Behavior and evolution of periodical cicadas (<italic>Magicicada</italic> spp.).

Abstract

Periodical cicadas (<italic>Magicicada</italic>) live underground for 13 or 17 years before emerging synchronously as adults in dense populations containing up to four synchronized species. Intensive study of <italic>Magicicada </italic> has yielded findings of relevance to topics including lek evolution and allochronic speciation. Conspecific male calls attract both sexes to mating aggregations, where females remain stationary while males alternate calling bouts with flights. This study revealed that pair-formation occurs when females respond to conspecific male calls with timed wing-flicks, perceived acoustically and visually by males. Playback experiments using model <italic>Magicicada septendecim</italic> calls suggest that one call component, the terminal downslur, increases recognizeability of the call terminus against the background chorus. When in courtship, males compete acoustically by jamming the downslurs of potential interlopers with interference buzzes. Intense female-choice-driven sexual selection does not characterize the non-resource-based leks of <italic>Magicicada septendecim</italic>. Most females mate only once, and most do not delay mating more than a day after becoming mature. Patterns of male mating success suggest threshold-based female mating criteria. Variance in male mating success in a cage population was insignificantly skewed from that expected under random mating, and not skewed among mated males. When small groups of males and females are mated, separated at the onset of copulation, and then mated again, male mating order is not repeated. Interspecific interactions have driven tandem evolution of acoustic calling and courtship signals in a previously unrecognized 13-year species, <italic> Magicicada neotredecim</italic>, which likely formed by allochronic speciation from central U.S. populations of a 17-year sibling, <italic>M. septendecim </italic>. Late-emerging stragglers from <italic>M. neotredecim</italic> may explain historical records that imply changing brood distributions in the Midwest. <italic>Magicicada neotredecim</italic> exhibits reproductive character displacement in call pitch where it overlaps its closest 13-year relative, <italic> M. tredecim</italic>. Playback trials with <italic>M. septendecim</italic> suggest that <italic>M. neotredecim</italic> females possessed the capacity to respond to <italic>M. tredecim</italic> calls upon first contact; however, patterns of abdomen color variation do not suggest hybridization in the 13-year overlap zone. Playback data suggest that song divergence can be driven in part by acoustic background interference.