EUNECTES NOTAEUS PDF

Yellow anacondas occur in southern South America, including Paraguay, southern Brazil, northeastern Argentina, and Bolivia. Burton, Yellow anacondas can be found in swamps and marshlands with slow-moving rivers or streams. They can also be observed in forests searching for large game, such as brocket deer or peccaries.

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Yellow anacondas Eunectes notaeus are large, semiaquatic boid snakes found in wetland systems in South America. These snakes are commercially harvested under a sustainable management plan in Argentina, so information regarding population structuring can be helpful for determination of management units. We evaluated genetic structure and migration using partial sequences from the mitochondrial control region and mitochondrial genes cyt- b and ND4 for samples collected within northern Argentina.

A group of landscape features and environmental variables including several treatments of temperature and precipitation were explored as potential drivers of observed genetic patterns. We found significant population structure between most putative population comparisons and bidirectional but asymmetric migration in several cases.

The configuration of rivers and wetlands was found to be significantly associated with yellow anaconda population structure IBD , and important for gene flow, although genetic distances were not significantly correlated with the environmental variables used here. More in-depth analyses of environmental data may be needed to fully understand the importance of environmental conditions on population structure and migration.

These analyses indicate that our putative populations are demographically distinct and should be treated as such in Argentina's management plan for the harvesting of yellow anacondas.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The Alfred P. Sloan Foundation funded laboratory work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist. Genetic data offer high resolution and power for evaluating population structure and dispersal patterns, which is especially useful in species that are difficult to find or observe such as yellow anacondas. Combined with landscape information, genetic approaches can increase our understanding of spatial, environmental and even ecological constraints to dispersal.

Yellow anacondas in northern Argentina are good candidates for these types of landscape genetics studies as they are found in a heterogeneous environment, with presumably limited opportunities for dispersal between populations [1].

They require wet, swampy habitats, and as such can mainly disperse along rivers and floodplains and their associated vegetative habitats [1] , [2]. Several mechanisms have been proposed for the formation of spatial genetic structuring; these mechanisms may act individually as main drivers or act in concert. Gene flow between populations might simply be limited due to the physical distance between groups, creating a spatial genetic pattern known as isolation by distance IBD [3].

Instead or in addition to IBD, environmental variables such as temperature, precipitation, etc. Furthermore, landscape features such as presence and directionality of rivers both present and historic can contribute to our understanding of relationships between populations [5] — [8]. By jointly evaluating the spatial patterns of genetic structure and magnitude and directionality of gene flow between yellow anaconda populations in this heterogeneous area, we can better understand factors influencing dispersal in these and possibly other large semiaquatic snakes.

Eunectes notaeus is a commercially-important species that was heavily exploited for their valuable skins until the late s [2]. In , a sustainable harvest plan for yellow anacondas was initiated in the province of Formosa, Argentina, to reconcile the traditional hunting of this species with its long term conservation [2] , [10]. In this context, evaluating for population structure in northern Argentina is important for identifying potential management units and priority areas for conservation [11] — [13].

A previous study by Mendez et al. This study, however, was conducted with relatively small sample sizes and only two genetic markers ND4 and cyt -b , with a resulting low degree of resolution. The current study aims to carry out a more detailed evaluation of population structure and connectivity in relation to presumably relevant habitat features, as well as estimating effective migration rates between anaconda groups in northern Argentina. Understanding the connections and movement between these populations will increase our knowledge about the species'ecology and demography and some of the environmental or ecological drivers of population structuring.

This, in turn, will be helpful for the sustainable harvesting and management of yellow anacondas in Argentina [2]. Yellow anacondas occur from the Pantanal region in Brazil and Bolivia, throughout Paraguay, to northeastern Argentina. Our study area encompasses the Argentinean portion of the species range, in the Formosa and Corrientes provinces Figure 1.

Both the Pilcomayo and Bermejo rivers flow to the southeast, while the Paraguay flows to the south. Study area and distribution of sampling sites with putative population assignments shown as colored polygons. Arrows represent directionality of flow of adjacent river. In order to evaluate the genetic structure of yellow anacondas in our study area, we grouped sampling sites into five putative populations based on environmental factors. In defining our populations we considered extensive dry areas as barriers to dispersal of Eunectes notaeus and continuous wetland systems as areas where gene flow is not prevented other than by geographical distance.

We also considered the different habitat types and wetland systems as possible isolating factors, as described below. Highly suitable habitats for Eunectes notaeus exist in Formosa Province. Most of them are the palm and wetland savannas of the Humid Chaco ecoregion [2] , [15] , the prevalent habitat types for populations Formosa SE and Formosa N. The putative population Formosa PR is found on the eastern limit of Formosa Province on the Paraguay River, an island and delta type ecosystem that is characterized by an extensive floodplain covered by riparian forests and oxbow lagoons [10] , [15].

This highly seasonal marsh is characterized by the presence of palms mixed with dead forest patches covered by climbing vegetation, and is flooded during the local summer, after which it progressively dries out until ninety percent of the land is again visible [10].

Multiple possible mechanisms of isolation were considered in the assignment of our five putative populations. Generally, Formosa SE and Corrientes E are not strongly connected to the large river systems but are found in relatively isolated wetland systems that behave independently and are modulated by local rains.

Within the riverine populations, Formosa N is an interconnected system of wetlands strongly influenced by the Pilcomayo River running down from the Andes. Formosa PR is closely associated with the Paraguay River that is mainly modulated by the Pantanal in Brazil, while Corrientes W receives the effects of both the Paraguay and Parana rivers. The difference in timing of flooding between these rivers may lead to temporal isolation of these habitat areas.

Finally, Corrientes W occurs far downstream of the other populations at the southern edge of the species range, where significant stretches of unsuitable habitat between populations are expected to occur. Yellow anacondas are abundant in these areas of northern Argentina, and are most easily found during winter when they emerge from water to bask [10].

Although elevation does not seem to be an important factor in the study area, as the entire region lies below meters above sea level, the presence of dry sectors between wetlands are expected to significantly affect dispersal and gene flow in this semiaquatic species. However, short seasonal movements of a few hundred meters over dry areas between adjacent wetlands are common, particularly during the dry season T. Waller, personal observation. Blood samples were obtained from yellow anacondas from 36 sampling sites within Formosa Province and Corrientes Province Fig 1 and exported under CITES permit numbers , , and Partial sequences of the mitochondrial genes cyt- b and ND4 were amplified and sequenced using primers and methods as described in Mendez et al.

Because the mitochondrial control region has been duplicated in Eunectes notaeus [17] , we designed primers to target and amplify only one of these regions for our analysis. DNAsp 5. We first visualized the overall structure of the genetic data and potential spatial patterns of genetic diversity through the construction of haplotype networks.

We used networks to visualize such relationships as they are more appropriate than trees at depicting data in which ancestral haplotypes are still present [23] , [24].

Median-joining networks [25] were created using the software Network 4. Fixation indices were tested for significance using 10, permutations of the data. We further evaluated structure using the exact test of population differentiation [29] , [30] in Arlequin with one million steps in the Markov chain and , dememorization steps. We did not apply a correction for multiple tests to significance levels [31] , [32].

We were particularly interested in the potential mechanisms that may cause the observed genetic structure and gene flow. As a first approach to this question, we evaluated the importance of a suite of spatial and environmental variables to the observed genetic patterns.

We evaluated the plausibility of a pattern of IBD for the arrangement of populations in our study using a regression of standardized fixation index i. First, polygons were drawn to represent putative populations by connecting the fewest number of sampling sites that bounded all sites within the populations, and centroids of the polygons calculated in ArcMap 9. Geographic distances between populations were first calculated as straight-line distance between centroids.

Alternatively, along-river distance was calculated as the shortest distance from centroid to a major river, and following a simplified river path to the next centroid. For tests of IBD, straight-line distance was log transformed while along-river distance was treated as a linear habitat and untransformed, as suggested by Rousset [33].

Regression analyses and Mantel tests [34] were performed using , randomizations of the data in the program Isolation by Distance 1. We also evaluated the plausibility of patterns of IBED, where some environmental variables would better explain the genetic distance patterns [4]. Worldclim data 1 km resolution [36] was used to represent the following suite of relevant climatic variables: average monthly precipitation, driest month average precipitation, whole-year mean temperature, coldest-month mean temperature, and coldest three months mean minimum temperature.

These environmental variables were tested for correlation to genetic distances between populations while controlling for the effect of spatial distance by conducting partial Mantel tests [37] with , randomizations in Isolation by Distance 1.

To complement this approach, we evaluated the possibility of asymmetric gene flow in the study area, as this information may enhance our understanding of the relative roles of the rivers and associated areas in mediating gene flow for this species.

We adopted a migration matrix model allowing for asymmetric migration rates between populations and variable subpopulation sizes. We ran five replicates of a Markov chain scheme to produce initial values for our parameter estimation. Here, our data was tested with default starting values for the population size and M parameters, in 5 independent runs of the Markov chain scheme: 20 short chains dememorization: 10, genealogies, recorded genealogies: , sampling increment: , and 3 long chains dememorization: 10, genealogies, recorded genealogies: 25,, sampling increment: Using as initial parameters the consistent resulting values from these five initial runs, we launched three series of longer Markov chain schemes to estimate our parameters of interest.

In the first series s1 , we launched in parallel 10 runs with 10 independent replicates each of the following Markov chain scheme: 15 short chains dememorization: 10, genealogies, recorded genealogies: , sampling increment: , and 5 long chains dememorization: 10, genealogies, recorded genealogies: 25,, sampling increment: The second series s2 was a run consisting of independent replicates of the same Markov chain scheme and starting parameter set.

The third series s3 was another run with replicates of the same Markov chain scheme and increased starting M values all initial M values multiplied by , to ensure a wider exploration of the parameter space.

For the first series we report the average results of the 10 individual runs and the frequency of runs that resulted in non-zero M values, to illustrate the relative importance of individual runs.

For the second and third series we simply report the resulting final matrices, each with the likelihood-weighted mean pairwise population size and bi-directional M values for each of their replicates. A total of bp for cyt- b and bp for ND4 were sequenced for individuals. Control region sequences of bp were obtained for individuals.

Full three-gene concatenated sequences of 1, bp were assembled for individuals. A total of 36 haplotypes were present yielding a haplotype diversity of 0. All putative populations contained unique haplotypes.

A cyt- b and ND4 concatenated network with individuals bp. B control region network representing individuals bp. C concatenated cyt- b , ND4, and control region median-joining network for individuals 1, bp.

Distances between haplotypes are proportional to number of mutations and are measured from the edge of each circle for all networks.

Size of circle indicates relative abundance of haplotype. The second and third series were almost identical qualitatively, with the third series displaying two additional non-zero pairwise M values as a result of the larger initial parameters.

Our analysis revealed clear evidence of spatial structure of yellow anacondas in the study area. Interestingly, as we detail below, such structure cannot be fully explained by simple spatial patterns but rather by a combination of spatial, environmental, and ecological factors.

Most putative population comparisons showed very strong population structuring, which is likely a result of the relative autonomy of the different wetland systems in our study area and also the absence of suitable habitat between populations throughout the wide latitudinal gradient they occupy. Comparisons of genetic structuring with other large semiaquatic snakes are difficult due to lack of published genetic studies in large snakes.

Lower levels of population structuring were found in studies of the closely-related Argentine boa constrictor, Boa constrictor occidentalis [39] , [40] , where the authors also found evidence for sex-biased dispersal.

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Yellow anacondas Eunectes notaeus are large, semiaquatic boid snakes found in wetland systems in South America. These snakes are commercially harvested under a sustainable management plan in Argentina, so information regarding population structuring can be helpful for determination of management units. We evaluated genetic structure and migration using partial sequences from the mitochondrial control region and mitochondrial genes cyt- b and ND4 for samples collected within northern Argentina. A group of landscape features and environmental variables including several treatments of temperature and precipitation were explored as potential drivers of observed genetic patterns. We found significant population structure between most putative population comparisons and bidirectional but asymmetric migration in several cases. The configuration of rivers and wetlands was found to be significantly associated with yellow anaconda population structure IBD , and important for gene flow, although genetic distances were not significantly correlated with the environmental variables used here. More in-depth analyses of environmental data may be needed to fully understand the importance of environmental conditions on population structure and migration.

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Yellow anacondas Eunectes notaeus are large, semiaquatic boid snakes found in wetland systems in South America. These snakes are commercially harvested under a sustainable management plan in Argentina, so information regarding population structuring can be helpful for determination of management units. We evaluated genetic structure and migration using partial sequences from the mitochondrial control region and mitochondrial genes cyt- b and ND4 for samples collected within northern Argentina. A group of landscape features and environmental variables including several treatments of temperature and precipitation were explored as potential drivers of observed genetic patterns. We found significant population structure between most putative population comparisons and bidirectional but asymmetric migration in several cases. The configuration of rivers and wetlands was found to be significantly associated with yellow anaconda population structure IBD , and important for gene flow, although genetic distances were not significantly correlated with the environmental variables used here.

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The yellow anaconda Eunectes notaeus , also known as the Paraguayan anaconda [1] is a boa species endemic to southern South America. It is one of the largest snakes in the world but smaller than its close relative, the green anaconda. Like all boas and pythons , it is non-venomous and kills its prey by constriction. No subspecies are currently recognized. In distinguishing his new species Eunectes notaeus from Eunectes murinus , Edward Drinker Cope stated, "Dorsal scales are larger and in fewer rows. Adults grow to an average of 3. Females are generally larger than males, [3] and have been reported up to 4.

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