A novel approach to field identification of cryptic Apodemus wood mice: calls differ more than morphology

Field identification of European wood mice Apodemus spp. is challenging due to their morphological resemblance and frequent sympatry. We developed discriminant functions based on body mass and acoustic variables of distress calls to identify three cryptic species of wood mice (Apodemus alpicola, Apodemus flavicollis and Apodemus sylvaticus) in Italy. We achieved an overall correct classification rate of 86–98%; the best results (100% correct classification) were obtained for Apodemus sylvaticus calls. This minimally invasive, effective and low‐cost method highlights the potential role of bioacoustics as a powerful tool for field discrimination of cryptic species of terrestrial mammals.     

Molecular identification of three sympatric species of wood mice (Apodemus sylvaticus,A. flavicollis,A. alpicola) in western Europe (Muridae: Rodentia)

The woodmouse (Apodemus sylvaticus) and yellow‐necked fieldmouse (Apodemus flavicollis) are sympatric and even syntopic in many regions throughout their European range. Their field discrimination on the basis of external characters is a real challenge for many fields of research. The problem is even more complicated in the Alpine chain where they live sympatrically with a third similar species: A. alpicola. A rapid and simple method is proposed to discriminate the three species in processing field‐collected biopsies as well as ethanol‐preserved museum samples.     

Comparative cytogenetic analysis of the “Sylvaemus” group of Apodemus (Rodentia, Muridae): A. sylvaticus from Sicily and A. flavicollis from the central Apennines

Chromosome mapping of three common markers, ie major and 5S rRNA genes (rDNA) and telomeric repeats, and conventional chromosome bandings were applied to two sibling species, Apodemus sylvaticus Linnaeus, 1758 and A. flavicollis Melchior, 1834, to further investigate intra- and interspecific karyological differentiation in the genus Apodemus. A slight variation of the rDNA-patterns was detected between the two Apodemus species. In both of them, the major NORs were located on autosome pairs 8, 11, 12 and 22, while the two other rDNA sites detected on chromosomes 7 and 21 were variable in, respectively, A. sylvaticus and A. flavicollis. Several tiny rDNA sites were present on the sex chromosomes in both species, but their incidence was lower in A. flavicollis. Single 5S rDNA chromosomal sites were conserved on chromosome pair 20. No interstitial sites of telomeric repeats were present in either species. In the Sicilian population of A. sylvaticus, the constitutive heterochromatin pattern corresponded to the “sylvaticus-E1” cytotype, while A. flavicollis had a species-specific pattern restricted to centromeres of all chromosomes. The results are discussed in relation to cytogenetic data available for the genus, with emphasis on the Sylvaemus group/subgenus.     

Seasonal acclimation of bank voles and wood mice: nonshivering thermogenesis and thermogenic properties of brown adipose tissue mitochondria

Summary Seasonal acclimation of nonshivering thermogenesis and brown adipose tissue was studied in wild bank voles (Clethrionomys glareolus), yellow necked field mice and wood mice (Apodemus flavicollis, A. sylvaticus). Both, voles and mice increased their capacity for nonshivering thermogenesis during winter. Thermogenic properties of brown fat (cytochrome c oxidase activity, mitochondrial protein content, GDP-binding of brown fat mitochondria) showed similar changes during seasonal acclimation;Clethrionomys andApodemus spp. both showed lowest thermogenic properties in the summer during August, a rapid increase during fall, and highest levels of thermogenic activity in the winter months. With regard to changes in body weight and brown fat mass these species show different strategies for seasonal acclimation. InClethrionomys a reduction of body mass in the winter was found, both in the wild population as well as in individual animals housed in the laboratory.A. flavicollis showed a reduction of body weight during fall, whereasA. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in theApodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas inClethrionomys brown fat mass and cellularity remained seasonally constant. These species live in the same habitat and were trapped in the same area. It is concluded that seasonal improvements of in vivo and in vitro thermogenesis are very similar in these species, although the physiological basis for this improvement is different inClethrionomys andApodemus.Abbreviations BAT brown adipose tissue - BMR basal metabolic rate (resting metabolic rate at thermoneutrality) - BW body weight - COX cytochrome c oxidase - GDP guanosine diphosphate - MP mitochondrial protein - NA noradrenaline - NST nonshivering thermogenesis - NSTcap NST capacity (NST maximum minus BMR) - T _a ambient temperature     

Morphometric study of two species of wood miceApodemus sylvaticus andA. flavicollis (Rodentia: Muridae): traditional and geometric morphometric approach

Skull shape and size were investigated in 311 specimens ofApodemus sylvaticus (Linnaeus, 1758) andA. flavicollis (Melchior, 1834), using traditional and geometric morphometric approach. We searched for potential morphometric diagnostic criteria between these morphologically similar mice and we an alyzed the interpopulation morphometric variation. Specific status of all individuals was identified by scoring four diagnostic allozyme markers. Discriminant analysis based on 16 cranial measure ments as well as that based on land mark data for ventral side of the skull discriminated in dividuals with 99.7% accuracy. The classification functions useful for practical discrimination of unknown specimens are given. Our data showed neither clear intraspecific geographical pattern among studied populations nor evidence for character displacement in syntopic populations ofA. sylvaticus andA. flavicollis.     

A removal experiment with sympatric populations of Apodemus sylvaticus (L.) and A. flavicollis (Melchior) (Rodentia: Muridae)

Summary This study examines the role of competition in the relationship between sympatric populations of Apodemus sylvaticus and A. flavicollis at Woodchester Park, Gloucestershire, England. Three grids were trapped for twelve months to monitor changes in population size, survival, reproduction, body weight, spatial segregation and microhabitat associations. The A. flavicollis was removed from one grid, A. sylvaticus from another while the rodent community on the third was left intact as a control. Subsequent changes in ecological parameters were observed over a further period of 7 months. Isolated populations of both species entered reproductive condition earlier than on the control grid. This resulted in a rapid increase of the A. flavicollis population but the dynamics of A. sylvaticus were unaffected. In the absence of their congener both species made greater use of areas of woodland once frequented by the absent species. However specific microhabitat associations observed in two species communities remained after experimental manipulation. It is concluded that although A. sylvaticus and A. flavicollis do compete for space, this is a comparatively weak interaction which does not lead to habitat exclusion. Competition is probably ameliorated by intrinsic differences in the biology of these Apodemus species.     

A comparative study of the heterochromatin of Apodemus sylvaticus and Apodemus flavicollis

The two closely related species Apodemus sylvaticus and Apodemus flavicollis (Muridae) differ in the distribution of their heterochromatin. Two major repetitive sequences known to occur in both species were isolated from A. flavicollis after digestion of total nuclear DNA with the restriction enzymes HindIII and EcoRI respectively and characterized in both species by filter hybridisation and in situ hybridisation to metaphase chromosomes. The EcoRI clone detects a dispersed repetitive sequence family in the genome of both species. Southern blot hybridisation with the HindIII satellite DNA probe reveals major similarities and minor differences in the two species. In situ hybridisation with the HindIII probe labels all chromosomes of A. flavicollis exclusively in the centromeric heterochromatin, whereas in A. sylvaticus several autosomes are also labelled distally. The labelling patterns correspond to the distribution of heterochromatin in the two species. It is concluded that the additional distal heterochromatin of A. sylvaticus contains similar sequences to those of the centromeric heterochromatin of both species. The distal heterochromatin in A. sylvaticus most likely evolved by transposition and amplification of centromeric satellite DNA elements, after the separation of the two species.     

Effect of the odour of weasels (Mustela nivalis L.) on trapped samples of their prey

Summary The presence of weasel anal gland secretion on rodent live traps substantially depresses population estimate by greatly reducing the catch of Microtus agrestis. The catch of Apodemus sylvaticus remains almost unaffected.     

Intra- and interspecific interactions of Apodemus sylvaticus (L.) and A. flavicollis (Melchoir) under laboratory conditions

Miller (1967) has indicated that the coexistence of Apodemus sylvaticus and A. flavicollis may be possible if A. flavicollis, a species with a more restricted niche, is competitively superior in interspecific encounters. Intra- and interspecific behaviour of male and female A. sylvaticus and A. flavicollis was examined in dyadic encounters in a small arena. Interactions between conspecifics indicate that intraspecific behaviour in A. sylvaticus and A. flavicollis is similar but, in interspecific interactions there were more submissive and agonistic acts, and less introductory and amicable behaviour. A. flavicollis was dominant to A. sylvaticus in 63 out of 70 encounters and A. sylvaticus dominant in only one. This superiority may contribute to the persistence of small, localized populations of A. flavicollis despite the presence of A. sylvaticus.     

Evolution of MHC-<Emphasis Type="Italic">DRB</Emphasis> class II polymorphism in the genus <Emphasis Type="Italic">Apodemus</Emphasis> and a comparison of <Emphasis Type="Italic">DRB</Emphasis> sequences within the family Muridae (Mammalia: Rodentia)

Allelic diversity at major histocompatibility complex (MHC) genes is thought to be maintained by balancing selection over long periods of time, even across multiple speciation events. Trans-species sharing of MHC alleles among genera has been supported by many studies on mammals and fish, but in rodents, the results are ambiguous. We investigated natural levels of MHC-DRB variability and evolutionary processes in the wood mouse (Apodemus sylvaticus) and the yellow-necked mouse (Apodemus flavicollis), which are common, sympatric murid rodents in European forests. Using single-strand conformation polymorphism analysis and DNA sequencing, 38 DRB exon 2 alleles were detected among 162 A. sylvaticus from nine different locations in Germany and Switzerland, and 15 DRB exon 2 alleles were detected among 60 A. flavicollis from three different locations in northern Germany. There was evidence for balancing selection in both species. Phylogenetic analysis, including additional murid taxa, showed that the DRB exon 2 sequences did not separate according to species, consistent with trans-species evolution of the MHC in these taxa.     

Changes in size of Baltic field voles over the last 50 years: are they really shrinking?

Using museum materials and recently trapped specimens of field voles (Microtus agrestis (Linnaeus, 1761)) from Lithuania and Estonia, we assessed temporal and latitudinal trends in body and skull size, comparing the periods 1980–1996 and 2014–2016. We measured four body and 23 skull characters, size-adjusting them using the geometric mean procedure. A pronounced decrease in the size of M. agrestis was noted in Estonia, where 23 out of 27 adjusted body and skull characters had decreased by up to 21.9%, with only the tail length, hind foot length, maximum height of mandibula excluding coronoid process and coronoid height of mandibula increasing significantly. Decreases were less marked in voles from Lithuania – most pronounced were a 6.1% decrease in adjusted body length, an 11.6% decrease in adjusted length of the braincase, a 3.85% decrease in the breadth of the braincase, measured at the widest part, a 2.9% decrease in condylobasal skull length and a 2.2% decrease in the height of the braincase. The coronoid height of the mandibula of Lithuanian individuals showed an 8.4% size increase. In both countries, the confounding effect of sex on the size changes of M. agrestis from 1980 to 2016 was much smaller than the effect of time period. Concluding, voles in Estonia became significantly smaller, while changes in the measured characters in Lithuania were heterogeneous.     

Changes in home range size during growth and maturation of the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus)

Summary A field study was carried out during winter and spring of 1982/83 to determine changes in home range size with increasing body weight and maturation in the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus). Individual home range sizes in males increased and in females decreased with increasing body weight. Relating these changes to changed energetic requirements failed. In these species behavioral aspects seem to be a more important determinant of home range size than body weight.     

Mitochondrial cytochrome <Emphasis Type="Italic">b</Emphasis> sequences resolve the taxonomy of field mice (<Emphasis Type="Italic">Apodemus</Emphasis>) in the western Balkan refugium

Apodemus sylvaticus stankovici, described from the topographically rough landscape of the western Balkan glacial refugium, was recently proposed as being either a junior synonym of Apodemus flavicollis or a species on its own right. To untangle this taxonomic vagueness, we sequenced complete cytochrome b gene in 28 field mice collected at 12 locations in the mountains of Bosnia and Herzegovina, Montenegro, western Macedonia and northern Greece. Samples yielded 27 new haplotypes which clustered into two distinct groups. One of these clades also included the reference haplotype of A. flavicollis, while another cluster emerged as being identical with the reference sample for A. sylvaticus. As is common in Apodemus, both species retrieved in our analysis were characterized by low levels of intraspecific variation (0.4–0.9%) as opposed to a high level of differentiation between them (8.0–10.0%); therefore, the taxonomic classification of our material was without doubt. We found no evidence regarding the presence of an additional cryptic species in the mountains of the western Balkans. The very similar values of genetic variability in the two species imply their common evolutionary history of a long-term coexistence in the western Balkan refugium.     

Discrimination of the sibling species Apodemus flavicollis and A. sylvaticus (Rodentia,Muridae)

Karyotyping and several molecular methods have allowed successful identification of two morphologically similar wide-ranging Western Palearctic species, the yellow-necked field mouse Apodemus flavicollis (Melchior, 1934) and the long-tailed wood mouse A. sylvaticus (Linnaeus, 1758), but reliable species diagnosis on the basis of morphometric characters is particularly problematic. Although they are easily morphologically distinguishable in Central and Northern Europe, this is not the case in southern parts of their distribution areas. Despite that, we have successfully discriminated A. flavicollis and A. sylvaticus from Serbia (Southern Europe) using geometric and traditional morphometric methods on a data set for ventral crania of specimens previously genotyped by the Inter Simple Sequence Repeat-PCR (ISSR-PCR). Discrimination power of applied approaches was more or less similar. The majority of our results were consistent with those obtained for specimens collected across the Czech Republic (Central Europe). Morphological differences observed herein, as well as those already reported between A. flavicollis and A. sylvaticus from the central and northern parts of their distribution areas, could be the outcome of their biology, i.e. ecological discrepancies, different assumed evolutionary scenarios considering biogeography, phylogeny, history and ontogeny.     

Bergmann's rule in shrews: geographical variation of body size in Palearctic Sorex species

According to Bergmann's rule, individuals of a given species tend to be larger in colder (northern) climates. Traditional explanation points to the relatively lower surface‐to‐volume ratio in larger animals and, consequently, relatively lower costs of thermoregulation. We examined intraspecific covariation of body size with geographical location and climate in five species of Sorex shrews, animals that are among the smallest extant mammals. The condylobasal length of skull (CBL), compiled from literature data and measured on museum specimens, was used as an indicator of the overall body size of shrews. Surprisingly, in three out of five shrew species, the CBL was negatively correlated with latitude, and the same trend, although not statistically significant, was found in the fourth species. In general, shrews were smaller in colder areas, as evidenced by the positive correlations between the CBL and temperature. In two species, these positive correlations appeared when the effect of longitude was held constant in the partial correlation analysis. Characteristically, the strongest negative correlation with latitude and positive with temperatures was found in S. minutus, the smallest species under study. Shrews were in general larger in environments with high actual evapotranspiration. Body mass reviewed in S. araneus paralleled the pattern found in the CBL variation in this species, i.e. it decreased northward, both in summer‐ and winter‐caught animals. In addition, contrary to the widely accepted ? but not rigorously tested ? belief, body mass recession from summer to winter (the Dehnel Effect) did not correlate with latitude. We concluded that shrews followed the converse to Bergmann's rule, and hypothesize that part of their body size variation along the west‐east axis may be explained by character displacement. We also hypothesize that scarcity of food, especially in winter, is a major factor selecting for small body size in shrews in northern areas, as smaller individuals should require less food. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78 , 365–381.     

The diet of the Alpine mouse Apodemus alpicola in the Swiss Alps

In this study, we used faecal analysis to determine the diet of the alpine mouse Apodemus alpicola in the field for the first time. This species consumes mainly insects in spring and fruits and seeds of small herbaceous dicotyledons in summer and autumn. Compared to the two congeneric species A. flavicollis and A. sylvaticus, which also occur in the Alps, the diet of A. alpicola is rich in contrasts, with a very pronounced difference between spring and summer. The absence of tree seeds also suggests a mostly terrestrial behaviour. We explain these facts by the specificity of the habitat of A. alpicola: the extreme weather conditions produce great seasonal changes in the vegetation, and the rocky ground favours the adaptation to rock climbing rather than to arboreal living.

Zusamenfassung

Nahrungszusammensetzung bei der Alpenwaldmaus Apodemus alpicola in den Schweizer AlpenDie Nahrungszusammensetzung der Alpenwaldmaus Apodemus alpicola wurde erstmals an Wildfängen und anhand von Kotanalysen qualitativ und quantitativ untersucht. Die Alpenwaldmaus konsumierte im Frühjahr hauptsächlich Insekten, im Sommer und Herbst Früchte und Samen kleiner Dicotyledonen der Krautschicht. Verglichen mit der Gelbhalsmaus A. flavicollis und der Waldmaus A. sylvaticus, die ebenfalls in den Alpen vorkommen, ist die Nahrungspalette von A. alpicola kontrastreicher, mit größeren Unterschieden zwischen Frühjahrs- und Sommerkost. Wir erklären dies durch extreme Klimabedingungen, die zu ausgeprägten jahreszeitlichen Änderungen in der Vegetation führen. Das Fehlen von Baumsamen läßt auf ein vorwiegend terrestrisches Futtersuchverhalten schließen. Große Hinterfüße und langer Schwanz sind offenbar Anpassungen ans Felsklettern und nicht an arboricoles Verhalten.     

A chromosomal study on Greek populations of the genusApodemus (Rodentia, Murinae) reveals new data on B chromosome distribution

During this study, 94 specimens (51 males, 43 females) of the wood mouseApodemus sylvaticus (Linnaeus, 1758), the yellow-necked mouseA. flavicollis (Melchior, 1834) and the western broad-toothed mouseA. epimelas (Nehring, 1902) from 20 localities of Greece were karyologically examined. The first two species were found to be widely distributed and their otherwise very similar karyotype (2n=48, FN=48) could be clearly distinguished, based on C-banding pattern. The third species appeared to have a more limited geographical distribution and its karyotype was distinguished from that of the previous two species, since it contained two pairs of small metacentric autosomes (2n=48, FN=52). The chromosomal study further revealed that nine individuals ofA. flavicollis possessed supernumerary B chromosomes (2n=49–50, FN=49–50). Meiotic chromosome preparations revealed that in contrast to sex chromosomes and autosomes, B chromosomes do not participate in bivalent formation. On the other hand, no supernumerary chromosomes were found in the studiedA. sylvaticus andA. epimelas material.     

Body mass and sex‐biased parasitism in wood mice Apodemus sylvaticus

Male sex‐biased parasitism (SBP) occurs across a range of mammalian taxa and two contrasting sets of hypotheses have been suggested for its establishment. The first invokes body size per se and suggests that larger individuals are either a larger target for parasites, trade off growth at the expense of immunity or cope better with parasitism than smaller individuals. The second suggests a sex‐specific handicap whereby males have reduced immunocompetence compared to females due to the immunodepressive effects of testosterone. The current study investigated whether sex‐biased parasitism is driven by host ‘body size’ or ‘sex’ using a rodent–tick (Apodemus sylvaticus–Ixodes ricinus) system. Moreover, the presence or absence of large mammals at study sites were used to control the presence of immature ticks infesting wood mice, allowing the impacts of parasitism on host body mass and female reproduction to be assessed. As expected, male mice had greater tick loads than females and analyses suggested this sex‐bias was driven by body mass as opposed to sex. It is therefore likely that larger individuals are a larger target for parasites, trade off growth at the expense of immunity or adapt behavioural responses to parasitism based on their body size. Parasite load had no effect on host body mass or female reproductive output suggesting individuals may alter behaviour or life history strategies to compensate for costs incurred through parasitism. Overall, this study lends support to the ‘body size’ hypothesis for the formation of sex‐biased parasitism.     

The prey of the Barn owl (Tyto alba alba) in East Norfolk

Some 5000 Barn owl pellets, collected from sites in East Norfolk during the past decade, have been examined. The most important prey species, by weight, were the Field vole (Microtus agrestis) 52%, the Brown rat (Rattus norvegicus) 17%, and the Common shrew (Sorex araneus) 12%. The prey varies over different habitats; Wood mice (Apodemus sylvaticus) and Bank vole (Clethrionomys glareolus) forming a higher proportion in localities with hedges, scrub and woodland than in open grasslands. These results are comparable with those of other recent work. However, when compared with studies conducted over 30 years ago, it would appear that the Field vole now constitutes a higher proportion, and the Brown rat a lower proportion, of the prey taken.     

Cyclic population changes in three mouse species in the same woodland

Summary In two forest areas of West Berlin the population-changes in three mouse species have been investigated over 28 years (1952–1979). Significant changes in absolute density have been established for the Short-Tailed Vole (Microtus agrestis) at 5-year intervals, for the Common Vole (Microtus arvalis) at 4-year intervals, and for the Yellow-Necked Field Mouse (Apodemus flavicollis) at 3-year intervals. The investigations were based on a total of 43,535 small vertebrates, 90% of which had been found in the pellets of breeding Tawny Owls. The remaining 10% belonged to pellets collected in the territories of breeding Long-Eared Owls. It is assumed that, for those prey animals whose percentage in the total prey of a predator is fairly high, the percentage proportionally approximates the real fluctuations in their (absolute) density.