importance of genetic research in zoo breeding programmes for threatened species: the African dwarf crocodiles (genus Osteolaemus) as a case study

The threatened African dwarf crocodiles (genus Osteolaemus) are distributed throughout West and Central Africa. Traditionally two subspecies were described (Osteolaemus tetraspis tetraspis and Osteolaemus tetraspis osborni), although recent molecular studies demonstrate the presence of three allopatric lineages that should be recognized as full species. These highly divergent taxa are distributed in the three major forested biogeographic zones of western Africa: Congolian (Osteolaemus osborni), Lower Guinean (Osteolaemus tetraspis) and Upper Guinean (Osteolaemus sp. nov. cf. tetraspis). Largely because of their diminutive size, dwarf crocodiles are regularly kept in zoos and aquariums worldwide. In Europe, the collection is managed by a European studbook coordinated by Leipzig Zoo, Germany, since 2006, while American zoological institutions do not yet manage these species as part of a studbook programme. To facilitate ex situ conservation efforts, it is important to identify accurately each individual to the appropriate species following the latest systematic understanding of the genus. Population aggregation analysis with mitochondrial and nuclear gene sequences was used for both species identification and detection of interspecific hybridization. The results of our study show that only European collections house all three Osteolaemus taxa, although only a single individual O. osborni was confirmed. The most prevelant species present in both European and North American institutions was O. tetraspis. Additionally, several O. sp. nov. cf. tetraspis were identified, likely originating from the Senegambia region, especially in the North American collections. This will represent an important resource for future conservation efforts as Osteolaemus are highly threatened in this region of West Africa. Unfortunately, both zoo populations showed relatively high frequencies (c. 25–28%) of hybridization between O. tetraspis and O. sp. nov. cf. tetraspis bred in captivity. We highly recommend that zoological institutions ensure they know the species identity of the Osteolaemus they maintain and work together to transfer individuals into single‐species colonies to avoid further hybridization. In the USA, this may necessitate the creation of a studbook programme. It may also prove valuable to consider a cooperative programme between the European Association of Zoos and Aquaria and the Association of Zoos & Aquariums, wherein each Association focuses its resources largel