Meeting Abstract
48.2 Saturday, Jan. 5 Differential adaptation to cold as a potential influence on a moving hybrid zone OLSON, J.R.*; WILLIAMS, J.B.; GRUBB, T.C.; BRAUN, M.J.; Ohio State Univ., Columbus; Ohio State Univ., Columbus; Ohio State Univ., Columbus; Smithsonian Institution, Suitland, MD olson.133@osu.edu
Black-capped chickadees (Poecile atricapillus, BC) are year-round residents in most of Canada and the northern half of the United States, whereas Carolina chickadees (Poecile carolinensis, CA) are found in the southeastern United States. The ranges of these two species meet along a narrow band extending from Kansas to New Jersey. Hybridization occurs throughout this contact zone, which has been moving north at a rate of approximately 1.6 km per decade. There is evidence the chickadee hybrid zone is correlated with temperature, as the east-west orientation closely matches general temperature trends. We tested for differential adaptation to cold in BC and CA, and examined how that disparity might influence the position of the hybrid zone. We predicted that northern chickadees would have higher metabolic rates than southern populations of the same species. We measured basal (BMR) and cold-induced peak metabolic rates (PMR) for BC near Oshkosh, WI and Ashland, OH and CA from Paris, TN and Ashland, OH. This design provided us with the unique opportunity to examine the metabolism of a species in two different environments, as well as two hybridizing species in the same environment. Both whole-organism BMR and PMR were significantly greater in BC than CA. However, metabolic rate did not differ intraspecifically for either BC or CA, regardless of location. We also calculated Tcl, the temperature that elicited hypothermia during sliding cold exposure, and determined that although OH-BC have higher BMR and PMR than OH-CA, the two species did not have significantly different Tcl. Thus, although OH-BC have a higher PMR, this does not convey any thermogenic advantage by providing them with a greater cold tolerance.
