Abstract
We investigate competition between separate periodical cicada populations each possessing different life‐cycle lengths. We build an individual‐based model to simulate the cicada life cycle and allow random migrations to occur between patches inhabited by the different populations. We show that if hybridization between different cycle lengths produces offspring that have an intermediate life‐cycle length, then predation acts disproportionately to select against the hybrid offspring. This happens because they emerge in low densities without the safety‐in‐numbers provided by either parent population. Thus, prime‐numbered life cycles that can better avoid hybridization are favored. However, we find that this advantage of prime‐numbered cycles occurs only if there is some mechanism that can occasionally synchronize emergence between local populations in sufficiently many patches.
Highlights
Periodical cicadas (Magicicada spp.) are famous for their long, synchronous, and prime-numbered life cycles
Our results show that if all the life cycles in the periodical cicada population share a common initial starting age, that is, all subpopulations consist of newborns at the beginning of a simulation, prime-numbered cycles are favored
If we assume random starting ages for each subpopulation, prime numbers have no particular advantage in terms of reduced number of coemergences and we do not observe that prime-numbered cycles would be favored over nonprime-numbered cycles
Summary
Periodical cicadas (Magicicada spp.) are famous for their long, synchronous, and prime-numbered life cycles. Size-based emergence refers to an emergence strategy, where an individual emerges from the ground to mate immediately upon reaching some threshold body size. Age-based emergence refers to an emergence strategy where an individual waits for a fixed number of years before emergence. In a nonperiodical cicada population, individuals have variable life-cycle lengths and typically some individuals emerge each year from the ground to mate. Periodical cicada populations on the other hand display a life cycle where all individuals stay in the ground for a fixed number of years and emerge synchronously at the end of their life cycle. The large numbers of individuals emerging simultaneously have been thought of as a mechanism to reduce per capita mortality due to predation, as in a large crowd the probability of any given individual to be eaten is small (Karban, 1982)
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