Comparative analyses of simple sequence repeats (SSRs) in 23 mosquito species genomes: Identification,...

Simple sequence repeats (SSRs) exist in both eukaryotic and prokaryotic genomes and are the most popular genetic markers, but the SSRs of mosquito genomes are still not well understood. In this study, we identified and analyzed the SSRs in 23 mosquito species using Drosophila melanogaster as reference at the whole-genome level. The results show that SSR numbers (33 076-560 175/genome) and genome sizes (574.57-1342.21 Mb) are significantly positively correlated (R² = 0.8992, P < 0.01), but the correlation in individual species varies in these mosquito species. In six types of SSR, mono- to trinucleotide SSRs are dominant with cumulative percentages of 95.14%-99.00% and densities of 195.65/Mb-787.51/Mb, whereas tetra- to hexanucleotide SSRs are rare with 1.12%-4.22% and 3.76/Mb-40.23/Mb. The (A/T)n, (AC/GT)n and (AGC/GCT)n are the most frequent motifs in mononucleotide, dinucleotide and trinucleotide SSRs, respectively, and the motif frequencies of tetra- to hexanucleotide SSRs appear to be species-specific. The 10-20 bp length of SSRs are dominant with the number of 110 561 ± 93 482 and the frequency of 87.25% ± 5.73% on average, and the number and frequency decline with the increase of length. Most SSRs (83.34% ± 7.72%) are located in intergenic regions, followed by intron regions (11.59% ± 5.59%), exon regions (3.74% ± 1.95%), and untranslated regions (1.32% ± 1.39%). The mono-, di- and trinucleotide SSRs are the main SSRs in both gene regions (98.55% ± 0.85%) and exon regions (99.27% ± 0.52%). An average of 42.52% of total genes contains SSRs, and the preference for SSR occurrence in different gene subcategories are species-specific. The study provides useful insights into the SSR diversity, characteristics and distribution in 23 mosquito species of genomes.