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Some of the most venomous snakes in the world like cobras, mambas, coral snakes and sea snakes evolved in Asia and then spread to the rest of the world, a new study has found.
Elapoidea, the snake superfamily, includes over 700 species in nine families and is geographically distributed in tropical and subtropical regions on all the planet’s major continents and in marine habitats of Indian and Pacific oceans.
However, its origins are a matter of debate. Elapids may have evolved in Africa and then spread to other continent, according to earlier studies.
But as per Novel phylogenomic inference and ‘Out of Asia’ biogeography of cobras, coral snakes and their allies published in the Royal Society Open Science on August 7, the origin of elapids is Asian, not African.
The researchers sampled 66 individuals from 65 species in 52 genera and 22 families of snakes. They did so from DNA isolated from ethanol-preserved tissue samples or from previously assembled genomes.
“Tissues were collected by numerous individuals (electronic supplementary material) during field expeditions (1990-2018) and deposited in the tissue collections at the University of Kansas Biodiversity Institute, University of Texas at El Paso or Villanova University (Villanova, PA),” the study noted.
The researchers’ results showed that there may have been four ‘Out of Asia’ colonisation events through which elapids spread into Africa.
An ancestor of the ‘Afro-Malagasy group’ comprising 330 species crossed over approximately 24.4-37.5 million years ago (Ma), which spans the latest Eocene and most of the Oligocene Epoch.
Some 12.5-23.9 Ma, an ancestor of the lineage containing African cobras (genera Aspidelaps, Hemachatus, Naja, Pseudohaje and Walterinnesia) crossed into Africa during the early and middle Miocene.
An ancestor of African garter snakes (genus Elapsoidea) may have crossed as early as 25.6 Ma while an ancestor of the Mambas (genus Dendroaspis) may have done so as early as 18.9 Ma.
“After these lineages colonized and diversified within Africa, our results supported successful ‘Out of Africa’ colonization of Europe by at least one sublineage in genus Malpolon, as early as 17.1 Ma, and separate recolonizations of Asia by Psammophis (less than 17.9 Ma) and Naja (less than 15.1 Ma),” the study read.
But how did the snakes cross over and colonise new lands?
The researchers hypothesised that cobras dispersed into Africa 12.5-23 Ma, a time when Africa and Eurasia collided, forming the Gomphotherium land bridge.
This development may have also facilitated expansions into Africa by ancestral populations of African garter snakes (Elapsoidea) and mambas (Dendroaspis).
From Asia, elapids may have also spread to North America via the Bering Land Bridge (BLB).
“In all instances inferred here, phylogenetic relationships now firmly point to their origins in Asia, followed by separate colonizations of western North America, possibly via a BLB-facilitated overland dispersal conduit,” the study noted.
However, the researchers added that snake fossils are net yet known from this region. Therefore, their results cannot be interpreted as evidence against oceanic dispersal colonization.
As for Australasia, the researchers’ results strongly support immigration to the region at least once by an elapoid sublineage from Asia, and consistent with earlier studies, by multiple colubroid sublineages. Colubrids includes harmless snakes such as grass snakes, garter snakes and rat snakes.
“Our biogeographic range evolution results strongly supported successful colonization of Australasia from Asia by an ancestor of the group containing all extant Australasian elapids and sea snakes,” the study read.
The snakes would have spread to Australasia by trans-oceanic dispersal or island-hopping, as per the researchers