A multivariate approach to variation in microfilariae: examination of species Wuchereria lewisi and Demes of the species W. bancrofti

Abstract

Morphological differences between W. lewisi and demes of W. bancrofti result primarily from differences in the size of the individual microfilaria. A canonical analysis shows complete separation of the species. Because of the poor correlations between the characters, shape differences are not consistent and are not revealed by this analysis. Shape differences may be postulated on the basis of the ratios of the means. However, these ratios tend to be highly variable within populations because of poor correlations between the characters, and there will be considerable overlap of the ratios between the two species. An assumption of high correlations (and hence consistent ratios) between characters results in two canonical variates which may be interpreted as reflecting shape differences. The relatively low correlations between the measurements tend to give a result similar to that by a principal components approach on the population means. Correlations within populations are generally low and therefore have little influence in determining between-population differences. Under these circumstances principal components and the more efficient canonical variates give similar results. The different assumptions implicit in the two approaches are discussed.