Comparison of five strains of a parthenogenetic species, Macrotrachela quadricornifera (Rotifera, Bdelloidea)

Abstract

Five strains of the species Macrotrachela quadricornifera were cultured under experimental conditions. Four strains were collected from different environments, geographically paired, each pair consisting of an aquatic habitat (strains P and C) and a moss habitat (strains M1 and M2). Another population, F, was collected from an alpine stream and was added for comparison. In preliminary experiments food preference was evaluated by giving each strain five different food sources. Life table experiments were run at 16°, 20° and 24 °C. The strains differed in response to food types, to temperatures and in life history traits. In detail, while the ‘aquatic’ populations responded to temperature by increasing or decreasing their life spans and their rates of increase as expected, the ‘moss’ populations responded irregularly. Moreover, two types of life tactics could be identified: the aquatic strains, P, C and F invested maximally in reproduction, reducing their survival, while the moss strains, M1 and M2, were long-lived and devoted less resources to reproduction. A single link cluster analysis of some life-history parameters confirmed this divergence. The differences among the strains may easily be regarded as the results of adaptation to the different environmental conditions faced by the strains in nature. Whether the differences are genetic or phenotypic is still an open question.