauenseei from French Guiana and Marajo Island in the phylogenetic analysis ( Figures 2 View Figure 2 and S 1 View Figure 1 ). In addition, other anacondas caught in Beni (B52 and B58) also had markings that best fit the description of E. deschauenseei , but these specimens were recovered with E. beniensis in the phylogenetic analysis ( Figures 2 View Figure 2 and 3 View Figure 3 ). For comparison, Figure 3 View Figure 3 also shows E. beniensis with a characteristic pattern of these lineages (larger lateral flecks), caught in Beni, that is recovered as E. beniensis in the tree ( Figure 2 View Figure 2 ). Therefore, our results challenge the validity of E. beniensis and E. deschauenseei as distinct species from E. notaeus .
Consistent with a previous study [ 23], we recovered the Yellow Anacondas as paraphyletic, with E. beniensis and E. deschauenseei nested within E. notaeus ( Figure 2 View Figure 2 ) and with shallow levels of divergence between the clades ( Table 3 View Table 3 ). Our sampled taxa included one from the Bolivian Beni that was both genetically and morphologically E. deschauenseei , despite being outside the known range of this species. In addition, two other anacondas from the Bolivian Beni had markings that would classify them as E. deschauenseei , while the phylogenetic analysis placed them within E. beniensis . Therefore, our results challenge the validity of the Yellow Anaconda being split into species.
3.1.3. Green Anaconda Phylogenetics and Taxonomy
Our analyses further identify two deeply divergent, highly supported sister clades of the Green Anaconda. One clade is composed of specimens sampled in the northern part of the E. murinus range; we find this clade in Ecuador, Venezuela, Trinidad, Guyana, Suriname, and French Guiana. It can be assumed that it is also present in Colombia. The other clade includes specimens from the southern part of South America, including Perú, Bolivia, French Guiana, and Brazil. Specimens of both clades are found in French Guiana, suggesting that this country may be a contact zone for these two groups ( Figure 2 View Figure 2 ). The northern and southern clades have levels of divergences much higher than those for the Yellow Anaconda variants ( Figure 2 View Figure 2 , Table 3 View Table 3 ). Our morphological data show that specimens from the northern and southern clades are indistinguishable morphologically ( Table 4 View Table 4 ). Irrespective of crypsis, our genetic data show that these two distinct lineages within Emurinus form well-supported deep clades, allowing the separation into two species based on their genetic divergence ( Tables 3 View Table 3 and S 2 View Table 2 , Figure 2 View Figure 2 ), temporal divergence ( Figure 4 View Figure 4 and Table 5 View Table 5 ), and branch length in both the Bayesian analysis and Maximum Likelihood trees ( Figures 2 View Figure 2 and S 1 View Figure 1 ). The high level of genetic divergence and geographic separation justifies the recognition of the northern population as a distinct species. Therefore, we propose the scientific name Eunectes akayima sp. Nov. (see Table 6 View Table 6 for holotype details, and Discussion Section 4.2 for the etymology and more in-depth considerations) and the common name Northern Green Anaconda.
Intriguingly, within both E. akayima and E. murinus , there are well-supported subclades with divergences at or above the level of the structures within the Yellow Anaconda clade. For the Southern Green Anaconda clade, further geographic structure is evident: one subclade is restricted to the east, around the Xingu river basin (eastern Brazil, in the states of Para, Mato Grosso, and Mato Grosso do Sul), and the other subclade extends from Peru and Bolivia to French Guiana, probably including the main channel of the Amazon River.
3.2. Divergence Time Estimation
The results of our multiple molecular clock analyses showed that the analysis based on paleontological information alone yielded slightly more recent splits than the other setups. On the other hand, the approach excluding the possibility of dispersal across Cretaceous land bridges gave older divergence times. Despite these minor differences, the ranges obtained from the different analyses were found to overlap to a large extent ( Figure 4 View Figure 4 , Table 5 View Table 5 ). Our estimate for the divergence of Eunectes from its sister lineage Epicrates is approximately 46–35 Mya (95% HPD: 66.58–28.40 to 45.41–23.98; Paleocene/Eocene), depending on the approach.
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