Variation and Selection in the Putative Sperm-Binding Region of ZP3 in Muroid Rodents: A Comparison between Cricetids and Murines

In mammals, the zona pellucida glycoprotein 3 (ZP3) is considered a primary sperm receptor of the oocyte and is hypothesized to be involved in reproductive isolation. We investigated patterns of diversity and selection in the putative sperm-binding region (pSBR) of mouse ZP3 across Cricetidae and Murinae, two hyperdiverse taxonomic groups within muroid rodents. In murines, the pSBR is fairly conserved, in particular the serine-rich stretch containing the glycosylation sites proposed as essential for sperm binding. In contrast, cricetid amino acid sequences of the pSBR were much more variable and the serine-rich motif, typical of murines, was generally substantially modified. Overall, our results suggest a general lack of species specificity of the pSBR across the two muroid families. We document statistical evidence of positive selection acting on exons 6 and 7 of ZP3 and identified several amino acid sites that are likely targets of selection, with most positively selected sites falling within or adjacent to the pSBR.

Identification keys to murid rodents of Argentina

Muroid rodents are the most species-rich superfamily of rodents occurring in Argentina. Increased fieldwork with these mammals depicts the need of adequate keys to identify species on the base of external characters. In this contribution we provide three keys (one for families and subfamilies, and another two for Sigmodontinae and Muridae, respectively) for all known species of Cricetidae and Muridae distributed in Argentina (42 genera and 110 species). In addition to the dichotomous keys, and as a way to facilitate the identification, we include for each species a brief description of its distribution and the main habitats where it occurs.

Linking Zoonosis Emergence to Farmland Invasion by Fluctuating Herbivores: Common Vole Populations and Tularemia Outbreaks in NW Spain

The expansion and intensification of agriculture are driving profound changes in ecosystems worldwide, favoring the (re)emergence of many human infectious diseases. Muroid rodents are a key host group for zoonotic infectious pathogens and frequently invade farming environments, promoting disease transmission and spillover. Understanding the role that fluctuating populations of farm dwelling rodents play in the epidemiology of zoonotic diseases is paramount to improve prevention schemes. Here, we review a decade of research on the colonization of farming environments in NW Spain by common voles (Microtus arvalis) and its public health impacts, specifically periodic tularemia outbreaks in humans. The spread of this colonizing rodent was analogous to an invasion process and was putatively triggered by the transformation and irrigation of agricultural habitats that created a novel terrestrial-aquatic interface. This irruptive rodent host is an effective amplifier for the Francisella tularensis bacterium during population outbreaks, and human tularemia episodes are tightly linked in time and space to periodic (cyclic) variations in vole abundance. Beyond the information accumulated to date, several key knowledge gaps about this pathogen-rodent epidemiological link remain unaddressed, namely (i) did colonizing vole introduce or amplified pre-existing F. tularensis? (ii) which features of the “Francisella—Microtus” relationship are crucial for the epidemiology of tularemia? (iii) how virulent and persistent F. tularensis infection is for voles under natural conditions? and (iv) where does the bacterium persist during inter-epizootics? Future research should focus on more integrated, community-based approaches in order to understand the details and dynamics of disease circulation in ecosystems colonized by highly fluctuating hosts.

Muroid rodents of the natural landmark “Chervone” (Dnister Canyon): specifics of species composition and community structure

We conducted an analysis of populations of muroid rodents of the Dnister Canyon National Nature Park on the example of the natural landmark “Chervone.” For the investigation of the muroid rodents, we applied the trap-line method using factory-made live traps. According to methodology, the traps were located within a homogeneous habitat and four different sites were studies. Field data collected during 2017 and 2018 (summer and autumn cenuses) in four different habitats were analysed. The species composition of muroid rodents was investigated in four different biotopes (habitats) near the Dzurynskiy waterfall: hornbeam forest, pine forest, floodplain of the Dzuryn river, and pasture. The studied habitats were identified according to the National Habitat Catalogue of Ukraine. During the research, 75 specimens of muroid rodents were caught in 800 trap-nights. We recorded six species of muroid rodents: Sylvaemus tauricus L., Sylvaemus sylvaticus L., Apodemus agrarius Pallas, Micromys minutus L., Myodes glareolus Schreber, and Microtus arvalis Pallas. The most numerous species was Sylvaemus tauricus — 23 individuals (31 %). The quantity of other species was as follows: Apodemus agrarius (28 %), Sylvaemus sylvaticus (17 %), Myodes glareolus (16 %), Microtus arvalis (7 %), and Micromys minutus (1 %). The abundance of rodents was lower during the summer period compared to autumn, which can be related to the anthropogenic pressure on the investigated area. In addition, we investigated the sex and age structure of muroid rodent populations. We discovered that 45 individuals out of 75 were males and 35 were females. Additionally, 63 individuals were adults (Ad.) and 12 were juveniles (juv.). To summarise the received data, we calculated the number of individuals per 100 trap-nights. The abundance of individuals fluctuated from near 3 ind./100 t.-n. (Sylvaemus tauricus) to 0.125 ind./100 t.-n. (Micromys minutus). The relatively low species diversity of muroid rodents in the Dnister Canyon National Nature Park could be the result of small areas of insular habitats (separated territories with relatively similar landscape) and strong fragmentation of the researched area.

Relationship Between the Social Structure and Potential Reproductive Success in Muroid Rodents (Rodentia, Myomorpha)

In many systematic groups of mammalian species, the evolution of sociality leads to the formation of large social groups (group-size evolution). In rodents, however, the most social species live in family groups consisting, as a rule, of not numerous individuals. The family-group lifestyle of some ground-dwelling sciurids (Sciuridae) and voles (Microtus) results in fewer breeding adult females, a decreased litter size, and a longer time till first reproduction. Statistical analysis of published data has been conducted in the present study and has shown that transition to the family-group lifestyle leads to a decreased potential reproductive success in many muroid rodents: females produce fewer litters and, consequently, fewer pups during the reproduction season. However, the potential reproductive success in muroid rodents with a family-group lifestyle could be increased due to delayed offspring dispersal (who spend the severe winter period in family groups) and extensive cooperation in foraging, defending their territory and food stores, as well as in care-giving activities. One can suggest that females of these species produce fewer offspring, but of “better quality”. Ultimately, social rodent species may gain inclusive fitness benefits because of the higher fitness of their offspring as compared to solitary dwellers and gregarious species.

Dynamic Evolution of De Novo DNA Methyltransferases in Rodent and Primate Genomes

Transcriptional silencing of retrotransposons via DNA methylation is paramount for mammalian fertility and reproductive fitness. During germ cell development, most mammalian species utilize the de novo DNA methyltransferases DNMT3A and DNMT3B to establish DNA methylation patterns. However, many rodent species deploy a third enzyme, DNMT3C, to selectively methylate the promoters of young retrotransposon insertions in their germline. The evolutionary forces that shaped DNMT3C’s unique function are unknown. Using a phylogenomic approach, we confirm here that Dnmt3C arose through a single duplication of Dnmt3B that occurred ∼60 Ma in the last common ancestor of muroid rodents. Importantly, we reveal that DNMT3C is composed of two independently evolving segments: the latter two-thirds have undergone recurrent gene conversion with Dnmt3B, whereas the N-terminus has instead evolved under strong diversifying selection. We hypothesize that positive selection of Dnmt3C is the result of an ongoing evolutionary arms race with young retrotransposon lineages in muroid genomes. Interestingly, although primates lack DNMT3C, we find that the N-terminus of DNMT3A has also evolved under diversifying selection. Thus, the N-termini of two independent de novo methylation enzymes have evolved under diversifying selection in rodents and primates. We hypothesize that repression of young retrotransposons might be driving the recurrent innovation of a functional domain in the N-termini on germline DNMT3s in mammals.

The giant pouched rat (Cricetomys ansorgei) olfactory receptor repertoire

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 the conventional laboratory mice and rats. 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 functional 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 99 orthologous genes conserved among 4 rodent species and an additional 167 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.