Ischemic tolerance and cardiac repair in the spiny mouse (Acomys)

Ischemic heart disease and by extension myocardial infarction is the primary cause of death worldwide, warranting regenerative therapies to restore heart function. Current models of natural heart regeneration are restricted in that they are not of adult mammalian origin, precluding the study of class-specific traits that have emerged throughout evolution, and reducing translatability of research findings to humans. Here, we present the spiny mouse (Acomys spp.), a murid rodent that exhibits bona fide regeneration of the back skin and ear pinna, as a model to study heart repair. By comparing them to ordinary mice (Mus musculus), we show that the acute injury response in spiny mice is similar, but with an associated tolerance to infarction through superior survivability, improved ventricular conduction, and near-absence of pathological remodeling. Critically, spiny mice display increased vascularization, altered scar organization, and a more immature phenotype of cardiomyocytes, with a corresponding improvement in heart function. These findings present new avenues for mammalian heart research by leveraging unique tissue properties of the spiny mouse.

Ecological niche modeling of genetic lineages of the great gerbil, Rhombomys opimus (Rodentia: Gerbillinae)

Great gerbil (Rhombomys opimus Lichtenstein, 1823) is distributed in Central Asia and some parts of the Middle East. It is widely found in central and northeast parts of Iran with two distinct genetic lineages: R. o. sodalis in the northern slopes of the Elburz Mountains and R. o. sargadensis in the southern slopes. This large rodent acts as the main host of natural focal diseases. No study has surveyed the ecological niche of the lineages and how their distribution might be influenced by different climatic variables. To examine the distribution patterns of this murid rodent, we aimed to determine the habitat preferences and effects of environmental variables on the ecological niche. Using a species distribution approach for modeling of regional niche specialization, suitable habitats predicted for R. o. sodalis were mainly located in Golestan province in northern Iran, along the northern slope of Elburz, while R. o. sargadensis, showed great potential distribution along the southern slope of Elburz and around the Kavir Desert and the Lut Desert. Despite the widest potential distribution of R. o. sargadensis from northeast to northwest and through Central Iran, the geographic range of R. o. sodalis was smaller and mostly confined to Golestan province. The results support the presence of the two genetic lineages of Rhombomys in Iran and confirm that there is no significant niche overlap between the two subspecies. Furthermore, it provided several perspectives for future taxonomic studies and prevention hygiene programs for public health.

Bright daytime light enhances circadian amplitude in a diurnal mammal

Mammalian circadian rhythms are orchestrated by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN), which receives information about the 24 h light–dark cycle from the retina. The accepted function of this light signal is to reset circadian phase in order to ensure appropriate synchronization with the celestial day. Here, we ask whether light also impacts another key property of the circadian oscillation, its amplitude. To this end, we measured circadian rhythms in behavioral activity, body temperature, and SCN electrophysiological activity in the diurnal murid rodent Rhabdomys pumilio following stable entrainment to 12:12 light–dark cycles at four different daytime intensities (ranging from 18 to 1,900 lx melanopic equivalent daylight illuminance). R. pumilio showed strongly diurnal activity and body temperature rhythms in all conditions, but measures of rhythm robustness were positively correlated with daytime irradiance under both entrainment and subsequent free run. Whole-cell and extracellular recordings of electrophysiological activity in ex vivo SCN revealed substantial differences in electrophysiological activity between dim and bright light conditions. At lower daytime irradiance, daytime peaks in SCN spontaneous firing rate and membrane depolarization were substantially depressed, leading to an overall marked reduction in the amplitude of circadian rhythms in spontaneous activity. Our data reveal a previously unappreciated impact of daytime light intensity on SCN physiology and the amplitude of circadian rhythms and highlight the potential importance of daytime light exposure for circadian health.

Mitochondrial Genome of Rattus tiomanicus (Rodentia: Muridae) and Molecular Phylogeny of Murinae

Rattus tiomanicus is a murid rodent of considerable agricultural and public health importance in Southeast Asia. The whole mitochondrial genome of R. tiomanicus was sequenced by the Ion Torrent PGM platform. It had a total length of 16,309 bp, consisting of 13 protein-coding genes, two rRNA genes, 22 tRNA genes and two non-coding regions (L-strand replication origin and control region). Only TAA and incomplete T-stop codons were represented in the protein-coding genes. Of the tRNAs, tryptophan (W) had ACU anticodon. The cloverleaf structure for serine S1 (AGN) tRNA lacked the entire D-arm, while in lysine (K) tRNA, the DHU arm lacked the D-loop. Molecular phylogeny based on 15 mt-genes indicated R. tiomanicus having closest genetic affinity to R. rattus complex (R. rattus, R. tanezumi). There were two major clades for the Murinae subfamily namely the Rattini tribe and the Apodemini, Murini and Hydromyini tribes. The whole mitogenome of R. tiomanicus will serve as a useful dataset for studying the systematics and phylogenetic relationships of the murid rodents.

Ischemic tolerance and cardiac repair in the African spiny mouse

Ischemic heart disease and by extension myocardial infarction is the primary cause of death worldwide, necessitating regenerative therapies to restore heart function. Current models of heart regeneration are restricted in that they are not of adult mammalian origin, precluding the study of class-specific traits that have emerged throughout evolution, and reducing translatability of research findings to humans. Here, we overcome those restrictions by introducing the African spiny mouse (Acomys spp.), a murid rodent that has recently been found to exhibit bona fide regeneration of the back skin and ear pinna. We show that spiny mice exhibit tolerance to myocardial infarction through superior survivability, improved ventricular conduction, smaller scar size, and near-absence of cardiac remodeling. Critically, spiny mice display increased vascularization and cardiomyocyte expansion, with an associated improvement in heart function. These findings present new avenues for mammalian heart research by leveraging unique tissue properties of the spiny mouse.

Daily electrical activity in the master circadian clock of a diurnal mammal

Daily or circadian rhythms in mammals are orchestrated by a master circadian clock within the hypothalamic suprachiasmatic nuclei (SCN). Here, cell-autonomous oscillations in gene expression, intrinsic membrane properties, and synaptic communication shape the electrical landscape of the SCN across the circadian day, rendering SCN neurons overtly more active during the day than at night. This well-accepted hallmark bioelectrical feature of the SCN has overwhelmingly emerged from studies performed on a small number of nocturnal rodent species. Therefore, for the first time, we investigate the spontaneous and evoked electrical activity of SCN neurons in a diurnal mammal. To this end, we measured the electrical activity of individual SCN neurons during the day and at night in brain slices prepared from the diurnal murid rodent Rhabdomys pumilio and then developed cutting-edge data assimilation and mathematical modelling approaches to uncover the underlying ionic mechanisms. We find that R. pumilio SCN neurons were more excited in the day than at night, recapitulating the prototypical pattern of SCN neuronal activity previously observed in nocturnal rodents. By contrast, the evoked activity of R. pumilio neurons included a prominent suppressive response that is not present in the SCN of nocturnal rodents. Our computational modelling approaches reveal transient subthreshold A-type potassium channels as the primary determinant of the suppressive response and highlight a key role for this ionic mechanism in tuning excitability of clock neurons and optimising SCN function to accommodate R. pumilio’s diurnal niche.

Daytime light enhances the amplitude of circadian output in a diurnal mammal

Mammalian circadian rhythms are orchestrated by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN), which receives information about the 24 h light:dark cycle from the retina. The accepted function of this light signal is to reset circadian phase in order to ensure appropriate synchronisation with the celestial day. Here, we ask whether light also impacts another key property of the circadian oscillation, its amplitude. To this end, we measured rhythms in behavioural activity and body temperature, and SCN electrophysiological activity in the diurnal murid rodent Rhabdomys pumilio following stable entrainment to 12:12 light:dark cycles at 4 different daytime intensities (ranging from 12.77 to 14.80 log melanopsin effective photons/cm2/s). Rhabdomys showed strongly diurnal activity and body temperature rhythms in all conditions, but measures of rhythm robustness were positively correlated with daytime irradiance under both entrainment and subsequent free run. Whole-cell and extracellular recordings of electrophysiological activity in ex vivo SCN revealed substantial differences in electrophysiological activity between dim and bright light conditions. At lower daytime irradiance, daytime peaks in SCN spontaneous firing rate and membrane depolarisation were substantially depressed, leading to an overall marked reduction in the amplitude of circadian rhythms in spontaneous activity. Our data reveal a previously unappreciated impact of daytime light intensity on SCN physiology and the amplitude of circadian rhythms, and highlight the potential importance of daytime light exposure for circadian health.

Dietary morphology of two island-endemic murid rodent clades is consistent with persistent, incumbent-imposed competitive interactions

A lineage colonizing a geographic region with no competitors may exhibit rapid diversification due to greater ecological opportunity. The resultant species diversity of this primary-colonizing (incumbent) clade may limit subsequent lineages' ability to persist unless these non-incumbent lineages are ecologically distinct. We compare the diversity in diet-related mandibular morphology of two sympatric murid rodent clades endemic to Luzon Island, Philippines—incumbent Phloeomyini and secondary-colonizing Chrotomyini—to the mandibular morphological diversity of Sahul Hydromyini, the sister clade of Chrotomyini and the incumbent murid lineage on the supercontinent of Sahul. This three-clade comparison allows us to test the hypothesis that incumbent lineages can force persistent ecological distinction of subsequent colonists at the time of colonization and throughout the subsequent history of the two sympatric clades. We find that Chrotomyini forms a subset of the diversity of their clade plus Sahul Hydromyini that minimizes overlap with Phloeomyini. We also infer that this differentiation extends to the stem ancestor of Chrotomyini and Sahul Hydromyini, consistent with a biotic filter imposed by Phloeomyini. Our work illustrates that incumbency has the potential to have a profound influence on the ecomorphological diversity of colonizing lineages at the island scale even when the traits in question are evolving at similar rates among independently colonizing clades.

Commensalism outweighs phylogeographical structure in its effect on phenotype of a Sudanian savanna rodent

The murid rodent Praomys daltoni is widespread in Sudanian savanna and woodlands of West Africa, and previous study of mitochondrial DNA variability suggested that it encompasses the phenotypically (small, grey-bellied) and ecologically (commensal) distinct form, Praomys derooi. Here, we comprehensively examined the genetic and morphological diversity within the complex. Six mitochondrial lineages showed a fine-scale phylogeographical pattern, whereas delimitation based on nuclear loci pooled four of them into a single widespread unit. A newly discovered lineage from southern Mauritania stands apart from the rest of the complex and might represent an unrecognized species. At the same time, the internal position of P. derooi (C2 mitochondrial lineage) was confirmed by the multilocus analysis. The magnitude of genetic distances between major phylogeographical lineages was typical for interspecific divergence in other clades of Praomys, despite the little differences among them in morphology (skull and upper molar row shapes). The most pronounced morphological shift was associated with a transition to commensalism, especially in P. derooi, but also in other lineages. This makes the whole complex a suitable model for the study of phenotypic novelty, the evolution of commensalism and conditions for ecological speciation.

A capture of a lesser bandicoot rat Bandicota bengalensis (Rodentia, Muridae) at Callao Port, Perú

The Lesser bandicoot rat Bandicota bengalensis (Gray and Hardwicke, 1833) is a murid rodent distributed mostly in Asia that can cause substantial negative economic impact in urban and rural areas. Until now, the species has been mostly restricted to the Asian region; and no specimen has been captured or reported as a stowaway arriving to an American port. Here, I report on one specimen captured in Callao’s maritime port, Peru, during sanitary inspection surveillance, identified based on external and cranial characteristics, and similar meristic reported values. This finding shows the potential threat of this species as an invasive alien species and highlights the need for strengthening invasive species protocols on ships.