Locomotory mode transitions alter phenotypic evolution and lineage diversification in an ecologically rich clade of mammals.

The relationship between organismal function and form is a cornerstone of biology because functional diversity is key to generating and maintaining ecological diversity. Morphological changes often occur in unison with behavioral or ecological transitions, and this process may foster diversification, but alternately could trap a species on an adaptive peak. We estimated the most comprehensive phylogenetic hypothesis of Murinae, a young (∼15 million years) and diverse (∼700 species) clade of mammals. We then tested for correlated evolution among four morphological traits with potential links to locomotor modes (Arboreal, General, Terrestrial, and Amphibious), then investigated the effects of locomotion on morphological and lineage diversification. We found unique combinations of trait values for each locomotor mode, including strong covariance between the tail and hindfoot lengths of specialized Arboreal and ecologically flexible General species. Low diversification rates and long branch lengths suggest that specialized lineages represent stable evolutionary "cul-de-sacs." General species, characterized by the classic "rat-like" body plan and broad locomotor abilities, have narrow optimal trait values and slow phenotypic evolution, but high lineage diversification rates. Our findings suggest that versatile, generalist forms act as seeds of species diversity and morphological specialization, which together build ecologically diverse radiations.

Geographical clines in the size of the herb field mouse (Apodemus uralensis).

Patterns of body size variation along geographical gradients have long been searched for and generalized into eco-geographical rules. However, no rodent species has yet been analyzed in relation to the 3 dimensions of latitude, longitude and altitude. We analyzed geographical clines and dimorphism of body and skull size in the herb field mouse (Apodemus uralensis) across the species range, based on field data and on data from the literature. Sexual dimorphism in adult A. uralensis was not expressed at a large scale, while local patterns were inconsistent. Age-dependent size changes were most expressed in adult individuals: most characters of adults exceeded in size those of subadults, while subadult-juvenile size differences were only significant in body weight and length, zygomatic skull width, length of cranial diastema and breadth of braincase. Despite central morphological niches along the clines being separated, A. uralensis populations showed a high degree of size overlap in morphological space. We found the species to be characterized by high size variability, with the largest individuals inhabiting the eastern and southern edges of the distribution range. Tail, hind foot and ear lengths were largest in the southern part of the range, in agreement with Allen's rule. The main measurements that we analyzed, namely body mass, zygomatic skull width and condylobasal skull length, show the presence of 3 clines in the size of adult A. uralensis: (i) a decreasing south-north cline, opposing Bergmann's rule; (ii) an increasing west-east cline, in accordance with Murphy's rule; and (iii) an increasing altitudinal cline.

Environment predicts repeated body size shifts in a recent radiation of Australian mammals.

Closely related species that occur across steep environmental gradients often display clear body size differences, and examining this pattern is crucial to understanding how environmental variation shapes diversity. Australian endemic rodents in the Pseudomys Division (Muridae: Murinae) have repeatedly colonized the arid, monsoon, and mesic biomes over the last 5 million years. Using occurrence records, body mass data, and Bayesian phylogenetic models, we test whether body mass of 31 species in the Pseudomys Division can be predicted by their biome association. We also model the effect of eight environmental variables on body mass. Despite high phylogenetic signal in body mass evolution across the phylogeny, we find that mass predictably increases in the mesic biome and decreases in arid and monsoon biomes. As per Bergmann's rule, temperature is strongly correlated with body mass, as well as several other variables. Our results highlight two important findings. First, body size in Australian rodents has tracked with climate through the Pleistocene, likely due to several environmental variables rather than a single factor. Second, support for both Brownian motion and predictable change at different taxonomic levels in the Pseudomys Division phylogeny demonstrates how the level at which we test hypotheses can alter interpretation of evolutionary processes.

Context-dependent responses of food-hoarding to competitors in Apodemus peninsulae: implications for coexistence among asymmetrical species.

Superior species may have distinct advantages over subordinates within asymmetrical interactions among sympatric animals. However, exactly how the subordinate species coexists with superior species is unknown. In the forests west of Beijing City, intense asymmetrical interactions of food competition exist among granivorous rodents (e.g. Apodemus peninsulae, Niviventer confucianus, Sciurotamias davidianus and Tscherskia triton) that have broadly overlapping habitats and diets but have varied body size (range 15-300 g), hoarding habits (scatter vs larder) and/or daily rhythm (diurnal vs nocturnal). The smallest rodent, A. peninsulae, which typically faces high competitive pressure from larger rodents, is an ideal model to explore how subordinate species coexist with superior species. Under semi-natural enclosure conditions, we tested responses of seed-hoarding behavior in A. peninsulae to intraspecific and interspecific competitors in the situations of pre-competition (without competitor), competition (with competitor) and post-competition (competitor removed). The results showed that for A. peninsulae, the intensity of larder-hoarding increased and the intensity of scatter-hoarding declined in the presence of intraspecifics and S. davidianus, whereas A. peninsulae ceased foraging and hoarding in the presence of N. confucianus and T. triton. A. peninsulae reduced intensity of hoarding outside the nest and moved more seeds into the nest for larder-hoarding under competition from intraspecific individuals and S. davidianus. In most cases, the experimental animals could recover to their original state of pre-competition when competitors were removed. These results suggest that subordinate species contextually regulate their food-hoarding strategies according to different competitors, promoting species coexistence among sympatric animals that have asymmetrical food competition.

Descriptive studies on the tongue of two micro-mammals inhabiting the Egyptian fauna; the Nile grass rat (Arvicanthis niloticus) and the Egyptian long-eared hedgehog (Hemiechinus auritus).

The current study aimed to describe the anatomical features of the tongues of two micro-mammals common in the Egyptian fauna; the Nile grass rat (Arvicathis niloticus), and the Egyptian long-eared hedgehog (Hemiechinus auritus). The tongues of five adult individuals of each species were excised and processed histologically, histochemically, and morphometrically. Statistical analysis comparing the relative tongue length in both species showed that there was a significant difference, which may correlate with the difference in feeding preferences. Grossly, the Nile grass rat has a dorsal lingual prominence with bifurcated apex while, the long-eared hedgehog has a median slight elevation with rounded apex. Numerous forms of mechanical and gustatory papillae are scattered along the lingual dorsal epithelium. The histochemical detection of keratin by Holland's trichrome stain showed an intense expression in the case of A. niloticus and mild expression in H. auritus. The framework of the tongue (entoglossum) is supported by either a core of cartilage in H. auritus or bone in A. niloticus which incorporated in the lingual root. The lingual glands also showed marked variation, the Nile grass rat exhibit dense populations of mucous-secreting glands and lesser populations of serous-secreting glands, the contrary is true in H. auritus. In conclusion, the micro and macro-anatomical features of the tongues of both species showed adaptive changes to accommodate the feeding lifestyle. Such type of studies using mammals from different phylogenetic traits and almost have different feeding preferences provide answers to many research questions related to tongue evolution among mammalian vertebrates.

Tempo and mode of mandibular shape and size evolution reveal mixed support for incumbency effects in two clades of island-endemic rodents (Muridae: Murinae).

Existing radiations in a spatially limited system such as an oceanic island may limit the ecological opportunity experienced by later colonists, resulting in lower macroevolutionary rates for secondary radiations. Additionally, potential colonists may be competitively excluded by these incumbent (resident) species, unless they are biologically distinct (biotic filtering). The extant phenotypic diversity of secondary colonists may thus be impacted by lower rates of phenotypic evolution, exclusion from certain phenotypes, and transitions to new morphotypes to escape competition from incumbent lineages. We used geometric morphometric methods to test whether the rates and patterns of mandibular evolution of the Luzon "old endemic" rodent clades, Phloeomyini and Chrotomyini, are consistent with these predictions. Each clade occupied nearly completely separate shape space and partially separate size space. We detected limited support for decelerating and clade-specific evolutionary rates for both shape and size, with strong evidence for a shift in evolutionary mode within Chrotomyini. Our results suggest that decelerating phenotypic evolutionary rates are not a necessary result of incumbency interactions; rather, incumbency effects may be more likely to determine which clades can become established in the system. Nonincumbent clades that pass a biotic filter can potentially exhibit relatively unfettered evolution.

Associated tympanic bullar and cochlear hypertrophy define adaptations to true deserts in African gerbils and laminate-toothed rats (Muridae: Gerbillinae and Murinae).

Hearing capabilities in desert rodents such as gerbils and heteromyids have been inferred from both anatomical and ecological aspects and tested with experiments and theoretical models. However, very few studies have focused on other desert-adapted species. In this study, a refined three-dimensional morphometric approach was used on three African rodent tribes (Otomyini, Taterillini and Gerbillini) to describe the cochlear and tympanic bullar morphology, and to explore the role of phylogeny, allometry and ecology to better understand the underlying mechanism of any observed trends of hypertrophy in the bulla and associated changes in the cochlea. As a result, desert-adapted species could be distinguished from mesic and semi-arid taxa by the gross cochlear dimensions, particularly the oval window, which is larger in desert species. Bullar and cochlear modifications between species could be explained by environment (bulla and oval window), phylogeny (cochlear curvature gradient) and/or allometry (cochlear relative length, oval window and bulla) with some exceptions. Based on their ear anatomy, we predict that Desmodillus auricularis and Parotomys brantsii should be sensitive to low-frequency sounds, with D. auricularis sensitive to high-frequency sounds, too. This study concludes that in both arid and semi-arid adapted laminate-toothed rats and gerbils there is bulla and associated cochlea hypertrophy, particularly in true desert species. Gerbils also show tightly coiled cochlea but the significance of this is debatable and may have nothing to do with adaptations to any specific acoustics in the desert environment.

Convergent evolution of an extreme dietary specialisation, the olfactory system of worm-eating rodents.

Turbinal bones are key components of the mammalian rostrum that contribute to three critical functions: (1) homeothermy, (2) water conservation and (3) olfaction. With over 700 extant species, murine rodents (Murinae) are the most species-rich mammalian subfamily, with most of that diversity residing in the Indo-Australian Archipelago. Their evolutionary history includes several cases of putative, but untested ecomorphological convergence, especially with traits related to diet. Among the most spectacular rodent ecomorphs are the vermivores which independently evolved in several island systems. We used 3D CT-scans (N = 87) of murine turbinal bones to quantify olfactory capacities as well as heat or water conservation adaptations. We obtained similar results from an existing 2D complexity method and two new 3D methodologies that quantify bone complexity. Using comparative phylogenetic methods, we identified a significant convergent signal in the rostral morphology within the highly specialised vermivores. Vermivorous species have significantly larger and more complex olfactory turbinals than do carnivores and omnivores. Increased olfactory capacities may be a major adaptive feature facilitating rats' capacity to prey on elusive earthworms. The narrow snout that characterises vermivores exhibits significantly reduced respiratory turbinals, which may reduce their heat and water conservation capacities.

How many species of Apodemus and Rattus occur in China? A survey based on mitochondrial cyt b and morphological analyses.

Apodemus (mice) and Rattus (rats) are the top rodent reservoirs for zoonoses in China, yet little is known about their diversity. We reexamined the alpha diversity of these two genera based on a new collection of specimens from China and their cyt b sequences in GenBank. We also tested whether species could be identified using external and craniodental measurements exclusively. Measurements from 147 specimens of Apodemus and 236 specimens of Rattus were used for morphological comparisons. We analysed 74 cyt b sequences of Apodemus and 100 cyt b sequences of Rattus to facilitate phylogenetic estimations. Results demonstrated that nine species of Apodemus and seven species of Rattus, plus a new subspecies of Rattus nitidus, are distributed in China. Principal component analysis using external and craniodental measurements revealed that measurements alone could not separate the recognized species. The occurrence of Rattus pyctoris in China remains uncertain.

Comparative non-metric and morphometric analyses of rats at residential halls of the University of Benin campus, Nigeria.

BACKGROUND: In mammals and across rat species, the variation in conformation is markedly observed in the head and the variation in the shape of the head is mostly determined by the shape of the skull. Hence comparative topographic analysis and morphometry is a veritable tool in precise categorization of peri-domestic rats and species identification. METHODS: Killed rodents around residential dwellings of students on campus were collected and measurements taken of external morphology. Thirty-one external head and corporal parameters; and 40 cranial measurements respectively were obtained. Topographic features and specific anatomical landmarks measured were matched using congruent anatomical landmarks and compared to referenced standard measurements. RESULTS: External morphometry suggests that all retrieved samples were more closely related to the species Rattus rattus. However, craniodental analysis of captured rats reveals variations from the mean of typical R. rattus. In comparison with Mastomys natalensis, the mean averages of the rat species were perceptibly different for only two of the parameters viz palatine fissure length (PL) (p=0.039) and distance between interparietal bone (DP) (p=0.06). In contrast, the mean of whole length of skull (WL), length of diastema (PI), length of nasal bone (NL), length of frontal bone (LF) and occipital width (OH) were significantly different from that of R. rattus with p values of 0.047, 0.036, 0.048, 0.032 and 0.034 respectively. CONCLUSION: This study focuses on peridomestic rat's identification within the University campus based on morphometry, providing unique landmarks for differentiation between Mastomys, Mus, Rattus and other rat species with emphasis on the need for more comprehensive investigation, categorization and morphometric profiling of rat population in Nigeria. Metric data generated for rat profiling in Nigeria is pivotal for a more comprehensive strategy for prevention of Lassa fever.

Reticulate Pleistocene evolution of Ethiopian rodent genus along remarkable altitudinal gradient.

The Ethiopian highlands are the most extensive complex of mountainous habitats in Africa. The presence of the Great Rift Valley (GRV) and the striking elevational ecological gradients inhabited by recently radiated Ethiopian endemics, provide a wide spectrum of model situations for evolutionary studies. The extant species of endemic rodents, often markedly phenotypically differentiated, are expected to possess complex genetic features which evolved asa consequence of the interplay between geomorphology and past climatic changes. In this study, we used the largest available multi-locus genetic dataset of the murid genus Stenocephalemys (347 specimens from ca 40 localities across the known distributional area of all taxa) to investigate the relative importance of disruptive selection, temporary geographic isolation and introgression in their adaptive radiations in the Pleistocene. We confirmed the four main highly supported mitochondrial (mtDNA) clades that were proposed as four species in a previous pilot study: S. albipes is a sister species of S. griseicauda (both lineages are present on both sides of the GRV), while the second clade is formed by two Afro-alpine species, S. albocaudata (east of GRV) and the undescribed Stenocephalemys sp. A (west of GRV). There is a clear elevational gradient in the distribution of the Stenocephalemys taxa with two to three species present at different elevations of the same mountain range. Surprisingly, the nuclear species tree corresponded only a little to the mtDNA tree. Multispecies coalescent models based on six nuclear markers revealed the presence of six separate gene pools (i.e. candidate species), with different topology. Phylogenetic analysis, together with the geographic distribution of the genetic groups, suggests a complex reticulate evolution. We propose a scenario that involves (besides classical allopatric speciation) two cases of disruptive selection along the elevational ecological gradient, multiple crosses of GRV in dry and cold periods of the Pleistocene, followed by hybridization and mtDNA introgression on imperfect reproductive barriers. Spatial expansion of the currently most widespread "albipes" mtDNA clade was followed by population fragmentation, lineage sorting and again by hybridization and mtDNA introgression. Comparison of this genetic structure to other Ethiopian endemic taxa highlight the geographical areas of special conservation concern, where more detailed biodiversity studies should be carried out to prevent many endemic taxa from going extinct even before they are recognized.

Masticatory muscle architecture in a water-rat from Australasia (Murinae, Hydromys) and its implication for the evolution of carnivory in rodents.

Murines are well known for their generalist diet, but several of them display specializations towards a carnivorous diet such as the amphibious Indo-Pacific water-rats. Despite the fact that carnivory evolved repeatedly in this group, few studies have investigated associated changes in jaw muscle anatomy and biomechanics. Here, we describe the jaw muscles and cranial anatomy of a carnivorous water-rat, Hydromys chrysogaster. The architecture of the jaw musculature of six specimens captured both on Obi and Papua were studied and described using dissections. We identified the origin and insertions of the jaw muscles, and quantified muscle mass, fiber length, physiological cross-sectional area, and muscle vectors for each muscle. Using a biomechanical model, we estimated maximum incisor and molar bite force at different gape angles. Finally, we conducted a 2D geometric morphometric analyses to compare jaw shape, mechanical potential, and diversity in lever-arm ratios for a set of 238 specimens, representative of Australo-Papuan carnivorous and omnivorous murids. Our study reveals major changes in the muscle proportions among Hydromys and its omnivorous close relative, Melomys. Hydromys was found to have large superficial masseter and temporalis muscles as well as a reduced deep masseter and zygomatico-mandibularis, highlighting major functional divergence among omnivorous and carnivorous murines. Changes in these muscles are also accompanied by changes in jaw shape and the lines of action of the muscles. A more vertically oriented masseter, reduced masseteric muscles, as well as an elongated jaw with proodont lower incisors are key features indicative of a reduced propalinality in carnivorous Hydromys. Differences in the fiber length of the masseteric muscles were also detected between Hydromys and Melomys, which highlight potential adaptations to a wide gape in Hydromys, allowing it to prey on larger animals. Using a biomechanical model, we inferred a greater bite force in Hydromys than in Melomys, implying a functional shift between omnivory and carnivory. However, Melomys has an unexpected greater bite force at large gape compared with Hydromys. Compared with omnivorous Melomys, Hydromys have a very distinctive low mandible with a well-developed coronoid process, and a reduced angular process that projects posteriorly to the ascending rami. This jaw shape, along with our mechanical potential and jaw lever ratio estimates, suggests that Hydromys has a faster jaw closing at the incisor, with a higher bite force at the level of the molars. The narrowing of the Hydromys jaw explains this higher lever advantage at the molars, which constitutes a good compromise between a wide gape, a reduced anterior masseteric mass, and long fiber lengths. Lever arms of the superficial and deep masseter are less favourable to force output of the mandible in Hydromys but more favourable to speed. Compared with the small input lever arm defined between the condyle and the angular process, the relatively longer mandible of Hydromys increases the speed at the expense of the output force. This unique combination of morphological features of the masticatory apparatus possibly has permitted Hydromys to become a highly successful amphibious predator in the Indo-Pacific region.

Geographic Variation of Absolute and Relative Lower Molar Sizes in Two Closely Related Species of Japanese Field Mice (Apodemus speciosus and Apodemus argenteus: Muridae, Rodentia).

Geographic variation of the sizes of lower molar (M1 size) and relative lower molar sizes (size proportions among M1, M2, and M3) were examined in two species of closely related Japanese field mice (Apodemus speciosus and Apodemus argenteus). To determine the cause of the geographic variations observed, phylogeographic structure, interspecific competition, climate, and location (mainland or island) were compared. With regard to the phylogeographic structure, the sizes of the molar and the relative molar sizes in A. speciosus did not differ between two major clades (mainland vs. Hokkaido and peripheral islands), whereas the phylogeographic structure was not examined in A. argenteus, as no clear phylogeographic structure was evident. The sizes of M1 and relative molar size (M3/M1 score) in A. speciosus differed significantly between the mainland and islands; however, there was no significant difference between islands within and outside the distribution of A. argenteus. Interspecific competition between the two species may thus not be considerable. Climatic factors (temperature) and relative molar sizes (M2/M1 and M3/M1 scores) were significantly correlated in the mainland populations of A. speciosus, indicating that geographic variations in relative molar sizes may be affected by climate. In addition, M3/M1 scores varied more in the islands than on the mainland, suggesting effects of genetic drift. However, M1 size increases in the island populations of the two species are not attributed to the climate, but are explained by the so-called Island Rule. Geographic variation in A. speciosus is thus likely attributable to various effects.

A redescription of the Long-tailed Nesokia, Nesokia bunnii, and designation of a neotype (Rodentia: Muridae).

Long-tailed Nesokia, Nesokia bunnii, is a large rat restricted to the Mesopotamian marshes in Basra Province in southern Iraq. The species is known from five museum vouchers collected between March 1974 and January 1977. The type and the paratype, deposited in the Natural History Research Centre and Museum, University of Baghdad, Iraq, were destroyed during War on Iraq in 2003. By studying morphological details on three museum specimens in the Senckenberg Institution, Frankfurt a. M., Germany, we show that N. bunnii is unique among the Bandicoot rats (Nesokia and Bandicota) in having (1) rufous dorsal pelage, (2) facial mask of rufous, dark brown, grey and whitish areas, (3) whitish belly which is clearly demarcated along flanks, (4) ventral hairs white to bases, (5) woolly underfur, (6) long front claws, and (7) large tail annulation. Similar to N. indica, but in contrast to Bandicota, N. bunnii displays short incisive foramina, posterior margin of hard palate which terminates at the level of the third molar, and robust, hypsodont and laminate molars which lack posterior cingula. To objectively define the taxon we designate a neotype, which was collected at Saraifa, 30 km north of Qurna, Iraq. Our study highlights the importance of museum collections in documenting biodiversity and the indifference of decision makers and international institutions regarding their safe future.

Care of Mastomys in the laboratory.

Mastomys rodents occupy a valuable niche in biomedical research, but there is very little published information regarding how to care for them in the laboratory. Here we provide information about the physical and behavioral characteristics of this unusual laboratory rodent, its taxonomic history, common diseases that affect it, and its use in research. We also provide housing recommendations based upon almost 15 years of experience successfully maintaining a colony of Mastomys coucha at our institution.

Geographic Variation in Skull Morphology of the Large Japanese Field Mice, Apodemus speciosus (Rodentia: Muridae) Revealed by Geometric Morphometric Analysis.

We analyzed geographic variation in skull morphology of the large Japanese field mouse (Apodemus speciosus) and determined changes in skull morphology that occurred during the evolutionary history of A. speciosus in relation to the estimated distribution range in the last glacial maximum (LGM). We analyzed 1,416 specimens from 78 localities using geometric morphometric techniques applied to the dorsal side of the cranium and mandible. While large variations within and among the populations in Honshu, Shikoku, and Kyushu were observed, geographic patterns were not observed. Hokkaido and peripheral island populations showed shared differentiation from the Honshu, Shikoku, and Kyushu populations with a larger skull and distinct mandible shape. In addition, these two groups also differed from each other in accumulated random shape variation. Common characteristics found in Hokkaido and peripheral island populations were considered to be the ancestral states, which were retained by geographic isolation from the main islands. Random variations in Hokkaido and the peripheral island populations were formed through stochastic processes in relation to their isolation. Characteristic morphologies widely found in the populations of Honshu, Shikoku, and Kyushu were considered to be derived states that expanded after separation from the peripheral islands. Complex geomorphology and a shift in distribution range related to climate change and altitudinal distribution are suggested to have formed the complex geographic variation in this species.

A new species of the rodent genus Hylomyscus from Angola, with a distributional summary of the H. anselli species group (Muridae: Murinae: Praomyini).

A new species of Hylomyscus, H. heinrichorum, is described from mountains in western Angola. Based on morphological traits and cranial morphometry, the new species is assigned to the H. anselli species group and is hypothesized to be most closely related to H. anselli Bishop proper, a species named from Zambia. Members of both the H. anselli and H. denniae species groups occupy the Afromontane Biotic Zone, found in various mountain systems to the south and east of the Congo Basin. Evidence is reviewed that supports the independent radiation of these two species groups within montane forest from different Guineo-Congolian ancestral stocks.

Host evolution in Mastomys natalensis (Rodentia: Muridae): An integrative approach using geometric morphometrics and genetics.

The commensal rodent Mastomys natalensis is the natural reservoir of Lassa arenavirus (LASV), which causes hemorrhagic fever in West Africa. To study a possible effect of the virus on phenotypic and genotypic variation of its persistently infected host, we compared LASV-positive and non-infected wild-caught M. natalensis. The LASV effects on the phenotypic variation were explored using standard external morphometric measurements, geometric morphometric analyses of the cranial size and shape, and brain case volume. The genetic variability of M. natalensis specimens was assessed using 9 polymorphic microsatellite markers. Independent of sex and age, LASV-infected animals had smaller external body measurements, reproductive organs, skull size and brain case volume. Cranial shape differences between the 2 groups are represented by a lateral constriction of the entire skull. The genetic variability revealed consanguinity only among the LASV-positive rodents. We hypothesize that growth impairment may result in a selective disadvantage for LASV-infected M. natalensis, leading to a preferably commensal lifestyle in areas where the LAVS is endemic and, thereby, increasing the risk of LASV transmission to humans.

Classification of the spermatogenic cycle, seasonal changes of seminiferous tubule morphology and estimation of the breeding season of the large Japanese field mouse (Apodemus speciosus) in Toyama and Aomori prefectures, Japan.

The large Japanese field mouse, Apodemus speciosus, is a potential indicator of environmental stress, but this function has not been confirmed by histological studies. Since environmental stress affects the reproductive function of mice, we determined the reproductive characteristics of this species at two locations: Toyama (36°35'N, 137°24'E) and Aomori (40°35'N, 140°57'E). Mice were captured during May-November (n=119) and July-November (n=146) at these locations, respectively. We classified the breeding season from the numbers of pregnant females and young, in addition to the spermatogenic cycle and seasonal changes in seminiferous tubule morphology of males. Testicular weight was measured, and seminiferous tubule morphology was examined histologically. Fourteen stages were found in the seminiferous epithelium cycle based on acrosome formation and spermatid head morphology. At both locations, the breeding season peaked from late summer to early autumn and possibly in spring. Spermatogenic activity was classified into 4 periods from June to November: resting around June and October-November; resumptive around July; active around August; and degenerative around September. During the resting period, the seminiferous tubules consisted of Sertoli cells, spermatogonia and spermatocytes. Spermatogenesis began during the resumptive period, and spermatids were observed. During the active period, active spermatogenesis and a broad lumen were observed. During the degenerative period, spermatogenesis ended, and Sertoli cells, spermatogonia, spermatocytes and degenerating exfoliated round spermatids were observed. This study provides scientific information about the testicular histopathological evaluations of the large Japanese field mouse for its use as an index species of environmental pollution.

Dietary ecology of Murinae (Muridae, Rodentia): a geometric morphometric approach.

Murine rodents represent a highly diverse group, which displays great ecological versatility. In the present paper we analyse the relationship between dental morphology, on one hand, using geometric morphometrics based upon the outline of first upper molar and the dietary preference of extant murine genera, on the other. This ecomorphological study of extant murine rodents demonstrates that dietary groups can be distinguished with the use of a quantitative geometric morphometric approach based on first upper molar outline. A discriminant analysis of the geometric morphometric variables of the first upper molars enables us to infer the dietary preferences of extinct murine genera from the Iberian Peninsula. Most of the extinct genera were omnivore; only Stephanomys showed a pattern of dental morphology alike that of the herbivore genera.