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

The widespread vulnerability of Hydra oligactis to tumourigenesis confirms its value as a model for studying the effects of tumoural processes on the ecology and evolution of species

Tumoural processes, ubiquitous phenomena in multicellular organisms, influence evolutionary trajectories of all species. To gain a holistic understanding of their impact on species' biology, suitable laboratory models are required. Such models are characterised by a widespread availability, ease of cultivation, and reproducible tumour induction. It is especially important to explore, through experimental approaches, how tumoural processes alter ecosystem functioning. The cnidarian Hydra oligactis is currently emerging as a promising model due to its development of both transmissible and non-transmissible tumours and the wide breadth of experiments that can be conducted with this species (at the individual, population, mechanistic, and evolutionary levels). However, tumoural hydras are, so far, only documented in Europe, and it is not clear if the phenomenon is local or widespread. In this study we demonstrate that Australian hydras from two independent river networks develop tumours in the laboratory consisting of interstitial stem cells and display phenotypic alterations (supernumerary tentacles) akin to European counterparts. This finding confirms the value of this model for ecological and evolutionary research on host-tumour interactions.

Cancer and One Health: tumor-bearing individuals can act as super spreaders of symbionts in communities

Recent theoretical advances in the One Health approach have suggested that cancer pathologies should be given greater consideration, as cancers often render their hosts more vulnerable to infectious agents, which could turn them into super spreaders within ecosystems. Although biologically plausible, this hypothesis has not yet been validated experimentally. Using a community of cnidarians of the Hydra genus (Hydra oligactis, Hydra viridissima, Hydra vulgaris) and a commensal ciliate species (Kerona pediculus) that colonizes them, we tested whether tumoral polyps of H. oligactis, compared to healthy ones, played an amplifying role in the number of ciliates, potentially resulting in a higher likelihood of infection for other community members through spillovers. Our results indicate that K. pediculus has a higher proliferation rate on tumoral polyps of H. oligactis than on healthy ones, which results in the infestation of other hydras. However, the magnitude of the spillover differed between recipient species. This study provides to our knowledge the first elements of proof of concept that tumoral individuals in communities could act as super spreaders of symbionts within and between species, and thus affect biotic interactions and dynamics in ecosystems.

The complex effects of modern oncogenic environments on the fitness, evolution and conservation of wildlife species

Growing evidence indicates that human activities are causing cancer rates to rise in both human and wildlife populations. This is due to the inability of ancestral anti-cancer defences to cope with modern environmental risks. The evolutionary mismatch between modern oncogenic risks and evolved cancer defences has far-reaching effects on various biological aspects at different timeframes, demanding a comprehensive study of the biology and evolutionary ecology of the affected species. Firstly, the increased activation of anti-cancer defences leads to excessive energy expenditure, affecting other biological functions and potentially causing health issues like autoimmune diseases. Secondly, tumorigenesis itself can impact important fitness-related parameters such as competitiveness, predator evasion, resistance to parasites, and dispersal capacity. Thirdly, rising cancer risks can influence the species' life-history traits, often favoring early reproduction to offset fitness costs associated with cancer. However, this strategy has its limits, and it may not ensure the sustainability of the species if cancer risks continue to rise. Lastly, some species may evolve additional anti-cancer defences, with uncertain consequences for their biology and future evolutionary path. In summary, we argue that the effects of increased exposure to cancer-causing substances on wildlife are complex, ranging from immediate responses to long-term evolutionary changes. Understanding these processes, especially in the context of conservation biology, is urgently needed.

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

Wildlife is increasingly exposed to sublethal transient cancer risk factors, including mutagenic substances, which activates their anti-cancer defences, promotes tumourigenesis, and may negatively impact populations. Little is known about how exposure to cancer risk factors impacts the behaviour of wildlife. Here, we investigated the effects of a sublethal, short-term exposure to a carcinogen at environmentally relevant concentrations on the activity patterns of wild Girardia tigrina planaria during a two-phase experiment, consisting of a 7-day exposure to cadmium period followed by a 7-day recovery period. To comprehensively explore the effects of the exposure on activity patterns, we employed the double hierarchical generalized linear model framework which explicitly models residual intraindividual variability in addition to the mean and variance of the population. We found that exposed planaria were less active compared to unexposed individuals and were able to recover to pre-exposure activity levels albeit with a reduced variance in activity at the start of the recovery phase. Planaria showing high activity levels were less predictable with larger daily activity variations and higher residual variance. Thus, the shift in behavioural variability induced by an exposure to a cancer risk factor can be quantified using advanced tools from the field of behavioural ecology. This is required to understand how tumourous processes affect the ecology of species.