SREL Reprint #2619




Analysis of an apparent genetic cline in the stonefly Pteronarcys scotti (Plecoptera: Pteronarcyidae)

Gordon R. Plague and James H. Larson

Savannah River Ecology Laboratory, University of Georgia, P. O. Drawer E, Aiken, SC 29802 USA

Introduction: Pteronarcys stonefly larvae (Plecoptera: Pteronarcyidae) inhabit lotic systems and are generally considered allochthonous shredders (Merritt and Cummins, 1996, An Introduction to the Aquatic Insects of North America, Kendall/Hunt, Dubuque, IA), primarily consuming leaf material that falls into streams. However, Pteronarcys spp. in the Little Tennessee River (LTR) drainage basin in southern North Carolina shift their diet through the stream continuum, with individuals in the relatively small and heavily canopied upstream reaches consuming mainly leaf material and individuals in the relatively large and open downstream reaches consuming mainly algae (Plague et al., 1998, Am. Midl. Nat. 139: 224-234). Commensurate with this diet shift, the Pteronarcys species composition also shifts through the continuum, with one species inhabiting the upstream reaches (fourth- through sixth-order sites), a second inhabiting the downstream reaches (sixth- and seventh-order sites), and a third inhabiting the mid-reach where the other two co-occur (sixth-order site) (Plague et al., 1998, Am. Midl. Nat. 139: 224-234). Furthermore, the phosphoglucomutase (Pgm) allele frequencies in the upstream species, Pteronarcys scotti Ricker, also shift through the continuum, thereby forming an apparent genetic cline: the most common allele (Pgm3 ) has a frequency of 0.91 at the fourth-order collecting site, 0.80 at a fifth-order site (2.2 km downstream), 0.65 at a second fifth-order site (3.4 km farther downstream), and 0.50 at a sixth-order site (6.0 km farther downstream) (Plague et al., 1998, Am. Midl. Nat. 139: 224-234). Although these allele frequencies are quite disparate through the LTR continuum, they are not significantly different from one another (P = 0.315, see below for statistical analysis description), largely because the sample sizes were relatively small (N = 11, 10, 10, and 3 individuals at each sampling site, respectively). . . .

Keywords: Allozyme, sampling error, stream

SREL Reprint #2619

Plague, G. R. and J. H. Larson. 2002. Analysis of an apparent genetic cline in the stonefly Pteronarcys scotti (Plecoptera: Pteronarcyidae). Journal of Entomological Science 37:278-280.

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