Primary and Secondary Transition Zones in Speciation and Population Differentiation: A Phylogenetic Analysis of Range Expansion

Transition (hybrid, tension, intergradation and contact) zones are the focus of attention of many evolutionary studies.Concepts of speciation and population evolution are dependent on whether the zone is thought to be due to the differentiation ofthe populations in situ (i.e., primary zones) as in area effect, elinal and stasipatric speciation (Endler, 1977;White, 1978) or due to secondary contact of populations (i.e., secondary zones) as in allopatric speciation or differentiation.It has been pointed out (Endler, 1977) that a major logical flaw in many such studies is that one cannot distinguish between a primary and secondary original event by the nature of the zone.Irrespective ofthe truth ofthis it is obviously logically desirable to hypothesize the origin of a zone independent of its nature.Using grass snake populations as an example, this paper describes some ideas * It is now appreciated that the distance Wagner trees are less appropriate than actual minimum length Wagner trees derived from a character x OTU matrix, Nevertheless the two procedures gave substantially similar or identical results when tested on some Natrix data.