DNA barcodes and morphometric data indicate that Codium fragile (Bryopsidales, Chlorophyta) may consist of two species

Abstract:

The siphonous green alga Codium fragile currently has 10 accepted subspecies, among which is the problematic invasive subsp. fragile. The subspecies are defined on the basis of five polymorphic nucleotides in the plastid rps3–rpl16 spacer region, and this subdivision into subspecies has not been investigated in detail with other DNA markers. Here, we compiled a data set of the green algal DNA barcoding marker tufA that includes 110 C. fragile specimens and an additional 80 specimens of eight related Codium species. Our tufA haplotype tree showed two distinct clades within C. fragile, and the three algorithmic species delimitation methods that were applied agreed that these are likely to represent separate species. The first clade consisted of the invasive subspecies fragile, whereas the second contained the remaining subspecies present among our sequences. Using a newly developed morphometric method to capture fine details of utricle morphology, we show that the two molecular clades also have subtle morphological differences. Despite all this new evidence in favour of two species being present in C. fragile, we refrain from making formal taxonomic changes, chiefly because our tufA data do not agree with previous rps3–rpl16 results. We propose four complementary approaches to resolve these conflicts.

Key Words::

• Codium fragile
• Chlorophyta
• DNA barcodes
• Green algae
• Invasive species
• Morphometrics
• Species delimitation
• Taxonomy
• tufA

ACKNOWLEDGEMENTS

This research was largely carried out as two undergraduate research projects. Part of the molecular work was done for MB's science research subject in the second semester of 2015. Two thirds of the morphometric work was done by a group of three students as a mini-research project that formed part of the Marine Botany subject at the University of Melbourne in November/December 2015. We thank Chris Ma, Nick Craig and Lillian Haines for this contribution. We thank R.J. Anderson, C. Boedecker, J. Bolton, B. L. Brooks, R. Brown, F. Bunker, E. Coppejans, O. De Clerck, P. Diaz, S. Draisma, C. Fernandez, G. Hansen, J. Huisman, J. Hernandez-Kantun, L. Le Gall, D.S. Littler, M.M. Littler, L. McIvor, F. Mineur, F. Rousseau, J. Tsarahevitra, T. Schils, K. Pauly, E. Demeulenaere, G.W. Saunders, C.W. Schneider, F. Steen, E. De Swaef, M. Taylor, E. Tronchin, S. Wilson, L. Tyberghein, J. West and B. Wysor for collecting samples. Funding for this study was provided by the Australian Research Council (FT110100585 to HV), the Australian Biological Resources Study (RFL213-08 to HV) and the University of Melbourne (MIRS/MIFRS to JFC). Some of the molecular data presented here were generated in the Saunders lab (University of New Brunswick) and we thank Gary Saunders, Daniel McDevit and Tanya Moore for that work and sharing the data. Work in the Saunders Lab was funded through the Canadian Barcode of Life Network from Genome Canada (through the Ontario Genomics Institute), and other sponsors listed at www.BOLNET.ca.

SUPPLEMENTARY DATA

Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/16-54.1.s1.