Cancer prevalence and etiology in wild and captive animals

Neoplasia has been recorded in the vast majority of metazoans. The frequent occurrence of cancer in multicellular organisms suggests that neoplasia, similar to pathogens/parasites, may have a significant negative impact on host fitness in the wild. This is supported by the fact that wildlife cancers have recently been shown to result in significantly increased levels of mortality and concomitant reduction in fitness. By thorough searches of the available literature we provide a comprehensive and an updated list of cancer prevalence and etiology in the wild. We were, however, unable to find data on nontransmissible cancer prevalence in invertebrates and consequently this chapter focuses on cancer in wild vertebrates. Although single cases of cancer are frequently encountered in the wildlife, we were only able to retrieve robust data on cancer prevalence for 31 vertebrate species (12 fish, 3 amphibians, 2 reptiles, 2 birds, and 12 mammals). Cancer prevalence among these vertebrates ranged from as low as 0.2% observed in Canada geese (Branta canadensis) to more than 50% recorded in both Santa Catalina Island foxes (Urocyon littoralis catalinae) and Cape mountain zebras (Equus zebra zebra). The high prevalence recorded in some vertebrates strongly suggests that cancer in wildlife may indeed carry significant fitness costs. In spite of this, the low number of published comprehensive studies clearly shows that so far cancer in wildlife has received insufficient attention by biologists. We hope that this chapter will act as a catalyst for further studies focusing on the impact of cancer in wild animals. The chapter additionally compares cancer recorded in French zoological parks to those obtained at other zoological parks. Finally, we provide an updated list of cancer recorded as single cases in the wild, as well as in captive animals.