The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M ^{0.17±0.08 (95% CI)}, jump take-off angle (A; degrees) scales as A = 52.5M ^0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M ^1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q₁₀ of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L _f+t; mm) of the femur and tibia of the hind leg, L _f+t = 34.9M ^0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur''s cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur''s cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.     

Mediator structure and conformation change

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Amino-Terminal Charge Affects the Periplasmic Accumulation of Recombinant Heregulin/EGF Hybrids Exported Using theEscherichia coliAlkaline Phosphatase Signal Sequence

AnEscherichia coliexpression system that exploits the bacterial alkaline phosphatase (PhoA) signal sequence to translocate recombinant human epidermal growth factor (hEGF) to the periplasm was used to evaluate how changes in the composition and sequence of amino acids near the PhoA–hEGF junction influence the periplasmic accumulation of recombinant protein. A series of chimeric structural genes was generated byin vitroreplacement of hEGF sequence with analogous segments from the EGF-like domain of human heregulin (HRG), significantly altering the electrostatic character of the amino-terminal region of the mature protein. Quantitation of HRG/EGF protein inE. coliperiplasmic extracts, by RP-HPLC, showed a fourfold decrease after one of two acidic residues located in the amino-terminal region of the mature hEGF, near the PhoA junction, was replaced. An additional threefold decrease was observed when the second acidic residue was replaced with a positively charged lysine. Further extension of the amino-terminal HRG sequence, beyond the first six residues, resulted in net neutralization of a more distant EGF acidic residue with no additional effect on protein yield. The importance of having a negatively charged group in the amino-terminal region of the mature protein was confirmed when insertion of an aspartic acid near the amino-terminus of two poorly expressed hybrid protein sequences resulted in a five- to eightfold increase in their recovery from the periplasm. This study demonstrates the importance of having negatively charged residues near the fusion junction of recombinant proteins expressed inE. coliusing the PhoA signal sequence for protein export.     

Fluorescence anisotropy from diphenylhexatriene in rat liver plasma membranes

Rat livers were fractionated to obtain intracellular membrane preparations and a highly purified preparation of bile canaliculi. The fraction containing bile canaliculi was homogenized and subfractionated to give fractions representing fragments of contiguous membrane and of canalicular microvilli. The relative purity and extent of contamination of each preparation was determined. When the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was incorporated into aliquots of each fraction at the same probe: lipid ratio and the steady-state anisotropy of its fluorescence measured, it was found that the plasma membrane preparations were much more ordered than the intracellular membrane preparations. Of the plasma membrane preparations, that containing the canalicular microvilli was the most ordered, even allowing for any contribution of contaminants. Thus the microvillus membrane of the bile canaliculus appears to be the most ordered domain of the plasma membrane of the hepatocyte. The high order in this domain may be a factor in reducing the susceptibility to bile salt damage during bile secretion, since it is this region which is exposed to high concentrations of bile salts in vivo.     

Risk of feather damage explains fault bar occurrence in a migrant hawk,the Swainson's hawk Buteo swainsoni

Fault bars are common stress‐induced feather abnormalities that could produce feather damage thus reducing flight performance. For that reason, it has been hypothesized that birds may have evolved adaptive strategies that reduce the costs of fault bars (the ‘fault bar allocation hypothesis’). An untested prediction of this hypothesis is that fault bars in important feathers for flight (wing and tail) should be less abundant where they produce more feather damage. We tested such a prediction using moulted wing and tail feathers of the long‐distance migrant Swainson's hawk Buteo swainsoni in its Argentinean wintering quarters. We recorded the occurrence of fault bars of different strengths (light, medium and strong) and the damage (lost of a portion of the vane) produced by them. The occurrence of fault bars was very variable, with strong ones being rare throughout and light and medium fault bars being more frequent in the tail than in the wing. Risk of feather damage was similarly high and low across feather groups for strong and light fault bars, respectively, and higher in the wing than in the tail for medium strength. The occurrence of fault bars of different strengths on different feather groups was negatively correlated with their propensity to produce feather damage. At low damage risk (<5%), the occurrence of fault bars was highly variable depending on the feather group, but above 5% of feather damage the occurrence of fault bars was highly reduced throughout. Our results supports the ‘fault bar allocation hypothesis’ of natural selection reducing fault bar occurrence where fault bars are more risky, but further suggest that selection pressure could be relaxed in other instances, leaving the way free for other mechanisms to shape fault bar occurrence.