Contrasting effects of summer and winter warming on body mass explain population dynamics in a food‐limited Arctic herbivore

The cumulative effects of climate warming on herbivore vital rates and population dynamics are hard to predict, given that the expected effects differ between seasons. In the Arctic, warmer summers enhance plant growth which should lead to heavier and more fertile individuals in the autumn. Conversely, warm spells in winter with rainfall (rain‐on‐snow) can cause ‘icing’, restricting access to forage, resulting in starvation, lower survival and fecundity. As body condition is a ‘barometer’ of energy demands relative to energy intake, we explored the causes and consequences of variation in body mass of wild female Svalbard reindeer (Rangifer tarandus platyrhynchus) from 1994 to 2015, a period of marked climate warming. Late winter (April) body mass explained 88% of the between‐year variation in population growth rate, because it strongly influenced reproductive loss, and hence subsequent fecundity (92%), as well as survival (94%) and recruitment (93%). Autumn (October) body mass affected ovulation rates but did not affect fecundity. April body mass showed no long‐term trend (coefficient of variation, CV = 8.8%) and was higher following warm autumn (October) weather, reflecting delays in winter onset, but most strongly, and negatively, related to ‘rain‐on‐snow’ events. October body mass (CV = 2.5%) increased over the study due to higher plant productivity in the increasingly warm summers. Density‐dependent mass change suggested competition for resources in both winter and summer but was less pronounced in recent years, despite an increasing population size. While continued climate warming is expected to increase the carrying capacity of the high Arctic tundra, it is also likely to cause more frequent icing events. Our analyses suggest that these contrasting effects may cause larger seasonal fluctuations in body mass and vital rates. Overall our findings provide an important ‘missing’ mechanistic link in the current understanding of the population biology of a keystone species in a rapidly warming Arctic.     

Crystal structures of recombinant human purple Acid phosphatase with and without an inhibitory conformation of the repression loop

The crystal structure of human purple acid phosphatase recombinantly expressed in Escherichia coli (rHPAP(Ec)) and Pichia pastoris (rHPAP(Pp)) has been determined in two different crystal forms, both at 2.2A resolution. In both cases, the enzyme crystallized in its oxidized (inactive) state, in which both Fe atoms in the dinuclear active site are Fe(III). The main difference between the two structures is the conformation of the enzyme "repression loop". Proteolytic cleavage of this loop in vivo or in vitro results in significant activation of the mammalian PAPs. In the crystals obtained from rHPAP(Ec), the carboxylate side-chain of Asp145 of this loop acts as a bidentate ligand that bridges the two metal atoms, in a manner analogous to a possible binding mode for a phosphate ester substrate in the enzyme-substrate complex. The carboxylate side-chain of Asp145 and the neighboring Phe146 side-chain thus block the active site, thereby inactivating the enzyme. In the crystal structure of rHPAP(Pp), the enzyme "repression loop" has an open conformation similar to that observed in other mammalian PAP structures. The present structures demonstrate that the repression loop exhibits significant conformational flexibility, and the observed alternate binding mode suggests a possible inhibitory role for this loop.     

Limitations of commonly used spectrophotometric assay methods for phosphoenolypyruvate carboxykinase activity in crude extracts of muscle.

An extracellular thiol proteinase was produced by the growth of a thermophilic fungus, Humicola lanuginosa, on a medium containing 2% casein, and was purified to virtual homogeneity by affinity chromatography on organomercurial columns. The essential thiol group for activity was confirmed by the inhibition of the enzyme by p-chloromercuribenzoate and mercuric ions. The enzyme, purified 27-fold from the extracellular fluid, exhibited an Mr of 23700 on gel filtration and sedimentation equilibrium. The H. lanuginosa proteinase preferentially cleaves at the C-terminal end of hydrophobic amino acid residues. This proteinase differed from the plant enzyme papain in its interaction with three affinity matrices and its substrate specificity towards synthetic substrates. This enzyme represents a unique example of a thiol proteinase obtained from a fungal source.     

The Pre-S1 and Antigenic Loop Infectivity Determinants of the Hepatitis B Virus Envelope Proteins Are Functionally Independent

The hepatitis B virus (HBV) envelope proteins bear two determinants of viral entry: a receptor-binding site (RBS) in the pre-S1 domain of the large envelope protein and a conformation-dependent determinant, of unknown function, in the antigenic loop (AGL) of the small, middle, and large envelope proteins. Using an in vitro infection assay consisting of susceptible HepaRG cells and the hepatitis delta virus (HDV) as a surrogate of HBV, we first investigated whether subelements of the pre-S1 determinant (amino acids 2 to 75), i.e., the N-terminal myristoyl anchor, subdomain 2-48 (RBS), and subdomain 49-75, were functionally separable. In transcomplementation experiments, coexpression of two distinct infectivity-deficient pre-S1 mutants at the surface of HDV virions failed to restore infectivity, indicating that the myristoyl anchor, the 2-48 RBS, and the 49-75 sequence, likely cooperate in cis at viral entry. Furthermore, we showed that as much as 52% of total pre-S1 in the HDV envelope could bear infectivity-deficient lesions without affecting entry, indicating that a small number of pre-S1 polypeptides—estimated at three to four per virion—is sufficient for infectivity. We next investigated the AGL activity in the small or large envelope protein background (S- and L-AGL, respectively) and found that lesions in S-AGL were more deleterious to infectivity than in L-AGL, a difference that reflects the relative stoichiometry of the small and large envelope proteins in the viral envelope. Finally, we showed that C147S, an AGL infectivity-deficient substitution, exerted a dominant-negative effect on infectivity, likely reflecting an involvement of C147 in intermolecular disulfide bonds.Hepatitis B virus (HBV) remains a major public health concern worldwide, affecting more than 350 millions of chronically infected individuals. Since the discovery of HBV, substantial information has been gathered on the viral replication cycle, but our understanding of the viral entry mechanism remains limited, and the identity of the receptor(s) for HBV is still unknown (15). HBV displays a very narrow host range, which is likely determined at viral entry by a highly specific interaction between the HBV envelope proteins and receptors at the surface of human hepatocytes. The envelope proteins designated large (L-HBsAg), middle (M-HBsAg), and small (S-HBsAg) are membrane-spanning glycoproteins that differ from each other by the size of their N-terminal ectodomain (21). L-HBsAg contains a N-terminal pre-S1, central pre-S2, and C-terminal S domains. M-HBsAg is shorter than L-HBsAg in lacking pre-S1, whereas S-HBsAg consists of the S domain only (Fig. ​(Fig.1).1). Envelope protein synthesis occurs at the endoplasmic reticulum (ER) membrane. Empty subviral particles (SVPs) assemble from aggregates at a pre-Golgi membrane and exit the cell through the secretory pathway (36). Assembly of mature HBV virions requires, in addition to S-HBsAg, the presence of L-HBsAg as a matrix protein for nucleocapsid envelopment (6). Recent findings indicate that HBV virions and SVPs follow distinct pathways for budding: the late endosomal multivesicular bodies (MVBs) for HBV virions, and the MVB-independent secretory pathway for SVPs (26, 28, 46). The HBV envelope proteins can also package the hepatitis delta virus (HDV) ribonucleoprotein (RNP), in case of HBV/HDV coinfection (5, 45), leading to the formation of HDV virions. Whether HDV uses the SVP secretion pathway rather than an MVB-dependent route is uncertain.Open in a separate windowFIG. 1.Schematic representation of HBV envelope proteins. The topology of the L-, M-, and S-HBsAg proteins at the viral membrane is represented. The pre-S2 domain of L- and M-HBsAg, and the determinants of viral entry, pre-S1 and AGL, are indicated. The M-HBsAg protein, represented in gray, is dispensable for infectivity. The myristic acid (Myr) linked to the L-HBsAg N terminus is indicated (closed box). Subdomains 2-48 and 49-75 of the pre-S1 infectivity determinant are indicated. Open boxes represent transmembrane regions in the S domain.L-HBsAg, but not M-HBsAg, is crucial to infectivity of both HBV and HDV particles (13, 31, 41, 42). L-HBsAg contains a major infectivity determinant located between amino acid residues 2 and 75 of its N-terminal pre-S1 domain (4, 30), including a myristoyl anchor linked to glycine-2 (1, 8, 18), a putative receptor binding site (RBS) between positions 2 and 48, and a domain of unknown function between amino acids 49 and 75. To date, the most compelling evidence that pre-S1 mediates receptor binding comes from studies demonstrating that myristoylated synthetic peptides specific for the N-terminal 2-to-48 pre-S1 domain can bind to hepatocyte plasma membranes and block infection in vitro (3, 16, 17) and in vivo (37). Beside pre-S1, a second determinant was recently identified in the antigenic loop (AGL) borne by the three HBV envelope proteins (Fig. ​(Fig.1).1). The AGL participation in viral entry was first established in the HDV model (23) and more recently directly in the HBV model (39). Interestingly, serine substitutions for the AGL cysteine residues, which prove detrimental to the conserved immunodominant “a” determinant, could also block viral entry. Note that the “a” determinant consists in conformational epitopes, which elicit highly neutralizing antibodies (22). Infectivity and the “a” determinant were also lost when virions were treated with membrane-impermeable inhibitors of thiol/disulfide isomerization (2). These findings clearly established a correlation between the AGL cysteine disulfide bonds network, the conformation of the “a” determinant, and infectivity. Hence, the strict conservation of the “a” determinant among all HBV genotypes is related to the AGL function at viral entry. The AGL determinant may operate in association with, or independently of pre-S1, in binding to receptors at the early step of entry and/or in the mechanism of envelope disassembly postentry.In the present study, we investigated the pre-S1 determinant by performing transcomplementation experiments between mutants of 3 pre-S1 subelements: the myristoyl anchor, subdomain 2-48, and subdomain 49-75. We analyzed the activity of the AGL determinant in the S- or L-HBsAg background (S- and L-AGL, respectively), and we examined the effect of introducing increasing amounts of infectivity-deficient pre-S1, or AGL, in the virion''s envelope on infectivity.     

A new cardiid bivalve from the Pliocene Baklan Basin (Turkey) and the origin of modern Ponto‐Caspian taxa

Abstract: We present the first record of the cardiid genus Monodacna from the Pliocene of Anatolia, Turkey. Monodacna imrei sp. nov. was found in the Pliocene Killik Formation from the western margin of the Baklan Basin, in very marginal brackish to freshwater lacustrine deposits. The new record extends the stratigraphic range of the modern Ponto‐Caspian genus back into the Pliocene and adds to earlier evidence that modern Ponto‐Caspian taxa originated in the Pliocene of south‐western Turkey.     

Discharge papilla development in the phycomycete Allomyces

The process of discharge papilla (DP) formation in Allomyces macrogynus was studied by light and electron microscopy. The plug of the DP was first deposited between the plasmalemma and the wall of the zoosporangium (ZS). The wall above the plug subsequently was eroded away. Deposition of a new inner wall layer in the sporangium held the plug in place and thickening of the layer formed a collar around the plug. Further deposition of material after this stage resulted in the characteristic pulley-shape. The plug material appeared homogeneous in electron micrographs but there was evidence of an outer layer. Digestion of the plug at the time of spore release was from within.Abbreviations DP discharge papilla - ZS zoosporangium     

Scanning Electron Microscopic Studies on Four Species of the Genus Syphacia (Nematoda, Oxyuridae)

The ultrastructure of the head end and surface structure of the cuticle of Syphacia petrusewiczi, S. nigeriana, S. frederici and S. stroma was studied. These species may be easily separated on the basis of the differences in their morphology: S. frederici possesses longitudinal septa on the body surface, a row of denticles on each of the three main teeth, and cervical alae; S. nigeriana has longitudinal septa and denticles but lack cervical alae; S. petrusewiczi has longitudinal septa and cervical alae but lacks denticles; S. stroma lacks these three characters.     

Structure and function of defensive glands in soldiers of Glossotermes oculatus (Isoptera: Serritermitidae)

The soldier caste represents the most conspicuous realization of termite eusociality, characterized by an extreme anatomical, behavioural, and physiological specialization. Numerous strategies have evolved in soldiers, including extreme adaptations such as self‐sacrifice by autothysis. In the present study, we investigated the structure and function of defensive glands in Glossotermes oculatus soldiers aiming to understand their use in combat. Three glands are involved in defence: labral, frontal, and labial glands. Mandibles are used to bite the enemy, whereas the secretions of labral and labial glands are discharged into the wound. A striking characteristic of G. oculatus is the lack of the frontal pore; the secretion of the frontal gland is discharged by a rupture of the body wall. We hypothesized that this self‐sacrifice is an efficient way of blocking a gallery under attack. A similar development of the frontal gland occurs in Serritermes serrifer, which supports the close relationship between the two genera inferred from morphological and genetic analyses. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 839–848.