Cancer prevalence is related to body mass and lifespan in tetrapods and remarkably low in turtles

Abstract

Abstract Identifying species with lower-than-expected cancer prevalence can help establish new models for understanding cancer resistance. Most studies of cancer prevalence have focused on mammals. Yet, other vertebrate groups vary tremendously in genetics, physiology, and ecology, which can all influence mechanisms of cancer resistance and may hold new keys to understanding cancer biology. Here, we present data on cancer prevalence in tetrapods, which includes all major vertebrate groups except fish, using necropsies from over a thousand different species. We investigated cancer prevalence within and among amphibians, birds, crocodilians, mammals, squamates, and turtles in relationship to body mass and lifespan. We are the first to (1) analyze non-avian reptile groups separately, (2) conduct statistical analyses appropriate for this type of discontinuous data, (3) more accurately use raw cancer occurrence data instead of species averages, and (4) look at how data resampling influences the robustness of results. We found remarkably low cancer prevalence in turtles and high prevalence in squamates and mammals. In contrast to previous studies, lifespan in mammals was negatively associated with neoplasia but positively associated with malignancy. We recovered the same results by reanalyzing data from these previous studies with our statistical approach. We also found that neoplasia prevalence was positively associated with body mass in amphibians and squamates. Overall, our results demonstrate a clear relationship between life history and neoplasia in most tetrapod groups. Our findings also indicate that choice of analytical methods is critical when examining cancer prevalence data. Finally, the exceptionally low cancer prevalence in turtles and extensive variation in cancer prevalence among tetrapod families hold particular promise for identifying species with novel mechanisms of cancer resistance.