Stable carbon isotopes in breath reveal fast metabolic incorporation rates and seasonally variable but rapid fat turnover in the common shrew (Sorex araneus).

Small non-migratory mammals with Northern distribution ranges apply a variety of behavioural and physiological wintering strategies. A rare energy-saving strategy is Dehnel's phenomenon, involving a reduction and later regrowth of the body size, several organs and parts of the skeleton in red-toothed shrews (Soricidae). The size extremes coincide with major life stages. However, the physiological consequences for the shrew's metabolism remain poorly understood. In keeping with the energetic limitations that may induce the size changes, we hypothesised that metabolic incorporation rates should remain the same across the shrews' lifetimes. In contrast, fat turnover rates should be faster in smaller subadults than in large juveniles and regrown adults, as the metabolic activity of fat tissue increases in winter individuals (subadults). Measuring the changes in the ratio of exhaled stable carbon isotopes, we found that the baseline diet of shrews changed across the season. A diet switch experiment showed that incorporation rates were consistently rapid (t50=38.2±21.1-69.3±53.5 min) and did not change between seasons. As predicted, fat turnover rates were faster in size-reduced subadults (t50=2.1±1.3 h) compared with larger juveniles (t50=5.5±1.7 h) and regrown adults (t50=5.0±4.4 h). In all three age/size classes, all body fat was turned over after 9-24 h. These results show that high levels of nutrient uptake are independent of body size, whereas fat turnover rates are negatively correlated with body size. Thus, the shrews might be under higher pressure to save energy in winter and this may have supported the evolution of Dehnel's phenomenon.

Expression patterns of Fgf8 and Shh in the developing external genitalia of Suncus murinus.

Reciprocal epithelial-mesenchymal interactions and several signalling pathways regulate the development of the genital tubercle (GT), an embryonic primordium of external genitalia. The morphology of the adult male external genitalia of the Asian house musk shrew Suncus murinus (hereafter, laboratory name: suncus) belonging to the order Eulipotyphla (the former order Insectivora or Soricomorpha) differs from those of mice and humans. However, the developmental process of the suncus GT and its regulatory genes are unknown. In the present study, we explored the morphological changes and gene expression patterns during the development of the suncus GT. Morphological observations suggested the presence of common (during the initial outgrowth) and species-specific (during the sexual differentiation of GT) developmental processes of the suncus GT. In gene expression analysis, fibroblast growth factor 8 (Fgf8) and sonic hedgehog (Shh), an indicator and regulator of GT development in mice respectively, were found to be expressed in the cloacal epithelium and the developing urethral epithelium of the suncus GT. This pattern of expression specifically in GT epithelium is similar to that observed in the developing mouse GT. Our results indicate that the mechanism of GT formation regulated by the FGF and SHH signalling pathways is widely conserved in mammals.

Petrosaltator gen. nov., a new genus replacement for the North African sengi Elephantulus rozeti (Macroscelidea; Macroscelididae).

In 2003, a molecular phylogeny was published that examined the role of the Sahara Desert as a vicariant event in the evolution of sengis (also known as elephant-shrews.) The phylogeny included a single sample from the North African sengi, Elephantulus rozeti (Duvernoy, 1833), which was found to be more closely related to the sengi genus Petrodromus Peters, 1846 than to other Elephantulus. Here we independently test the monophyly of Elephantulus using an additional specimen of E. rozeti and similar phylogenetic analyses, and discuss additional morphological and behavioral data that support the phylogeny. We propose a revised taxonomy that reflects the current paraphyly of Elephantulus and the sister relationship of E. rozeti and Petrodromus, including a new genus name for the North African sengi, Petrosaltator rozeti gen. nov., nov. comb. We additionally define two tribes within the subfamily Macroscelidinae, the Macroscelidini (including Macroscelides, Petrodromus, and Petrosaltator), and the Elephantulini (including all other members of Elephantulus).

Vocal development during postnatal growth and ear morphology in a shrew that generates seismic vibrations, Diplomesodon pulchellum.

The ability of adult and subadult piebald shrews (Diplomesodon pulchellum) to produce 160Hz seismic waves is potentially reflected in their vocal ontogeny and ear morphology. In this study, the ontogeny of call variables and body traits was examined in 11 litters of piebald shrews, in two-day intervals from birth to 22 days (subadult), and ear structure was investigated in two specimens using micro-computed tomography (micro-CT). Across ages, the call fundamental frequency (f0) was stable in squeaks and clicks and increased steadily in screeches, representing an unusual, non-descending ontogenetic pathway of f0. The rate of the deep sinusoidal modulation (pulse rate) of screeches increased from 75Hz at 3-4 days to 138Hz at 21-22 days, probably relating to ontogenetic changes in contraction rates of the same muscles which are responsible for generating seismic vibrations. The ear reconstructions revealed that the morphologies of the middle and inner ears of the piebald shrew are very similar to those of the common shrew (Sorex araneus) and the lesser white-toothed shrew (Crocidura suaveolens), which are not known to produce seismic signals. These results suggest that piebald shrews use a mechanism other than hearing for perceiving seismic vibrations.

Invading and expanding: range dynamics and ecological consequences of the greater white-toothed shrew (Crocidura russula) invasion in Ireland.

Establishing how invasive species impact upon pre-existing species is a fundamental question in ecology and conservation biology. The greater white-toothed shrew (Crocidura russula) is an invasive species in Ireland that was first recorded in 2007 and which, according to initial data, may be limiting the abundance/distribution of the pygmy shrew (Sorex minutus), previously Ireland's only shrew species. Because of these concerns, we undertook an intensive live-trapping survey (and used other data from live-trapping, sightings and bird of prey pellets/nest inspections collected between 2006 and 2013) to model the distribution and expansion of C. russula in Ireland and its impacts on Ireland's small mammal community. The main distribution range of C. russula was found to be approximately 7,600 km2 in 2013, with established outlier populations suggesting that the species is dispersing with human assistance within the island. The species is expanding rapidly for a small mammal, with a radial expansion rate of 5.5 km/yr overall (2008-2013), and independent estimates from live-trapping in 2012-2013 showing rates of 2.4-14.1 km/yr, 0.5-7.1 km/yr and 0-5.6 km/yr depending on the landscape features present. S. minutus is negatively associated with C. russula. S. minutus is completely absent at sites where C. russula is established and is only present at sites at the edge of and beyond the invasion range of C. russula. The speed of this invasion and the homogenous nature of the Irish landscape may mean that S. minutus has not had sufficient time to adapt to the sudden appearance of C. russula. This may mean the continued decline/disappearance of S. minutus as C. russula spreads throughout the island.

Shape, variance and integration during craniogenesis: contrasting marsupial and placental mammals.

Studies of morphological integration can provide insight into developmental patterns, even in extinct taxa known only from skeletal remains, thus making them an important tool for studies of evolutionary development. However, interpreting patterns of integration and assessing their significance for organismal evolution requires detailed understanding of the developmental interactions that shape integration and how those interactions change through ontogeny. Thus far, relatively little comparative data have been produced for this important topic, and the data that do exist are overwhelmingly from humans and their close relatives or from laboratory models such as mice. Here, we compare data on shape, variance and integration through postnatal ontogeny for a placental mammal, the least shrew, Cryptotis parva, and a marsupial mammal, the gray short-tailed opossum, Monodelphis domestica. Cranial variance decreased dramatically from early to late ontogeny in Cryptotis, but remained stable through ontogeny in Monodelphis, potentially reflecting functional constraints related to the short gestation and early ossification of oral bones in marsupials. Both Cryptotis and Monodelphis showed significant changes in cranial integration through ontogeny, with a mixture of increased, decreased and stable levels of integration in different cranial regions. Of particular note is that Monodelphis showed an unambiguous decrease in integration of the oral region through ontogeny, potentially relating to their early ossification. Selection at different stages of development may have markedly different effects if patterns of integration change substantially through ontogeny. Our results suggest that high integration of the oral region combined with functional constraints for suckling during early postnatal ontogeny may drive the stagnant variance observed in Monodelphis and potentially other marsupials.

Colonization of Ireland: revisiting 'the pygmy shrew syndrome' using mitochondrial, Y chromosomal and microsatellite markers.

There is great uncertainty about how Ireland attained its current fauna and flora. Long-distance human-mediated colonization from southwestern Europe has been seen as a possible way that Ireland obtained many of its species; however, Britain has (surprisingly) been neglected as a source area for Ireland. The pygmy shrew has long been considered an illustrative model species, such that the uncertainty of the Irish colonization process has been dubbed 'the pygmy shrew syndrome'. Here, we used new genetic data consisting of 218 cytochrome (cyt) b sequences, 153 control region sequences, 17 Y-intron sequences and 335 microsatellite multilocus genotypes to distinguish between four possible hypotheses for the colonization of the British Isles, formulated in the context of previously published data. Cyt b sequences from western Europe were basal to those found in Ireland, but also to those found in the periphery of Britain and several offshore islands. Although the central cyt b haplotype in Ireland was found in northern Spain, we argue that it most likely occurred in Britain also, from where the pygmy shrew colonized Ireland as a human introduction during the Holocene. Y-intron and microsatellite data are consistent with this hypothesis, and the biological traits and distributional data of pygmy shrews argue against long-distance colonization from Spain. The compact starburst of the Irish cyt b expansion and the low genetic diversity across all markers strongly suggests a recent colonization. This detailed molecular study of the pygmy shrew provides a new perspective on an old colonization question.

Developmental plasticity links local adaptation and evolutionary diversification in foraging morphology.

Developmental plasticity is thought to reconcile the constraining role of natural selection in maintaining local adaptation with evolutionary diversification under novel conditions, but empirical documentations are rare. In vertebrates, growth and development of bones is partially guided by contractions of attached musculature and such muscle activity changes progressively through embryonic development from sporadic motility to direct functional effects. In species with short generation times, delayed skull maturation extends the guiding effects of muscle activity on formation of foraging morphology into adulthood, providing an opportunity to directly examine the links between plasticity of bone development, ecological adaptations, and evolutionary diversification in foraging morphology. In this case, the morphological consequences of inputs due to local functional requirements should be evident in adaptive divergence across taxa. Here we provide evidence that epigenetic regulation of bone growth in Soricid shrews may enable both development of local adaptations and evolutionary divergence in mandibular morphology. We contrast the effects of muscle stimulation on early- vs. late-maturing components of, foraging apparatus to show that the morphology of late-maturing components is more affected by functional requirements than are early-ossifying traits. Further, the divergence in foraging morphology across shrew species occurs along the directions delineated by inductive effects of muscle loading and bite force on bone formation in late-maturing but not early-maturing mandible components within species. These results support the hypothesis that developmental plasticity can link maintenance of local adaptations with evolutionary diversification in morphology.

Neonatal DHT but not E2 speeds induction of sexual receptivity in the musk shrew.

Neural aromatization of testosterone (T) to estrogen during development is thought to be important for sexual differentiation of many altricial mammals. We evaluated the effects of neonatal injections of the non-aromatizable androgen dihydrotestosterone propionate (DHTP) and estradiol (E2) on the copulatory behavior of the female musk shrew, an altricial insectivore. Following adult ovariectomy and replacement T, animals were paired with a stimulus female for two 60-minute copulatory behavior tests. The latency to induce sexual receptivity (in the form of tail-wagging by the female), mount latency and total number of mounts were recorded in experimental females and in a group of untreated control males. While neither hormone treatment significantly affected mounting behavior, DHTP-treated animals induced receptivity faster and with latencies not significantly different from intact males, suggesting that early non-aromatizable androgens can have masculinizing actions by either increasing sexual motivation or making the treated animal more attractive to the stimulus female. Reliance on androgenic rather than estrogenic metabolites for the differentiation of courtship behaviors conforms to the pattern seen more typically in primates than rodents.

Modeling zinc regulation in small mammals.

Due to large zinc discharges into the global environment, both terrestrial and aquatic environments have been polluted with zinc. The embanked floodplains of the lower Rhine River in the Netherlands contain large amounts of heavy metals, including zinc. These large amounts of heavy metals may pose risks to flora and fauna by accumulation in food webs, and risk assessment may be required. However, toxicokinetic models for zinc metabolism in mammalian wildlife species are currently lacking. The present study describes the development of a zinc kinetics model that predicts internal zinc concentrations in small mammals by modeling zinc absorption and excretion dependent on the dietary zinc intake using adapted Michaelis-Menten equations. The equations were parameterized based on experimental data reported in the scientific literature. Within the dietary zinc range of 3 to 104 mg/kg dry weight, the model predicts internal zinc concentrations and shows that the internal zinc is regulated within this range. Outside this range, the model could not be calibrated due to a lack of data. Validation of the model with four small mammal species living in an embanked floodplain along a distributary of the Rhine River illustrated that the model predicts internal zinc concentrations differing up to a factor of 1.6 (Common shrew) to 1.7 (Common vole) from field measurements.

Lung development of monotremes: evidence for the mammalian morphotype.

The reproductive strategies and the extent of development of neonates differ markedly between the three extant mammalian groups: the Monotremata, Marsupialia, and Eutheria. Monotremes and marsupials produce highly altricial offspring whereas the neonates of eutherian mammals range from altricial to precocial. The ability of the newborn mammal to leave the environment in which it developed depends highly on the degree of maturation of the cardio-respiratory system at the time of birth. The lung structure is thus a reflection of the metabolic capacity of neonates. The lung development in monotremes (Ornithorhynchus anatinus, Tachyglossus aculeatus), in one marsupial (Monodelphis domestica), and one altricial eutherian (Suncus murinus) species was examined. The results and additional data from the literature were integrated into a morphotype reconstruction of the lung structure of the mammalian neonate. The lung parenchyma of monotremes and marsupials was at the early terminal air sac stage at birth, with large terminal air sacs. The lung developed slowly. In contrast, altricial eutherian neonates had more advanced lungs at the late terminal air sac stage and postnatally, lung maturation proceeded rapidly. The mammalian lung is highly conserved in many respects between monotreme, marsupial, and eutherian species and the structural differences in the neonatal lungs can be explained mainly by different developmental rates. The lung structure of newborn marsupials and monotremes thus resembles the ancestral condition of the mammalian lung at birth, whereas the eutherian newborns have a more mature lung structure.

Habitat-quality effects on metapopulation dynamics in greater white-toothed shrews, Crocidura russula.

The effects of patch size and isolation on metapopulation dynamics have received wide empirical support and theoretical formalization. By contrast, the effects of patch quality seem largely underinvestigated, partly due to technical difficulties in properly assessing quality. Here we combine habitat-quality modeling with four years of demographic monitoring in a metapopulation of greater white-toothed shrews (Crocidura russula) to investigate the role of patch quality on metapopulation processes. Together, local patch quality and connectivity significantly enhanced local population sizes and occupancy rates (R2 = 14% and 19%, respectively). Accounting for the quality of patches connected to the focal one and acting as potential sources improved slightly the model explanatory power for local population sizes, pointing to significant source-sink dynamics. Local habitat quality, in interaction with connectivity, also increased colonization rate (R2 = 28%), suggesting the ability of immigrants to target high-quality patches. Overall, patterns were best explained when assuming a mean dispersal distance of 800 m, a realistic value for the species under study. Our results thus provide evidence that patch quality, in interaction with connectivity, may affect major demographic processes.

The taming of the shrew milk teeth.

A characteristic feature of mammalian dentition is the evolutionary reduction of tooth number and replacement. Because mice do not replace teeth, here we used Sorex araneus, the common shrew, as a model to investigate the loss of tooth replacement. Historically, shrews have been reported to initiate the development of several, milk or deciduous teeth but these soon become rudimentary and only the replacement teeth erupt. Shrews thus offer a living example of a derived mammalian pattern where the deciduous tooth development is being suppressed. Based on histological and gene expression analyses of serial sections, we suggest that S. araneus has discernible tooth replacement only in the premolar 4 (P4) position. Both generations of teeth express Shh in the enamel knot and in the inner enamel epithelium. Nevertheless, the deciduous P4 (dP4) is reduced in size during embryogenesis and is eventually lost without becoming functional. Analysis of growth shows that P4 replaces the dP4 in a "double-wedge" pattern indicative of competitive replacement where the suppression of the deciduous tooth coincides with the initiation of its replacement. Because activator-inhibitor mechanisms have been implicated in adjacent mouse molars and in transgenic mice with continuous tooth budding, we suggest that evolutionary suppression of deciduous teeth may involve early activation of replacement teeth, which in turn begin to suppress their deciduous predecessors.

Generation recruitment and death of brain cells throughout the life cycle of Sorex shrews (Lipotyphla).

Young shrews of the genus Sorex that are born in early summer reduce their body size before wintering, including a reduction of brain weight of 10-30%. In the spring they mature sexually, double their body weight and regain about half of the loss in brain weight. To investigate the mechanisms of brain weight oscillations we studied the rate of cell death and generation in the brain during the whole life cycle of the common shrew (Sorex araneus) and pygmy shrew (S. minutus). After weaning, shrews generate new brain cells in only two mammalian neurogenic zones and approximately 80% of these develop into neurones. The increase of the shrew brain weight in the spring did not depend on recruitment of new cells. Moreover, adult Sorex shrews did not generate new cells in the dentate gyri. Injections of 5-HT1A receptor agonists in the adult shrews induced neurogenesis in their dentate gyri, showing the presence of dormant progenitor cells. Generation of new neurones in the subventricular zone of the lateral ventricles and their recruitment to olfactory bulbs continued throughout life. TUNEL labelling showed that the rate of cell death in all brain structures, including the proliferation zones and olfactory bulb, was very low throughout life. We conclude that neither cell death nor recruitment significantly contributes to seasonal oscillations and the net loss of brain weight in the Sorex shrews. With the exception of dentate gyrus and olfactory bulb, cellular populations of brain structures are stable throughout the life cycle of these shrews.

Mandible asymmetry and genetic diversity in island populations of the common shrew, Sorex araneus.

Mandibles from 13 island and six mainland populations of common shrews from the west coast of Scotland were subjected to geometric morphometric analysis in order to investigate the relationship between genetic diversity and fluctuating asymmetry. Although population mean shape fluctuating asymmetry (FA) and size FA were significantly inversely correlated with population genetic diversity this result was substantially due to one island. Sanda, the smallest island with by far the lowest genetic diversity, also had the highest FA. When Sanda was removed from the analysis, the relationship was not significant. There was no relationship between genetic diversity and FA at the individual level, whether measured as mean locus heterozygosity or d(2). In general, if genetic variation affects FA at all, the effect is weak and may only be of biological interest in very small populations.

Demography of short-tailed shrew populations living on polychlorinated biphenyl-contaminated sites.

In ecological risk assessment, a key necessity is to understand how contaminants known to have negative impact on laboratory mammals affect the population demography of mammals living in their natural environment. We examined the demography of six local populations of the short-tailed shrew (Blarina brevicauda) living in eastern deciduous forest palustrine habitat along the Housatonic River (MA, USA) on soils contaminated with a range of polychlorinated biphenyl (PCB) concentrations (1.5-38.3 ppm). The objective of the study was to assess whether PCBs adversely affect the population demography of these small mammals living in their natural environment. Blarina were selected for study because they would be expected to readily bioaccumulate PCBs from the soil. Populations were intensively live trapped on 1-ha grids from spring to autumn 2001. There was no relationship between any demographic parameter and PCB soil concentrations. Densities were high (usually exceeding 20/ha, and on two grids exceeded 60/ha in summer); survival was good (typically 60-75% per 30 d); and sex ratio, reproduction rates, growth rates, and body mass were within the ranges reported in the literature. Thus, these shrew populations showed no detectable impact on their population demography from living on PCB-contaminated sites.

Developmental study of the anal tonsil in the laboratory shrew, Suncus murinus.

The laboratory shrew, Suncus murinus, which lacks such gut associated lymph organs as the appendix and Peyer's plates, was recently demonstrated (Kubo and Isomura, 1996) to possess a pair of anal tonsils at the end of its rectum. The present paper deals with the development of this lymphoid organ as observed by light and electron microscopy. The anal tonsil was characterized by the initial postnatal development. On neonatal Day 1, a pair of epithelial crypts formed at the dorsal boundary between the anus and the ostium urogenitoanale. On Day 2 after birth, lymphocytes began to accumulate in the subepithelial mesenchymal tissue under the crypt. From Day 3 on, the lymphocytes increased to form a lymph nodule, from which, on Day 5, some lymphocytes began to penetrate into the crypt epithelium. The crypt and the nodule were fused together between Days 6 and 8. A germinal center-like structure was observed on Day 20 after birth. Around Day 40, the invading cells comprised cellular units consisting of large and small lymphocytes and plasma cells. High endothelial venules were observed in the parafollicular area at this time. These findings indicate that the anal tonsil originates from an accumulation of lymphocytes in the mesenchymal tissue close to a particular epithelium of the crypt, presumably in response to antigens in foods; the tonsilar structure is then gradually completed by fusion of the lymphoid and epithelial elements. This paper further reports on an electron microscope finding on Day 8 where the anal tonsillar crypt epithelium was seen to contain some basal-granulated cells of the open type.

Comparison of expression patterns of fibroblast growth factor 8, bone morphogenetic protein 4 and sonic hedgehog in jaw development of the house shrew, Suncus murinus.

To elucidate the mechanism underlying jaw development in mammals, we used a new laboratory animal, Suncus murinus (house shrew, an insectivore) as the subject for the investigation, because Suncus has all types of teeth (incisor, canine, premolar and molar) in its upper and lower jaws and is thought to be a good model animal having a general mammalian tooth pattern. At the start, by use of degenerate primers we cloned Suncus homologues of fibroblast growth factor 8 (sFgf8), bone morphogenetic protein 4 (sBmp4) and sonic hedgehog (sShh) genes from cDNA library derived from whole Suncus embryos at day 12 (E12). Thereafter, we examined the expression patterns of these genes in the jaw development of Suncus E11-16 embryos (for mouse E9.5-12 embryos). sFgf8 and sBmp4 were expressed in E11 but not in E15 and onward during orofacial development. sShh was expressed from E11 onward, and its expression was increased in the orofacial area. The expression pattern of sFgf8 in the maxillary and mandibular arches of E14 coincided with the area of the presumptive tooth arch. However, sShh and sBmp4 were expressed only in the outer area (= buccal/labial side) of presumptive tooth arch. Thus, these 3 genes showed specific expression pattern in jaw development of Suncus, and their distributions did not overlap each other except in a few regions. These findings suggest that sFgf8, sBmp4 and sShh have a specific function respectively during jaw development in Suncus murinus.

The inner ear macular sensory epithelia of the Daubenton's bat.

The inner ear macular sensory epithelia of the Daubenton's bat were examined quantitatively to estimate the area and total number of hair cells. Ultrastructural examination of the sensory epithelium reveals two main types of hair cells: the chalice-innervated hair cell and the bouton-innervated hair cell. The existence of an intermediate type, with a nerve ending covering the lateral side of the hair cell, indicates that the chalice-innervated hair cells are derived from bouton-innervated hair cells. Thus, at least a part of the bouton-innervated hair cells forms a transitional stage. A number of immature as well as apoptotic hair cells were observed. It is suggested that a continuous production of new hair cells takes place in mature individuals, probably based on transdifferentiation of supporting cells.