Genetic variation and environmental heterogeneity: Studies on a metapopulation of the bdelloid rotifer Habrotrocha rosa

Background/Question/Methods

This study is part of a larger project that looks at the influence of environmental heterogeneity on the dynamics of ecological communities and the close interplay between processes at both local and regional scales. We focus on the population genetic structure and dispersal abilities of Habrotrocha rosa, an asexual rotifer that lives in the water-filled, pitcher-shaped leaves of the carnivorous pitcher plant Sarracenia purpurea. Each pitcher represents an ephemeral habitat patch within the bog landscape, and H. rosa exists as a metapopulation, persisting through the colonization of new pitchers. We are attempting to correlate environmental variation within habitat patches with genotypic and phenotypic differences among clones. We hypothesize that the metapopulation is composed of multiple genotypes whose presence/absence is determined by colonization rate, calendar date, leaf age, and types of bacteria present.  During July-September, 2008, and continuing in spring-fall, 2009, rotifer clones were established from pitcher fluid isolates. The sampling scheme was designed to provide samples from within habitats (pitchers), between habitats (pitchers on the same plant) and among locations on the bog (between plants); in other words the collecting protocol will permit detection of alpha, beta and gamma level diversity respectively. Three rotifers were randomly selected from each pitcher sample, and each one became the foundress of a clone representing one H. rosa genotype that was present in the pitcher on the date of collection. Sampling through the growing season permits selection of clones that have been exposed to environmental stresses such as periodic droughts and floods, extremes of temperature, and variations in food (bacteria) quality and quantity.  Proteomic (cellulose acetate gel electrophoresis of isozymes) and genomic (sequencing sections of the Cox1 and Cob genes) analyses are being used to detect variations among clones and the linkage between the variations and adaptations to environmental stresses. We are also measuring r at 19^oC and 27^oC to determine whether there are adaptations for growth and reproduction at either cool (spring, fall) or warm (summer) temperatures. 

Results/Conclusions

Our results show 100% heterozygosity and identical migration patterns for phospoglucose isomerase in all H. rosa clones; analysis of other enzymes is in progress. Other results show that early to midspring and fall clones, which have a high likelihood of freezing, exhibit higher levels of resistance to freezing and lower resistance to desiccation. These traits are reversed in clones isolated during late spring and summer.