Assessing the severity of diatom deformities using geometric morphometry

ABSTRACT

Deformities in diatoms are increasingly used as an indicator of toxic stress in freshwaters. However, the percentage of deformities alone often fails at highlighting the magnitude of toxic exposure. An approach combining the assessment of deformities coupled with information on their severity could improve the sensitivity of this biomarker. With the aim of quantifying the deviation from the normal form, we tested the applicability of geometric morphometry to evaluate the degree of deformities in different diatom species. We used photomicrographs of normal and deformed specimens from laboratory cultures of Gomphonema gracile, Nitzschia palea, and of Achnanthidium minutissimum from field samples collected along a gradient of toxic contamination. The geometric morphometry approach is based on several landmarks positioned on the outline of the diatom valves. Statistical analyses were conducted based on the geometrical coordinates of the landmarks. This technique allowed to discriminate between normal and deformed individuals. The geometric morphometry approach revealed a gradient in the intensity of the deformities observed on Gomphonema gracile and Achnanthidium minutissimum, in-line with a priori, visually determined (subjective) classifications. A relationship between the degree of deformity in Achnanthidium minutissimum and a gradient of zinc contamination was found. In contrast, the approach failed to obtain good fit for Nitzschia palea individuals because deformities in this species were more variable in terms of their location on the valves. Geometric morphometry provided encouraging results to objectively quantify the intensity of diatom deformities affecting valve outline, and could easily be implemented in further automatic diatom identification developments.

KEYWORDS:

• Diatoms
• morphometrics
• landmarks
• teratologies
• image analysis

Acknowledgments

Hélène Arambourou (Irstea, Lyon), is warmly acknowledged for advice and comments on the applicability of geometric morphometry to diatom deformities.

We also thank Émilie Saulnier-Talbot for language revision and comments on the study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary materials

Supplementary data for the article can be accessed here.

Additional information

Funding

This study was carried out with financial support from the French National Research Agency (ANR) within the framework of the Investments for the Future Programme, within the Cluster of Excellence COTE (ANR-10-LABX-45).

Notes on contributors

Angélique Cerisier

Angélique Cerisier is a MSc candidate at the University of Bordeaux, France.

Jacky Vedrenne

Jacky Vedrenne is engineer working on biofilms at Irstea, Bordeaux, France.

Isabelle Lavoie

Isabelle Lavoie is professor at INRS-ETE, Québec, Canada.

Soizic Morin

Soizic Morin is a research scientist in biofilm ecotoxicology at Irstea, Bordeaux, France.