Multiple isotope tracers in fur keratin discriminate between mothers and offspring

Abstract

Rationale Isoscape origin models for mammals may be impaired by fractionation and routing of isotopes during lactation. Here, we tested if the stable carbon, nitrogen and hydrogen ratios of juvenile bats differ from those of their mothers and if derived isotopic dietary niches and geographical assignments vary accordingly between mothers and juveniles. Methods During the post‐lactation period, we collected fur of juvenile and female common noctule bats (Nyctalus noctula) from the same maternity roost. Using a combination of elemental analysis and stable isotope ratio mass spectrometry, we measured the hydrogen, carbon and nitrogen isotope ratios in fur keratin. The hydrogen isotope ratios were measured for the non‐exchangeable portion of hydrogen in keratin. The derived isotopic niches and isoscape origin models were compared between mothers and juveniles. Results The fur keratin of juveniles was enriched by 1.6‰ in 15N and depleted by 2.9‰ in 13C compared with that of the mothers. In addition, the hydrogen isotope ratios were 13.4‰ lower in the fur keratin of juveniles than in that of mothers. The estimated isotopic niches of nursing females and juveniles were not overlapping and differed in size. Overall, the isoscape origin models projected juveniles as being from a more northern origin than the mothers; yet both models suggested the study site as a likely place of origin. Conclusions Our results suggest that isotope ratio data of juvenile bats should not be used for transfer functions in isoscape origin models because of isotopic routing and discrimination during lactation. Not accounting for age effects may increase the inaccuracy of geographical assignments in mammals when based on stable hydrogen isotopes.

The Use of Intrinsic Markers for Studying the Migratory Movements of Bats

“…Research at hibernacula and swarming sites has identified sites with greater and lesser catchment areas [ 62 , 64 ] and has revealed changes over time in bat migratory habits [ 63 ]. There is clear evidence that many bat species have partial and differential migratory patterns, with variation among sexes [ 19 , 20 , 29 , 63 ], age groups, e.g., [ 65 , 66 ], and among bats with varying anatomy [ 63 ].…”

“…While there are strong transfer functions for many species, there is still substantial variation in the δ 2 H fur values of bats within and among species at common locations [ 68 , 69 ]. Mean δ 2 H fur values may vary significantly among proximate roosts [ 55 , 69 ] and reproductive females may have fur that is depleted of 2 H compared to juveniles [ 66 , 69 ]. Variation among species can be even more significant.…”

“…Voigt et al [ 55 ] reported 65‰ variation among neotropical bats of 36 species and much of this variation may be caused by a trophic effect of discrimination [ 55 , 60 , 70 ], as well as substantial differences in the δ 2 H fur values of bats consuming aquatic and terrestrial prey [ 54 ]. Understanding the sources of variation in the δ 2 H fur values of resident bats can improve both the accuracy and precision of origin estimates, e.g., [ 66 , 67 ].…”

“… A generalized workflow for conception and implementation of a study using intrinsic markers to track migratory bat species. The far-right column lists bat-specific literature (except where more general literature is appropriate) that specifically addresses each stage [ 19 , 31 , 32 , 37 , 38 , 39 , 43 , 46 , 60 , 61 , 63 , 66 , 67 , 69 , 70 , 84 , 86 , 99 , 101 , 114 , 141 , 164 , 172 , 192 , 201 , 219 , 220 , 221 , 222 , 223 , 224 , 225 , 226 ]. Notice the extensive knowledge gaps that exist for the lesser used markers, especially in the last step “conduct origin assignment”.…”

Generational shift in the migratory common noctule bat: first-year males lead the way to hibernacula at higher latitudes

“…Stable hydrogen isotope ratios of bat fur were analysed at the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin as described before [24]. Samples were dried in silver capsules over several days in a drying oven and then transferred to an autosampler.…”