Trilobite cuticle thickness in relation to palaeoenvironment

100 thickness measurements from thin sections of cephala or pygidia of early Ordovician trilobites occurring across an onshore to offshore environmental gradient show that progressively greater maximum cuticle thickness was characteristic of increasingly inshore sites. There is a 40-fold difference between the thinnest and thickest cuticles, and exclusively thin cuticles are confined to the offshore Olenid Biofacies. Variability in cuticle thickness increases offshore to onshore. Environmental control is shown to be more influential on cuticle thickness than is the overall length of the trilobite: some comparatively large trilobites having thin cuticles and small trilobites thick cuticles. The environmental factors which might be responsible for the pattern are briefly discussed. The thin cuticles dominating the offshore Olenid Biofacies were probably appropriate for dysaerobic conditions. Thick cuticles in the most inshore biofacies may have offered protection against predators and turbulence, but the additional presence there of trilobites with thinner cuticles is considered to reflect the greater heterogeneity of the epeiric habitat.     

Changes in proteoglycan synthesis of chondrocytes in articular cartilage are associated with the time-dependent changes in their mechanical environment

Explant loading experiments were conducted to investigate the effect of load duration on proteoglycan synthesis. A compressive load of 0.1 MPa applied for 10 min was found to stimulate proteoglycan synthesis, while the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanical stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells within soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extracellular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue height, h (i.e. h/a 1). A closed-form analytical solution for this inclusion problem is then presented for the confined compression configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneous, and can be significantly influenced by differences in properties between the cell and the extracellular matrix.     

Establishment of the biological control agent Hypocosmia pyrochroma for Dolichandra unguis-cati (Bignoniaceae) is limited by microclimate

Cat's claw creeper, Dolichandra unguis-cati (Bignoniaceae), a perennial woody vine native to tropical America, is a target for biological control in Australia and South Africa. The cat's claw creeper leaf-tying moth Hypocosmia pyrochroma (Lepidoptera: Pyralidae) from tropical South America was released as a biological control agent for cat's claw creeper in Australia from 2007 to 2010. A total of 2,277 adults, 837 pupae and 77,250 larvae were released at 40 sites in Queensland and New South Wales. Releases were made mostly in open fields (85%), and at limited sites (15%) in insect-proof cages erected over naturally occurring cat's claw creeper infestations in the field. Sampling was conducted annually in spring and autumn to monitor the establishment and dispersal of H. pyrochroma. Establishment of H. pyrochroma was first noticed in 2012 at three release sites and since then the number of established sites has increased to 80 in 2020. Establishment was evident on both ‘short-pod’ and ‘long-pod’ forms of cat's claw creeper and was more widespread in sites where releases were made within insect-proof field cages (50%) than in sites with open field releases (9%). The moth was active from late spring to late autumn with peak larval activity in late summer. To date, all field establishments have been in areas predicted by a CLIMEX model as climatically suitable but restricted mostly to riparian environment (93% of establishment), where the moth has continued to spread from 1.5 to 23 km from release sites. In contrast, there is the only limited establishment and spread in non-riparian corridors, highlighting the role of microclimate (riparian) as a limiting factor for establishment and spread. Future efforts will focus on redistribution of the agent to river/creek systems where the moth is currently not present.     

The tightly bound calcium of MauG is required for tryptophan tryptophylquinone cofactor biosynthesis

The diheme enzyme MauG catalyzes a six-electron oxidation required for posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. The crystal structure of the MauG-preMADH complex revealed the presence of a Ca(2+) in proximity to the two hemes [Jensen, L. M. R., Sanishvili, R., Davidson, V. L., and Wilmot, C. M. (2010) Science 327, 1392-1394]. This Ca(2+) did not readily dissociate; however, after extensive treatment with EGTA or EDTA MauG was no longer able to catalyze TTQ biosynthesis and exhibited altered absorption and resonance Raman spectra. The changes in spectral features are consistent with Ca(2+)-dependent changes in heme spin state and conformation. Addition of H(2)O(2) to the Ca(2+)-depleted MauG did not yield spectral changes characteristic of formation of the bis-Fe(IV) state which is stabilized in native MauG. After addition of Ca(2+) to the Ca(2+)-depleted MauG, full TTQ biosynthesis activity and reactivity toward H(2)O(2) were restored, and the spectral properties returned to those of native MauG. Kinetic and equilibrium studies of Ca(2+) binding to Ca(2+)-depleted MauG indicated a two-step mechanism. Ca(2+) initially reversibly binds to Ca(2+)-depleted MauG (K(d) = 22.4 μM) and is followed by a relatively slow (k = 1.4 × 10(-3) s(-1)) but highly favorable (K(eq) = 4.2) conformational change, yielding an equilibrium dissociation constant K(d,eq) value of 5.3 μM. The circular dichroism spectra of native and Ca(2+)-depleted MauG were essentially the same, consistent with Ca(2+)-induced conformational changes involving domain or loop movements rather than general unfolding or alteration of secondary structure. These results are discussed in the context of the structures of MauG and heme-containing peroxidases.