Phenotypic Variation in Electromorphs Previously Considered to Be Genetic Markers in Microtus Ochrogaster

The allelic frequencies of the plasma enzymes transferrin (Tf) and leucine aminopeptidase (LAP) have been shown previously to correlate with population density, population growth rate and mortality in Microtus ochrogaster. Such changes in allozymic frequencies of Tf and LAP have been used by others as evidence supporting the Chitty/Krebs genetic-behavioral hypothesis of population growth. In this study, prairie voles were captured in midwinter and in midsummer, and brought to the lab where their allozymes of Tf and LAP were determined. The voles were then placed in controlled environments approximating some of the conditions of other seasons of the year, and their allozymes were redetermined in subsequent weeks. Changes in allozymes occurred in all experiments. Animals subected to opposite seasons (i.e. captured in winter and subjected to summer conditions, and captured in summer and subjected to winter environments) had the highest percentage of changes in electromorphs. A review of the literature revealed a plethora of evidence that Tf and LAP proteins could change electromorphs on starch gels in response to differences in blood chemistry and presumably to physiological state influenced by diet, reproductive state, and disease. Thus, since it appears that electromorphs of Tf and LAP proteins can change in voles subjected to different environments, and that these proteins may change in electronegativity in response to the physiological state of the animals, observed changes in allelic frequencies in populations of voles may be of limited value as evidence for the proposed genetic-behavioral hypothesis explaining population cycles.