Functional differentiation of trailing and leading forelimbs during locomotion on the ground and on a horizontal branch in the European red squirrel (Sciurus vulgaris, Rodentia)

Mammalian locomotion is characterized by the frequent use of in-phase gaits in which the footfalls of the left and right fore- or hindlimbs are unevenly spaced in time. Although previous studies have identified a functional differentiation between the first limb (trailing limb) and the second limb (leading limb) to touch the ground during terrestrial locomotion, the influence of a horizontal branch on limb function has never been explored. To determine the functional differences between trailing and leading forelimbs during locomotion on the ground and on a horizontal branch, X-ray motion analysis and force measurements were carried out in two European red squirrels (Sciurus vulgaris, Rodentia). The differences observed between trailing and leading forelimbs were minimal during terrestrial locomotion, where both limbs fulfill two functions and go through a shock-absorbing phase followed by a generating phase. During locomotion on a horizontal branch, European red squirrels reduce speed and all substrate reaction forces transmitted may be due to the reduction of vertical oscillation of the center of mass. Further adjustments during locomotion on a horizontal branch differ significantly between trailing and leading forelimbs and include limb flexion, lead intervals, limb protraction and vertical displacement of the scapular pivot. Consequently, trailing and leading forelimbs perform different functions. Trailing forelimbs function primarily as shock-absorbing elements, whereas leading forelimbs are characterized by a high level of stiffness. This functional differentiation indicates that European red squirrels ‘test’ the substrate for stability with the trailing forelimb, while the leading forelimb responds to or counteracts swinging or snapping branches.     

Timing of epiphyseal development in the flipper skeleton of the harbour porpoise (Phocoena phocoena) as an indicator of paedomorphosis

Epiphyseal development was investigated on X‐rays of flippers from 158 harbour porpoises from Danish waters. Development followed a proximodistal pattern similar to what is known in other cetacean species. Ossification of epiphyses was rare in the phalanges of the first and fifth digits and in the more distal phalanges of the second, third and fourth digits. Along with the morphology of the first metacarpal and the more distal phalanges this suggested paedomorphosis relative to delphinids. Male and female porpoises showed similar progression of epiphyseal development until approximately the sixth year. From then on, female porpoises showed more progressed development than males. This suggests a higher level of paedomorphosis in the male porpoise. The mechanism behind phocoenid paedomorphosis seems to be progenesis, probably as an adaptation towards a high reproductive rate relative to the delphinids.     

Phenotypic selection on morphology at independence in the Chinstrap penguin Pygoscelis antarctica

Every year, shortly after the emancipation of chicks at our study colony (Deception Island, South Shetlands), hundreds of carcasses of presumably starved Chinstrap penguin Pygoscelis antarctica chicks are washed on the shore. In 1997 we measured the flippers of fresh carcasses and compared their lengths with those of live chicks about to become independent. There was a highly significant difference of 6.5 mm between both distributions, which suggests strong directional phenotypic selection on skeletal size operating through its association with body reserves at independence. Given that heritabilities of flipper length and body weight measured on 36 families are 0.73(± 0.32) and 0.075(± 0.081), and that both characters show a genetic correlation of 0.44(± 0.14), we can expect an evolutionary response to this selection episode. Assuming that the target of selection is weight at emancipation (heavier chicks carry proportionally larger reserves), and that flipper length changes as a consequence of its genetic correlation with weight, we can predict a response of 1.32–2.87 mm or 0.23–0.51 standard deviation units for flipper length. This substantial evolutionary response may be countered by other selective pressures affecting other life stages of these birds. Selection on reserve storage capacity at independence may affect morphological traits also in other species.     

McKusick-Kaufman or Bardet-Biedl syndrome? A new borderline case in an Italian nonconsanguineous healthy family

McKusick-Kaufman syndrome (MKS, OMIM #236700) is a rare syndrome inherited in an autosomal recessive pattern with a phenotypic triad comprising hydrometrocolpos (HMC), postaxial polydactyly (PAP), and congenital cardiac disease (CHD). The syndrome is caused by mutations in the MKKS gene mapped onto chromosome 20p12 between D20S162 and D20S894 markers. Mutations in the same gene causes Bardet-Biedl-6 syndrome (BBS-6, OMIM #209900) inherited in an autosomal recessive pattern. BBS-6 comprises retinitis pigmentosa, polydactyly, obesity, mental retardation, renal and genital anomalies. HMC, CHD, and PAP defects can also occur in BBS-6, and there is a significant clinical overlap between MKS and BBS-6 in childhood. We describe a new borderline case of MKS and BBS syndrome and suggest insights for understanding correlation between MKKS gene mutations and clinical phenotype. Here, we report the results of molecular analysis of MKKS in a female proband born in an Italian nonconsanguineous healthy family that presents HMC and PAP. The mutational screening revealed the presence of two different heterozygous missense variants (p.242A>S in exon 3, p.339 I>V in exon 4) in the MKKS gene, and a nucleotide variation in 5'UTR region in exon 2 (-417 A>C).     

张和兽(Zhangheotherium)的齿列和前肢形态

张和兽（Zhangheotherium）是目前唯一保存完整骨架的对齿兽类。其西列特征表明它属于兽科（Spalacotheriidae）,该科为原始兽类中主要繁衍于北方大陆中生代后期一个咀嚼方式以上下日齿对咬为主的单系类群。张和兽骨骼形态显示其前肢姿势处于外展趴卧（sprawling）与内收直立（parasagittal）之间,兼有树上和地面活动的能力,是原始兽类中趋于以地面活动为主的成员。附录列举了哺乳类的主要齿列和骨骼性状序列及分布矩阵。     

A biomechanical perspective on the use of forelimb length as a measure of sexual selection in frogs

Differences in forelimb length between male and female frogs and between amplexing and non-amplexing males have been interpreted to be the results of sexual selection on forelimb length. The causal feature of the forelimb that has been posited to cause such selection is the observation that non-amplexing males attempt to disrupt breeding by prying amplexing males from females. A biomechanical model of forelimb function suggests that total length per se may not be the most appropriate measure to use. There are more functionally significant aspects of forelimb morphology, such as lever arm lengths, that should influence amplexing ability and may make measures of overall forelimb length misleading. This example highlights the relevance of functional analysis to current questions in evolutionary biology that rely on postulated roles for morphological structures under selection.     

Aberrant FGF signaling, independent of ectopic hedgehog signaling, initiates preaxial polydactyly in Dorking chickens

The formation of supernumerary digits, or polydactyly, is a common congenital malformation. Although mutations in a number of genes have been linked to polydactyly, the molecular etiology for a third of human disorders with polydactyly remains unknown. To increase our understanding of the potential causes for polydactyly, we characterized a spontaneous chicken mutant, known as Dorking. The hindlimbs of Dorkings form a preaxial supernumerary digit. During the early stages of limb development, ectopic expression of several genes, including Sonic Hedgehog (Shh) and Fibroblast Growth Factor 4 (Fgf4), was found in Dorking hindlimbs. In addition to ectopic gene expression, a decrease in cell death in the anterior of the developing Dorking hindlimb was observed. Further molecular investigation revealed that ectopic Fgf4 expression was initiated and maintained independent of ectopic Shh. Additionally, inhibition of Fgf signaling but not hedgehog signaling was capable of restoring the normal anterior domain of cell death in Dorking hindlimbs. Our data indicates that in Dorking chickens, preaxial polydactyly is initiated independent of Shh.     

脊椎动物多趾性状的研究进展

多趾是脊椎动物常见的肢体异常,在不同物种间具有相似的表型。研究表明,有相同的基因和发育机理控制不同物种间的多趾表型;最近在人和鼠上的研究进一步表明PPD应是由于干扰了位于Lmbr1内含子内的Shh长程顺式调控元件引起的。对脊椎动物多趾性状的发生机理和相关基因的研究进展进行了综述。Abstract: Polydactyly is a common abnormal limb phenotype in vertebrate and there is similar limb phenotype among different species. Research shows that polydactyly has a similar development mechanism, and this kind of polydactyly character seems to be controlled by homologous genes among species. The latest research results on human and mouse further shows that PPD should be caused by the disruption of a long range cis-acting regulator for Shh within Lmbr1 intron. Here the development mechanism and related genes controlling polydactyly character of vertebrate are reviewed.     

大鼠前肢运动能力的定量测定

使用一项定量测定大鼠前肢运动能力的新方法,训练大鼠抓握与张力传感器相接的圆柱形按钮并向上拉,以牛奶为奖励,利用强化阈值递增的方法测定前肢最大拉力。拉力波形可用微机记录和存储。本方法较为简便和经济,还具有能定量反映大鼠前肢抓握能力的优点。