Reproductive proteins, including those expressed in the testes, are among the fastest evolving proteins across the tree of life. Sexual selection on traits involved in sperm competition is thought to be a primary driver of testes gene evolution and is expected to differ between promiscuous and monogamous species due to intense competition between males to fertilize females in promiscuous lineages and lack thereof in monogamous ones. Here, we employ the rodent genus Peromyscus as a model to explore differences in evolutionary rates between testis-expressed genes of monogamous and promiscuous species. We find candidate genes that may be associated with increased sperm production in promiscuous species and gene ontology categories that show patterns of molecular convergence associated with phenotypic convergence in independently evolved monogamous species. Overall, our results highlight possible molecular correlates of differences in mating system, which can be contextualized in light of expected selective pressures.
Broad transcriptomic sequencing of eukaryotes has revealed the ubiquity of splicing of nuclear genes. While the vast majority of splicing events join segments of the same RNA transcript, various studies have found a few intriguing cases of trans--splicing of introns, in which splicing events within protein coding regions join segments of different RNA transcripts. The most structurally intricate case known involves the bursicon gene in mosquitos, in which an internal exon is encoded at a distinct locus, requiring multiple trans--splicing events form the mature mRNA. This arrangement is known to be ancestral to mosquitos, however the exact timing of the origin of trans--splicing and the history of the bursicon gene within mosquitos is unknown. Taking advantage of the recent availability of genomes from various Anopheles mosquitos and from relatives of mosquitos, I determined trans versus cis encoding of bursicon across Culicomorpha. I conclude that trans--splicing emerged in the last common ancestor of mosquitos, and that trans--splicing has been retained in all 19 studied Anopheles species. The retention of trans--splicing could indicate functional importance of this arrangement, or could alternatively reflect the rarity of mutations giving rise to viable allelic alternatives. In eukaryotic nuclear genes, the protein--coding regions of mRNA transcripts do not represent a single contiguous genomic region, but rather are spliced together from RNA segments representing different DNA regions (Roy and Irimia 2014). Almost always, these segments represent subsegments of a single RNA transcript which are joined by a molecular machine called the spliceosome. Portions that are retained in the mature mRNA are termed exons while the internal removed sections are termed introns. Much more rarely, the protein--coding region of an mRNA can be formed by splicing together portions of RNA transcripts transcribed from different genomic loci, that is, trans--splicing of introns (Li et al.
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