Climatic change and body size in two species of Japanese rodents

Using museum specimens, we studied temporal changes in skull size in two species of Japanese rodents, the large Japanese field mouse ( Apodemus speciosus ) and Pratt's vole ( Eothenomys smithii  =  E. kageus ) during the 20th century. We used the greatest length of the skull (GTL), zygomatic breadth (ZB), narrowest width of the skull across the interorbital region (IC) and the length of the upper cheek teeth row (M) as indicators to such changes. We found that GTL and ZB (but not IC and M) increased during the study period in mice, and that IC and M (but not GTL and ZB) increased marginally in voles. We attribute these changes to elevated ambient minimal temperatures, which increased food availability and energy savings for the mice, and required diet change in the voles.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 263–267.     

金华北山三种啮齿动物身体热值、脂肪和水分含量的研究

研究了浙江金华３种啮齿动物的身体热值,脂肪含量和水分含量。成年社鼠、褐家鼠和白腹巨鼠生物量热值季节变动范围分别为６．２０９７－７．６５７ＫＪ／ｇ,６．１５３－７．０９６ＫＪ／ｇ,６．１９９－１２．０３３ＫＪ／ｇ;水分含量为６６．６４％－６９．７５％,６７．４８％－７０．１９％,５４．６４％－７２．３７％;灰分含量不存在季节差异,年平均值分别为１２．５０％,１２．２３％,１０．４９％。神鼠脂肪含量春     

荒漠区两种优势鼠种的活动节律及其影响因子

子午沙鼠(Meriones meridianus)和三趾跳鼠(Dipus sagitta)是阿拉善荒漠区同域共存的两种优势鼠种,研究其活动节律对于了解荒漠啮齿动物的共存机制具有重要意义。本研究于2017年4月(春季)、7月(夏季)、9月(秋季)和10月(初冬)在阿拉善荒漠区,利用红外相机陷阱技术对子午沙鼠和三趾跳鼠的活动节律进行监测,以期深入了解极端干旱环境中子午沙鼠和三趾跳鼠不同季节活动节律动态,探索优势鼠种共存策略。结果表明:(1)子午沙鼠的种群数量受三趾跳鼠种群密度的抑制,其活动高峰期随三趾跳鼠活动高峰期的推迟而推迟,存在明显错峰现象,受光照强度的影响,二者的活动时长与夜长均呈正相关关系,其活动开始时间随日落时间的推迟、环境温度的升高而推迟;(2)子午沙鼠的活动强度在不同季节间无显著差异,三趾跳鼠的活动强度在不同季节有显著差异(F=3.202;P=0.032),表现为4月>7月>9月>10月;(3)子午沙鼠和三趾跳鼠通过调整其夜间时间利用模式以减少竞争,实现同域共存。     

Comparative analysis of the DXPas34 regulatory region in rodents

Mouse X chromosome inactivation center contains the DXPas34 minisatellite locus which plays an important role in expression regulation of the Tsix and Xist genes, involved into female dosage compensation. Comparative analysis of the DXPas34 locus from mouse, rat, and four common vole species revealed similar organization of this region in the form of tandem repeat blocks. A search for functionally important elements in this locus showed that all the species examined carried the conservative motif monomers, which could be involved in regulation of X inactivation.     

Sexual size dimorphism within species increases with body size in insects

Studies examining interspecific differences in sexual size dimorphism (SSD) typically assume that the degree of sexual differences in body size is invariable within species. This work was conducted to assess validity of this assumption. As a result of a systematic literature survey, datasets for 158 insect species were retrieved. Each dataset contained adult or pupal weights of males and females for two or more different subsets, typically originating from different conditions during immature development. For each species, an analysis was conducted to examine dependence of SSD on body size, the latter variable being used as a proxy of environmental quality. A considerable variation in SSD was revealed at the intraspecific level in insects. The results suggest that environmental conditions may strongly affect the degree, though not the direction of SSD within species. In most species, female size appeared to be more sensitive to environmental conditions than male size: with conditions improving, there was a larger relative increase in female than male size. As a consequence, sexual differences in size were shown to increase with increasing body size in species with female-biased SSD (females were the larger sex in more than 80% of the species examined). The results were consistent across different insect orders and ecological subdivisions. Mechanisms leading to intraspecific variation in SSD are discussed. This study underlines the need to consider intraspecific variation in SSD in comparative studies.     

The postabsorptive and postprandial metabolic rates of praying mantises: Comparisons across species,body masses,and meal sizes

The metabolic rate of an animal affects the amount of energy available for its growth, activity and reproduction and, ultimately, shapes how energy and nutrients flow through ecosystems. Standard metabolic rate (SMR; when animals are post-absorptive and at rest) and specific dynamic action (SDA; the cost of digesting and processing food) are two major components of animal metabolism. SMR has been studied in hundreds of species of insects, but very little is known about the SMR of praying mantises. We measured the rates of CO₂ production as a proxy for metabolic rate and tested the prediction that the SMR of mantises more closely resembles the low SMR of spiders – a characteristic generally believed to be related to their sit-and-wait foraging strategy. Although few studies have examined SDA in insects we also tested the prediction that mantises would exhibit comparatively large SDA responses characteristic of other types of predators (e.g., snakes) known to consume enormous, protein-rich meals. The SMR of the mantises was positively correlated with body mass and did not differ among the four species we examined. Their SMR was best described by the equation μW = 1526 * g^0.745 and was not significantly different from that predicted by the standard ‘insect-curve’; but it was significantly higher than that of spiders to which mantises are ecologically more similar than other insects. Mantises consumed meals as large as 138% of their body mass and within 6–12 h of feeding and their metabolic rates doubled before gradually returning to prefeeding rates over the subsequent four days. We found that the SDA responses were isometrically correlated with meal size and the relative cost of digestion was 38% of the energy in each meal. We conclude that mantises provide a promising model to investigate nutritional physiology of insect predators as well as nutrient cycling within their ecological communities.     

Interactions among unrelated species: Granivorous rodents,a parasitic fungus,and a shared prey species

Summary Granivorous rodents and a parasitic fungus in the Sonoran Desert utilize a common prey species, Erodium cicutarium, a desert annual plant. Experimental removal of rodents from field exclosures resulted in significantly higher densities of E. cicutarium. Fungal infection was significantly higher in the absence of rodents, suggesting that, while they do not interact directly, rodents and the fungus affect each other's densities by their use of a common prey species.     

Reactive oxygen species and melanoma: an explanation for gender differences in survival?

Epidemiological research consistently shows a female advantage in melanoma survival. So far, no definite candidate for the explanation of this phenomenon has emerged. We propose that gender differences in oxidative stress caused by radical oxygen species (ROS) underlie these survival differences. It is known that males express lower amounts of anti-oxidant enzymes, resulting in more oxidative stress than females. The primary melanoma environment is characterized by high ROS levels, from exogenous sources as well as ROS production within melanoma cells themselves. ROS are known to be able to promote metastasis through a wide variety of mechanisms. We hypothesize that the higher levels of ROS in men enhance selection of ROS-resistance in melanoma cells. Subsequently, ROS can stimulate the metastatic potential of melanoma cells. In addition, due to the lower anti-oxidant defenses in men, ROS produced by melanoma cells cause more damage to healthy tissues surrounding the tumor, further stimulating metastasis. Therefore, ROS may explain the observed differences between males and females in melanoma survival.     

Developmental stages in diapausing eggs: an investigation across monogonont rotifer species

Monogononts reproduce by parthenogenesis punctuated by events of mixis that generate ‘resting eggs’, which actually are embryos whose development is arrested. We document the nuclei number and position of the resting eggs of nine rotifer species (Brachionus plicatilis, B. calyciflorus, B. manjavacas, Plationus patulus, Epiphanes senta, E. chihuahuaensis, Rhinoglena frontalis, Lecane bulla and Sinantherina socialis) in the attempt to assess the stage at which dormant embryos are arrested. The morphology of the entire embryos was reconstructed visualising nuclear DNA using confocal microscopy, and their developmental stage identified. Two groups of species were identified: dormant embryos of one group possessed on average less than 30 nuclei, with low variation within and between species, and the stage may correspond to early gastrula; embryos in the second group contain relatively more nuclei, averaging around 40–60, with higher variation within species. The two groups of species seem not to reflect any phylogenetic relationship. Consequences of the dormant embryo stages are discussed.     

Country-based patterns of total species richness,endemicity, and threatened species richness in African rodents and insectivores

Country-based patterns of total species richness, endemicity, and threatened species richness in African rodents and insectivores are studied in this paper. We found several patterns which were similar between insectivores and rodents. Indeed, in both groups we observed: (i) a significantly uneven distribution of species richness across countries and geographic regions with highest species richness peaks being in Middle Africa and lowest peaks in Northern Africa, (ii) species richness increasing with rainfall but being independent on a country’s surface area, (iii) in each country, the insectivore total species richness and endemic species richness increases were positively correlated with rodent total species richness and endemic species richness increases. However, number of endemics peaked in South Africa and D.R. Congo in both groups, but also in Tanzania for Insectivores and in Ethiopia for rodents. In addition, the highest numbers of threatened species occurred in D.R. Congo, Rwanda and Uganda for rodents and in South Africa, Tanzania and Cameroon for insectivores. The conservation implications of these results were discussed.     

Latitudinal variation in the shape of the species body size distribution: an analysis using freshwater fishes

Many taxonomic and ecological assemblages of species exhibit a right-skewed body size-frequency distribution when characterized at a regional scale. Although this distribution has been frequently described, factors influencing geographic variation in the distribution are not well understood, nor are mechanisms responsible for distribution shape. In this study, variation in the species body size-frequency distributions of 344 regional communities of North American freshwater fishes is examined in relation to latitude, species richness, and taxonomic composition. Although the distribution of all species of North American fishes is right-skewed, a negative correlation exists between latitude and regional community size distribution skewness, with size distributions becoming left-skewed at high latitudes. This relationship is not an artifact of the confounding relationship between latitude and species richness in North American fishes. The negative correlation between latitude and regional community size distribution skewness is partially due to the geographic distribution of families of fishes and apparently enhanced by a nonrandom geographic distribution of species within families. These results are discussed in the context of previous explanations of factors responsible for the generation of species size-frequency distributions related to the fractal nature of the environment, energetics, and evolutionary patterns of body size in North American fishes.     

Sexual dimorphism in cranial shape and size in geomyoid rodents: multivariate and evolutionary perspectives

Geomyoid rodents provide a great study system for the analysis of sexual dimorphism. They are polygynic and many inhabit harsh arid environments thought to promote sexual dimorphism. In fact, there has been extensive work published on the sexual size dimorphism of individual populations and species within this rodent clade. However, little work has been undertaken to assess the evolutionary patterns and processes associated with this sexual dimorphism. We use multivariate analyses of cranial measurements in a phylogenetic framework to determine the distribution of size and shape dimorphism among geomyoids and test for Rensch’s rule. Our results suggest that sexual dimorphism is more common in geomyids than heteromyids, but it is not in fact universal. There is evidence for variation in sexual dimorphism across populations. Additionally, in many taxa, geographic variation appears to overwhelm existing sexual dimorphism. We find support for the repeated independent evolution of shape and size dimorphism across geomyoid taxa, but we do not find support for an association between size and shape dimorphism. There is no evidence for Rensch’s rule in geomyoids, whether at the superfamily or family level. Together, our findings suggest that there is no single explanation for the evolution of sexual dimorphism in geomyoids and that, instead, it is the product of numerous evolutionary events. Future studies incorporating phylogenetic relationships will be necessary to paint a more complete picture of the evolution of sexual dimorphism in geomyoids.     

Partitioning species diversity across landscapes and regions: a hierarchical analysis of alpha, beta, and gamma diversity

Species diversity may be additively partitioned within and among samples (alpha and beta diversity) from hierarchically scaled studies to assess the proportion of the total diversity (gamma) found in different habitats, landscapes, or regions. We developed a statistical approach for testing null hypotheses that observed partitions of species richness or diversity indices differed from those expected by chance, and we illustrate these tests using data from a hierarchical study of forest-canopy beetles. Two null hypotheses were implemented using individual- and sample-based randomization tests to generate null distributions for alpha and beta components of diversity at multiple sampling scales. The two tests differed in their null distributions and power to detect statistically significant diversity components. Individual-based randomization was more powerful at all hierarchical levels and was sensitive to departures between observed and null partitions due to intraspecific aggregation of individuals. Sample-based randomization had less power but still may be useful for determining whether different habitats show a higher degree of differentiation in species diversity compared with random samples from the landscape. Null hypothesis tests provide a basis for inferences on partitions of species richness or diversity indices at multiple sampling levels, thereby increasing our understanding of how alpha and beta diversity change across spatial scales.     

Comparative analysis of the DXPas34 regulatory region in rodents

Mouse X chromosome inactivation center contains the DXPas34 minisatellite locus which plays an important role in expression regulation of the Tsix and Xist genes, involved into female dosage compensation. Comparative analysis of the DXPas34 locus from mouse, rat, and four common vole species revealed similar organization of this region in the form of tandem repeat blocks. A search for functionally important elements in this locus showed that all the species examined carried the conservative motif monomers, which could be involved in regulation of X inactivation.