Phenotypic plasticity in diatoms: Janus cells in four Gomphonema taxa

Abstract

We observed four Gomphonema taxa with a high abundance of Janus cells, which are cells that have valves of two different morphologies, also termed heterovalvar cells. The specimens were collected from a habitat with periodic drying, alternating with standing water. A high proportion of Gomphonema Janus cells (up to 20% of the frustules for each taxon) were found. Heterovalvy within a frustule is based on stria count, and two types of heterovalvy were observed. Cells produced either coarsely or finely striated valves with discontinuous phenotypic plasticity or highly variable stria density within a frustule along a continuous phenotypic gradient. In our study, we measured stria density in complete frustules and single valves. Other features of the frustules showed no noticeable variation. Variable stria density was found in frustules and single valves, although it is not possible to determine whether the single valves were part of Janus cells or homomorphic frustules. Therefore, our conclusions are based on the measurements of complete frustules only. We propose that Janus cells result from two ecophenotypic responses (reaction norm and polyphenism) of these taxa to one or more environmental factors. As such, Gomphonema taxa that produce Janus cells may be model organisms for deciphering the genetic basis of developmental plasticity in diatoms.

Keywords:

• Phenotypic plasticity
• reaction norm
• polyphenism
• morphology
• morphogenesis
• Gomphonema

Acknowledgements

This work is dedicated to Dr G. Dennis Cook, emeritus professor of Biology at Kent State University. The 2009 Dennis Cook Aquatic Scholarship to JZA made this work possible. The authors thank Steve Main, Peter van der Linden, Sylvia Lee, Marina Potapova, the late Eugene Stoermer, and David Mann for useful discussions and help. In addition, this study was kindly supported by the 2009 Ecology and Systematics of Diatoms class at the Iowa Lakeside Laboratory Regents Resource Center. The final version of this work benefitted from the suggestions of an anonymous reviewer and the editor.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The underlying research materials for this article can be accessed at the University of the Bahamas (Nassau, the Bahamas) and at the Georgia College and State University, Milledgeville, GA, USA.

Additional information

Funding

The Dennis Cooke Aquatic Ecology Scholarship was awarded to Jelena Z. Andrejic to support aquatic ecology studies at Iowa Lakeside Laboratory, Iowa, USA.