The structure of a chromosomal hybrid zone of house mice (Mus domesticus) in central Italy: cytogenetic analysis

Parapatric hybridization between the chromosomal race “CD” (2n = 22) and standard karyotype populations (2n = 40) of Mus domesticus occurs extensively in central Italy. The present paper reports the results of a ctogenetic surve on a transect crossin the hybrid zone north of Rome. No clinal variation in eitier diloid nuders and chromosome frequencies was found to occur in this area, and drift seems to be responsible for the observed atchy pattern of variation. The previous assumption of a strong fertility reduction in structuray heterozyous hybrids contrasts sharply with the width (32 km) of the zone and the average structural aeterozygosity of the hybrid poulations. It is suggested that fitness of structural heterozygotes in nature is not strongly aPfected as has been inferred from laboratory experiments. The results of this study are discussed in context together with the role of hybrid zones in chromosomal speciation in Mus domesticus.     

Chromosomal location of soluble glutamic-pyruvic transaminase-1 (Gpt-1) in the mouse

Three alleles at the Gpt-1 (glutamic-pyruvic transaminase-1) locus in the mouse, as identified by electrophoresis on cellulose acetate, and their distribution among inbred mouse strains and wild stocks are described. The Gpt-1 locus was shown to control the soluble form of the enzyme. Three-point linkage analysis established the location of Gpt-1 on chromosome 15 between uw and bt. In addition, a new staining procedure is described that allows the visualization of GPT activity on gels by the deposition of formazan. This is an improvement over previous methods that produced bands of nonfluorescence against a fluorescent background.This investigation was supported in part by Research Grant GM 20919 from the National Institute of General Medical Sciences, and by contract NO1-ES-4-2159 with the National Institute of Environmental Health Sciences. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care.     

Phenotypic variation in respiratory metabolism and complementation of murine hepatic mitochondria

Summary Genetically standardized inbred mice exhibit interstrain differences in hepatic mitochondrial respiration rate, respiratory control, efficiency of oxidative phosphorylation with Krebs cycle substrates, and quantity of protein in the mitochondrial fraction. Mitochondria of females of strains with positive combining ability for postweaning growth mixed in vitro show complementation for respiratory traits. Mitochondria of males when mixed do not exhibit complementation. Mitochondria isolated from female mice respire more rapidly, are more tightly coupled and have higher phosphorylation efficiencies compared to those from male mice across all strains assayed. Direct evaluation of androgen effects on mitochondrial respiratory capacity supported this conclusion.Journal paper no. 4277 of the Arizona Agricultural Experiment Station. Supported in part by a University of Arizona Foundation fellowship (DRB)     

Chronic calorie restriction increases susceptibility of laboratory mice (Mus musculus) to a primary intestinal parasite infection

Long-term calorie restriction (CR) has numerous benefits; however, effects of CR on susceptibility to intact pathogens are not well understood. Because CR enhances immune function of laboratory mice ( Mus musculus ), it was hypothesized that mice subjected to CR would be less susceptible to experimental infections of the intestinal parasite Heligmosomoides bakeri . Furthermore, because H. bakeri must combat a greater host immune response by CR mice compared to fully fed mice, it also was also hypothesized that (i) worms living in CR hosts would have lower reproduction than worms from ad libitum -fed mice, and (ii) CR mice would have a more female-biased sex ratio as male worms may be more vulnerable to host immune response than female worms. Mice were subjected to CR for 6.7 months and were then infected with H. bakeri for one additional month. As expected, CR mice had equal or enhanced immune response (eosinophils and immunoglobin G1 production) to H. bakeri infection compared to ad libitum -fed mice, and CR mice harbored a more female-biased sex ratio than ad libitum -fed mice. Contrary to predictions, CR mice had more worms than ad libitum -fed mice and the worms from CR mice produced more eggs than worms from ad libitum -fed mice. These data indicate that, despite the evidence that long-term CR enhances traditional measures of immune function, CR may actually increase susceptibility to intact parasite infection. Furthermore, changes in worm reproduction and differential survival of male vs. female worms may influence host–parasite transmission dynamics during long-term host CR.     

WHERE ARE THE WORMY MICE? A REEXAMINATION OF HYBRID PARASITISM IN THE EUROPEAN HOUSE MOUSE HYBRID ZONE

Wormy mice in a hybrid zone have been interpreted as evidence of low hybrid fitness, such that parasites contribute to species separation. However, because of its natural heterogeneity, observations of parasite load must be numerous with good field area coverage. We sampled 689 mice from 107 localities across the Bavaria-Bohemia region of the European house mouse hybrid zone and calculated their hybrid indices using 1401 diagnostic single nucleotide polymorphisms (SNPs). We tested whether hybrids have greater or lesser diversity and load of parasite helminths than additive expectations, performing load analyses on the four most common taxa. We found hybrids have significantly reduced diversity and load of each of the commonest helminths; rarer helminths further support reduced load. Although within-locality comparisons have little power, randomization tests show the repeated pattern is unlikely to be due to local parasite heterogeneity, and simulations show a patch of low parasite diversity is unlikely to fall by chance just so in the field area, such that it produces the observed effects. Our data therefore contradict the idea that helminths reduce hybrid fitness through increased load. We discuss a vicariant Red Queen model that implies immune genes tracking parasites will escape Dobzhansky-Muller incompatibilities, generating hybrid variants untargeted by parasites.     

Identification of microRNAs from different tissues of chicken embryo and adult chicken

We report for the first time the identification of 25 microRNAs from tissues originating from chicken embryo and adult chicken. Most of the cloned microRNAs are expressed in both adult chickens and chicken embryos. Fourteen were identified without any prior prediction. One microRNA, miR-757, is thought to be chicken-specific. Three of the microRNAs appear to be extremely tissue specific.     

Variability of diurnality in laboratory rodents

The locomotor activity rhythms of domestic mice, laboratory rats, Syrian hamsters, Siberian hamsters, Mongolian gerbils, degus, and Nile grass rats were compared. Running-wheel activity was monitored under a light–dark cycle with 12 h of light and 12 h of darkness per day. Nile grass rats were found to be reliably diurnal, whereas laboratory rats, Siberian hamsters, domestic mice, and Syrian hamsters were reliably nocturnal. Both diurnal and nocturnal subgroups were observed in Mongolian gerbils and degus. A downward gradient of diurnality was observed from Mongolian gerbils classified as diurnal, degus classified as diurnal, gerbils classified as nocturnal, and degus classified as nocturnal. Nocturnal degus remained nocturnal when tested with an infrared motion detector without running wheels. Thus, although the diurnal–nocturnal dichotomy could be applied to some of the species, it was not appropriate for others. The dichotomy may reflect researchers’ needs for systematization more than a natural distinction between species. Through mechanisms as yet poorly understood, the balance between entraining and masking processes seems to generate a gradient of temporal niches that runs from predominantly diurnal species to predominantly nocturnal species with many chronotypes in between, including species that exhibit wide intra-species gradients of temporal niche.     

Of mice and (Viking?) men: phylogeography of British and Irish house mice

The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.     

Insights into the population structure of blue whales in the Eastern North Pacific from recent sightings and photographic identification

Blue whales were widely distributed in the North Pacific prior to the primary period of modern commercial whaling in the early 1900s. Despite concentrations of blue whale catches off British Columbia and in the Gulf of Alaska, there had been few documented sightings in these areas since whaling for blue whales ended in 1965. In contrast, large concentrations of blue whales have been documented off California and Baja California and in the eastern tropical Pacific since the 1970s, but it was not known if these animals were part of the same population that previously ranged into Alaskan waters. We document 15 blue whale sightings off British Columbia and in the Gulf of Alaska made since 1997, and use identification photographs to show that whales in these areas are currently part of the California feeding population. We speculate that this may represent a return to a migration pattern that has existed for earlier periods for eastern North Pacific blue whale population. One possible explanation for a shift in blue whale use is changes in prey driven by changes in oceanographic conditions, including the Pacific Decadal Oscillation (PDO), which coincides with some of the observed shifts in blue whale occurrence.     

单宁酸对棕色田鼠和小鼠食物选择、日食量和蛋白质消化率的影响

目的用不同浓度单宁酸（tannic acid,TA）处理后的花生喂养棕色田鼠（Lasiopodomys mandarinus）和小鼠（Mus musculus）,研究单宁酸对两种鼠食物选择倾向、食物摄入量、蛋白质消化率的影响。方法本研究的设计如下：1）选择一批棕色田鼠和小鼠,单笼饲养,自由饮水。用正常花生饲喂二周实验用棕色田鼠和小鼠,使其适应这种食物;2）随机选出棕色田鼠和小鼠各10只（雌雄各半）,单笼饲养。用经0%、5%、10%TA处理的花生饲喂供试鼠一周,观察和记录两种鼠对TA处理后花生的选择和取食特征;3）随机选出18只棕色田鼠和18只小鼠,单笼饲养,并各分为3组（每组均为6只）,按两种鼠分别命名为对照组、低单宁酸组、高单宁酸组,并分别用经0%、5%和10%TA处理的花生饲喂一周,测定两种鼠的食物摄入量;同时收集粪便,用凯氏定氮仪测定粗蛋白含量,计算蛋白质消化率。结果1）棕色田鼠和小鼠均优先选择无TA食物（P〈0.001）,二者间差异达显著性水平（P〈0.001）;2）食物中的TA降低棕色田鼠和小鼠的相对日食量（P〈0.001）和食物中蛋白质的消化率,随TA含量的升高,棕色田鼠和小鼠的相对日食量和蛋白质消化率均显著下降。结论TA降低棕色田鼠和小鼠的食物摄入量和食物中蛋白质的消化率。TA对鼠类的食物摄入量和蛋白质消化率的影响有种间差异性,小鼠对TA的适应性更强。