9812779 Simon Collection of the co-emergence of 13- and 17-year periodical cicadas In 1998 there will be a joint emergence of the only two broods of 13- and 17-year cicadas whose ranges currently overlap. This happens only once every 221 years, and will provide a unique opportunity to study interactions between the two life-cycle-types in natural populations. Previous research by the principal investigator and co-workers has demonstrated that 13- and 17-year cicadas, Magicicada tredecim and M. septendecim, have evolved as distinct evolutionary units or species but that in an area of the midwestern United States termed "the anomalous zone" 17-year cicadas have permanently switched their life cycle to 13-years. This life-cycle-switching has allowed genetic mixing between formerly isolated species and could lead to significant genetic changes in the 13-year cicadas. The 17-year cicadas will not be affected because the movement of genes goes only in one direction--from 17- to 13-year cicadas via a four-year shortening of the 17-year life cycle. In this project we will collect and observe 13- and 17-year cicadas in their zones of overlap. In addition, past studies have concentrated on the largest pair of 13- and 17-year cicadas, Magicicada tredecim and M. septendecim. There are two smaller species pairs-- Magicicada tredecassini/M. cassini and M. tredecula/M. septendecula--that have not been studied in detail and will provide replicates for comparison. Periodical cicadas occur only in the eastern U.S. east of the great plains. Earlier studies have identified three strong genetic boundaries where gene exchange may be occurring between life cycles and species. We will collect specimens and study species interactions in the field. The most interesting areas are those where 13- and 17-year cicadas are sympatric (Oklahoma) or parapatric (North Carolina, Eastern Tennessee and North Georgia). One team will focus in the S W and the other in the SE; each will then work toward the Midwest. The Midwest is extremely important because the "anomalous zone" had not been discovered the last time that Brood XIX emerged, and sampling did not focus on the most important areas. Similarly, when Brood IV was sampled in 1981, it was not known that in 1985 13-year Brood XIX would emerge in the same trees in McCurtain County, Oklahoma. McCurtain County, Oklahoma, is the only area of the country where true 13- and 17-year cicadas overlap. By a stroke of good luck, the exact locality where Brood IV and XIX were observed in the same trees in 1981 and 1985--where the Little River crosses Hwy 259-lies in the heart of a US Fish and Wildlife Service (USFWS) refuge that was created 11 years ago. "The Little River National Wildlife Refuge" comprises 12,000 acres of mixed hardwood and pine forests and should ensure the future of the periodical cicadas in this area. Another focus for collecting will be the area where 13-year Brood XIX overlaps 17-year Brood III in southeastern Iowa. Last year 17-year Brood III was collected in areas in which eggs scars of both Brood III (from 1980) and Brood XIX (from 1985) had been found in the same trees. In the spring of 1998, collections will be made of Brood XIX in this same area for comparison. Finally, in North Carolina, eastern Tennessee and North Georgia, 13-year Brood XIX emerges in close proximity to three 17-year Broods (II, VI, and/or XIV). It is possible that formation of these four broods was interrelated and specimens collected this year in this area may shed light on this process. In preparation for the joint emergence, five diverse genetic markers were developed that can be used to explore hypotheses generated by previous research in our lab. If successful, this research will contribute to the growing body of evidence that hybridization between species is more common than previously recognized and can significantly influence the genetics of evolving species.
