两种近缘鸟种麻雀和山麻雀的咬合力比较

鸟类的咬合力受食性、种内竞争和捕食压力等多种生态因素的影响,可作为其生态适应特征的重要指标。但目前关于鸟类的咬合力及其影响因素却鲜有研究,为此,我们使用咬合力传感器,对同属的两个近缘鸟种,麻雀(Passer montanus)和山麻雀(P.cinnamomeus)的咬合力进行了比较研究。结果表明,山麻雀(n=12)的咬合力显著大于麻雀(n=59)(t=3.754,P0.01),但山麻雀(t=0.449,P0.05)和麻雀(Z=﹣1.198,P0.05)的雌雄个体间咬合力均无差异,同时,山麻雀的头宽(t=﹣3.713,P0.01)、头高(t=﹣5.405,P0.01)和喙宽(t=﹣6.201,P0.01)均显著大于麻雀。尽管个体的咬合力与其身体各参数指标无显著相关性,但在种间,头和喙的大小可能是影响两者咬合力的重要因素,由于两者的一些生态适应特征可通过头大小和喙型体现,推测两者生境和食性的差异可能是影响其咬合力大小的主要原因。     

犬咬合力测试方法研究进展

咬合力是动物生存能力的重要指标。测量犬咬合力,对犬牙修复、犬食物与玩具评估以及警方筛选并使用犬、评估警犬武力性质等都有积极意义。我国学者对犬咬合力测试的研究更多的是警方人员,且更多以产品研发为主,很少开展实际的测量工作。本文综述了咬合法、肌电法、杠杆模型法和有限元分析测量法等各种犬咬合力测试方法,以期为我国犬类咬合力研究提供参考。     

两种常见麻蜥的生态生物学比较及分析

丽斑麻蜥(Eremias argus)和山地麻蜥(Eremiasbrenchleyi)是我国长江以北数量较多、分布较广的常见小型蜥蜴类,在动物学教材中常作为爬行纲的代表动物。为便于教学和研究,现将这两种麻蜥的生态生物学特征比较如下。1 两种麻蜥的分布及形态全世界约有麻蜥50种,我国有9种,其中丽斑麻蜥和山地麻蜥是我国长江以北地区分布较广、数量较多的种类。关于两种麻蜥在我国的具体分布地点和形     

草蜥属两种蜥蜴卵和幼体特征的比较研究

比较研究了南草蜥和北草蜥实验条件下的卵及幼体特征。南草蜥产卵雌体的体长、最大窝卵数、平均卵重小于北草蜥 ,相对窝卵重与北草蜥相似。两种蜥蜴均通过增加卵长径和卵短径来增加卵重 ,但卵外形明显不同 ,南草蜥的卵较长。两种蜥蜴卵孵化过程中均吸水增重。相同孵化温度 ( 2 6℃ )条件下 ,南草蜥的孵化期明显比北草蜥长。南草蜥幼体的体重、体长、头长和头宽的实测值小于北草蜥 ,尾长实测值与北草蜥无显著差异。南草蜥幼体的体重、头长和头宽的矫正平均值小于北草蜥 ,尾长矫正平均值大于北草蜥 ,体长矫正平均值与北草蜥无显著差异。     

两种麻蜥卵和孵出幼体的特征

研究了山地麻蜥和丽斑麻蜥实验条件下的卵及孵出幼体的特征.山地麻蜥产卵雌体的体长大于丽斑麻蜥,窝卵重小于丽斑麻蜥,但平均卵重和相对窝卵重与丽斑麻蜥相似.两种蜥蜴均通过增加卵长径和卵短径来增加卵重,但卵的外形不同,山地麻蜥卵较长.两种蜥蜴卵孵化过程中均吸水增重.相似孵化条件(波动温度、-12 kPa)下,山地麻蜥的孵化期明显比丽斑麻蜥长.山地麻蜥幼体的尾、头部大于丽斑麻蜥,但体重和SVL相似.     

丽斑麻蜥和草原沙蜥静止代谢率的研究

丽斑麻蜥和草原沙蜥静止代谢率的研究陈强（兰州大学生物系兰州７３００００）关键词静止代谢率，体重，温度，丽斑麻蜥，草原沙蜥ＡＳＴＵＤＹＯＮＴＨＥＲＥＳＴＩＮＧＭＥＴＡＢＯＬＩＣＲＡＴＥＯＦＥｒｅｍｉａｓａｒｇｕｓＡＮＤＰｈｒｙｎｏｃｅｐｈａｌｕｓｆｒｏ...     

云南西双版纳蝙蝠咬合力及生态位分化

咬合力与动物咀嚼系统的形态特征以及食物硬度有关,是评价动物取食行为的重要指标之一。本文于2012年4月在云南西双版纳对食果、食蜜和食虫3种食性的12种蝙蝠咬合力进行研究,使用咬合力探测仪测量蝙蝠手持状态下的咬合力,分析不同食性蝙蝠咬合力的差异,并与其体型（体重、前臂长、头长）进行相关分析。结果表明,3种食性蝙蝠的咬合力存在显著差异,食果蝙蝠咬合力最大,其次为食蜜蝙蝠,食虫蝙蝠咬合力最小;但是去除体重因素的影响之后,不同食性蝙蝠的咬合力则差异不显著。蝙蝠咬合力与体重、前臂长、头长均呈显著正相关。本文研究结果表明,体重是影响蝙蝠咬合力的主要因素,食性在一定程度上也对咬合力产生影响,食蜜蝙蝠吻部延长,头长上的特化导致其咬合力的减弱。     

大熊猫咬合力和采食速率的发育及其影响因素

咬合力在食物获取和雄性竞争等多方面影响大熊猫的生存和繁殖,同时,食性和咀嚼系统的独特性使大熊猫(Ailuropoda melanoleuca)成为研究咬合力的理想物种。以往研究仅局限在通过测量大熊猫头骨进行力学模型估测,未经实体测量验证。本研究采用测力传感器定量测量了不同年龄段46只大熊猫的体重、切齿咬合力和采食速率,并重点关注幼仔期的发育过程。结果显示：幼年大熊猫的切齿咬合力在切齿由乳齿到恒齿的过渡期呈较快速度的增长,与此同时,采食竹笋的速率也呈快速上升趋势;在全部切齿更换为恒齿后,其切齿咬合力仍然呈上升趋势,但速度变缓,而采食速率进入平台期。经Logistics模型对采食速率增长曲线拟合,表明月龄可以解释速率变异的87.56%。不同年龄阶段的大熊猫咬合力中位数随年龄呈现明显的增长趋势,8～12月龄组的咬合力显著小于其他年龄组,13～18月龄的咬合力显著小于亚成年组、成年组以及老年组;亚成年组、成年组和老年组间尚未检测出显著性差异。竹笋和胡萝卜的采食速率以成年大熊猫最高,亚成年次之,老年略低于亚成年,幼年最低。本研究验证了测力传感器测量大熊猫咬合力的可行性,记录了咬合力和采食速率在幼...     

鄂尔多斯丽斑麻蜥两性异形及繁殖输出

两性异形和雌性繁殖输出是丽斑麻蜥(Eremias argus)种群生活史研究的重要内容。本文研究了丽斑麻蜥成体两性异形及雌性繁殖输出,研究用的95条怀卵雌体和38条(18♂、20♀)成体于2013年6月及8月捕自内蒙古鄂尔多斯。被测形态特征有体重、头体长、头长、头高、头宽、上臂长、前臂长、腕指长、大腿长、小腿长、踝趾长、腋跨距和尾长;怀卵雌性个体在实验室条件下饲养至产卵,称量产后母体体重、卵重,记录窝卵数。丽斑麻蜥成体存在两性异形,表现为雄性个体的头部、四肢长及尾长都显著大于雌性,腋跨距显著小于雌性。本实验中最小的产卵雌体头体长为44.0 mm,产卵期在6月4日至7月15日,窝卵数2~5枚,平均2.9枚,窝卵数(P=0.043)、窝卵重(P=0.026)与头体长显著正相关,相对窝卵重(P=0.001)与头体长负相关;窝卵数(P=0.000)、卵均重(P=0.000)与窝卵重显著正相关,窝卵数与卵均重不显著负相关(P=0.200)。     

Maximum Bite Force and Prey Size of Tyrannosaurus rex and Their Relationships to the Inference of Feeding Behavior

The feeding behavior of the theropod dinosaur Tyrannosaurus rex is investigated through analysis of two variables that are critical to successful predation, bite force and prey body mass, as they scale with the size of the predator. These size-related variables have important deterministic effects on the predator’s feeding strategy, through their effects on lethal capacity and choice of prey. Bite force data compiled for extant predators (crocodylians, carnivorans, chelonians and squamates) are used to establish a relationship between bite force and body mass among extant predators. These data are used to estimate the maximum potential bite force of T. rex, which is between about 183,000 and 235,000 N for a bilateral bite. The relationship between maximum prey body mass and predator body mass among the same living vertebrates is used to infer the likely maximum size of prey taken by T. rex in the Late Cretaceous. This makes it possible to arrive at a more rigorous assessment of the role of T. rex as an active predator and/or scavenger than has hitherto been possible. The results of this analysis show that adult Triceratops horridus fall well within the size range of potential prey that are predicted to be available to a solitary, predaceous T. rex. This analysis establishes boundary conditions for possible predator/prey relationships among other dinosaurs, as well as between these two taxa.     

Physiological Comparison of Concentric and Eccentric Arm Cycling in Males and Females

Lower body eccentric exercise is well known to elicit high levels of muscular force with relatively low cardiovascular and metabolic strain. As a result, eccentric exercise has been successfully utilised as an adaptive stressor to improve lower body muscle function in populations ranging from the frail and debilitated, to highly-trained individuals. Here we investigate the metabolic, cardiorespiratory, and energy costs of upper body eccentric exercise in a healthy population. Seven men and seven women performed 4-min efforts of eccentric (ECC) or concentric (CON) arm cycling on a novel arm ergometer at workloads corresponding to 40, 60, and 80% of their peak workload as assessed in an incremental concentric trial. The heart rate, ventilation, cardiac output, respiratory exchange ratio, and blood lactate concentrations were all clearly greater in CON condition at all of the relative workloads (all p<0.003). Effect size calculations demonstrated that the magnitude of the differences in VO₂ and work economy between the ECC and CON exercise ranged from very large to extremely large; however, in no case did mechanical efficiency (η_MECH) differ between the conditions (all p>0.05). In contrast, delta efficiency (η_Δ), as previously defined by Coyle and colleagues in 1992, demonstrated a sex difference (men>women; p<0.05). Sex differences were also apparent in arteriovenous oxygen difference and heart rate during CON. Here, we reinforce the high-force, low cost attributes of eccentric exercise which can be generalised to the muscles of the upper body. Upper body eccentric exercise is likely to form a useful adjunct in debilitative, rehabilitative, and adaptive clinical exercise programs; however, reports of a shift towards an oxidative phenotype should be taken into consideration by power athletes. We suggest delta efficiency as a sensitive measure of efficiency that allowed the identification of sex differences.     

Ecophysiological consequences of differences in plant size: in situ carbon gain and water relations of the epiphytic bromeliad, Vriesea sanguinolenta

This field study with the C₃ bromeliad Vriesea sanguinolenta (Cogn. & Marchal 1874) was initiated to explore the importance of size‐related ecophysiological changes in vascular epiphytes in a natural tropical setting. In this species, a step change from atmospheric to tank‐forming life form occurs during early ontogeny, followed by a continuous size increase of individuals with water‐impounding tanks. Although our study focused on the water‐impounding phase, this growth pattern also allowed us to compare ecophysiological consequences of a step change in life form with those associated with size increments among plants of identical life form. The shift in life form was accompanied by relatively minor changes, for example in leaf morphology (decrease in leaf thickness and trichome density) and leaf physiology (decrease in photosynthetic capacity), while there were more substantial changes during the tank‐forming phase. A major trend was a decreasing dependence of larger plants on internally stored water due to a more efficient tank. We suggest that the resulting, more reliable water supply in larger plants may be the proximate cause for the observed size‐related differences in leaf anatomy (relative reduction of water storage tissue, and relative and absolute increase in chlorenchyma thickness), leaf morphology (increase in stomatal density, decrease in trichome density), and leaf physiology (increase in net rates of CO₂ uptake, more conservative stomatal behaviour, higher residual transpiration). The results are compared with previous studies on heteroblasty in bromeliads, but are also discussed in the context of a gradual shift from a drought‐tolerance to a drought‐avoidance strategy.     

Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics

The relationship between human craniofacial morphology and the biomechanical efficiency of bite force generation in widely varying muscular and skeletal types is unknown. To address this problem, we selected 22 subjects with different facial morphologies and used magnetic resonance imaging, cephalometric radiography, and data from dental casts to reconstruct their craniofacial tissues in three dimensions. Conventional cephalometric analyses were carried out, and the cross-sectional sizes of the masseter and medial pterygoid muscles were measured from reconstituted sections. The potential abilities of the muscles to generate bite forces at the molar teeth and mandibular condyles were calculated according to static equilibrium theory using muscle, first molar, and condylar moment arms. On average, the masseter muscle was about 66% larger in cross section than the medial pterygoid and was inclined more anteriorly relative to the functional occlusal plane. There was a significant positive correlation (P less than 0.01) between the cross-sectional areas of the masseter and medial pterygoid muscles (r = 0.75) and between the bizygomatic arch width and masseter cross-sectional area (r = 0.56) and medial pterygoid cross-sectional area (r = 0.69). The masseter muscle was always a more efficient producer of vertically oriented bite force than the medial pterygoid. Putative bite force from the medial pterygoid muscle alone correlated positively with mandibular length and inversely with upper face height. When muscle and tooth moment arms were considered together, a system efficient at producing force on the first molar was statistically associated with a face having a large intergonial width, small intercondylar width, narrow dental arch, forward maxilla, and forward mandible. There was no significant correlation between muscle cross-sectional areas and their respective putative bite forces. This suggests that there is no simple relationship between the tension-generating capacity of the muscles and their mechanical efficiency as described by their spatial arrangement. The study shows that in a modern human population so many combinations of biomechanically relevant variables are possible that subjects cannot easily be placed into ideal or nonideal categories for producing molar force. Our findings also confirm the impression that similar bite-force efficiencies can be found in subjects with disparate facial features.     

Incisal bite force direction in humans and the functional significance of mammalian mandibular translation

Incisal bite force direction was recorded and analyzed in ten human subjects using a specially designed force transducer. In all ten subjects the maxillary incisal bite force was vertically and anteriorly directed both during static biting and during biting associated with simultaneous mandibular translation and rotation. Since the resultant muscle force could not have been equal and opposite to the mandibular bite force, the mandibular condyles must have been loaded. These data demonstrate that the mandible acts as a lever during incisal biting and that there is no consistent relationship between incisal bite force direction and object size. In some individuals the bite force direction was more vertical during biting on a large transducer (30 mm high), while in other subjects it was more vertical during biting on a small transducer (10 mm high).     

Determinants of Affiliative Interactions between Adult Males and Lactating Females in Pigtail Macaques (Macaca nemestrina nemestrina)

In some species of Cercopithecine primates, unrelated adult males and females maintain affiliative relationships ('friendships') that are apparently unrelated to mating or parental care. This study investigated the occurrence of friendships in a captive group of pigtail macaques, and some of their possible determinants. Study subjects were six adult males and 15 adult females with their newborn infants. Females were focally observed for 2 h every week during the first 12 wk of lactation. With the exception of the fourth-ranking male, adult males showed little interest in initiating affiliative interactions with lactating females and their infants. Most episodes of contact and grooming were initiated by high-ranking females and directed to the alpha male. Because female grooming was not generally reciprocated by the alpha male, it is likely that females benefited from associating with him in terms of agonistic support or protection. Genetic data on paternity determination indicated that the fourth-ranking male, who displayed high levels of affiliation towards mother-infant dyads, sired most of the infants born in the group in the year prior to this study. Thus, whereas females may be interested in associating with males to obtain their support, some males may affiliate with females as a consequence of their previous mating relationships with them or to increase the chances of future mating success. Taken together, however, the findings of this study provide little evidence that adult males and lactating females maintain strong reciprocal bonds that may qualify as friendships.     

An Efficient,Box Shape Independent Non-Bonded Force and Virial Algorithm for Molecular Dynamics

Abstract

A notation is introduced and used to transform a conventional specification of the non-bonded force and virial algorithm in the case of periodic boundary conditions into an alternative specification. The implementation of the transformed specification is simpler and typically a factor of 1.5 faster than a conventional implementation. Moreover, it is generic with respect to the shape of the simulated system, i.e. the same routines can be used to handle triclinic boxes, truncated octahedron boxes etc. An implementation of this method is presented, and the speed achieved on various machines is given. Essence of the new method is that the number of calculations of image particle positions is strongly reduced during non-bonded force calculations.