Presentation Title

P-23 High-resolution Record of Temporal Variation in δ13C from Intra-Tooth Sampling of Incisor Enamel of Free-ranging Thirteen-lined Ground Squirrels

Presenter Status

BS Student, Department of Biology

Second Presenter Status

BS Student, Department of Biology

Third Presenter Status

BS Student, Department of Biology

Fourth Presenter Status

Department of Biology

Fifth Presenter Status

Department of Earth and Planetary Sciences

Sixth Presenter Status

Department of Biology

Location

Buller Hallway

Start Date

1-11-2013 1:30 PM

End Date

1-11-2013 3:00 PM

Presentation Abstract

We tested the hypothesis that δ13C profiles of incisor enamel from free-ranging thirteen-lined ground squirrels (Ictidomys tridecemlineatus) record seasonality in diet. We used laser ablation to densely sample lower incisor enamel (on average, one sample per 3 days of tooth growth) from 20 squirrels collected in SW Michigan, and analyzed samples using GC-IRMS. The basal ~20-35 increments of record always displayed a negative trend in δ13C, probably reflecting contamination by organic carbon in developing enamel; we excluded these values. At one colony, squirrels collected within 25 m of a cornfield displayed significantly higher and more variable δ13C (variable C4-rich diet; mean=-5.03, SD=2.38, n=6) than did squirrels from mowed lawn distant from the cornfield (C3-rich diet; mean=-13.92, SD=0.61, n=6); this pattern persisted from early May-late August and was confirmed to reflect dietary differences (δ13C of fecal pellets). Both groups displayed a positive excursion in δ13C in late August. Late-season use of C4-rich vegetation was also documented at a second colony (n=8) without access to a cornfield, studied in late summer through hibernation. Isotope values peaked rapidly from mid-August to mid-September, and subsequently dropped precipitously to hibernation. We suggest rodent incisors as possible recorders of fine-scale seasonal variation of interest to paleoecologists.

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Nov 1st, 1:30 PM Nov 1st, 3:00 PM

P-23 High-resolution Record of Temporal Variation in δ13C from Intra-Tooth Sampling of Incisor Enamel of Free-ranging Thirteen-lined Ground Squirrels

Buller Hallway

We tested the hypothesis that δ13C profiles of incisor enamel from free-ranging thirteen-lined ground squirrels (Ictidomys tridecemlineatus) record seasonality in diet. We used laser ablation to densely sample lower incisor enamel (on average, one sample per 3 days of tooth growth) from 20 squirrels collected in SW Michigan, and analyzed samples using GC-IRMS. The basal ~20-35 increments of record always displayed a negative trend in δ13C, probably reflecting contamination by organic carbon in developing enamel; we excluded these values. At one colony, squirrels collected within 25 m of a cornfield displayed significantly higher and more variable δ13C (variable C4-rich diet; mean=-5.03, SD=2.38, n=6) than did squirrels from mowed lawn distant from the cornfield (C3-rich diet; mean=-13.92, SD=0.61, n=6); this pattern persisted from early May-late August and was confirmed to reflect dietary differences (δ13C of fecal pellets). Both groups displayed a positive excursion in δ13C in late August. Late-season use of C4-rich vegetation was also documented at a second colony (n=8) without access to a cornfield, studied in late summer through hibernation. Isotope values peaked rapidly from mid-August to mid-September, and subsequently dropped precipitously to hibernation. We suggest rodent incisors as possible recorders of fine-scale seasonal variation of interest to paleoecologists.