title: Cancer susceptibility and reproductive trade-offs: a model of the evolution of cancer defences.
abstract: The factors influencing cancer susceptibility and why it varies across species are major open questions in the field of cancer biology. One underexplored source of variation in cancer susceptibility may arise from trade-offs between reproductive competitiveness (e.g. sexually selected traits, earlier reproduction and higher fertility) and cancer defence. We build a model that contrasts the probabilistic onset of cancer with other, extrinsic causes of mortality and use it to predict that intense reproductive competition will lower cancer defences and increase cancer incidence. We explore the trade-off between cancer defences and intraspecific competition across different extrinsic mortality conditions and different levels of trade-off intensity, and find the largest effect of competition on cancer in species where low extrinsic mortality combines with strong trade-offs. In such species, selection to delay cancer and selection to outcompete conspecifics are both strong, and the latter conflicts with the former. We discuss evidence for the assumed trade-off between reproductive competitiveness and cancer susceptibility. Sexually selected traits such as ornaments or large body size require high levels of cell proliferation and appear to be associated with greater cancer susceptibility. Similar associations exist for female traits such as continuous egg-laying in domestic hens and earlier reproductive maturity. Trade-offs between reproduction and cancer defences may be instantiated by a variety of mechanisms, including higher levels of growth factors and hormones, less efficient cell-cycle control and less DNA repair, or simply a larger number of cell divisions (relevant when reproductive success requires large body size or rapid reproductive cycles). These mechanisms can affect intra- and interspecific variation in cancer susceptibility arising from rapid cell proliferation during reproductive maturation, intrasexual competition and reproduction.
authors.affiliation: Department of Psychology, Arizona State University, Tempe, AZ, USA Center for Evolution and Cancer, University of California San Francisco, San Francisco, CA, USA Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193 Berlin, Germany amyboddy@gmail.com.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Boddy
authors.affiliation: Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193 Berlin, Germany Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Kokko
authors.affiliation: Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193 Berlin, Germany Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Felix
authors.initials: F
authors.lastname: Breden
authors.affiliation: Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193 Berlin, Germany Department of Biology, University of Maryland, College Park, MD 20742, USA.
authors.forename: Gerald S
authors.initials: GS
authors.lastname: Wilkinson
authors.affiliation: Department of Psychology, Arizona State University, Tempe, AZ, USA Center for Evolution and Cancer, University of California San Francisco, San Francisco, CA, USA Wissenschaftskolleg zu Berlin, Institute for Advanced Study, 14193 Berlin, Germany.
authors.forename: C Athena
authors.initials: CA
authors.lastname: Aktipis
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049109:Cell Proliferation; D004198:Disease Susceptibility; D017753:Ecosystem; D005260:Female; D006801:Humans; D008136:Longevity; D008297:Male; D008954:Models, Biological; D009369:Neoplasms / Q000209:etiology*; D012098:Reproduction; D012307:Risk Factors; D012727:Sex Characteristics
keywords: cancer defences; comparative oncology; life-history trade-offs; reproductive competition; sexual selection