Abstract
For rodents, olfaction is essential for locating food, recognizing mates and competitors, avoiding predators, and navigating their environment. It is thought that rodents may have expanded olfactory receptor repertoires in order to specialize in olfactory behavior. Despite being the largest clade of mammals and depending on olfaction relatively little work has documented olfactory repertoires outside of conventional laboratory species. Here we report the olfactory receptor repertoire of the African giant pouched rat (Cricetomys ansorgei), a Muroid rodent distantly related to mice and rats. The African giant pouched rat is notable for its large cortex and olfactory bulbs relative to its body size compared to other sympatric rodents, which suggests anatomical elaboration of olfactory capabilities. We hypothesized that in addition to anatomical elaboration for olfaction, these pouched rats might also have an expanded olfactory receptor repertoire to enable their olfactory behavior. We examined the composition of the olfactory receptor repertoire to better understand how their sensory capabilities have evolved. We identified 1145 intact olfactory genes, and 260 additional pseudogenes within 301 subfamilies from the African giant pouched rat genome. This repertoire is similar to mice and rats in terms of size, pseudogene percentage and number of subfamilies. Analyses of olfactory receptor gene trees revealed that the pouched rat has 6 expansions in different subfamilies compared to mice, rats and squirrels. We identified 81 orthologous genes conserved among 4 rodent species and an additional 147 conserved genes within the Muroid rodents. The orthologous genes shared within Muroidea suggests that there may be a conserved Muroid-specific olfactory receptor repertoire. We also note that the description of this repertoire can serve as a complement to other studies of rodent olfaction, as the pouched rat is an outgroup within Muroidea. Thus, our data suggest that African giant pouched rats are capable of both natural and trained olfactory behaviors with a typical Muriod olfactory receptor repertoire.
Highlights
In rodents, olfaction is essential for a number of behaviors including social recognition [1], sexual behavior [2], predator detection [3], and finding food [4]
We identified 1145 intact pouched rat olfactory receptors (ORs) from the pouched rat genome using our manual pipeline method, which is -sized compared to repertoires of mouse and rat (S2 and S3 Files)
To compare pouched rat subfamilies with other species, we produced a gene tree using the sequences identified during manual pipeline search (Fig 4; S5 File), which illustrates that for most mouse, rat, and squirrel ORs subfamilies, there is at least one pouched rat OR (A comparative tree using pouched rat sequences obtained from the Olfactory Receptor Assigner (ORA) was visually similar in structure, and the tree file is provided in the supplement: S6 File)
Summary
Olfaction is essential for a number of behaviors including social recognition [1], sexual behavior [2], predator detection [3], and finding food [4]. The giant pouched rat (Cricetomys ansorgei) olfactory receptor repertoire system, the former of which contains the olfactory receptors (ORs) which transduce odorants into a perceived ‘smell’ [5]. The repertoire of these ORs has been of particular interest, as the OR gene family is one of the largest in the genome, and the overall number of functional receptor genes is thought to correlate with olfactory perceptual ability [6]. Expansion and contraction of the OR repertoire (i.e. functional OR genes) among species is thought to correlate with changing environmental niche–e.g., animals that use vision primarily for navigation and recognition tend to have more pseudogenes compared to functional ORs [7,8,9]. Certain families of ORs are associated with diet and niche, with larger repertoires generally associated with asocial, terrestrial, and diurnal species [[10,11] but see [12]]
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