Cicadas, especially the 17-year periodical cicadas, have captivated scientists for decades with their extraordinary life cycle. Those remarkable insects spend an incredible 99.5% of their lives as nymphs underground, emerging only after 17 years. Recent scientific studies show that cicadas do not only emerge on prime-numbered years. Their timing might be affected by a four-year gestation period determined by their anthropometry and genomic makeup.
The 17-year cicadas, which are famous for their long juvenile development time, come out in the spring of their 17th year. Only every four years do they weigh in. This observation is key in seeing which ideas will rise to the top. This is the first study to show such an interesting result. If cicadas exceed a certain critical weight threshold every four years, they actively decide to emerge the following spring.
The Four-Year Counting Mechanism
More recently, research suggests that the timing of cicada emergence could be dependent on an epigenetic cycle. This cycle includes developmental gates that are set every four years according to the cicadas’ weight. Observational evidence suggests that 16-year-old cicada nymphs had red eyes and had probably exceeded the critical weight required for emergence.
To our surprise, even a few nymphs as old as 12 years had red eyes. For example, these nymphs exhibited increased body weights over their white-eyed counterparts. This implies that even sub-annual cicadas may be measuring their development against the known rhythms of emergence cycles.
“The most enigmatic and challenging component of our life-cycle control hypothesis is the clock-like mechanism that counts a four-year cycle.” – Teiji Sota
These results uncover a unique interplay between genetic expression and environmental conditions. It’s this interaction that can help explain when exactly cicadas hit that critical weight where emergence becomes possible.
Emergence and Adult Life
Cicadas weigh themselves prior to emergence. When they hit maturity and reach the specified threshold, they come in with a big splash. This ruling provides for the close of a long, subterranean life. Adult cicadas explode aboveground, screaming in open air. During their brief four- to six-week life span, they cause a ruckus with their distinctive mating call, ensuring that they’re hard to miss.
Fascinatingly, genes involved in adult metamorphosis and molting are expressed only after a period of overwintering at 17 years. This almost poetic movement reveals the intricate biological processes that govern their dynamic life cycle. It recommends that genetic programming and environmental signals are equally important to their development.
Implications for Future Research
The ramifications of this research are not only limited to the 17-year cicadas, but may apply to the 13-year cicadas as well. Researchers do anticipate that the basic elements of the life-cycle control mechanisms should be comparable across both types. This is likely due to an intrinsic genetic growth rate difference that favors the faster growing species. This difference may help to understand why they have different timelines for achieving culling body weights.
Namiho Saito and colleagues posed a pertinent question in their research: “When and how do 17-year periodical cicada nymphs decide to emerge?” As they continue to investigate this phenomenon, understanding the precise nature of these growth cycles could shed light on broader ecological impacts and evolutionary strategies within the insect world.