Transcriptome analysis of Calligrapha (Chrysomelidae) testis: functional annotation and orthology assessment of male-biased genes

Abstract

We report the architecture of testis transcriptomes of four closely related species of Calligrapha (Chrysomelidae) beetles, which diverged during the last 3 million years. Our main goal is finding male - biased genes in this genus, which has the added interest of including several female - only species, evolutionarily derived via interspecific hybridization from bisexual species. Five cDNA libraries were sequenced using Illumina HiSeq technology, retrieving 102,884 - 176,514 assembled reads, 43 - 61% of which were functionally annotated. Annotation and sequence similarity comparisons of these libraries revealed high homogeneity in gene composition and the presence of several functional candidates related to reproduction or reproductive processes (0.86 - 1. 41% of annotated genes). Stringent sequence similarity analyses of these transcriptomes against male - biased genes empirically demonstrated in Drosophila melanogaster and Tribolium castaneum allowed identifying 76 candidate genes putatively over - expressed i n Calligrapha males. Some of these genes — including CG9313, Tektin - A or tomboy40 — are confirmed as orthologs of these male - biased genes using phylogenetic inference and available model insect data. The obtained phylogenies show the expected relationships amo ng insect groups, with some lineage - specific gene duplications, although never affecting Coleoptera or the clade of Calligrapha . Extrapolating from the functional study of T. castaneum , we can deduce that our Calligrapha genes may represent functional homo logs to these male - biased genes too. Our transcriptomes therefore represent a valuable genomic resource for the analysis of male - biased genes in Calligrapha . This resource simultaneously represents a landmark for similar studies in Coleoptera, broadening t he taxonomic diversity currently represented only by the model species T. castaneum , and incipient genomic data in other herbivorous lineages, including weevils, longhorn beetles and leaf beetles.