Yes, animals in the wild do develop cancer. While it might seem less common compared to humans or domesticated animals, cancer is a complex biological phenomenon that affects a wide range of species across diverse ecosystems. Its occurrence in wild populations is influenced by various factors, including environmental exposures, infectious agents, and the natural process of aging. Understanding cancer in wildlife presents unique challenges due to the difficulties in observation and long-term monitoring of free-ranging animals.
Documented Cases and Observations
Cancer has been observed in numerous wild animal populations. For instance, marine bivalves, such as clams, can suffer from a type of leukemia where cancerous cells accumulate in their hemolymph. This disease can be severe, often leading to the death of affected clams.
The Tasmanian devil is severely impacted by an infectious cancer known as Devil Facial Tumor Disease (DFTD). This cancer spreads through biting and has caused a significant decline in their population, exceeding 60 percent. Sharks, once thought to be resistant to cancer, have also been found to develop tumors, with over thirty tumors reported in elasmobranchs, a group including sharks, rays, and skates.
Fish populations, like coral trout along the Great Barrier Reef, have shown instances of melanoma, with UV radiation suspected as a contributing factor. Sea turtles can develop fibropapilloma, a cancer that forms visible tumors on their flippers, around their mouths, and eyes. The incidence of this condition has increased significantly, raising suspicions about environmental pollution as a cause. Even ancient creatures like dinosaurs exhibited signs of cancer, with tumors found in approximately 3% of duck-billed dinosaur vertebrae specimens.
Underlying Causes of Cancer in Wildlife
The development of cancer in wild animals stems from environmental factors, infectious agents, genetic predispositions, and age-related cellular changes. Environmental pollutants play a substantial role, with chemical contaminants such as polycyclic aromatic hydrocarbons (PAHs), PCBs, and DDT linked to cancer epidemics in various fish species and mammals. Radiation releases and microplastic accumulation also contribute to increased cancer rates. Artificial light pollution, particularly near urban areas, can cause hormonal changes in wild animals that may lead to cancer.
Infectious agents, particularly viruses, are recognized as causes of cancer in wildlife. Papillomaviruses and retroviruses are examples of pathogens known to induce tumor formation.
Genetic factors also influence susceptibility to cancer in wild populations. Natural genetic variations within a species can increase an individual’s likelihood of developing tumors. A reduction in genetic diversity within a population, often a consequence of human activities, can further elevate cancer prevalence.
Age is a significant risk factor for cancer development. As wild animals age, they accumulate cellular damage, which can lead to uncontrolled cell growth. Tracking age-related cancer incidence in the wild is challenging, but studies on zoo animals suggest older animals are more prone to the disease.
Why Cancer is Less Apparent in the Wild
The perception that cancer is rare in wild animals often arises from several observational challenges. Sick or weakened animals are quickly removed from the population by predators or succumb to other natural causes. This natural selection process means that animals with advanced cancer are less likely to survive long enough to be observed with obvious symptoms or to be found for examination.
Unlike humans or domesticated animals, wild animals are not routinely monitored, examined, or treated by veterinarians. This lack of regular clinical oversight means that many cancer cases go undetected. Early stages of cancer in wild animals may also present subtle or no obvious symptoms, making diagnosis difficult without specialized tools or close observation.
Post-mortem examination of wild animals is often challenging. Carcasses can be rapidly scavenged by other animals or decompose quickly, which hinders necropsy and accurate diagnosis of the cause of death. Even when carcasses are found, high levels of autolysis, or organ disintegration, can make histopathological analysis inaccurate. These factors collectively contribute to the underestimation of cancer prevalence in wild populations.
Ecological Implications
The presence of cancer in wild animals carries significant consequences for individuals, populations, and the broader ecosystem. At an individual level, cancer can reduce an animal’s fitness, impairing its ability to forage effectively, escape predators, or reproduce. This diminished capacity makes affected animals more vulnerable to other diseases or environmental stressors.
At the population level, cancer can impact survival rates and reproductive success, particularly in vulnerable or endangered species. High cancer prevalence in a population can lead to increased mortality, which in turn can reduce overall population health and resilience.
Beyond individual and population effects, the prevalence of certain cancers in wildlife can serve as an indicator of broader environmental health issues. Increased cancer rates can signal exposure to specific pollutants or habitat degradation, acting as a biomarker for ecosystem stressors. Studying cancer in wild animals provides insights into the health of natural systems and the potential impacts of human activities on wildlife and their environments.