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Abstract. Acoustic mate‐attracting signals of related sympatric, synchronic species are always distinguishable, but those of related allopatric species sometimes are not, thus suggesting that such signals may evolve to “reinforce” premating species isolation when similar species become sympatric. This hypothesis predicts divergences restricted to regions of sympatry in partially overlapping species, but such “reproductive character displacement” has rarely been confirmed. We report such a case in the acoustic signals of a previously unrecognized 13‐year periodical cicada species, Magicicada neotredecim, described here as a new species (see Appendix). Where M. neotredecim overlaps M. tredecim in the central United States, the dominant male call pitch (frequency) of M. neotredecim increases from approximately 1.4 kHz to 1.7 kHz, whereas that of M. tredecim remains comparatively stable. The average preferences of female M. neotredecim for call pitch show a similar geographic pattern, changing with the call pitch of conspecific males. Magicicada neotredecim differs from 13‐year M. tredecim in abdomen coloration, mitochondrial DNA, and call pitch, but is not consistently distinguishable from 17‐year M. septendecim; thus, like other Magicicada species, M. neotredecim appears most closely related to a geographically adjacent counterpart with the alternative life cycle. Speciation in Magicicada may be facilitated by life‐cycle changes that create temporal isolation, and reinforcement could play a role by fostering divergence in premating signals prior to speciation. We present two theories of Magicicada speciation by life‐cycle evolution: “nurse‐brood facilitation” and “life‐cycle canalization.”

Abstract. Acoustic mate-attracting signals of related sympatric, synchronic species are always distinguishable, but those of related allopatric species sometimes are not, thus suggesting that such signals may evolve to ''reinforce'' premating species isolation when similar species become sympatric. This hypothesis predicts divergences restricted to regions of sympatry in partially overlapping species, but such ''reproductive character displacement'' has rarely been confirmed. We report such a case in the acoustic signals of a previously unrecognized 13-year periodical cicada species, Magicicada neotredecim, described here as a new species (see Appendix). Where M. neotredecim overlaps M. tredecim in the central United States, the dominant male call pitch (frequency) of M. neotredecim increases from approximately 1.4 kHz to 1.7 kHz, whereas that of M. tredecim remains comparatively stable. The average preferences of female M. neotredecim for call pitch show a similar geographic pattern, changing with the call pitch of conspecific males. Magicicada neotredecim differs from 13-year M. tredecim in abdomen coloration, mitochondrial DNA, and call pitch, but is not consistently distinguishable from 17-year M. septendecim; thus, like other Magicicada species, M. neotredecim appears most closely related to a geographically adjacent counterpart with the alternative life cycle. Speciation in Magicicada may be facilitated by life-cycle changes that create temporal isolation, and reinforcement could play a role by fostering divergence in premating signals prior to speciation. We present two theories of Magicicada speciation by life-cycle evolution: ''nurse-brood facilitation'' and ''life-cycle canalization.''

The evolution of 13-and 17-y periodical cicadas (Magicicada) is enigmatic because at any given location, up to three distinct species groups (Decim, Cassini, Decula) with synchronized life cycles are involved. Each species group is divided into one 13-and one 17-y species with the exception of the Decim group, which contains two 13-y species-13-y species are Magicicada tredecim, Magicicada neotredecim, Magicicada tredecassini, and Magicicada tredecula; and 17-y species are Magicicada septendecim, Magicicada cassini, and Magicicada septendecula. Here we show that the divergence leading to the present 13-and 17-y populations differs considerably among the species groups despite the fact that each group exhibits strikingly similar phylogeographic patterning. The earliest divergence of extant lineages occurred ∼4 Mya with one branch forming the Decim species group and the other subsequently splitting 2.5 Mya to form the Cassini and Decula species groups. The earliest split of extant lineages into 13-and 17-y life cycles occurred in the Decim lineage 0.5 Mya. All three species groups experienced at least one episode of life cycle divergence since the last glacial maximum. We hypothesize that despite independent origins, the three species groups achieved their current overlapping distributions because life-cycle synchronization of invading congeners to a dominant resident population enabled escape from predation and population persistence. The repeated life-cycle divergences supported by our data suggest the presence of a common genetic basis for the two life cycles in the three species groups.life-cycle shift | nurse brood | parallel evolution | speciation P eriodical cicadas (Magicicada) in the eastern United States represent one of the most spectacular life history and population phenomena in nature (1-10). These periodical cicadas spend most of their lives (13 y in the south, 17 y in the north) as underground juveniles except for a brief 2-to 4-wk period when adults emerge simultaneously in massive numbers. With few exceptions, at any given location, all of the periodical cicadas share the same life cycle and emerge on the same schedule, forming a single-year class referred to as a "brood." Surprisingly, each brood consists of multiple species from three species groups (Decim, Cassini, Decula).These three groups were considered to have diverged from each other allopatrically and to have later become sympatric and formed 13-and 17-y life cycles (2). The prolonged, primenumbered life cycles were hypothesized to have evolved in response to Pleistocene climatic cooling (9, 11) to avoid the adverse effect of low population density on mating success (9, 12, 13). Another view hypothesized that the long synchronized life cycles evolved in association with the predator avoidance strategy (2,4,8) and that this took place before both the glacial periods and the split of the three species groups (10) based on approximate genetic distances among species groups (8). To test these hypotheses, phylogenetic information about the r...