Insights into chromosomal evolution of Cicadomorpha using fluorochrome staining and mapping 18S rRNA and H3 histone genes

Abstract

The infraorder Cicadomorpha (Hemiptera) is a cosmopolitan species-rich lineage of phytophagous insects. They have holocentric chromosomes and vary greatly in diploid number across families, with X0 as the predominant sex male mechanism. Here, we advance the understanding of chromosome mapping of repetitive elements of four families of cicadomorphan insects, the spittlebugs (Cercopidae), leafhoppers (Cicadellidae), and treehoppers (Aetalionidae and Membracidae). Sampled individuals from 19 species show considerable variation in diploid number, which may have originated from fusions between autosomes or between autosomes and the ancient X. The distribution of CMA3+ blocks, primarily observed in low numbers in autosomal regions, was a conserved trait. Likewise, fluorescence in situ hybridization (FISH) mapping revealed mainly one locus per haploid genome for the 18S rRNA gene and for H3, each of which is located on distinct chromosomes. Despite the extensive variation in the number of autosomes and sex systems, the number of loci of ribosomal and H3 genes remained stable and may reflect the ancestral genome organizations in these groups. These results shed light on the chromosomal-level organization in Cicadomorpha and provide new insights into the evolutionary history of karyotypes and repetitive elements in this diverse insect lineage.