Rainfall Influences Ant Sampling in Dry Forests

The standardized 'Ants of the Leaf Litter' protocol aims to facilitate the use of ground-foraging and litter-dwelling ants in biodiversity assessment and monitoring programs. It was initially developed to characterize assemblages from tropical rain forests and is based on two main techniques: Winkler extractions and pitfall traps. Here, we tested to what extent this protocol was adapted to tropical dry forests and affected by the rainfall regime. Our 10 study sites were located along an aridity gradient (average annual rainfall: 350–1300mm) in the Gran Chaco. The number of species collected per sampling effort increased with aridity for pitfalls but followed an opposite trend for Winkler samples. This trend could be explained by the low daytime foraging activity in the leaf litter during drought periods. In arid and semiarid regions the good performance of pitfalls was probably related to their 24-h operation and to the attractiveness of the water they contained. Our results stress that the Winkler method used in the Ants of the Leaf Litter protocol may not be cost-effective during periods of drought and may lead to severe underestimations of litter ant diversity in tropical dry forests.     

The dynamics of spleen morphogenesis

The mammalian spleen has important functions in immunity and haematopoiesis but little is known about the events that occur during its early embryonic development. Here we analyse the origin of the cells that gives rise to the splenic mesenchyme and the process by which the precursors assume their position along the left lateral side of the stomach. We report a highly conserved regulatory element that regulates the Nkx2-5 gene throughout early spleen development. A transgenic mouse line carrying this element driving a reporter gene was used to show that morphogenesis of the spleen initiates bilaterally and posterior to the stomach, before the splenic precursors grow preferentially leftward. In addition the transgenic line was used in an organ culture system to track spleen precursor cells during development. Spleen cells were shown to move from the posterior mesenchyme and track along the left side of the stomach. Removal of tissue from the anterior stomach resulted in splenic cells randomly scattering suggesting a guidance role for the anterior stomach. Using a mouse line carrying a conditional Cre recombinase to mark early precursor cell populations, the spleen was found to derive from posterior mesenchyme distinct from the closely adjacent stomach mesenchyme.     

Ecosystem fluxes of hydrogen in a mid‐latitude forest driven by soil microorganisms and plants

Molecular hydrogen (H₂) is an atmospheric trace gas with a large microbe‐mediated soil sink, yet cycling of this compound throughout ecosystems is poorly understood. Measurements of the sources and sinks of H₂ in various ecosystems are sparse, resulting in large uncertainties in the global H₂ budget. Constraining the H₂ cycle is critical to understanding its role in atmospheric chemistry and climate. We measured H₂ fluxes at high frequency in a temperate mixed deciduous forest for 15 months using a tower‐based flux‐gradient approach to determine both the soil‐atmosphere and the net ecosystem flux of H₂. We found that Harvard Forest is a net H₂ sink (?1.4 ± 1.1 kg H₂ ha^?1) with soils as the dominant H₂ sink (?2.0 ± 1.0 kg H₂ ha^?1) and aboveground canopy emissions as the dominant H₂ source (+0.6 ± 0.8 kg H₂ ha^?1). Aboveground emissions of H₂ were an unexpected and substantial component of the ecosystem H₂ flux, reducing net ecosystem uptake by 30% of that calculated from soil uptake alone. Soil uptake was highly seasonal (July maximum, February minimum), positively correlated with soil temperature and negatively correlated with environmental variables relevant to diffusion into soils (i.e., soil moisture, snow depth, snow density). Soil microbial H₂ uptake was correlated with rhizosphere respiration rates (r = 0.8, P < 0.001), and H₂ metabolism yielded up to 2% of the energy gleaned by microbes from carbon substrate respiration. Here, we elucidate key processes controlling the biosphere–atmosphere exchange of H₂ and raise new questions regarding the role of aboveground biomass as a source of atmospheric H₂ and mechanisms linking soil H₂ and carbon cycling. Results from this study should be incorporated into modeling efforts to predict the response of the H₂ soil sink to changes in anthropogenic H₂ emissions and shifting soil conditions with climate and land‐use change.     

Agonistic Behavior of the Termite <Emphasis Type="Italic">Prorhinotermes canalifrons</Emphasis> (Isoptera: Rhinotermitidae)

While intercolonial and interspecific agonism has been broadly documented in termites, detailed studies of individual behavior and its differentiation among castes are scarce. We studied the responses of non-reproductive castes of Prorhinotermes canalifrons (pseudergates, presoldiers, soldiers of different age and artificial intercastes) to conspecific and heterospecific aliens. Each caste displayed a specific behavioral repertoire. Soldiers, but to a lesser extent pseudergates as well, are responsible for colony defense. The behavioral repertoire of the soldier appears on the second day after exuviation and becomes complete on the third day, well before its defensive secretion is present. The behavior of artificial intercastes induced by a JH analog is intermediate between that of pseudergates and soldiers. Reactions to heterospecific aliens were much quicker and more violent than reactions to conspecifics, which suggests that individuals experience difficulties in identifying conspecific aliens.     

The membrane ATPase of Escherichia coli I. Ion dependence and ATP-ADP exchange reaction

The properties of the membrane-bound ATPase (EC 3.6.1.3) of Escherichia coli have been reexamined using membranes obtained by mechanical disruption of exponentially growing cells.

The activity exhibited an absolute requirement for Mg²⁺ in the neutral pH range, while Ca²⁺ was found able to activate ATPase at more alkaline pH. Optimal activity was observed at pH 7.5, with a Mg/ATP ratio of 0.5.

ADP was found to inhibit ATP hydrolysis and to transform the Michaelian ATP concentration dependence with a K_m of 0.5 mM into a sigmoid curve with increasing K_m and decreasing V.

In contrast ADP activated an ATP-ADP exchange process and this shift from hydrolysis to exchange was stimulated by high Mg²⁺ and by orthophosphate.

All nucleoside triphosphates tested interfered with ATP hydrolysis, all could be hydrolyzed and could donate their terminal phosphate group to ADP. The relative efficiencies of nucleoside triphosphates in these three processes varied in parallel with minor discrepancies.

ATP hydrolysis was inhibited by N,N′-dicyclohexylcarbodiimide (DCCD) Dio 9, NaN₃ and pyrophosphate, the first two being ineffective against ATP-ADP exchange, the third being stimulatory and the last inhibitory.

ATP hydrolysis and ATP-ADP exchange are tentatively attributed to the terminal enzyme of oxidative phosphorylation.     

Orexins in rat dorsal motor nucleus of the vagus potently stimulate gastric motor function

Orexins regulate food intake, arousal, and the sleep-wake cycle. They are synthesized by neurons in the lateral hypothalamus and project to autonomic areas in the hindbrain. Orexin A applied to the dorsal surface of the medulla stimulates gastric acid secretion via a vagally mediated pathway. We tested the hypothesis that orexins in the dorsal motor nucleus (DMN) of the vagus regulate gastric motor function. Multibarelled micropipette assemblies were used to administer vehicle, L-glutamate, orexins A (1 and 10 pmol) and B (10 pmol), and a dye marker into this site in anesthetized rats. When the pipette was positioned in the DMN rostral to the obex (where excitation of neurons by L-glutamate evoked an increase in contractility), orexins A and B increased intragastric pressure and antral motility. In contrast, 10 pmol orexin A microinjected into the DMN caudal to the obex (where L-glutamate evokes gastric relaxation through a vagal inhibitory pathway) did not significantly alter gastric motor function. In separate immunocytochemical studies, orexin receptor 1 was highly expressed in neurons in the DMN. Specifically, it was present in retrogradely labeled preganglionic neurons in the DMN that innervate the stomach. These data are consistent with the idea that orexin A stimulates vagal excitatory motor neurons. These are the first data to suggest that orexins in the DMN have potent and long-lasting effects to increase gastric contractility.     

Involvement of the mitogen-activated protein (MAP) kinase signalling pathway in host cell invasion by Toxoplasma gondii

Little is known about signalling in Toxoplasma gondii, but it is likely that protein kinases might play a key role in the parasite proliferation, differentiation and probably invasion. We previously characterized Mitogen-Activated Protein (MAP) kinases in T. gondii lysates. In this study, cultured cells were tested for their susceptibility to Toxoplasma gondii infection after tachyzoite pretreatment with drugs interfering with MAP kinase activation pathways. Protein kinases inhibitors, i.e. genistein, RO31-8220 and PD098059, reduced tachyzoite infectivity by 38 +/- 4.5%, 85.5 +/- 9% and 56 +/- 10%, respectively. Conversely, protein kinases activators, i.e. bombesin and PMA, markedly increased infectivity (by 202 +/- 37% and 258 +/- 14%, respectively). These results suggest that signalling pathways involving PKC and MAP kinases play a role in host cell invasion by Toxoplasma.     

Asexual queen succession in the higher termite Embiratermes neotenicus

Asexual queen succession (AQS), in which workers, soldiers and dispersing reproductives are produced sexually while numerous non-dispersing queens arise through thelytokous parthenogenesis, has recently been described in three species of lower termites of the genus Reticulitermes. Here, we show that AQS is not an oddity restricted to a single genus of lower termites, but a more widespread strategy occurring also in the most advanced termite group, the higher termites (Termitidae). We analysed the genetic structure in 10 colonies of the Neotropical higher termite Embiratermes neotenicus (Syntermitinae) using five newly developed polymorphic microsatellite loci. The colonies contained one primary king accompanied either by a single primary queen or by up to almost 200 neotenic queens. While the workers, the soldiers and most future dispersing reproductives were produced sexually, the non-dispersing neotenic queens originated through thelytokous parthenogenesis of the founding primary queen. Surprisingly, the mode of thelytoky observed in E. neotenicus is most probably automixis with central fusion, contrasting with the automixis with terminal fusion documented in Reticulitermes. The occurrence of AQS based on different mechanisms of ploidy restoration raises the hypothesis of an independent evolutionary origin of this unique reproductive strategy in individual lineages of lower and higher termites.     

A novel Toxoplasma gondii calcium-dependent protein kinase

Toxoplasma gondii is an obligate intracellular parasite that infects all types of cells in humans. A family of calcium-dependent protein kinases (CDPKs), previously identified as important in the development of plants and protists, was recently shown to play a role in the infectivity of apicomplexans, and in motility and host cell invasion in particular. We report here the isolation of a new calcium-dependent protein kinase gene from the human toxoplasmosis parasite, Toxoplasma gondii. The gene consists of 12 exons. The encoded protein, TgCDPK4, consists of the four characteristic domains of members of the CDPK family and is most similar to PfCDPK2 from Plasmodium falciparum. We measured TgCDPK4 activity, induced by calcium influx, using a kinase assay. A calcium chelator (EGTA) inhibited this activity. These findings provide evidence of signal transduction involving members of the CDPK family in T. gondii.     

Developmental pathways of Glossotermes oculatus (Isoptera, Serritermitidae): at the cross-roads of worker caste evolution in termites

SUMMARY The onset of a specialized ("true") worker caste is a crucial step in the evolution of termite societies. Such workers, permanently excluded from wing development, repeatedly evolved from totipotent immatures, called "false" workers or pseudergates. In the family Rhinotermitidae, the presence of true workers and the level of specialization of this caste are highly variable, and key taxa illustrate transitional situations providing clues about worker evolution. Here we focused on the status of working immatures of Glossotermes oculatus , from the family Serritermitidae, now thought to represent either the sister-group of the Rhinotermitidae or a basal lineage nested within them. Contrary to previous assumptions, we show that the apterous immatures performing worker tasks in G. oculatus are the source of the single wing-budded nymphal instar preceding the alate. Consequently, they qualify as pseudergates rather than true workers. However, the sex ratio is strongly male biased in pseudergates and soldiers, which is a trait usually restricted to termites with true workers. We therefore argue that pseudergates of G. oculatus are close to a point where the species could easily shift toward the differentiation of a true worker caste, and that G. oculatus pinpoints a new possible route for the evolution of true workers from pseudergates.