Ecology and genetics of Philodina megalotrocha (Rotifera, Bdelloidea) from Chihuahuan Desert populations
The Chihuahuan Desert is a unique region with high biodiversity. There is a high degree endemism of freshwater biota, but relatively few studies have been focused on zooplankton. Bdelloid rotifers are one component of these ecosystems and often dominate very temporary habitats. Bdelloids are usually assumed to be cosmopolitan species due to their potentially high dispersal rates. Distribution records of the bdelloid Philodina megalotrocha extend from North America to New Zealand. However, little is known about its ecology or genetics. The aims of this study are to: (1) determine whether the distribution of P. megalotrocha in the Chihuahuan Desert is associated with ecological characteristics of habitats, (2) investigate whether P. megalotrocha is a truly a cosmopolitan species and not a complex of cryptic species, and (3) determine patterns of gene flow among populations of P. megalotrocha with respect to their geographical distribution. Redundancy Analysis was applied to investigate relationships between rotifer species and 30 environmental factors. To determine the extent of genetic differentiation among geographically isolated populations, cox1 sequences were used to construct phylogenetic hypotheses using Neighbor Joining, Maximum Parsimony, and Bayesian Analysis. The first 4 canonical axes in the Redundancy Analysis explained only 7.6% of the variance in the species data. Although environmental factors did not explain much variation in the distribution of rotifers among ecological habitats, this analysis indicated that P. megalotrocha is associated with the Cattail Falls Spring Pools (Big Bend National Park), presence of macrophytes, elevation, and to some degree with flowing waters and the summer season. High levels of genetic variation among populations of P. megalotrocha were found in cox1 sequences (ranging from 0% to 19.7%). Levels of sequence divergence among some P. megalotrocha Chihuahuan Desert populations were equivalent to or greater than those of other well-defined bdelloid species. P. megalotrocha was monophyletic in two of three analyses and contained at least five independent clades. Haplotype diversity was 0.98, with 22 haplotypes identified from 28 sequences. This may indicate that P. megalotrocha populations in the Chihuahuan Desert are, in fact, members of a complex of cryptic species. This study is the first to provide a detailed ecological survey of P. megalotrocha in a large geographic area. Further, this is the first analysis of phylogenetic relationships within P. megalotrocha populations using a molecular approach. Phylogenetic analyses demonstrate that morphological taxonomy in this group underestimates genetic diversity as has been recently found other bdelloid species.
Hamdan, Lina Kamel, "Ecology and genetics of Philodina megalotrocha (Rotifera, Bdelloidea) from Chihuahuan Desert populations" (2010). ETD Collection for University of Texas, El Paso. AAI1477791.