PARENT SESSION
Contributed Oral Session 99: Populations and Genetics: Diversity and Population Dynamics
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal

Cryptic speciation in the cosmopolitan Epiphanes senta complex (Monogononta, Rotifera) II: Genetic differentiation within populations and among geographical regions.

Walsh, Elizabeth^*,1, Schroeder, Thomas^{1, 2}, ¹ University of Texas at El Paso, El Paso, TX, USA² Academy of Natural Sciences of Philadelphia, Philadelphia, PA, USA

ABSTRACT- Epiphanes senta has been considered to be one of the many cosmopolitan species in the phylum Rotifera. These species are believed to have a high dispersal capacity through transportation of their diapausing eggs by wind and birds, permitting gene flow over large distances. We studied genetic differentiation among and within populations of Epiphanes senta from 3 geographic regions (Germany, Texas, Hawaii), which have been shown to be partially reproductively isolated. We used RAPD data and analyzed variation in a 629 bp fragment of the mitochrondrial COI gene. The RAPD data show that subpopulations in different ponds even in close distance to each other are genetically differentiated. That is true for populations in the Chihuahuan Desert (Texas) and in floodplain habitats of the Oder River (Germany). F_ST values range from 0.1 to 0.23. On Hawaii Epiphanes senta has only been found in a single alpine lake. The genetic variation found in this population was much lower than in the other populations: only 7% of the loci found in the RAPD analysis were polymorphic compared to 43 to 52% in the Chihuahuan Desert population and 33 to 36% in the Oder floodplain population. A Bayesian analysis of the RAPD data using the program STRUCTURE showed that the populations from the 3 regions are clearly separated. Whereas the populations in the Chihuahuan Desert and in the Oder floodplains have a substructure, the Hawaiian population is genetically homogenous. Calculation of the genetic distance between the populations using the model by Nei and Li (1979) revealed deep divergences among the populations from the 3 regions with the Hawaiian population being the most distant. This does not correlate with mating barriers as the European floodplain population is reproductively isolated from the Hawaiian and the Chihuahuan Desert population, but hybridization is possible between the Hawaiian and the Chihuahuan Desert population. The results suggest that dispersal over long distances is not as common as the term "cosmopolitan species" would imply. Rather it seems to be a rare event leading to founder effects in isolated populations and cryptic speciation.

Key words: cryptic speciation, dispersal, rotifers, genetic differentiation