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

Open Access
Publisher Website
Google Scholar
Abstract
Morphological features are similar to most other types of features insofar as their patterns of geographic variation can be caused by both current ecological conditions and historical factors i.e. phylogenesis. Geographic variation in morphology is almost universal and often complex. Morphological and other features show a wide range of patterns of geographic variation i.e. clinal, categorical, and mosaic etc. The extent of pattern congruence between characters is to some extent predicted by both the extent of genetic independence and the cause of the geographic variation. The existing ≪conventional≫ procedure of naming subspecies typically fails to take into account the facts of intraspecific variation and consequently does not elucidate the patterns of geographic variation or their cause. Multivariate character analysis, based on ordination analysis and assisted by mapping techniques, can elucidate the range of patterns of geographic variation and may indicate their congruence, predictivity and cause. A more directly hypothesized intraspecific phylogeny can be obtained from qualitative karyotypic information or numerical phylogenetic analysis of quantitative morphological (and other) data. When the pattern of anagenesis is considered numerical phylogenetic analysis of morphological data indicates the primary or secondary origin of some transition (hybrid) zones. It is evident from the morphological and other studies that intraspecific lineages and their reticulation can be defined and that their ability to reticulate is not necessarily related to rank. Conventional subspecies are found not to relate to multivariate patterns or hypothesized phylogeny. If subspecific nomenclature is to be used then consideration should be given to the nature of the geographic variation, its cause and its rank.