Thirteen-lined Ground Squirrels

Thomas Goodwin (Biology)

Dietary and seasonal signals in stable isotopes of incisor enamel from freeranging, thirteen-lined ground squirrels

This study will investigate whether, and to what degree, dietary and seasonal variation in stable isotopes of carbon (∂¹³C) and oxygen (∂¹⁸O) are reflected in isotopic patterns within incisor enamel of free-ranging thirteen-lined ground squirrels (Ictidomys tridecemlineatus), sampled at ~weekly frequency. Our intent is to develop a modern analog that will assist in fine-scale paleoecological interpretation of fossil ground squirrels.

Beginning in early May and extending into early August, we will capture, tag, inject with oxytetracycline to label injection date in the tooth’s growth record, and release ~30 ground squirrels at staggered times. Marked animals will be tracked for several weeks to months, and they will periodically be recaptured, up to early October, to allow collection of fecal pellets (which closely track dietary carbon sources) and injection with oxytetracycline (to further label injection dates in the tooth). At intervals, a sample of marked animals (~12 individuals across the entire season) will be captured and humanely euthanized to allow extraction and study of their incisors.

Analyses will include: 1) analysis of stable isotopes of carbon and nitrogen (∂¹⁵N–allows discrimination of plant and animal food sources) of ~90 fecal samples at the SIRFER lab at the University of Utah; 2) laser-ablation micro-sampling of enamel from ~12 squirrel incisors, and analysis of enamel stable isotopes in these samples at the lab of Dr. Benjamin Passey (John Hopkins University–see attached letter of support); and 3) graphical and statistical analyses of seasonal patterns in stable isotopes across squirrels, and correlations between enamel and fecal-pellet stable isotope (a proxy for diet).