Abstract
The periodical cicadas of the genus Magicicada Davis, 1925 inhabiting eastern United States are characterized by a long juvenile period of 17 or 13 years and periodical mass emergence of adults. In this genus, only seven species are distinguished and are distributed into three species groups, Decim, Cassini and Decula. We performed comparative cytogenetic study of all seven Magicicada species, and 6 of them were explored for the first time. The techniques used included standard chromosome staining, differential chromosome staining techniques (C-banding, AgNOR-banding and fluorochrome DAPI-staining) and FISH (fluorescence in situ hybridization) with 18S rDNA and (TTAGG)n-telomeric probes. All these species have holokinetic chromosomes, like other Hemiptera. Karyotypes of all species appeared to be remarkably conserved with 2n = 19/20 (18 + X0/XX) (male/female); one very large pair of autosomes and all other chromosomes constituting a decreasing size series; X chromosomes were indistinguishable, at least, at mitotic metaphases. The nucleolus organizer regions (NORs) revealed on one of the medium-sized chromosome pairs in all species and were shown to coincide with the rDNA clusters revealed by FISH. In all species, very small blocks of C-heterochromatin were variously located on chromosomes clearly using DAPI but less distinctly by C-banding. The chromosomes of all the species studied were confirmed to contain the "insect type" motif of telomeres (TTAGG)n.
Highlights
IntroductionThe genus Magicicada Davis, 1925 includes periodical cicadas that occur in the eastern United States, have a long juvenile period of 17 or 13 years and periodical mass emergence of adults
The periodical cicadas of the genus Magicicada Davis, 1925 inhabiting eastern United States are characterized by a long juvenile period of 17 or 13 years and periodical mass emergence of adults
The nucleolus organizer regions (NORs) revealed on one of the medium-sized chromosome pairs in all species and were shown to coincide with the rDNA clusters revealed by fluorescence in situ hybridization (FISH)
Summary
The genus Magicicada Davis, 1925 includes periodical cicadas that occur in the eastern United States, have a long juvenile period of 17 or 13 years and periodical mass emergence of adults. There are seven species in Magicicada in three species groups (Decim, Cassini and Decula). The Decim group contains the 17-year species M. septendecim (Linnaeus, 1758) and two 13-year species M. neotredecim (Marshall & Cooley, 2000) and M. tredecim (Walsh & Riley, 1868). The Decula group contains the 17-year species M. septendecula Alexander & Moore, 1962 and the 13-year species from the Midwestern and southern part of the eastern United States: M. tredecula Alexander & Moore, 1962 (Alexander & Moore, 1962; Marshall & Cooley, 2000; Cooley et al, 2001; for other references see Williams & Simon, 1995). The 17- and 13-year species within the same species groups differ only in the length of juvenile period, except for M. tredecim for which the pitch of male song differs. The parallel divergence of 13- and 17-year life cycles in the three periodical cicada groups was recently evidenced by molecular phylogenetic and population genetic analyses (Sota at al., 2013; Fujisawa et al, 2018; Du et al, 2019)
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