Variability in the growth patterns of the cornified claw sheath among vertebrates: implications for using biogeochemistry to study animal movement

Abstract

We review the role of biogeochemical signatures, such as stable isotopes and trace elements, in the cornified claw tissue as a means of studying movement and foraging behaviour of vertebrates because this approach is noninvasive and can capture contemporary and historic signatures. Because biogeochemical techniques are still relatively new in studies of animal movement, we are only beginning to understand how the growth patterns of the cornified claw sheath may affect our ability to interpret the biogeochemical signals in these tissues. To move towards resolving this, we review the morphology of the epidermal cornified claw sheath in several taxa that illustrate substantial variation in growth patterns both between taxa and between individual distinct claw regions. For instance, in mammalian claws, deposition of keratinizing cells from the epidermis is nonlinear because the claw tip is composed of old and new cornified epidermal cells, whereas the cornified blade horn covering the claw’s lateral walls is deposited continuously and without assortment, providing unbroken time-series data. We also consider patterns of growth in mammalian hooves, as well as reptilian, avian, and amphibian cornified claw sheaths, and address the need for expanded research in this field. We conclude this synthesis by describing a noninvasive technique for monitoring growth rates in a model mammal, the American badger ( Taxidea taxus (Schreber, 1777)), and provide guidelines for future sampling of claw keratin, which will improve our ability to back-calculate the time of biogeochemical integration into this tissue.

Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore

“…Fortunately, avian claws grow relatively slowly and can retain a winter-dominated stable isotope signature after arrival on the breeding grounds (Bearhop et al, 2003;Mazerolle and Hobson, 2005;Fraser et al, 2008;Ethier et al, 2010). The central toe on whip-poor-will feet bears a pectinate claw, meaning that it is edged with a comb-like structure with 5-9 wide barbs (Supplemental Figure 1).…”

Turnover rates of stable isotopes in avian blood and toenails: Implications for dietary and migration studies

“…The proposed time window for the information this structure integrates was estimated based on toenail growth rates (Bearhop et al, 2003;Hahn et al, 2014) and the only study we are aware of that attempted to measure the turnover rate of SI in toenails through a controlled diet switch experiment reported no shift in isotopic values even after five months (Barquete et al, 2013). Also, nail growth in higher vertebrates is a complex and not necessarily linear process (Ethier et al, 2010;Hahn et al, 2014), and some evidence suggests that toenail growth during migration may limit the use of SI data in toenails for determining breeding and wintering origins in ground foraging birds due to differences between the base and the tip of the toenail (Mazerolle and Hobson, 2005). These issues emphasize the need for more controlled experiments in order to correctly interpret SI data from bird toenails.…”

Stable Isotopes in Fish Eye Lenses as Potential Recorders of Trophic and Geographic History

“…Although this paper focuses on fish, it should be noted that there are a number of isotopic records for terrestrial animals as well. These include claws, hooves, hair, feathers, and teeth [18], [19]. Although these tissues are isotopically conservative, the period of time represented by the record varies with tissue wear (e.g.…”