A protocol to correct for intra‐ and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line

Abstract

RationaleIn recent years, segmental stable isotope analysis of hair has been a focus of research in animal dietary ecology and migration. To correctly assign tail hair segments to seasons or even Julian dates, information on tail hair growth rates is a key parameter, but is lacking for most species.MethodsWe (a) reviewed the literature on tail hair growth rates in mammals; b) made own measurements of three captive equid species; (c) measured δ2H, δ13C and δ15N values in sequentially cut tail hairs of three sympatric, free-ranging equids from the Mongolian Gobi, using isotope ratio mass spectrometry (IRMS); and (d) collected environmental background data on seasonal variation by measuring δ2H values in precipitation by IRMS and by compiling pasture productivity measured by remote sensing via the normalized difference vegetation index (NDVI).ResultsTail hair growth rates showed significant inter- and intra-specific variation making temporal alignment problematic. In the Mongolian Gobi, high seasonal variation of δ2H values in precipitation results in winter lows and summer highs of δ2H values of available water sources. In water-dependent equids, this seasonality is reflected in the isotope signatures of sequentially cut tails hairs.ConclusionsIn regions which are subject to strong seasonal patterns we suggest identifying key isotopes which show strong seasonal variation in the environment and can be expected to be reflected in the animal tissue. The known interval between the maxima and minima of these isotope values can then be used to correctly temporally align the segmental stable isotope signature for each individual animal. © 2015 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

Stable isotopes reveal diet shift from pre-extinction to reintroduced Przewalski’s horses

“…obs. ), which was additionally confirmed by the δ 2 H values in the corresponding hair (summer: high δ 2 H values; winter: low values 21 ). All tails of the museum specimens were still attached to the hide, making species discrimination straight forward.…”

“…21, 24 . The precision of measurements was always better than 0.1‰ for δ 13 C and δ 15 N, and 1.0‰ for δ 2 H values, based on repeated analysis of laboratory standards, calibrated with international standards.…”

“…The precision of measurements was always better than 0.1‰ for δ 13 C and δ 15 N, and 1.0‰ for δ 2 H values, based on repeated analysis of laboratory standards, calibrated with international standards. In the context of this study, δ 2 H values were primarily used to assign the δ 13 C profiles to the correct seasons (data not shown) 21 . We corrected all δ 13 C results from historic samples by subtracting 1.5‰, the difference in the δ 13 C of the atmospheric CO 2 between 1900 (−6.8‰) 46 and 2009/2010 (−8.3‰) 47 , to account for the Suess effect caused by burning of fossil fuels over the last 150 years (see Supplementary Table S2 for mean values of raw isotope values by individual).…”

Grazing high and low: Can we detect horse altitudinal mobility using high‐resolution isotope (δ13C and δ15N values) time series in tail hair? A case study in the Mongolian Altai

“…We measured a mean tail hair growth rate of 0.69 ± 0.11 mm.d −1 (Table S2, supporting information). This range of values is similar to those previously reported in domestic horses or wild equids . Potential variability in the growth rate of a unique hair could reduce the temporal precision of chronologies, given the high frequency of mobility of some individuals, as well as the correlation between different hairs, dampening the peaks of existing seasonal patterns.…”

Stable isotopic signatures in modern wood bison (Bison bison athabascae) hairs as telltale biomarkers of nutritional stress

“…The increase in ␦ 15 N values in this individual is also consistent with increased use of endogenous nitrogen (Lee et al 2012). Based on current knowledge of hair growth in domestic cattle, it seems likely that hair could reduce in growth rate during times of extreme nutritional stress (West et al 2004;Auerswald et al 2011;Burnik Šturm et al 2015). It is difficult to interpret the exact timing of the greatest changes in ␦ 13 C and ␦ 15 N values and whether they occurred during her period of rapid mobility or during the portion of winter that followed.…”