Microevolution and taxonomy of European reptiles with particular reference to the grass snake Natrix natrix and the wall lizards Podarcis sicula and P. melisellensis

Abstract

The grass snake Natrix natrix and the wall lizards Podarcis simla and P. vre[irrll~n~is are used as examples to compare the procedure and achievements of the conventional approach to naming subspecies with the use of inultivariate morphometrics to investigate racial dilTerrntiation.The conventional procedure, which has changed little over the last 50 yrars, fails to take into account the appropriate evolutionary facts or refer to any abstractcd levels of divergence necessary for subspecific recognition. Consequently, the patterns of population diflrentiation are obscured by the recognition o f a large number of rather meaningless subspecies. Thew is a tendency t o section dines into artificial categories and arbitrarily delimit subspecies by physiographic li.atures.On the other hand, the use of multivariate morphometrics reveals the patterns of population dillerentiation which can be related to geological events and patterns ofdifferentiation in other species and species groups. The nature of 'hybrid' zones and population differentiation enables the relative importance of evolutionary forces such as gene flow, selection and genetic drift to be discussed and provides evidence concerning speciation mechanisms. These techniques also contribute to the discussion regarding the nature of species and provide abstracted and operational criteria for taxonomic decisions.The difference between the results of multivariate analysis and the conventional approach cannot be explained solely on the basis ofchoice of characters. Some of the advantagea and disadvantagcs of using multivariate morphometrics, as opposed to other modern techniques, lo1 investigating racial affinities are discussed.

Geographic variation: A synthesis of cause, data, pattern and congruence in relation to subspecies, multivariate analysis and phylogenesis

“…Categories of island populations are exemplified by the northern and southern categories of the Adriatic island wall lizards Podards sicula and meliselknsis (Clover, 1979;Thorpe, 1980), and the geographic categories of green geckos Phelsuma in the Seychelles (Thorpe, 1983a;Gardner, 1984).…”

“…An example of purported allopatric mainland categories is afforded by eastern and western lowland gorillas (Groves, 1970). When morphology is plotted against a geographical transect then parapatric mainland categorical variation is seen as a flat plateau joined to a flat valley by a transition zone, as in the eastern and western races of N. natrix (Thorpe, 1979(Thorpe, , 1980(Thorpe, , 1985a. Other examples of this type of geographical variation in the morphology of vertebrates include the variation of the mouse Mus musculus/'domesticus (Ursin, 1952) and the hooded and carrion crow races, Corvus corone, in Europe (Meise, 1928).…”

“…Danube, Rhine and Dnepr for IV. natrix subspecies in Thorpe, 1979Thorpe, , 1980. This has led to the circular argument that gene flow is important sensu Mayr(1970).…”

“…This has led to the circular argument that gene flow is important sensu Mayr(1970). c) Numerous subspecies tend to be erected and they obscure the major patterns of geographic variation (Thorpe, 1980;Clover, 1979). d) Subspecies erected in this way generally tend to be highly author-dependent and do not relate to external factors such as geological events or patterns of geographic variation in other species.…”

“…d) Subspecies erected in this way generally tend to be highly author-dependent and do not relate to external factors such as geological events or patterns of geographic variation in other species. They generally offer little or no clue to the cause of the variation other than a false and circular assumption that physiographic features are the cause (Thorpe, 1980).…”