Olfactory receptors (ORs) are membrane proteins that mediate the detection of odorants in the environment, and are the largest vertebrate gene family. Comparative studies of mammalian genomes indicate that OR repertoires vary widely, even between closely related lineages, as a consequence of frequent OR gains and losses. Several studies also suggest that mammalian OR repertoires are influenced by life history traits. Sauropsida is a diverse group of vertebrates group that is the sister group to mammals, and includes birds, testudines, squamates, and crocodilians, and represents a natural system to explore predictions derived from mammalian studies. In this study, we analyzed olfactory receptor (OR) repertoire variation among several representative species and found that the number of intact OR genes in sauropsid genomes analyzed ranged over an order of magnitude, from 108 in the green anole to over 1,000 in turtles. Our results suggest that different sauropsid lineages have highly divergent OR repertoire composition that derive from lineage-specific combinations of gene expansions, losses, and retentions of ancestral OR genes. These differences also suggest that varying degrees of adaption related to life history have shaped the unique OR repertoires observed across sauropsid lineages.

BackgroundAround 40 million years ago DNA transposons began accumulating in an ancestor of bats in the family Vespertilionidae. Since that time, Class II transposons have been continuously reinvading and accumulating in vespertilionid genomes at a rate that is unprecedented in mammals. Miniopterus (Miniopteridae), a genus of long-fingered bats that was recently elevated from Vespertilionidae, is the sister taxon to the vespertilionids and is often used as an outgroup when studying transposable elements in vesper bats. Previous wet-lab techniques failed to identify Helitrons, TcMariners, or hAT transposons in Miniopterus. Limitations of those methods and ambiguous results regarding the distribution of piggyBac transposons left some questions as to the distribution of Class II elements in this group. The recent release of the Miniopterus natalensis genome allows for transposable element discovery with a higher degree of precision.ResultsHere we analyze the transposable element content of M. natalensis to pinpoint with greater accuracy the taxonomic distribution of Class II transposable elements in bats. These efforts demonstrate that, compared to the vespertilionids, Class II TEs are highly mutated and comprise only a small portion of the M. natalensis genome. Despite the limited Class II content, M. natalensis possesses a limited number of lineage-specific, low copy number piggyBacs and shares several TcMariner families with vespertilionid bats. Multiple efforts to identify Helitrons, one of the major TE components of vesper bat genomes, using de novo repeat identification and structural based searches failed.ConclusionsThese observations combined with previous results inform our understanding of the events leading to the unique Class II element acquisition that characterizes vespertilionids. While it appears that a small number of TcMariner and piggyBac elements were deposited in the ancestral Miniopterus + vespertilionid genome, these elements are not present in M. natalensis genome at high copy number. Instead, this work indicates that the vesper bats alone experienced the expansion of TEs ranging from Helitrons to piggyBacs to hATs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13100-016-0071-y) contains supplementary material, which is available to authorized users.