Spontaneously occurring tumors in different wild-derived strains of hydra

Abstract

Hydras are freshwater cnidarians widely used as a biological model to study different questions such as senescence or phenotypic plasticity but also tumoral development. The spontaneous tumors found in these organisms have been so far described in two female lab strains domesticated years ago (Hydra oligactis and Pelmatohydra robusta) and the extent to which these tumors can be representative of tumors within the diversity of wild hydras is completely unknown. In this study, we examined individuals isolated from recently sampled wild strains of different sex and geographical origin, which have developed outgrowths looking like tumors. These tumefactions have common features with the tumors previously described in lab strains: are composed of an accumulation of abnormal cells, resulting in a similar enlargement of the tissue layers. However, we also found diversity within these new types of tumors. Indeed, not only females, but also males seem prone to form these tumors. Finally, the microbiota associated to these tumors is different from the one involved in the previous lineages exhibiting tumors. We found that tumorous individuals hosted yet undescribed Chlamydiales vacuoles. This study brings new insights into the understanding of tumor susceptibility and diversity in brown hydras from different origins.

De novoevolution of transmissible tumors in Hydra

“…First, this study confirms that H. oligactis is a species that easily develops spontaneous tumors in the lab [23]. In line with the tumors described by Boutry et al [23], those from this study (that are coming from hydras collected in the same sampling area) also involve abnormal proliferation of large interstitial stem cells.…”

“…As transmissible cancers are most often detected once they have already spread within host populations, the conditions associated with their emergence remain poorly understood. The cnidarian H. oligactis is emerging as a particularly promising model to investigate the evolution of transmissible tumors because it can develop spontaneous tumors relatively easily in the lab [23], and one lab strain harbors a transmissible tumor [24]. In this experimental study, we succeeded for the first time to observe the evolution of a transmissible tumor in the hydra.…”

“…To characterize the etiology of the tumors, we conducted a microbiome and cell type analysis. This aimed to determine (i) whether they are associated with a specific microbiome, as observed in the transmissible hydra tumors described by Domazet-Lošo et al [24], and (ii) whether the cell type forming the tumor is similar to that reported by Boutry et al [23] in the same hydra population.…”

“…Subsequent research revealed that some of these transmissible tumors were linked to a specific microbiome, notably involving the co-occurrence of spirochetes and Pseudomonas [25]. Additionally, Boutry et al [23] recently demonstrated that some wild H. oligactis , when brought back to the laboratory, develop spontaneous tumors at relatively high frequencies (i.e. up to 30%, see [22]), depending on the population of origin.…”

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].…”