Invasive Species and Cancer: How Do These Seemingly Separate Concepts Relate?
This is an original article written by Evrim Ağacı. The references used in this article is given at the bottom of the article. All the content created by Evrim Ağacı can be shared and distributed as long as a clearly identifiable, hyperlinked reference is given back to this page.
Invasive species and cancer are two seemingly separate issues. However, their development is very similar to one another. They both invade, grow, and spread to large numbers if left unchecked.
When a species is transported (e.g. hitching a ride on boats or humans intentionally introducing them, such as horses to North America from early colonizers) from its well-established community or home environment to a new environment, it is now considered an “invasive species”. The species may not survive in the new environment (e.g. starvation or inhospitable environment), but if it does, it will enter what researchers call a “lag period”. This period may take several years to several decades. During this time, the species is adjusting and growing its population size. This will eventually lead to an ecological impact that will have consequences for all the species living in that ecosystem, including humans.
Giant African Snails also known as Lissachatina fulica can grow 6-8 inches and are an invasive species in North America that really illustrate how a few can turn into many with huge impacts to the environment. One state in the United States, Florida, has already had 2 separate invasions of this species; once in 1966 and again in 2011. The first invasion started when a child decided to bring back 3 snails from a vacation trip. His grandparents eventually decided to release the snails in their backyard. In only 7 years, these 3 snails grew to over 18 thousand, largely because each of these snails can lay 1000-1,200 hundred eggs per year, and each have an average lifespan of nine years. Their numbers were also not curbed as Florida contained no natural enemies to the snails.
The main ecological impact is related to the snails being prolific eaters and their ability to adapt and invade the habitats of many native species, including humans’ agricultural lands. They also eat calcium rich building materials off houses to build their shells. Their mucus may contain rat lungworm parasite (as they digest rat feces), this can cause meningitis in humans (although no known cases have happened in Florida). To fight with this invasion, dogs have been trained to sniff out the invasive snails and state officials have to gather and track them. The public is warned to report any sighting of the snails. As you can imagine, the costs of controlling these snails is astronomical. The US has already spent millions and millions of dollars to keep these invaders under control.
You might be wondering, “How in the world are invasive species related to anything like cancer?”. Well the are many similarities between the two. As invasive snails can become tens of thousands in number from a population that had only a few individuals, cancer growth in the body will occur in a primary site with only a handful of cells too. Then, as it progresses it will spread to nearby tissues, organs, and lymph nodes through the blood or lymphatic system. Just like the snails multiplying and spreading in a new location. Moreover, like an invasive species, cancer also often has a lag period. Most individuals, when exposed to a causative agent (e.g. viruses, ultraviolet radiation), will not develop clinical symptoms (e.g. unusual bleeding, thickening or lump development, changes in bowel and bladder) for several years to decades. In fact, during and after the collapse of the World Trade Center, many individuals were exposed to cancer causing agents, such a type of asbestos (chrysotile). It is a known cancer-causing agent (development of Mesothelioma) that was released into the air as the buildings collapsed. Individuals present during that event and developed this type of cancer could receive governmental assistance only if a minimum of 11 years had passed since the collapse of the World Trade Center when they received a diagnosis. In other words, if an individual had a diagnosis of mesothelioma a year or two after the collapse the cancer was more than likely present already and not caused during the collapse of the building as cancer has a lag period.
Why Are These Important?
The similarity between cancer and invasive species growth helps guide research. It might seem weird to study an invasive snail and how it reproduces and spreads. This type of research is based on curiosity of understanding how nature works, but often this type of research can help solve human problems, like cancer. When we look at these interesting patterns in nature, we can better understand how patterns in our bodies work. So, a very specific-looking case of a giant snail invasion can potentially lead to a better understanding of cancer. In fact, in 2018, researchers discovered that a recently evolved species of asexual crayfish has been invading vast regions of Europe and Africa. This animal can almost “clone” itself through a process known as parthenogenesis – and it does not need males to reproduce! The species was thought to have been created in an aquarium in Germany in 1995 – but it was released to the wild where it has exploded in numbers! In their paper, the researchers claim that understanding the genome, spread, and evolution of this species could potentially be a model system for clonal genome evolution in cancer. So, looking at crazy phenomena in nature can really help us solve the mysteries of our bodies.
- J. Gutekunst, et al. (2018). Clonal Genome Evolution And Rapid Invasive Spread Of The Marbled Crayfish. Nature Ecology & Evolution, sf: 567–573.
- National Toxicology Program. Substances Listed In The Fourteenth Report On Carcinogens. (2018, November 03). Access Date: 14 September 2018. Reference URL: Department of Health and Human Services
- Animal and Plant Health Inspection Service. Pest Alert: Giant African Snails. (2018, May 01). Access Date: 14 September 2018. Reference URL: USDA
- Florida Department of Agriculture and Consumer Services. Giant African Land Snail. (2018, September 14). Access Date: 14 September 2018. Reference URL: Florida Department of Agriculture and Consumer Services
- CDC. World Trade Center Health Program. (2018, September 14). Access Date: 14 September 2018. Reference URL: CDC