Snake Island, Brazil

Rising sea levels can cause speciation (the evolution of new species) by geographically isolating populations.  A small rocky island off the coast of Brazil is home to a perfect example of this.  Genetic evidence suggests the golden lancehead viper (Bothrops insularis) diverged from the jaracara (B. jaracara) approximately 2 million years ago when sea level rise isolated Snake Island from the rest of South America.  The ancestral population of snakes that became stranded on this island evolved different characteristics than the jaracara, a species that is widespread throughout the mainland of eastern South America.  Jaracaras primarily feed upon rodents, birds, and lizards; but there are no rodents on Snake Island.   Resident birds co-exist with the high density of snakes on this island.  The birds that live on this small island quickly learn to be wary and avoid snake predation.  So golden lanceheads depend heavily upon naïve transient birds that are just visiting the island.  Golden lanceheads evolved more potent venom, shorter fangs, and longer heads.  The more potent venom kills the birds faster, and the shorter fangs are less likely to break when the golden lanceheads hang on to a struggling bird.  By contrast jaracaras strike, release, and wait for their prey to die; thus avoiding injury.  The longer head on the golden lancehead allows them to switch to larger prey at an earlier age than a jaracara.  Golden lanceheads grow to almost 4 feet long, over a foot less than jaracaras.  The smaller size means they require less food.  They do also take lizards and other lanceheads.

Location of the island just off the coast of Brazil

Location of Snake Island.

Snake Island.

 

 

 

 

 

 

 

 

 

The golden lancehead snake (Bothrops insularis.)  Beautiful snake.

Jaracara (B. jaracara).  Genetic studies suggest golden lance heads evolved from this species about 2 million years ago when sea level rise isolated them from the parent population on Snake Island.  The fer-de-lance also belongs to this genus.

There are 37 species of snakes in the Bothrops genus, and all live in South America.  Every species has potent venom, but the golden lancehead’s venom is 5x more potent than that of the jaracara.  The venom causes extensive tissue damage.  People bitten by these vipers sometimes require amputation, but antivenin has reduced the rate of death.  Marlin Perkins of Wild Kingdom fame was bitten by venomous snakes several times during his career.  He wrote the only good thing about getting bitten by a venomous snake was that after the effects dissipated, he recovered completely.  There is no evidence a human has ever been bitten by a golden lancehead.  A legend that a lighthouse keeper and his family were killed by golden lanceheads in 1920 has never been confirmed.  There are 200 golden lanceheads on Snake Island.  They exist in the wild nowhere else in the world.

Reference:

Wuster, Wolfgang; et. al.

“Morphological Correlates of Incipient Arboreality and Ornithophagy in Island Pit Vipers and the Phylogenetic Position of Bothrops insularis”

Journal of Zoology 2005

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