Hemoglobin concentration in normal diploid and intersex triploid chickens: genetic inactivation or canalization?

Of 19 adult intersex chickens examined, 17 were triploid animals with ZZW sex chromosomes. Triploid erythrocytes were about 1.5 times the size of diploid erythrocytes, and were present in amounts that were about two-thirds the number of diploid erythrocytes. Both diploid and triploid animals had similar hematocrits and hemoglobin concentrations. Triploidy is reflected in a relative increase in RNA, as well as in DNA, per erythrocyte. This, in addition to the trisomic mode of inheritance observed in several genetically distinct loci determining isoantigens, indicates that all three sets of chromosomes in the triploid animals are genetically active. Apparently, there is a homeostatic mechanism maintaining the concentration of hemoglobin for the species in spite of triploidy and its effect on erythrocyte size.     

Scaling stride frequency and gait to animal size: mice to horses

The stride frequency at which animals of different size change from one gait to another (walk, trot, gallop) changes in a regular manner with body mass. The speed at the transition from trot to gallop can be used as an equivalent speed for comparing animals of different size. This transition point occurs at lower speeds and higher stride frequencies in smaller animals. Plotting stride frequency at the trot-gallop transition point as a function of body mass in logarithmic coordinates yields a straight line.     

VARYING SENSITIVITY OF C57B CRGL MICE TO GROUPING

Mice responded differentially to increases in population size, depending on their prior experience. Compared to animals grouped prior to an increase in population size, animals housed as isolates responded to grouping with more fighting, a greater diminuation of testis weight, and a higher level of locomotor activity. They also had lower testis weight and higher locomotor activity than individually housed, nongrouped controls.     

Comment on "Population size does not influence mitochondrial genetic diversity in animals"

Bazin et al. (Reports, 28 April, 2006, p. 570) found no relationship between mitochondrial DNA (mtDNA) diversity and population size when comparing across large groups of animals. We show empirically that species with smaller populations, as represented by eutherian mammals, exhibit a positive correlation between mtDNA and allozyme variation, suggesting that mtDNA diversity may correlate with population size in these animals.     

玉林农区鼠形动物群落结构及危害分析

[目的]摸清玉林市主要农区鼠形动物群落结构及对农业的危害,为玉林农区鼠形动物综合防治提供科学依据.[方法]2011年3月～2012年4月,以果园、菜地、农田、旱地及居民区等5个生境为样品采集地,根据随机取样原则,利用铗日法对玉林农区鼠形动物群落结构、数量及动态进行调查,并采用胃检法进行食性分析.[结果]5种生境中共捕获鼠形动物423只,隶属2目2科5属9种,其中食虫目1科1属1种251只,啮齿目1科4属8种172只.平均捕获率为8.66％,其中居民区捕获率最高,占捕获总数的39.01％.以臭鼩为绝对优势种,占59.34％,褐家鼠、黄胸鼠、黄毛鼠、社鼠、板齿鼠、小家鼠等为常见种,针毛鼠、黑家鼠为少见种.一年中有两个捕获高峰,分别为7和10月.食性分析显示,臭鼩以动物性食物为主,啮齿类以植物性食物为主,褐家鼠、黄胸鼠和板齿鼠对农业危害较大.[结论]玉林农区鼠形动物种群密度较高,啮齿类对农业危害较大,应采取有效措施进行防治.     

Imaginal discs secrete insulin-like peptide 8 to mediate plasticity of growth and maturation

Developing animals frequently adjust their growth programs and/or their maturation or metamorphosis to compensate for growth disturbances (such as injury or tumor) and ensure normal adult size. Such plasticity entails tissue and organ communication to preserve their proportions and symmetry. Here, we show that imaginal discs autonomously activate DILP8, a Drosophila insulin-like peptide, to communicate abnormal growth and postpone maturation. DILP8 delays metamorphosis by inhibiting ecdysone biosynthesis, slowing growth in the imaginal discs, and generating normal-sized animals. Loss of dilp8 yields asymmetric individuals with an unusually large variation in size and a more varied time of maturation. Thus, DILP8 is a fundamental element of the hitherto ill-defined machinery governing the plasticity that ensures developmental stability and robustness.     

Scaling body support in mammals: limb posture and muscle mechanics

The scaling of bone and muscle geometry in mammals suggests that peak stresses (ratio of force to cross-sectional area) acting in these two support elements increase with increasing body size. Observations of stresses acting in the limb bones of different sized mammals during strenuous activity, however, indicate that peak bone stress is independent of size (maintaining a safety factor of between 2 and 4). It appears that similar peak bone stresses and muscle stresses in large and small mammals are achieved primarily by a size-dependent change in locomotor limb posture: small animals run with crouched postures, whereas larger species run more upright. By adopting an upright posture, large animals align their limbs more closely with the ground reaction force, substantially reducing the forces that their muscles must exert (proportional to body mass) and hence, the forces that their bones must resist, to counteract joint moments. This change in limb posture to maintain locomotor stresses within safe limits, however, likely limits the maneuverability and accelerative capability of large animals.     

The energetic cost of limbless locomotion

The net energetic cost of terrestrial locomotion by the snake Coluber constrictor, moving by lateral undulation, is equivalent to the net energetic cost of running by limbed animals (arthropods, lizards, birds, and mammals) of similar size. In contrast to lateral undulation and limbed locomotion, concertina locomotion by Coluber is more energetically expensive. The findings do not support the widely held notion that the energetic cost of terrestrial locomotion by limbless animals is less than that of limbed animals.     

热应激对动物生殖机能的影响及其防止措施

温度对动物生殖机能具有重要影响.根据相关文献,分别阐述热应激对雌性动物发情、受胎率、胚胎成活率、产仔数以及对雄性动物繁殖性能的影响,提出了控制热应激对动物生殖机能影响的具体措施.     

The role of surface chemistry in filter feeding by zooplankton

Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was, added to reduce wettability.     

Comment on "On the regulation of populations of mammals, birds, fish, and insects" III

Stochasticity in time series explains concave responses of per capita growth rate to population size. The gradients with the natural log of population size have more biological importance because they measure strength of density compensation. Its weakening with increasing body size across taxa (Sibly et al., Reports, 22 July 2005, p. 607) is consistent with slower responses in ascent than descent toward carrying capacity. Time series therefore suggest that populations of large-bodied animals underfill their environments.     

Allometry of alarm calls: black-capped chickadees encode information about predator size

Many animals produce alarm signals when they detect a potential predator, but we still know little about the information contained in these signals. Using presentations of 15 species of live predators, we show that acoustic features of the mobbing calls of black-capped chickadees (Poecile atricapilla) vary with the size of the predator. Companion playback experiments revealed that chickadees detect this information and that the intensity of mobbing behavior is related to the size and threat of the potential predator. This study demonstrates an unsuspected level of complexity and sophistication in avian alarm calls.     

Geometrical differences among homologous neurons in mammals

The dendritic arbors of sympathetic neurons in different species of mammals vary systematically: the superior cervical ganglion cells of smaller mammals have fewer and less extensive dendrites than the homologous neurons in larger animals. This difference in dendritic complexity according to body size is reflected in the convergence of ganglionic innervation; the ganglion cells of progressively larger mammals are innervated by progressively more axons. These relations have implications both for the function of homologous neural systems in animals of different sizes and for the regulation of neuronal geometry during development.     

Tandem duplication of D-loop and ribosomal RNA sequences in lizard mitochondrial DNA

Some Cnemidophorus exsanguis have mitochondrial DNA's (mtDNA's) that are 22.2 kilobases (kb) in size, whereas most have mtDNA's of 17.4 kb. Restriction site mapping, DNA transfer hybridization experiments, and electron microscopy show that the size increment stems from the tandem duplication of a 4.8-kb region that includes regulatory sequences and transfer and ribosomal RNA genes. This observation is notable in that sequences outside of the control region are involved in major length variation. Besides revealing a novel form of mtDNA evolution in animals, these duplications provide a useful system for investigating the molecular and evolutionary biology of animal mtDNA.     

Heat production and temperature regulation in eastern skunk cabbage

The spadix of Symplocarpus foetidus L. maintains an internal temperature 15 degrees to 35 degrees C above ambient air temperatures of -15 degrees to +15 degrees C. For at least 14 days it consumes oxygen at a rate comparable to that of homeothermic animals of equivalent size. Temperature regulation is accomplished by variations in respiratory rate.     

The cellular and physiological mechanism of wing-body scaling in Manduca sexta

In animals, appendages develop in proportion to overall body size; when individual size varies, appendages covary proportionally. In insects with complete metamorphosis, adult appendages develop from precursor tissues called imaginal disks that grow after somatic growth has ceased. It is unclear, however, how the growth of these appendages is matched to the already established body size. We studied the pattern of cell division in the tobacco hornworm Manduca sexta and found that both the rate of cell division and the duration of growth of the wing imaginal disks depend on the size of the body in which they develop. Moreover, we found that both of these processes are controlled by the level and duration of secretion of the steroid hormone ecdysone. Thus, proportional growth is under hormonal control and indirectly regulated by the central nervous system.     

Immunization as a factor affecting the course of septicemic anthrax

Immunization of guinea pigs with alum-precipitated antigen increased resistance approximately 1600 times. The growth rate of Bacillus anthracis, in the septicemic phase, was the same in both normal and immunized animals; however, the number of bacilli per milliliter of blood at death was decreased by 75 percent in immunized animals. Neither the enhancement of virulence by treatment with egg yolk nor the size of the challenge dose affected the growth rate or the number of bacilli per milliliter of blood at death. Mean time to death for the treatments tested varied from approximately 20 to 100 hours. Nonimmunized animals challenged with a strain of low virulence had a terminal number of bacilli per milliliter of blood and a growth rate in the blood the same as that for the highly virulent strain     

Natural selection and developmental constraints in the evolution of allometries

In animals, scaling relationships between appendages and body size exhibit high interspecific variation but low intraspecific variation. This pattern could result from natural selection for specific allometries or from developmental constraints on patterns of differential growth. We performed artificial selection on the allometry between forewing area and body size in a butterfly to test for developmental constraints, and then used the resultant increased range of phenotypic variation to quantify natural selection on the scaling relationship. Our results show that the short-term evolution of allometries is not limited by developmental constraints. Instead, scaling relationships are shaped by strong natural selection.     

Scaling population density to body size in rocky intertidal communities

Interspecific comparisons of animal population density to body size has been the subject of active research in the last decade, especially for terrestrial animals when considering particular taxa or taxonomic assemblages. Studies of rocky intertidal communities showed that animal population density scales with body size to the -0.77 power. This relation held within local communities representing a broad array of animal taxa and was not affected by a dramatic alteration in the network of between-species interactions, as revealed by two long-term human exclusion experiments.     

Age, sex, density, winter weather, and population crashes in Soay sheep

Quantifying the impact of density, extrinsic climatic fluctuations, and demography on population fluctuations is a persistent challenge in ecology. We analyzed the effect of these processes on the irregular pattern of population crashes of Soay sheep on the St. Kilda archipelago, United Kingdom. Because the age and sex structure of the population fluctuates independently of population size, and because animals of different age and sex respond in different ways to density and weather, identical weather conditions can result in different dynamics in populations of equal size. In addition, the strength of density-dependent processes is a function of the distribution of weather events. Incorporating demographic heterogeneities into population models can influence dynamics and their response to climate change.