Re: ancestral apistos

["William Vannerson" <William_Vannerson@ama-assn.org>]

>>There are at least 2 lineages of apistos that have invaded Guianan coastal streams.<<

Tomas Hrbek spoke at one of our killie club meeting regarding the lineage of Rivulins in South America.  One of the interesting comments that is import to keep in mind is that the continent's geography has gone under massive changes over the millennia.  At one point, the oceans water levels rose so that the entire Amazon basin was part of a large saltwater sea.  The South American continent was basically two "island" land masses.  Then the waters receded and fresh water fish re-invaded the "new" rivers.

So tracking lineage via today's geography may not tell the entire story.  Tomas was using DNA research in conjunction with the know continental plate Teutonics in order to establish the relationships of the Rivuus and Cynolebias species.

An interesting side note was that he shows where the killifish trait of diapause, where their eggs go into a resting stage, developed twice along two separate lineages.  That means the line lost the trait when it was no longer advantageous for the habitat when the basin flooded and the savannas disappeared.  But it returned when the salt water receded and it became an advantage again.

Bill Vannerson
McHenry, IL
http://ourworld.compuserve.com/homepages/william_vannerson



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