The tenth skeletal specimen of Archaeopteryx

We describe the tenth skeletal specimen of the Upper Jurassic Archaeopterygidae. The almost complete and well-preserved skeleton is assigned to Archaeopteryx siemensii Dames, 1897 and provides significant new information on the osteology of the Archaeopterygidae. As is evident from the new specimen, the palatine of Archaeopteryx was tetraradiate as in non-avian theropods, and not triradiate as in other avians. Also with respect to the position of the ectopterygoid, the data obtained from the new specimen lead to a revision of a previous reconstruction of the palate of Archaeopteryx . The morphology of the coracoid and that of the proximal tarsals is, for the first time, clearly visible in the new specimen. The new specimen demonstrates the presence of a hyperextendible second toe in Archaeopteryx . This feature is otherwise known only from the basal avian Rahonavis and deinonychosaurs (Dromaeosauridae and Troodontidae), and its presence in Archaeopteryx provides additional evidence for a close relationship between deinonychosaurs and avians. The new specimen also shows that the first toe of Archaeopteryx was not fully reversed but spread medially, supporting previous assumptions that Archaeopteryx was only facultatively arboreal. Finally, we comment on the taxonomic composition of the Archaeopterygidae and conclude that Archaeopteryx bavarica Wellnhofer, 1993 is likely to be a junior synonym of A. siemensii , and Wellnhoferia grandis Elżanowski, 2001 a junior synonym of A. lithographica von Meyer, 1861.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 149 , 97–116.     

Transmission of Spiroplasma citri by the aster leafhopper Macrosteles fascifrons (Homoptera: Cicadellidae)

The aster leafhopper (Macrosteles fascifrons), injected with an isolate of Spiroplasma citri obtained from brittle root-diseased horseradish (Armoracia rusticana), transmitted the spiroplasma to horseradish and China aster (Callistephus chinensis.) After feeding on plants infected with S. citri, M. fascifrons transmitted the spiroplasma from aster to aster and horseradish, from yellow rocket (Barbarea vulgaris) to aster, and from turnip (Brassica rapa) to turnip. Symptoms in infected horseradish were chlorosis and stunting of newly formed leaves, discoloration of root phloem, and reduced plant growth typical of brittle root disease. Chlorosis, stunting, and asymmetry of young leaves occurred in affected aster and turnip. Flowers of infected aster were small and pale in colour and occasionally showed other symptoms including asymmetry, petal distortion, or light green petals. Spiroplasmas were isolated from all plants showing symptoms. Transmission rates by M. fascifrons which acquired S. citri by feeding on infected plants were very low, but injected leafhoppers transmitted more frequently. This is the first report of the transmission of S. citri from diseased to healthy plants by M. fascifrons.     

Zebra Mussel Infestation of Unionid Bivalves (Unionidae) in North America

SYNOPSIS. In 1989, zebra mussels received national attentionin North America when they reached densities exceeding 750,000/m2in a water withdrawal facility along the shore of western LakeErie of the Laurentian Great Lakes. Although water withdrawalproblems caused by zebra mussels have been of immediate concern,ecological impacts attributed to mussels are likely to be themore important long-term issue for surface waters in North America.To date, the epizoic colonization (i.e., infestation) of unionidbivalve mollusks by zebra mussels has caused the most directand severe ecological impact. Infestation of and resulting impactscaused by zebra mussels on unionids in the Great Lakes beganin 1988. By 1990, mortality of unionids was occurring at somelocations; by 1991, extant populations of unionids in westernLake Erie were nearly extirpated; by 1992, unionid populationsin the southern half of Lake St. Clair were extirpated; by 1993,unionids in widely separated geographic areas of the Great Lakesand the Mississippi River showed high mortality due to musselinfestation. All infested unionid species in the Great Lakes(23) have become infested and exhibited mortality within twoto four years after heavy infestation began. Data indicate thatmean zebra mussel densities >5,000–6,000/m² and infestationintensities >100-200/unionid in the presence of heavy zebramussel recruitment results in near total mortality of unionids.At present, all unionid species in rivers, streams, and akesthat sympatrically occur with zebra mussels have been infestedand, in many locations, negatively impacted by zebra mussels.We do not know the potential consequences of infestation onthe 297 unionid species found in North America, but believezebra mussels pose an immediate threat to the abundance anddiversity of unionids.     

Evidence against Hydrogen–Calcium Competition Model for Activation of Electrically Excitable Membranes

TO explain the voltage-dependent sodium permeability of excitable membranes, Stephens¹ proposed a model in which sodium-selective channels are normally blocked by calcium ions bound to negatively charged sites located near the outer end of the channels. The calcium ions can be displaced competitively by hydrogen ions, opening the channels to sodium. According to this model, depolarization of an excitable membrane causes an outward flow of hydrogen ions across the membrane. The consequent transient increase in hydrogen ion concentration at the outer surface of the membrane displaces calcium and opens the sodium channels. This model is particularly interesting because it is sufficiently specific to allow direct tests. Stephens shows that it is in general agreement with a variety of experimental data. To test the model further, we have determined the effect of variation in the internal and external concentration of hydrogen ions on sodium currents.     

The acclimation of photosynthesis and respiration to temperature in the C3–C4 intermediate Salsola divaricata: induction of high respiratory CO2 release under low temperature

Photosynthesis in C₃–C₄ intermediates reduces carbon loss by photorespiration through refixing photorespired CO₂ within bundle sheath cells. This is beneficial under warm temperatures where rates of photorespiration are high; however, it is unknown how photosynthesis in C₃–C₄ plants acclimates to growth under cold conditions. Therefore, the cold tolerance of the C₃–C₄ Salsola divaricata was tested to determine whether it reverts to C₃ photosynthesis when grown under low temperatures. Plants were grown under cold (15/10 °C), moderate (25/18 °C) or hot (35/25 °C) day/night temperatures and analysed to determine how photosynthesis, respiration and C₃–C₄ features acclimate to these growth conditions. The CO₂ compensation point and net rates of CO₂ assimilation in cold‐grown plants changed dramatically when measured in response to temperature. However, this was not due to the loss of C₃–C₄ intermediacy, but rather to a large increase in mitochondrial respiration supported primarily by the non‐phosphorylating alternative oxidative pathway (AOP) and, to a lesser degree, the cytochrome oxidative pathway (COP). The increase in respiration and AOP capacity in cold‐grown plants likely protects against reactive oxygen species (ROS) in mitochondria and photodamage in chloroplasts by consuming excess reductant via the alternative mitochondrial respiratory electron transport chain.     

Wing shape,wing size,and sexual dimorphism in eye‐span in stalk‐eyed flies (Diopsidae)

The eyes of stalk‐eyed flies (Diopsidae) are positioned at the end of rigid peduncles (‘stalks’) protruding laterally from the head. Eye‐stalk length varies within the family and, in some species, varies between males and females. Larger eye‐stalks in males result from sexual selection for longer stalks, a trait that increases male reproductive success. In the present study, we examined whether an increase in eye‐stalk length results in an adjustment of wing size and shape to deal with the burden of bearing an exaggerated ‘ornament’. We compared wing morphology among ten species of stalk‐eyed flies that differ in eye‐span and the degree of sexual dimorphism. Mass‐specific wing length differed between males and females in seven out of the ten species. Nondimensional wing shape parameters differed between the species (P < 0.001), but mostly did not differ between males and females of the same species. Dimorphism in eye‐span closely correlated with dimorphism in wing length (r = 0.89, P < 0.001) and the correlation remained significant (r = 0.81, P = 0.006) after correcting for phylogenetic relationships. Once corrected for phylogenetic relatedness, the mass‐specific wing length of males (but not females) was weakly correlated with mass‐specific eye‐span (r = 0.66, P = 0.042). We propose that the observed proportional increase in wing length associated with increased eye‐span can facilitate aerial manoeuverability, which would otherwise be handicapped by the elevated moment of inertia imposed by the wider head. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 860–871.     

Low Molecular Weight Active Form of Inducible Liver Tyrosine Aminotransferase

RECENT experiments^1–4 suggest that there are several forms of inducible liver tyrosine aminotransferase and that they may be stimulated by different hormones and expressed differently by genetic mutation. We now report the occurrence of a low molecular weight form of enzymatically active soluble tyrosine aminotransferase, which is inducible as is the larger molecular weight enzyme. Assuming that the latter is a tetramer⁵, the former has a tentative molecular weight equivalent to a subunit of the larger enzyme.     

Post-Activation Potentiation--A Clue for Simplifying Models of Muscle Dynamics

SYNOPSIS. Post-activation potentiation is a phenomena that occursonly in fasttwitch muscle fibers. Its main effect is to enhancemuscle force at sub-maximal activation levels for a short durationof time following previous muscle activation. We characterizedthis phenomenon in feline caudofemoralis (CF) muscle (composedof 100% fast-twitch muscle fibers) to understand its importanceduring physiological patterns of activation. During such patterns(e.g., 43 pps, 8 pulse trains delivered at 1 sec intervals)CF potentiated rapidly and apparently maximally. When CF wasallowed to relax, potentiation decayed slowly with a time constant20–40 x slower than the rise-time. The level of potentiationreached during the potentiating paradigm was stable in responseto a wide range of stimuli, including various stimulation rates(15–120 pps) and various inter-train intervals (up to10 sec). The shape of the twitch force-length curve for potentiatedCF was similar to that of the tetanic force-length curve ineither the potentiated or unpotentiated state. In contrast,the shape of the twitch force-length curve for unpotentiatedCF was shifted markedly to the right accompanied by a narrowingof the curve's peak. We conclude from our observations thatfast-twitch muscle fibers operate and should be modeled in astate of full potentiation, and that modeling the potentiatedstate may actuaUy be simpler than modeling the unpotentiatedstate.