Triplicate parallel life cycle divergence despite gene flow in periodical cicadas

Area of Science:

• Evolutionary Biology
• Genomics
• Entomology

Background:

• Periodical cicadas display parallel divergence in 13- and 17-year life cycles across multiple species groups.
• The underlying genetic mechanisms and evolutionary processes driving this synchronized divergence remain largely unknown.
• An anciently diverged 13-year species, *Magicicada tredecim*, presents a unique case within this evolutionary pattern.

Purpose of the Study:

• To investigate the demographic history and genomic evolution associated with the parallel divergence of periodical cicada life cycles.
• To identify potential genetic factors responsible for maintaining distinct 13- and 17-year life cycles despite gene flow.

Main Methods:

• Comparative analysis of orthologous transcriptome sequences from different periodical cicada species.
• Demographic modeling to infer historical population dynamics.
• Examination of sequence divergence, single-nucleotide polymorphisms (SNPs), and specific loci across species groups.

Main Results:

• Species pairs with 13- and 17-year cycles share similar demographic histories, with divergence estimated between 200,000-100,000 years ago.
• Significant gene flow occurs between 13- and 17-year species during co-emergences, yet life cycle differences persist.
• Minimal sequence divergence was observed between 13- and 17-year species (excluding *M. tredecim*), with no universally shared divergent SNPs or loci identified.

Conclusions:

• The parallel evolution of 13- and 17-year life cycles in periodical cicadas appears to be governed by a highly restricted set of genomic differences.
• Life cycle divergence is maintained despite ongoing gene flow, highlighting potential mechanisms for reproductive isolation or selection on limited genetic variation.