Short answer
The answer in plain English
A 2024 analysis found two deep geographic lineages among green anacondas and proposed the northern lineage as Eunectes akayima. The mitochondrial split is real in the sampled data, but the species conclusion remains debated. Critics questioned whether mitochondrial DNA, limited nuclear evidence, and the original description were sufficient. A follow-up addressed naming requirements, but it did not end the scientific disagreement.
Why it matters
What to understand
Northern and southern green anacondas can look nearly identical while carrying distinct maternal genetic histories. Researchers reported about 5.5% mitochondrial divergence and a broad north–south geographic pattern, then named the northern lineage Eunectes akayima. Other taxonomists challenged the evidence and nomenclature. The careful conclusion is that DNA revealed an important, old lineage; whether that lineage should be treated as a separate species depends on additional genetic, anatomical, ecological, and reproductive evidence.
Visual guide
How the pieces fit together
DNA found a boundary that eyes did not
Green anacondas from northern and southern South America are not conveniently color-coded. Their heavy bodies, olive patterning, high-set eyes, and aquatic habits look remarkably similar. That is why the proposed northern species is a case of hidden history rather than a newly noticed body shape.
Researchers compared genetic samples across the range previously assigned to one green-anaconda species. Their mitochondrial family trees separated the samples into two major geographic branches. Northern samples grouped together; southern samples formed another branch. The team reported roughly 5.5% divergence across the mitochondrial sequences it analyzed and proposed that the northern lineage be called Eunectes akayima.
That is strong evidence that the populations have different maternal histories. The argument begins—not ends—with what kind of biological boundary that history represents.
What mitochondrial DNA can reveal
Mitochondria are the energy-producing structures inside cells, and they carry a small genome of their own. In animals, mitochondrial DNA is usually inherited through the mother. Mutations accumulating through generations let researchers reconstruct maternal lineages.
This makes mitochondrial DNA useful for finding deep splits that external anatomy hides. If samples from distant northern rivers repeatedly cluster apart from southern samples, the pattern is difficult to dismiss as one unusual snake.
The geographic pattern also makes evolutionary sense. Rivers and wetlands connect anacondas, but changing river courses, uplands, dry regions, and drainage divides can isolate populations. Over long periods, separated maternal lineages can accumulate substantial differences while similar aquatic selection keeps the animals looking alike.
A cryptic species is a species that is difficult to distinguish from another by ordinary appearance. Genetics often reveals the first clue. It does not excuse researchers from asking what else the clue means.
Why one genetic branch is not automatically one species
Mitochondrial DNA represents one inherited history. The nuclear genome, which contains most genetic information, can tell a more complicated story. Populations may retain old mitochondrial branches while exchanging nuclear genes. Female movement can differ from male movement. A historical split can persist in mitochondria even when the populations still interbreed where they meet.
Species concepts also answer different questions. One approach emphasizes independently evolving lineages. Another asks whether populations exchange genes. Taxonomists may weigh genetic distance, diagnosable traits, geography, ecology, and reproductive isolation differently.
The original anaconda revision attracted criticism on both evidence and naming. Critics argued that the species claim relied too heavily on mitochondrial results, that the nuclear evidence did not establish the same clean separation, and that the initial diagnosis and name did not satisfy all formal requirements.
What the follow-up description fixed
The proponents published a detailed follow-up description in Diversity. It provided a formal diagnosis, addressed nomenclatural issues, discussed the geographic and evolutionary argument, and clarified the name Eunectes akayima.
That matters because zoological names follow rules. A recognizable lineage does not automatically receive an available scientific name. Authors must state distinguishing criteria and anchor the name in reference material so later researchers know what biological population it denotes.
Formal correction does not settle the broader species question by administrative force. It makes the proposed name usable under the relevant rules. Researchers can still disagree about whether the lineage deserves species rank and which evidence should decide.
This distinction appears throughout taxonomy. Our explanation of why scientists keep finding Amazon species follows the longer path from field and museum evidence to a diagnosis other specialists can test.
What would make the case stronger
Broader nuclear-genome sampling could show whether the same north–south split appears across many independently inherited regions. Dense sampling near the possible contact zone could reveal whether lineages overlap and exchange genes. Researchers can also test anatomy, scale counts, skull measurements, growth, habitat use, diet, and mating behavior for consistent differences.
None of those tests requires the snakes to look dramatically different. Stable combinations of subtle traits can diagnose species. Conversely, a large mitochondrial gap does not guarantee that two populations function as separate reproductive or ecological units.
Better sampling is particularly important for anacondas because they are hard to survey. Large ranges on a map can hide sparse samples, local structure, and enormous wetland systems that are difficult to reach.
Why the argument matters outside naming
A species name influences conservation assessments, distribution maps, permits, captive records, and which populations receive attention. Treating two lineages as one can hide a decline in the smaller range. Splitting too quickly can create false precision and divert limited conservation effort.
Local and Indigenous knowledge matters as well. The proposed name draws on a word associated with a great snake in Cariban languages, and Waorani collaborators helped field teams encounter and sample animals. Formal science may be newly describing a lineage that people living with the animals have long recognized in other ways.
The careful answer
DNA did reveal a deep, geographically structured divide among green anacondas. Calling the northern branch Eunectes akayima is a published and formally clarified taxonomic proposal.
It is still too simple to say that one percentage “proved” two species. The mitochondrial evidence is important, the name is available, and the taxonomic interpretation remains contested. That is not science failing to decide. It is science separating a solid observation—the lineage—from the harder question of what rank that lineage should receive.
