The origin of multicellularity in cyanobacteria

Background: Cyanobacteria are one of the oldest and morphologically most diverse prokaryotic phyla on our planet. The early development of an oxygen-containing atmosphere approximately 2.45 - 2.22 billion years ago is attributed to the photosynthetic activity of cyanobacteria. Furthermore, they are one of the few prokaryotic phyla where multicellularity has evolved. Understanding when and how multicellularity evolved in these ancient organisms would provide fundamental information on the early history of life and further our knowledge of complex life forms. Results: We conducted and compared phylogenetic analyses of 16S rDNA sequences from a large sample of taxa representing the morphological and genetic diversity of cyanobacteria. We reconstructed ancestral character states on 10,000 phylogenetic trees. The results suggest that the majority of extant cyanobacteria descend from multicellular ancestors. Reversals to unicellularity occurred at least 5 times. Multicellularity was established again at least once within a single-celled clade. Comparison to the fossil record supports an early origin of multicellularity, possibly as early as the “Great Oxygenation Event” that occurred 2.45 - 2.22 billion years ago. Conclusions: The results indicate that a multicellular morphotype evolved early in the cyanobacterial lineage and was regained at least once after a previous loss. Most of the morphological diversity exhibited in cyanobacteria today —including the majority of single-celled species— arose from ancient multicellular lineages. Multicellularity could have conferred a considerable advantage for exploring new niches and hence facilitated the diversification of new lineages

The Experience of Academic Non-Mothers in the Gendered University

In this article we report on data from an empirical study concerned to explore the experience of women academics managing non-motherhood and work in the gendered university. Although there is a growing body of work on the gendered experience of higher education in general and the experience of mothers as academics in particular, as yet there is little on non-mothers and work. Drawing on our data we suggest that non-mothers as well as mothers are affected by the ideology of motherhood and this has consequences for non-mothers as workers within the academy. In addition to being perceived by students and other staff as \u27natural\u27 carers because they are women, academic non-mothers are expected to put in the time and energy that mothers can not. However, as our data demonstrate, non-mothers often have caring responsibilities outside the institution too. Overall, we argue that non-motherhood needs to be recognized for the complex identity that it is. © Blackwell Publishing Ltd 2006