Lopez Peredo, Elena , Les, Donald , Benoit, Lori , Tippery, Nicholas .
Cryptic speciation in Najas marina L. (Hydrocharitaceae) .
Najas marina is a cosmopolitan aquatic monocot currently viewed as comprising 12 subspecies with six varieties. This is the only dioecious species in an otherwise monoecious group of annual hydrophiles and resolves phylogenetically as the sister to the remainder of the genus. Three distinct karyotypes have been reported for N. marina, including one autotetraploid ('BB') and two diploid ('A', 'B') races. The A and B karyotypes differ extensively by rearrangements resulting from the breakage and reunion of chromosomal segments. Previous studies have associated these rearrangements with high infertility, which is manifest by extreme genetic divergence between the diploid karyotypes (e.g., no allozyme alleles shared at 23 loci surveyed). As part of an ongoing systematic study of Najas, we are evaluating the intraspecific taxonomy of N. marina using DNA sequence analysis. In contrast to the currently proposed taxonomy, an analysis of DNA sequence data for 22 globally distributed populations resolves only two distinct lineages within N. marina, which arguably correspond to the two fundamental karyotypes. Our results confirm that these karyotypes rarely are interfertile as indicated by their substantial level of DNA sequence divergence at both cpDNA and nuclear regions. Unexpectedly, all Eurasian material analyzed (China, Czech Republic,Latvia) presumably corresponds to the A karyotype (i.e., subsp. marina) despite the known occurrence of B karyotypes in this region. Conversely, all North American material (ostensibly karyotype B; subsp. intermedia) is essentially identical to plants from Australia, thereby supporting an earlier hypothesis that New World plants represent a recent introduction. Our inability to detect B karyotypes from other regions is curious and we are expanding our geographical survey to resolve this discrepancy. Except for minor seed characters (which differ between the two karytotypes), we cannot detect any consistent pattern of morphological variation to support those infraspecific taxa delimited previously. Rather, we regard N. marina as an aggregate taxon of two cryptic species, which are effectively isolated reproductively by their extensively rearranged genomes.
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1 - University Of Connecticut, Ecology & Evolutionary Biology, 75 N. Eagleville Road, Unit 3043, Storrs, CT, 06269-3043, USA
2 - University Of Wisconsin-Whitewater, Department of Biological Sciences, 800 W Main St, Whitewater, WI, 53190
Presentation Type: Oral Paper:Papers for Sections
Location: Lindell C/Chase Park Plaza
Date: Tuesday, July 12th, 2011
Time: 2:00 PM