Posts Tagged ‘speciation’

Snake Island, Brazil

August 12, 2015

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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There May Be 5 Species of Shoal Bass Previously Described as 1

August 23, 2014

New discoveries await those entering the field of biological research.  Scientists have uncovered volumes of knowledge, yet we still know so little.  Nevertheless, it’s surprising that in Georgia, in the midst of what most would consider an advanced civilization,  there may be as many as 5 distinct species of bass left undescribed by science.  Byron Freeman and other scientists are using anatomical and DNA comparisons to remedy this unlikely gap in ichthylogical classification.

 

Redeye bass.  There may be 5 different species of shoal bass wrongly considered the same species.

Shoal basses; along with largemouth bass, crappies, and sunfish; belong to the Centrarchidae family.  Shoal basses favor rocky stretches of river too warm for trout, yet too cool for largemouth bass, though there is some overlap on both ends.  Dr. Freeman discovered that various specimens of a species of shoal bass, known as the redeye bass (Micropterus coosae), differed strikingly, depending upon which river they came from.  By comparing 20 anatomical characteristics, Dr. Freeman was able to determine that shoal basses from the Coosa, Apalachicola, Chattahoochee, Savannah, and Altamaha rivers all differed from each other enough to be considered separate species.  Differences in shoal bass DNA sequencing supports his discovery. The scientific name, Micropterus bartrami, or Bartram’s bass, has been proposed for a species living in the Savannah River.

All of these species share a close evolutionary relationship.  It’s likely the founding population of shoal bass became geographically isolated due to stream capture events when the headwaters of 1 stream eroded backwards and captured the flow of another. For example a tributary of the Savannah River captured a tributary of the Chattahoochee, explaining how speciation occurred between shoal basses from these 2 rivers.  (See:https://markgelbart.wordpress.com/2014/02/06/tallulah-gorge/) Similar geological events probably explain the evolutionary divergence of other shoal basses.

All of these species hybridize with each other, showing the difference between species is a gray area.  Hybridization via backcrossing is another way new species can originate.  By introducing a species of shoal bass into another species of shoal bass’s range, man may inadvertently create a new species.  However, scientists are concerned that introductions of smallmouth bass into shoal bass habitat will result in the latter’s extinction.

See also: https://markgelbart.wordpress.com/2013/04/26/the-evolutionary-history-of-the-black-bass-genus-micropterus-sp/

Reference:

Freeman, Byron; et. al.

“Shoal Basses, a Clade of Cryptic Identity”

Black Bass Symposium 2013

The Squirrel-Conifer-Fungi Connection

June 14, 2014

The evolutionary divergence of the northern flying squirrel (Glaucomys sabrinus) from the southern flying squirrel (G. volans) is an excellent example of speciation resulting from environmental change.  Genetic studies suggest both of these American species of flying squirrels diverged from Eurasian flying squirrels between 4-6 million years ago.  Eurasian flying squirrels are much more diverse and include 44 species, most of which live in southeast Asia–evidence this part of the world is where they originally evolved.  During the late Miocene about 5 million years ago, a forested landbridge connected Asia with America, explaining how the ancestor of both American species of flying squirrels colonized this continent.  Genetic evidence suggests the 2 American species of flying squirrels diverged from each other early during the Pleistocene between 1-2 million years ago when Ice Ages began to become more severe.  Boreal spruce forests expanded during Ice Ages, growing as far south as middle Georgia and Alabama.  In the middle south spruce forests grew in higher elevations while deciduous oak forests still occurred in adjacent lower elevation.  Oak forests are rich in mast such as acorns and nuts, but spruce forests offer less food for squirrels–seeds from spruce cones are only available for 2 months of the year.  However, underground fungi, also known as truffles, are available year round in spruce forests.  For most species of squirrels, fungi is a minor component of their diet, but truffles and other fungi make up 85% of the northern flying squirrel’s diet whereas southern flying squirrels eat more acorns, nuts, berries, and animal matter.  The ancestors of the northern flying squirrel were those individuals from the parent population best able to subsist on a diet of mostly fungi.  These individuals were able to colonize spruce forests, while the rest of the parent population remained in oak forests.  Eventually, this habitat partition resulted in a divergence between the 2 American species.

Photo: Northern Flying Squirrel, Glaucomys sabrinus.

Northern flying squirrels eat mostly fungi which is a minor component in most squirrel’s diet.  The ability to subsist on a diet of mostly fungi enabled this species to colonize spruce forests.  Eventually, they evolved into a different species than southern flying squirrels because of this capability.

Elaphomyces or truffle–favorite food of the northern flying squirrel.

 

 Red Spruce (Picea rubens)

Red spruce (Picea rubens).  Red spruce, truffles, and northern flying squirrels are beneficial and interdependent to each other.

Fossils of both species of flying squirrels have been found at Ladds and Kingston Saltpeter Cave in Bartow County, Georgia.  This is evidence that patches of spruce forest grew near patches of oak forest in this region during some climatic stages of the Pleistocene.  Northern flying squirrels are confined to the former; southern flying squirrels require the latter.

There is an interesting ecological interdependence between northern flying squirrels, red spruce, and several species of fungi.  Truffles grow intertwined with the red spruce roots, and they exchange nutrients.  The squirrels eat the truffles and spread their spores throughout the forest in their droppings.  A healthy spruce forest requires an abudance of truffles.  Many red spruce forests have been logged, and without the squirrel’s help, trees such as oak, maple, beech, and cherry are replacing them.  In West Virginia the U.S. Forest Service has successfully re-established red spruce forests.  Foresters discovered that red spruce seedling grow best in ground ripped apart by bulldozers and strewn with woody debris.  Some of these young spruce forests are on land reclaimed from strip mining. 

 Report fox squirrel sightings in Florida Sherman's Fox Squirrel

Fox squirrel.  This species may play a role in distributing fungi in longleaf pine savannah. 

Rhizopogon nigrescens–a fungi common to longleaf pine savannahs and likely an item in the diet of the fox squirrel.

Virgin stand of longleaf pine (Pinus palustris) in east Texas (circa 1908).

Although fox squirrels (Scirius niger) have a much more varied diet than northern flying squirrels, they occasionally eat fungi and may play a role in the health of longleaf pine savannahs.  Certain kinds of fungi that grow in the soil of savannahs also exchange nutrients with longleaf pine trees, and fox squirrels spread these spores in their dung as well.  Fox squirrels and longleaf pine savannahs were formerly common in the south, particularly on the coastal plain, but today both are rare.  The changes man has wrought have really sickened the natural communites of the world.

Reference:

Arbogast, Brian

“A Brief History of the New World Flying Squirrel: Phylogeny, Biogeography, and Conservation Genetics”

Journal of Mammalogy 88 (4) 2008