Genetic distinctiveness and population size trends of a peripheral metapopulation of the southern two-lined salamander (Eurycea cirrigera) in Will County, Illinois

Background/Question/Methods

Recently, rapid declines of numerous amphibian populations have been noted worldwide. Evaluating amphibian populations is hampered, however, by the fact that many populations fluctuate widely and few long-term data sets of amphibian populations exist. There is also little information on the degree of genetic distinctiveness of isolated populations. The southern two-lined salamander (Eurycea cirrigera) is a predominantly southeastern U.S. species with a peripheral range extending north and west into eastern Illinois. There, E. cirrigera inhabits tributaries of the Kankakee River (within the Kankakee River State Park: KRSP) in Will County, the northwestern-most extent of its known range. Chicago State University ecology classes have monitored populations living in tributaries on the north bank of the Kankakee River since 1996 by Visual Inspection Surveys (VIS: normalized to the number of adults or larvae encountered/meter of stream/person searching/minute). We compared these results with both single- and triple-catch recapture methods to estimate subpopulation sizes in individual tributaries. We also compared the genetic distinctiveness of the KRSP Illinois population of E. cirrigera, relative to the next-nearest known population (Warren County, Indiana: WC) and with a population within the main body of the species’ range (Aiken County, South Carolina: AC) to evaluate whether genetic differentiation could be detected from distances extending from 1000 km across states to < 1 km distances among subpopulations within the KRSP (especially those divided by the Kankakee River, which may represent demes). Genetic variability was evaluated using seven microsatellite loci developed for a related Plethodontid salamander (Plethodon cinereus) and pair-wise comparisons of  F_st (a correlation measurement of genetic differentiation between pairs of populations) were calculated.

Results/Conclusions

With the exception of a single year (1999) when salamanders were unusually abundant, there were no significant changes in the size estimates for the surveyed KRSP populations over the past 14 years. There were significant differences at all loci between the KRSP and AC samples and significant differences in six out of seven loci between KRSP and WC population samples. There was a significant correlation (r² = 0.96) between the mean genetic differentiation and geographical distance over all. Differentiation within the KRSP samples demonstrated significant variability at three of the seven loci, showing significant genetic differences in eight of ten population matches. These included two of three site comparisons on the north and south sides of the Kankakee River, suggesting that the river forms an isolating boundary between these subpopulations.