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Abstract. In an effort to meet the demand for the trade and to reduce pressure on wild populations
of monitor lizards (Varanus spp.), several countries have encouraged the establishment of captive
breeding facilities. The fear has been expressed, however, that these facilities are not able to produce
the quantity of specimens they claim and therefore supplement their supply with wild specimens.
Thus, reliable methods are required for verifying the declaration of origin. Stable isotope analyses
have been discussed as a potential method to discriminate wild from captive specimens. We herein
designed a controlled feeding study and marked ten specimens of three Varanus species (V. acanthurus,
V. macraei, and V. melinus) at the Cologne Zoo in Germany with 15N enriched glycine in order to
examine the time lag for the isotopic signal to appear in renewed epidermis. We found that the 15N
enriched marker was detected within two to five weeks after exposition and conclude that 15N isotopic
signature in keratin skin tissue is likely to change quickly after the introduction of novel diets. Thus,
distinguishing captive-bred from wild origin based on δ15N values in shed skin material might not
be effective due to permanent, rapid epidermal renewal and therefore of limited forensic relevance.
Thus, the study of isotopic signals from tissue samples including several layers and tissues could be
an alternative approach. Furthermore, diet shift studies relating to isotopic incorporation rates as
well as reconsidering the examination of site-specific markers are recommended. Additional methods
need to be tested for suitability to identify the origin of monitor lizards being declared as captivebred,
which can prevent the laundering of wild-caught individuals through breeding farms.
Reptile Trade
