Davallia repens

Chen, C. - W., Ngan, L. T., Hidayat, A., Evangelista, L., Nooteboom, H. P. & Chiou, W. - L., 2014, First insights into the evolutionary history of the Davallia repens complex, Blumea 59 (1), pp. 49-58 : 57

Cytogeography of D. repens complex

Tryon & Lugardon (1991) mention that the highly variable spore size observed in D. repens complex might imply its cytological complexity. In this study, multiple approaches, including chromosome number count, flow cytometry and spore size measurement, show three different ploidy levels, i.e., diploid, triploid and tetraploid. The number and distribution of diploids and polyploids (triploid and tetraploid) are very different. In our herbarium specimens analysis, ploidy level of 44 specimens was estimated and only 11 of them are diploids. The polyploids are widely distributed on Caroline Island, China, Indonesia, Japan, Madagascar, Malaysia, New Caledonia, Sri Lanka, Taiwan, the Philippines and Vietnam, whereas the diploids were only found in Malesia and South Pacific regions, including Admiralty Islands, Indonesia, Malaysia, Papua New Guinea, Solomon Islands, the Philippines and Vanuatu. The Malesia region then not only harbours more than 90 % of the species of Davalliaceae ( Nooteboom 1992, 1994), but also contains a high morphological variation of D. repens complex (this study). Since diploids are generally considered to thought to be the primitive cytotype ( Ebihara et al. 2005, Grusz et al. 2009, Rousseau-Gueutin et al. 2009, Dyer et al. 2012), the Malesian region is not only the diversity hotspot for Davalliaceae , but also the centre of origin of the D. repens complex.

Results of spore number count and gametophyte cultivation further indicate that all these polyploids reproduce by apogamy ( Table 1). Since no sexual polyploid has been found, we propose that apogamy is the major mechanism for hybrid stabiliza- tion in the D. repens complex. Previous studies have shown a difference in habitat preference between different ploidy levels ( Soltis & Soltis 2000, Shinohara et al. 2006, Huang et al. 2007, Libor & Milan 2008). In this study, some polyploid genotypes might have adapted to a cooler habitat and thus were able to disperse northward (in the northern hemisphere) or southward (in the southern hemisphere). The apogamous reproductive mode further enhances the chance of successful colonization of new habitats for these genotypes through the long distance dispersal of single spores ( Schneller et al. 1998, Page 2002, Trewick et al. 2002, Pangua et al. 2003, De Groot et al. 2012).