Print PageA current debate in ecology centers on the idea that microscopic organisms have global dispersal capabilities but nature selects which species are represented locally (the Baas-Becking Hypothesis). These organisms often play important roles in nutrient cycling and food webs of aquatic communities. Recently, with the use of molecular tools to characterize taxa, it has been shown that the biodiversity of some taxa has been highly underestimated. Bdelloid rotifers are one component of these ecosystems and often dominate very temporary habitats. Because of their anhydrobiotic ability, it has been suggested that bdelloid rotifers are cosmopolitan in distribution. However, recent molecular findings refute this assumption as many cryptic species complexes are emerging. The Chihuahuan Desert is an ideal region to investigate genetic divergence of bdelloid populations because the aquatic habitats are often temporary and highly disconnected. In addition high levels of diversity and endemism have been found in fishes and spring snails, but relatively few studies have been focused on rotifers. The goals of this study are 1) to determine levels of genetic variation within and among populations of Philodina megalotrocha and 2) determine whether the distribution of P. megalotrocha in the Chihuahuan Desert is associated with ecological characteristics of habitats.
Results/Conclusions
To determine the extent of genetic differentiation within geographically isolated populations, cox1 sequences were used to construct a genetic distance matrix and phylogenetic hypotheses using Neighbor Joining and Bayesian analyses. High levels of genetic variation within and among populations of P. megalotrocha were found in cox1 sequences ranging from 0 to 15.3% and from 0% to 19.7%, respectively. Haplotypes analyses revealed 13 haplotypes within populations and 28 haplotypes among populations, and the overall haplotype diversity within and among populations was 0.78 and 0.98, respectively. P. megalotrocha individuals were distributed among at least five independently evolving clades. This may indicate that P. megalotrocha populations in the Chihuahuan Desert are, in fact, members of a complex of cryptic species. Redundancy Analysis was applied to investigate relationships between rotifer species and 30 environmental factors. The first 4 canonical axes in the Redundancy Analysis explained only 7.6% of the variance in the species data and the most important habitat characteristics for predicting P. megalotrocha presence are macrophytes, summer season and large, flowing spring systems. Our results confirm hidden diversity in bdelloid populations and additional work is needed to fully characterize the ecological implications of this diversity.
