Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 1. Size and shape of colonies and cells

Abstract

M. Rico, M. Altamirano, V. López-Rodas and E. Costas. 2006. Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 1. Size and shape of colonies and cells. Phycologia 45: 237–242. DOI: 10.2216/03-44.1Traditionally, morphometrical traits are used to classify cyanobacteria. However, neither the importance of genetic factors in morphological variability nor genetic correlations between different morphometrical traits are known. Six morphometrical traits of individual cells and six morphometrical traits of colonies have been measured in 21 strains of Microcystis aeruginosa. A fixed model and a mixed model allowing genetic relationships between traits were both used to estimate genetic and residual correlations, and genetic variance/total phenotypic variance ratios were used to estimate the 12 morphometrical traits. Results showed that (1) colony size has a low genetic correlation with traits of individual cells; (2) traits measured on individual cells present a higher genetic variance/total phenotypic variance ratio than the corresponding trait in colonies; and (3) genetic correlations between directly measured traits (maximal diameter and axis, minimal diameter and axis, perimeter, and surface) are so high that they may be considered different expressions of the same underlying trait, namely size, so any one of them could be used without significant loss of information, instead of all of them. Fixed and mixed models showed the same conclusions, although mixed models preferably should be used because they take into account the common random genetic basis of traits. Maximal cell diameter was used as a discriminator trait for studying morphological differences between strains from different origins. Results suggest that environment may modulate strain mixtures in Microcystis populations.