Evolution

Cicada Cycles

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Science  05 Apr 2013:
Vol. 340, Issue 6128, pp. 10
DOI: 10.1126/science.340.6128.10-a
CREDIT: © SHELLIE GONZALEZ

The bizarre life cycle of the cicadas (genus Magicada) of eastern North America entails many years spent underground as larvae, before emerging synchronously as adults for a few brief weeks of sexual activity. Southern species have 13-year life cycles, whereas northern species have 17-year cycles. At any location, there are generally three species groups, all of which are synchronized with each other. The species groups are thought to have diverged allopatrically (i.e. geographically separated) before becoming sympatric as they are now. Several selective factors leading to the evolution of these life history patterns have been hypothesized, but in the absence of comprehensive phylogenetic data, they have proved difficult to test. Sota et al. have now addressed this gap, by conducting a thorough phylogenetic analysis of all known Magicicada species using nuclear and mitochondrial DNA markers. The resulting combination of phylogenetic and geographical patterns suggests a complex history of evolution—some of it quite recent—accompanying the habitat shifts in North America during the Pleistocene glacial cycles. The results are consistent with the allopatric divergence model and show that the splits into 13-year and 17-year species occurred multiple times within each species group. It appears that selection favored the evolution of synchronized population cycles between invading and resident species, simultaneously affording invaders protection from predation and avoidance of the adverse reproductive consequences of low population density.

Proc. Natl. Acad. Sci. U.S.A., 110, 10.1073/pnas.1220060110 (2013).

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