Genetically recognizable but not morphologically: the cryptic nature of Hydropuntia cornea and H. usneoides (Gracilariales, Rhodophyta) in the Yucatan Peninsula

Abstract:

Species recognition in algae is often extremely difficult due to the paucity of morphological characters and high environmental plasticity. If environment is important to morphology, then related species growing in sympatry are good candidates to discover diagnostic characters. We studied algae collected in sympatric populations in tropical Atlantic Mexico. Hydropuntia cornea and H. usneoides have high morphological variation and have been difficult to diagnose morphologically. We used four molecular markers (RuBisCo spacer, cox2–3 spacer, rbcL and COI) to investigate the genetic relationship between samples that correspond to either H. cornea or H. usneoides; in addition, we determined if molecular-characterized groups were morphologically distinguishable. RuBisCo and cox2–3 spacers revealed low genetic variation but showed two genetic groups: groups I and II. rbcL and COI phylogenies also showed a separation into two groups, corresponding with cox2–3 spacer groups I and II. Group I matched sequences in GenBank of H. usneoides and group II with H. cornea. Populations were mixed for these genetic groups, with group I prominent in Quintana Roo populations. Morphological analysis of samples in both genetic clades showed that they are not distinguishable. As the difference between the two groups is only genetic, they are, consequently, cryptic species. While the extremes of morphology in allopatric populations may be distinguishable, we do not feel that in most cases these species can be recognized. Therefore, we propose that these two ‘species’ should be designated as a species complex (the Hydropuntia cornea/H. usneoides complex).

Key Words::

• COI
• cox2–3 spacer
• Morphology
• rbcL
• RuBisCo spacer
• Species complex
• Variation

ACKNOWLEDGEMENTS

We thank Biological Sciences and Health, UAM, the National Council for Science and Technology (CONACyT number of scholarship 239902) and the financing of PROMEP project PROMEP/103.5/13/13/6732: ‘Variación de Hydropuntia cornea (Gracilariales, Rhodophyta) en las costas del Golfo de México y el Caribe mexicano’. This article contains some results from the doctoral thesis of María Luisa Núñez in the Doctorado en Ciencias Biológicas y de la Salud graduate program of the Universidad Autónoma Metropolitana.

SUPPLEMENTARY DATA

Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/15-009.1.s1.