Paedogamy and auxosporulation in Nitzschia sect. Lanceolatae (Bacillariophyta)

Abstract

Mann D.G., Sato S., Rovira L. and Trobajo R. 2013. Paedogamy and auxosporulation in Nitzschia sect. Lanceolatae (Bacillariophyta). Phycologia 52: 204–220. DOI: 10.2216/12-077.1

Paedogamy (fusion of gametes produced within the same gametangium following meiosis) has rarely been reported in diatoms, with fewer than 10 confirmed examples. One of these, reported by L. Geitler, was in a diatom from Illmitz, Lake Neusiedl (Austria), identified as ‘Nitzschia frustulum var. perpusilla’. We observed uniparental auxosporulation in two Nitzschia clones isolated from the lower Ebro River (Catalonia, Spain), morphologically similar to Geitler's material and belonging to the N. inconspicua species complex. We established that the auxospores were formed paedogamously by Feulgen staining of the nuclei and time-lapse microscopy of living cells. However, reinvestigation of Geitler's original cytological preparations revealed differences between the Illmitz and Ebro material with respect to the length of the initial cells, the structure of the perizonium, and the timing of degeneration of superfluous haploid nuclei during gametogenesis, indicating a genetic and possibly a taxonomic separation. Scanning electron microscopic studies of Ebro auxospores revealed a novel form of longitudinal perizonium with bilateral asymmetry, and also scaly incunabula surrounding the unexpanded zygote, which contrast with the strip incunabula of another paedogamous Nitzschia species, N. fonticola. Molecular phylogenies, based on rbcL and partial LSU rDNA sequences, and evaluation of trees constrained to make the paedogamous species monophyletic, indicate that paedogamy probably evolved at least twice independently in Nitzschia sect. Lanceolatae, in the N. inconspicua and N. fonticola lineages.

Key Words::

• Archived cytological material
• Auxosporulation
• Cytology
• Feulgen stain
• Inbreeding
• Incunabula
• LSU rDNA
• Nitzschia
• Paedogamy
• Perizonium
• rbcL
• Sexual reproduction

ACKNOWLEDGEMENTS

This research received support from the SYNTHESYS Project, http://www.synthesys.info, which is financed by European Community Research Infrastructure Action under the FP7 “Capacities” Program. We are grateful for this and also the earlier SYNTHESYS Project under FP6Support from European Distributed Institute of Taxonomy (EDIT) Research Grant (from the EDIT WP2, funded by EU FP6) made possible through a visit by Rosa Trobajo to the Natural History Museum London in the summer of 2010, during which the first observations were made of paedogamous Nitzschia from the Ebro. We are also very grateful to Frieda Christie for training and advice in use of the SEM and to Dr Walter Till, curator of the University of Vienna herbarium, for his encouragement and help in locating and using the Geitler collection.

SUPPLEMENTARY DATA

Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/12-077.1.s1.