Abstract
Although combining genetic and endocrine data from non-invasively collected hair samples has potential to improve the conservation of threatened mammals, few studies have evaluated this opportunity. In this study, we determined if steroid hormone (testosterone, progesterone, estradiol and cortisol) concentration profiles in 169 hair samples collected from free-ranging brown bears (Ursus arctos) could be used to accurately discriminate between immature and adult bears within each sex. Because hair samples were acquired opportunistically, we also needed to establish if interactions between hormones and several non-hormone factors (ordinal day, year, contact method, study area) were associated with age class. For each sex, we first compared a suite of candidate models by Akaike Information Criteria model selection, using different adult-age thresholds (3, 4 and 5 years), to determine the most supported adult age. Because hair hormone levels better reflect the endocrine state at an earlier time, possibly during the previous year, then at the time of sampling, we re-analysed the data, excluding the records for bears at the adult-age threshold, to establish if classification accuracy improved. For both sexes, candidate models were most supported based on a 3-year-old adult-age threshold. Classification accuracy did not improve with the 3-year-old bear data excluded. Male age class was predicted with a high degree of accuracy (88.4%) based on the concomitant concentrations of all four hormones. Female age class was predicted with less accuracy (77.1%) based only on testosterone and cortisol. Accuracy was reduced for females, primarily because we had poor success in correctly classifying immature bears (60%) whereas classification success for adult females was similar to that for males (84.5%). Given the small and unbalanced sample used in this study, our findings should be viewed as preliminary, but they should also provide a basis for more comprehensive future studies.
Highlights
Hair is one of several biological media that can be collected non-invasively from wild mammals
We determined if steroid hormone concentration profiles in 169 hair samples collected from freeranging brown bears (Ursus arctos) could be used to accurately discriminate between immature and adult bears within each sex
Hair collected from wildlife has been analysed in various ways, and for various purposes, including identification of individuals based on macro- and microscopic features (Stains, 1958; de Marinis and Asprea, 2006), genetic sampling of populations based on DNA extraction from hair follicles (Woods et al, 1999; Wilson et al, 2016), endocrine system function of individuals based on steroid hormone levels in hair (Koren et al, 2002; Schell et al, 2017), migration patterns and/or dietary habits of individuals based on stable isotope levels (Hobson, 1999; Cerling et al, 2006), and contaminant exposure of individuals based on hair levels of toxicants (d’Havé et al, 2005; Hernout et al, 2016)
Summary
Hair is one of several biological media that can be collected non-invasively from wild mammals. These research pursuits have generally followed independent paths, with combined studies being relatively uncommon, several recent studies have combined genetic, endocrine and/or stable isotope analyses of hair to address issues relevant to methodology (Sergiel et al, 2017) and ecology (Bryan et al, 2013; Lafferty et al, 2015) This contrasts with numerous studies based on non-invasive faecal collections in which DNA and hormone metabolites have been measured in tandem to increase understanding of the state of free-ranging populations (Wasser et al, 2004; Mesa-Cruz et al 2016; Rehnus and Palme, 2017)
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