A comparative characterization of laryngeal anatomy in the singing mouse.

Sexual displays are some of the most dramatic and varied behaviors that have been documented. The elaboration of such behaviors often relies on the modification of existing morphology. To understand how display elaboration arises, we analyzed the laryngeal anatomy of three species of mice that vary in the presence and complexity of their vocal displays. Mice and rats have a specialized larynx that enables them to produce both low-frequency "audible" sounds, perhaps using vocal fold vibration, as well as distinct mechanisms that are thought to enable higher frequency sounds, such as vocal membrane vibration and intralaryngeal whistles. These mechanisms rely on different structures within the larynx. Using histology, we characterized laryngeal anatomy in Alston's singing mouse (Scotinomys teguina), the northern pygmy mouse (Baiomys taylori), and the laboratory mouse (Mus musculus), which produce different types of vocalizations. We found evidence of a vocal membrane in all species, as well as species differences in vocal fold and ventral pouch size. Presence of a vocal membrane in these three species, which are not known to use vocal membrane vibration, suggests that this structure may be widespread among muroid rodents. An expanded ventral pouch in singing and pygmy mice suggests that these mice may use an intralaryngeal whistle to produce their advertisement songs, and that an expanded ventral pouch may enable lower frequencies than laboratory mouse whistle-produced sounds. Variation in the laryngeal anatomy of rodents fits into a larger pattern across terrestrial vertebrates, where the development and modification of vocal membranes and pouches, or air sacs, are common mechanisms by which vocalizations diversify. Understanding variation in the functional anatomy of relevant organs is the first step in understanding how morphological changes enable novel displays.

A new explanation for unexpected evolution in body size.

Bigger is apparently frequently fitter, and body size is typically heritable, so why don't animals in wild populations evolve towards larger sizes? Different explanations have been proposed for this apparent "paradox of stasis." A new study of snow voles in the Swiss Alps finds higher survival in animals with larger body mass and heritability of body mass, but, surprisingly, a genetic decline in body mass is also indicated. The authors suggest a novel explanation for this observation: the appearance of positive phenotypic selection is driven by a confounding variable of the age at which a juvenile is measured, whereas the evolutionarily relevant selection actually acts negatively on mass via its association with development time. Thus, genes for larger mass are not actually "fitter" because they are associated with longer development times, and juvenile snow voles with longer development times run the risk of not completing development before the first winter snow. However, the genetic decline in body size is not apparent at the phenotypic level, presumably because of countervailing trends in environmental effects on the phenotype.

Bigger Is Fitter? Quantitative Genetic Decomposition of Selection Reveals an Adaptive Evolutionary Decline of Body Mass in a Wild Rodent Population.

In natural populations, quantitative trait dynamics often do not appear to follow evolutionary predictions. Despite abundant examples of natural selection acting on heritable traits, conclusive evidence for contemporary adaptive evolution remains rare for wild vertebrate populations, and phenotypic stasis seems to be the norm. This so-called "stasis paradox" highlights our inability to predict evolutionary change, which is especially concerning within the context of rapid anthropogenic environmental change. While the causes underlying the stasis paradox are hotly debated, comprehensive attempts aiming at a resolution are lacking. Here, we apply a quantitative genetic framework to individual-based long-term data for a wild rodent population and show that despite a positive association between body mass and fitness, there has been a genetic change towards lower body mass. The latter represents an adaptive response to viability selection favouring juveniles growing up to become relatively small adults, i.e., with a low potential adult mass, which presumably complete their development earlier. This selection is particularly strong towards the end of the snow-free season, and it has intensified in recent years, coinciding which a change in snowfall patterns. Importantly, neither the negative evolutionary change, nor the selective pressures that drive it, are apparent on the phenotypic level, where they are masked by phenotypic plasticity and a non causal (i.e., non genetic) positive association between body mass and fitness, respectively. Estimating selection at the genetic level enabled us to uncover adaptive evolution in action and to identify the corresponding phenotypic selective pressure. We thereby demonstrate that natural populations can show a rapid and adaptive evolutionary response to a novel selective pressure, and that explicitly (quantitative) genetic models are able to provide us with an understanding of the causes and consequences of selection that is superior to purely phenotypic estimates of selection and evolutionary change.

Seasonal expressions of growth hormone receptor, insulin-like growth factor 1 and insulin-like growth factor 1 receptor in the scented glands of the muskrats (Ondatra zibethicus).

The growth hormone (GH)/insulin-like growth factor-1 (IGF-1) system plays an important role in regulating the cellular growth and organ development. The present study investigated the seasonal expressions of growth hormone receptor (GHR), IGF-1 and insulin-like growth factor 1 receptor (IGF-1R) in the scented glands of the muskrats. Morphological changes in the scented glands of the muskrats were observed significantly between the breeding and non-breeding seasons. Immunohistochemically, the expressions of GH, GHR, IGF-1 and IGF-1R were found in glandular cells and epithelial cells of the scented glands in both seasons. The protein and mRNA expression levels of GHR, IGF-1 and IGF-1R in the scented glands during the breeding season were noticeably higher than those of the non-breeding season. In parallel, the levels of GH and IGF-1 in the sera and scented glands were remarkably higher during the breeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed hsa-miR-5100 and mmu-miR-6937-5p might regulate the expressions of Ghr, Igf-1 or Igf-1r. These results suggested that the morphological changes in the scented glands of the muskrats during the different seasons might be related to the expression levels of GHR, IGF-1 and IGF-1R. Meanwhile, GHR/IGF-1 system might regulate the scented glandular functions via endocrine or autocrine/paracrine manners.

Morphological Variability of the Mandible Shape of the Common Vole Microtus arvalis (Rodentia, Arvicolidae) Semi-species from the Hybrid Zone.

The mandible shape of the common vole semi-species from the hybrid zone was studied for the first time using the methods of geometric morphometry. The hybrid specimens were found to display high morphological variability being closer to the parental Microtus obscurus than to M. arvalis form. The main trends of changes in the mandible shape were primarily observed in the horizontal plane.

A Finding of a Frozen Mummy of a Lemming (Rodentia, Cricetidae, Lemmus) in the Upper Pleistocene of Yakutia.

The external morphological, X-ray, and tomographic study of a frozen rodent mummy from the Upper Pleistocene Yedoma deposits on the Tirekhtyakh River (a Semyuelyakh River tributary, Abyi ulus, Republic of Sakha (Yakutia), Russia) showed its belonging to Lemmus sp. The radiocarbon age of the finding is 41 305-41 885 cal B.P. This is the first Pleistocene discovery of a frozen mummy of a genus Lemmus representative. In terms of the body and skull sizes, coat color, the lower incisor length, and the molar structure, the specimen studied is similar to the recent Lemmus sibiricus (Kerr, 1792). Comparison of the mitochondrial COB gene sequence with the DNA sequences presented in the GenBank database also testified to the maximum similarity with the Recent Siberian brown lemming.

Dental Microwear and Mesowear of the Microtus Voles Molars before and after Experimental Feeding of Owls.

In small mammals, the degree of micro- and mesowear of molars depends on the feed hardness, abrasiveness, and some other characteristics. Analysis of micro- and mesorelief of the paleontological material is used for reconstruction of some animal diet parameters. Small mammals pass through a series of complex transformations on the way from the objects of biocenosis to paleontological objects. Bone remains underwent transformations during accumulation and fossilization. In particular, bone remains from ornithogenous deposits were exposed to the bird digestive system elements. We have experimentally studied changes in some parameters of the narrow-headed vole (Microtus gregalis) molars derived from the owl pellets. Comparison of the same samples before and after exposure to the digestive system of the polar owl (Nyctea scandiaca) and eagle owl (Bubo bubo) showed that the tooth enamel microrelief undergoes serious changes and therefore, provides no information on the intravital diet of voles. A different degree of preservation of the characteristics of the mesorelief was shown. Depending on this, an assessment of their applicability to paleoreconstructions was given.

Molar Microwear of Narrow-Headed Vole (Microtus gregalis Pall., 1779) Depending on the Feed Abrasiveness.

In the narrow-headed vole, enamel microwear of the first mandibular molar (of the protoconid and entoconid anterior enamel wall) was studied under the laboratory conditions and at the fixed feed composition. The classic parameters and the area of the enamel prism lesion were taken into account. The enamel lesion patterns caused by the tooth-tooth and tooth-food interactions have been determined. Differences were found between the voles kept on feed with different abrasive properties, as well as between the lingual and buccal conids of the first mandibular molar. In the Microtus species, the ratio of micro-lesions (pits and scratches) did not depend on the abrasive properties of the feed consumed. The extent of preservation of the enamel contour anterior edge depended on the feed composition and could be used as an indicator for indirect evaluation of the Microtus species diet.

Morphogenetic Effects of Resettlement of Mole Voles (Ellobius talpinus Pall., 1770) from the Southern Population to the Northern Boundary of the Species Range.

Geometric morphometry has been used to reveal transformations of mandible morphogenesis in the offspring of mole voles resettled to the northern part of the species range from a southern population. The transformations were new compared to both the original (southern) and the aboriginal (northern) populations. A significant increase in the intragroup morphological disparity estimated by the mean nearest neighbor distance (MNND) in the resettled animals compared to both aboriginal populations is an indirect indication of an increased developmental instability in the resettled animals exposed to new climatic conditions.

Seasonal expression of P450c17 and 5α-reductase-2 in the scented gland of male muskrats (Ondatra zibethicus).

Cytochrome P450 17A1 (P450c17) is the key enzyme required for the production of androgenic sex steroids by converting progestogens to androgens. 5α-reductases are enzymes that convert testosterone (T) to dihydrotestosterone (DHT), which has a greater affinity for androgen receptors (AR) and stronger action than T. Our previous studies revealed that the scented glands of male muskrats expressed AR during the breeding and nonbreeding seasons. To further seek evidence of the activities of androgens in scented glands, the expression patterns of P450c17 and 5α-reductase 2 were investigated in the scented glands of male muskrats during the breeding and nonbreeding seasons. The weight and size of scented glands in the breeding season were significantly higher than those of the nonbreeding season. Immunohistochemical data showed that P450c17 and 5α-reductase 2 were presented in the glandular cells and epithelial cells of scented glands in both the seasons. The protein and mRNA expression of P450c17 and 5α-reductase 2 were significantly higher in the scented gland during the breeding season than those during the nonbreeding season. In addition, the levels of DHT and T in the scented gland were remarkably higher during the breeding season. Taken together, these results suggested that the scented glands of male muskrats were capable of locally synthesizing T and DHT, and T and DHT might play an important role in the scented glandular function via an autocrine or paracrine manner.

Silicon-based plant defences, tooth wear and voles.

Plant-herbivore interactions are hypothesized to drive vole population cycles through the grazing-induced production of phytoliths in leaves. Phytoliths act as mechanical defences because they deter herbivory and lower growth rates in mammals. However, how phytoliths impair herbivore performance is still unknown. Here, we tested whether the amount of phytoliths changes tooth wear patterns. If confirmed, abrasion from phytoliths could play a role in population crashes. We applied dental microwear texture analysis (DMTA) to laboratory and wild voles. Lab voles were fed two pelleted diets with differing amounts of silicon, which produced similar dental textures. This was most probably due to the loss of food mechanical properties through pelletization and/or the small difference in silicon concentration between diets. Wild voles were trapped in Poland during spring and summer, and every year across a population cycle. In spring, voles feed on silica-rich monocotyledons, while in the summer they also include silica-depleted dicotyledons. This was reflected in the results; the amount of silica therefore leaves a traceable record in the dental microwear texture of voles. Furthermore, voles from different phases of population cycles have different microwear textures. We tentatively propose that these differences result from grazing-induced phytolith concentrations. We hypothesize that the high amount of phytoliths in response to intense grazing in peak years may result in malocclusion and other dental abnormalities, which would explain how these silicon-based plant defences help provoke population crashes. DMTA could then be used to reconstruct vole population dynamics using teeth from pellets or palaeontological material.

Broadening diversity in the Arostrilepis horrida complex: Arostrilepis kontrimavichusi n. sp. (Cyclophyllidea: Hymenolepididae) in the western red-backed vole Myodes californicus (Merriam) (Cricetidae: Arvicolinae) from temperate latitudes of the Pacific Northwest, North America.

Specimens originally identified provisionally as Hymenolepis horrida (Linstow, 1901) [later Arostrilepis horrida (Linstow, 1901)] in Myodes californicus (Merriam) from near the Pacific coastal zone of southern Oregon are revised. Specimens in western red-backed voles represent an undescribed species of Arostrilepis Mas Coma & Tenora, 1997, contributing to recognition and resolution of a broadening complex encompassing cryptic diversity for these hymenolepidid tapeworms distributed across the Holarctic region. Consistent with recent studies defining diversity in the genus, the form, dimensions, and spination (pattern, shape and size) of the cirrus are diagnostic. Among 12 nominal congeners, specimens of A. kontrimavichusi n. sp. are further distinguished by the relative position and length of the cirrus-sac, arrangement of the testes and relative size of the external seminal vesicle and seminal receptacle. Specimens from Oregon voles represent the fifth endemic hymenolepidid in this genus from the Nearctic. Host range for the North American assemblage of species includes Cricetidae (Arvicolinae and Neotominae), Heteromyidae, Geomyidae, and rarely Sciuridae.

Morphological diversity of mole vole mono- and polymorphic populations: Does Chernov's "compensation principle" work within a population?

The ecological "compensation principle" enunciated by Yu.I. Chernov, who suggested a higher level of compensatory diversity in communities depleted in composition, proved to be also applicable to a single population, as demonstrated in a model rodent species, mole vole with mono- and polymorphic coat color, using the methods of geometric morphometrics. The mandible shape diversity was significantly increased in the monomorphic as compared to polymorphic populations, in which the division of foraging activities between animals of different morphs led to a suppression of general morphological diversity.

Ontogenetic and evolutionary trends in the tooth enamel features in Craseomys voles (Arvicolinae, Rodentia).

In Craseomys rufocanus and Craseomys rex, the age-related and species differences in thickness and microstructure of the first lower molars (ml) have been identified and studied. The results suggest that the enamel dimensional and microstructural features may serve as additional indicators of the vole tooth evolutionary stage within a single phyletic lineage.

[MORPHOLOGICAL PECULIARITIES OF THE LIVER IN COMMON VOLES INHABITING THE TERRITORY OF BORODINO COAL DEPOSITS AND RECULTIVATION AREAS].

The aim of this work was to study the morphological changes of liver in common voles (Microtus arvalis Pallas) inhabiting the territories of brown coal deposition in Borodino coal opencast (Krasnoyarsk region) and on reclaimed dumps 10 and 20 years after its production. Trapping of the voles (10 animals in each group) living under natural conditions on each territory, was conducted for 30 days. Histological examination of the liver in all animals demonstrated degenerative changes and necrosis of hepatocytes, expressed to a various degree. Morphometric study has shown that the greatest changes in the structure of hepatic stroma and parenchyma took place in voles that lived in the dumps of coal, reclaimed 10 years before. It was found that in the animals of this group, the thickness of hepatocyte plates was increased 1.3 times, while the specific volume of necrotic hepatocytes was twice as much as this parameter in the animals that lived on intact territory.

Developmental integration in a functional unit: deciphering processes from adult dental morphology.

The evolution of mammalian dentition is constrained by functional necessity and by the non-independence of morphological structures. Efficient chewing implies coherent tooth coordination from development to motion, involving covariation patterns (integration) within dental parts. Using geometric morphometrics, we investigate the modular organization of the highly derived vole dentition. Integration patterns between and within the upper and lower molar rows are analyzed to identify potential modules and their origins (functional and developmental). Results support an integrated adult dentition pattern for both developmental and functional aspects. The integration patterns between opposing molar pairs suggest a transient role for the second upper and lower molars during the chewing motion. Upper and lower molar rows form coherent units but the relative integration of molar pairs is in contradiction with existing developmental models. Emphasis on the first three cusps to grow leads to a very different integration pattern, which would be congruent with developmental models. The early developmental architecture of traits is masked by later stages of growth, but may still be deciphered from the adult phenotype, if careful attention is paid to relevant features.

Contrasting effects of large density changes on relative testes size in fluctuating populations of sympatric vole species.

Across species, there is usually a positive relationship between sperm competition level and male reproductive effort on ejaculates, typically measured using relative testes size (RTS). Within populations, demographic and ecological processes may drastically alter the level of sperm competition and thus, potentially affect the evolution of testes size. Here, we use longitudinal records (across 38 years) from wild sympatric Fennoscandian populations of five species of voles to investigate whether RTS responds to natural fluctuations in population density, i.e. variation in sperm competition risk. We show that for some species RTS increases with density. However, our results also show that this relationship can be reversed in populations with large-scale between-year differences in density. Multiple mechanisms are suggested to explain the negative RTS-density relationship, including testes size response to density-dependent species interactions, an evolutionary response to sperm competition levels that is lagged when density fluctuations are over a certain threshold, or differing investment in pre- and post-copulatory competition at different densities. The results emphasize that our understanding of sperm competition in fluctuating environments is still very limited.

Nasal aerodynamics protects brain and lung from inhaled dust in subterranean diggers, Ellobius talpinus.

Inhalation of air-dispersed sub-micrometre and nano-sized particles presents a risk factor for animal and human health. Here, we show that nasal aerodynamics plays a pivotal role in the protection of the subterranean mole vole Ellobius talpinus from an increased exposure to nano-aerosols. Quantitative simulation of particle flow has shown that their deposition on the total surface of the nasal cavity is higher in the mole vole than in a terrestrial rodent Mus musculus (mouse), but lower on the olfactory epithelium. In agreement with simulation results, we found a reduced accumulation of manganese in olfactory bulbs of mole voles in comparison with mice after the inhalation of nano-sized MnCl2 aerosols. We ruled out the possibility that this reduction is owing to a lower transportation from epithelium to brain in the mole vole as intranasal instillations of MnCl2 solution and hydrated nanoparticles of manganese oxide MnO · (H2O)x revealed similar uptake rates for both species. Together, we conclude that nasal geometry contributes to the protection of brain and lung from accumulation of air-dispersed particles in mole voles.

[A modular approach to studying of fluctuating asymmetry of complex morphological structures in rodents with the mandible of the bank vole (Clethrionomys glareolus, Arvicolinae, Rodentia) as an example].

The expediency of a modular approach to estimating fluctuating asymmetry (FA) of complex morphological structures was shown using the mandible of the bank vole (Clethrionomys glareolus Schreber, 1780) as an example. FA of the shape of two mandibular regions (modules) defined developmentally and functionally, was assessed by means of geometric morphometrics. The differences between mandibular regions in the FA levels were found for both individual landmarks and integral indices of asymmetry. Regardless of age, gender or sampling year, FA estimates obtained for posterior region including part of the ramus and processes were higher than those for anterior region including the diastemal area. The results suggest that modularity of complex morphological structures should be taken into account when analyzing FA.

Do fossorial water voles have a functional vomeronasal organ? A histological and immunohistochemical study.

The fossorial water vole, Arvicola scherman, is an herbivorous rodent that causes significant agricultural damages. The application of cairomones and alarm pheromones emerges as a promising sustainable method to improve its integrated management. These chemical signals would induce stress responses that could interfere with the species regular reproductive cycles and induce aversive reactions, steering them away from farmlands and meadows. However, there is a paucity of information regarding the water vole vomeronasal system, both in its morphological foundations and its functionality, making it imperative to understand the same for the application of chemical communication in pest control. This study fills the existing gaps in knowledge through a morphological and immunohistochemical analysis of the fossorial water vole vomeronasal organ. The study is primarily microscopic, employing two approaches: histological, using serial sections stained with various dyes (hematoxylin-eosin, Periodic acid-Schiff, Alcian blue, Nissl), and immunohistochemical, applying various markers that provide morphofunctional and structural information. These procedures have confirmed the presence of a functional vomeronasal system in fossorial water voles, characterized by a high degree of differentiation and a significant expression of cellular markers indicative of active chemical communication in this species.