Analysis of Phosphoglucose Isomerase (PGI) within and among Habrotrocha rosa metapopulations

Background/Question/Methods

Phosphoglucose isomerase (PGI), a dimeric enzyme that catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate, plays a key role in glucose metabolism and the resupply of ATP.  PGI variants have been correlated with habitat migration in metapopulations of the endangered Glansville Fritillary butterfly, and in metapopulations of the terrestrial rotifer Macrotrachela quadricornifera.  The bdelloid rotifer Habrotrocha rosa exists as a metapopulation in the leaves of the northern pitcher plant Sarracenia purpurea.  We hypothesize that variation in H. rosa PGI isozymes may correlate with its life history - these rotifers must migrate to a new leaf habitat patch before the old leaf dies.  Our sampling scheme was designed to provide samples from within habitats, between habitats and among locations on a bog.  We also tested for reproducibility of isozyme patterns by collecting rotifers from four other bogs.  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 was conducted at all sites within a two week period to avoid any time effects.  We examined PGI using the protocols of Gomez (1998) and Hebert (1993) with modifications. 

Results/Conclusions

Contrary to the data in the literature for other invertebrates, we found that the H. rosa clones from Cedarburg bog exhibited identical heterozygous genotypes for phosphoglucose isomerase. This strong stabilizing selection poses the question of whether this rotifer travels from one habitat patch to another phoretically, and therefore does not rely upon high ATP demand for migration.  We are currently analyzing the results from the other sampling sites.  We are also investigating how phoresy might take place.