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The largest lizards on earth, the monitor lizards, inhabit various habitats in tropical and subtropical areas of Africa, Asia and Australia. The species have extremely different colours and colour patterns. For example, there is the bright green emerald monitor (Varanus prasinus), but also species with dot patterns or cross-banding. The colour is often adapted to the habitat, serves as camouflage or contains intraspecific signals.
Even within a monitor species, colouration can vary. Black specimens are found more or less regularly in populations of different species. This black colouration is called melanism, a dark pigmentation of skin, hair and scales caused by very dark brown or black colour pigments (melanins) that occurs in the animal kingdom. "Black panthers", i.e. black individuals of leopard or jaguar, are considered the best known. Black colouration is often genetic. The causes of black colouration are very different: Sometimes increased sunlight, greater humidity, lower temperature or other factors cause individuals to be black in colour. The evolutionary advantage that black colouration can bring is often not known.
Melanism in reptiles is indeed a widespread phenomenon and is often associated with thermoregulatory advantages. In some species, entire populations can be black in colour. In most cases, however, these are only isolated findings within normally coloured populations. Black-coloured individuals have been found in several groups of the monitor lizard family (Varanidae). But the animal in question here, our treasure of the month, is the first and only record of a melanistic monitor lizard of the subgenus Polydaedalus on the entire continent of Africa: the first black Nile monitor lizard, Varanus (Polydaedalus) niloticus.
However, there was no herpetologist in the field to specifically search for the black Nile monitor. It was Dr Vera Rduch, one of our mammalogists, who was once again on the road in Zambia for her research on antelopes. The enthusiastic zoologist and photographer caught this monitor lizard on camera - just a very brief moment, but enough for a "snapshot". On her return to Germany, she exchanged ideas with her colleagues in reptile research, who were particularly interested in her observations of the monitor lizards. In fact, Prof Dr Wolfgang Böhme immediately noticed that this monitor lizard in the pictures was special. Quite incidentally, and almost by chance, it turned out that the picture was the very first evidence of a melanistic Nile monitor. This photographic documentation was presented in a scientific publication last year in connection with melanism within the monitor lizards.
Our collections comprise several million specimens of various animal species, including parts of species. Like all other collections, the tissue collection is constantly growing and provides material for genetic analyses. At the same time, there is an important photo database that provides essential scientific data in addition to the more well-known collections. The find is now recorded here. The inclusion of an image in the database fulfils defined minimum requirements that apply to all scientific collections: In addition to a reliable identification of the species, i.e. the species name, the exact date of collection and details such as the habitat are recorded. Our experts check all data for accuracy before adding it to the database. Of course, we pay particular attention to specially protected species of conservation importance.
Worldwide, 82 described monitor lizard species are currently protected by CITES, the Washington Convention on International Trade in Endangered Species of Wild Fauna and Flora. The uncontrolled trade in live monitor lizards for the pet market and in their skins for the leather industry is threatening many of these species. Thousands of monitor lizards and monitor lizard skins are imported into Germany every year for the leather industry. Unfortunately, it is often very difficult to distinguish between the 82 scientifically described species. Together with the Federal Agency for Nature Conservation, the LIB played a key role in the development of a visual identification aid for the world's monitor lizard species. In order to truly protect monitor lizards, the different species must also be clearly identified.
Further information on melanism in monitor lizards can be found in the publication associated with this find:
MELANISM IN MONITOR LIZARDS (SQUAMATA: VARANIDAE), WITH A FIRST CASE IN THE NILE MONITOR, VARANUS (POLYDAEDALUS) NILOTICUS (SQUAMATA: VARANIDAE)
by Wolfgang Böhme, Thore Koppetsch and Vera Rduch in Herpetology Notes, volume 15: 257-262 (2022) (published online on 26 April 2022)