The effect of placentation type, litter size, lactation and gestation length on cancer risk in mammals

Abstract

Reproduction is a central activity for all living organisms but is also associated with a diversity of costs that are detrimental for survival. Until recently, the cost of cancer as a selective force has been poorly considered. Considering 191 mammal species, we found cancer mortality was more likely to be detected in species having large, rather than low, litter sizes and long lactation lengths regardless of the placentation types. However, increasing litter size and gestation length are not per se associated with an enhanced cancer mortality risk. Contrary to basic theoretical expectations, the species with the highest cancer mortality were not those with the most invasive (i.e. haemochorial) placentation, but those with a moderately invasive (i.e. endotheliochorial) one. Overall, these results suggest that (i) high reproductive efforts favour oncogenic processes' dynamics, presumably because of trade-offs between allocation in reproduction effort and anti-cancer defences, (ii) cancer defence mechanisms in animals are most often adjusted to align reproductive lifespan, and (iii) malignant cells co-opt existing molecular and physiological pathways for placentation, but species with the most invasive placentation have also selected for potent barriers against lethal cancers. This work suggests that the logic of Peto's paradox seems to be applicable to other traits that promote tumorigenesis.

Cancer hygiene hypothesis: A test from wild captive mammals

“…absence of predators or fights with competitors from other species, Hosey et al, 2009). Since cancer dynamics are at a crossroad and involve many trade‐offs (Jacqueline et al, 2017), we cannot exclude that compensatory mechanisms boosting cancer defences hide higher cancer risks, with a net effect being an apparent absence of relationship (see also Dujon et al, 2023). For instance, the relatively high food quality provided by zoological institutions might buffer the trade‐off among growth, reproduction and immuno‐competence in the other hand, which could ultimately constitute an additional protection against cancer.…”

Behavioural ecology meets oncology: quantifying the recovery of animal behaviour to a transient exposure to a cancer risk factor

“…Because of the exacerbated need to activate anti-cancer defences [7], and/or because of the adverse effects of the disease itself [8], many phenotypic traits are substantially altered in these individuals, which may even ultimately influence ecosystem functioning [9,10]. For example, oncogenic processes can alter life-history traits in their host at both early and late stages of tumour development [11][12][13][14], increase the risk of predation [15,16] and modify their commensal, parasitic and microbiome communities [15,[17][18][19]. By causing massive mortalities in populations of key ecosystem species, cancers can have major cascading effects on ecosystem biodiversity [20].…”