The role of epiphytism in architecture and evolutionary constraint within mycorrhizal networks of tropical orchids

Characterizing the architecture of bipartite networks is increasingly used as a framework to study biotic interactions within their ecological context and to assess the extent to which evolutionary constraint shape them. Orchid mycorrhizal symbioses are particularly interesting as they are viewed as more beneficial for plants than for fungi, a situation expected to result in an asymmetry of biological constraint. This study addressed the architecture and phylogenetic constraint in these associations in tropical context. We identified a bipartite network including 73 orchid species and 95 taxonomic units of mycorrhizal fungi across the natural habitats of Reunion Island. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial subnetworks. By testing for phylogenetic signal, the overall signal was stronger for both partners in the epiphytic subnetwork. Moreover, in the subnetwork of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may co‐evolve more than terrestrial ones. We suggest that such tighter phylogenetic specialization may have been driven by stressful life conditions in the epiphytic niches. In addition to paralleling recent insights into mycorrhizal networks, this study furthermore provides support for epiphytism as a major factor affecting ecological assemblage and evolutionary constraint in tropical mycorrhizal symbioses.     

Entomofauna resource distribution associated with pig cadavers in Bogotá DC

A cadaver represents a temporal energy‐loaded resource, which provides arthropods with food, protection and a place in which to find a mate. Insects are usually the first organisms to discover and colonize a cadaver; as decomposition progresses, insects colonize cadavers in a predictable sequence. This work aimed to establish cadaverous entomofauna relationships with regard to stages of decomposition and environmental conditions using multiple correspondence analysis and thereby to identify the way in which insects distribute a perishable and changing resource. Entomofauna were thus collected in a semi‐rural area near Bogotá from the cadavers of three pigs (Sus scrofa L.) which had been shot. Environmental variables were recorded for each sampling. Multiple correspondence analyses were carried out for adult forms belonging to Diptera and Coleoptera families and stages of decomposition, and for Diptera and Coleoptera adult forms and environmental conditions. Stages of decomposition were a primary determining factor for structuring four guilds of entomofauna. However, environmental conditions influenced insect activity and were therefore a relevant factor in the structure of the entomofauna community. The results showed that the insects' distribution of available resources was related to changes in the stage of decomposition.     

Identification of respiratory vagal feedback in awake normal subjects using pseudorandom unloading.

Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus.     

Farms,pastures and woodlands: the fine‐scale distribution of Palearctic Culicoides spp. biting midges along an agro‐ecological gradient

The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.     

Termination of inspiration by phase-dependent respiratory vagal feedback in awake normal humans.

Imperceptible levels of proportional assist ventilation applied throughout inspiration reduced inspiratory time (TI) in awake humans. More recently, the reduction in TI was associated with flow assist, but flow assist also reaches a maximum value early during inspiration. To test the separate effects of flow assist and timing of assist, we applied a pseudorandom binary sequence of flow-assisted breaths during early, late, or throughout inspiration in eight normal subjects. We hypothesized that imperceptible flow assist would shorten TI most effectively when applied during early inspiration. Tidal volume, integrated respiratory muscle pressure per breath, TI, and TE were recorded. All stimuli (early, late, or flow assist applied throughout inspiration) resulted in a significant increase in inspiratory flow; however, only when the flow assist was applied during early inspiration was there a significant reduction in TI and the integrated respiratory muscle pressure per breath. These results provide further evidence that vagal feedback modulates breathing on a breath-by-breath basis in conscious humans within a physiological range of breath sizes.     

Localization of sources of thalamic inputs into the sensorimotor cortex in the rabbit using retrograde axonal transport technique

It was shown that the rabbit sensorimotor cortex received afferent fibers from neurons located in the specific, nonspecific, and association thalamic nuclei using the retrograde axonal transport technique. The distribution, dimensions, and shape of the somata of relay neurons spread through the thalamic nuclei were analyzed. The total number of neurons sending out thalamo-sensorimotor-cortical fibers was calculated and the coordinates of loci with the highest density of these cells in each thalamic nucleus were identified. Multipolar and stellate cells with somata measuring 12–20 µm and 10–15 µm in diameter, respectively, prevailed amongst relay neurons. Amongst the specific nuclei, the majority of afferent fibers are sent out by the ventrolateral, ventral anterior, and anterior ventral nuclei. A comparable number of afferent fibers are sent out by the mediodorsal and paracentral nuclei; these split up among the association nuclei and paracentral nuclei, respectively. It is suggested that afferents from many different groups of thalamic nuclei are essential for the sensorimotor cortex to participate in thalamocortical interaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 87–94, January–February, 1987.     

Aging and glucose homeostasis in C57BL/6J male mice

Age-dependent changes in glucose homeostasis were assessed in specific pathogen-free C57BL/6J male mice. Increased islet size and pancreatic insulin content in old (21-25-month-old) mice were associated with lower nonfasting plasma glucose levels and improved clearance of either an oral or an i.p. administered glucose load in comparison with young, mature (4-5-month-old) males. The almost twofold increase in islet size correlated with a twofold increase of glucose-stimulated insulin secretion from perifused islets from 25-month-old males compared with 5-month-old males. These aging male mice did not become obese, and there were no fibrotic changes associated with the hyperplastic islets observed in the old males. Thus, the findings that glucose tolerance did not deteriorate with age, coupled with the lack of evidence for impaired beta cell responsiveness to glucose in old males, suggest that deterioration in glucose homeostasis is not an inevitable consequence of aging in the mouse.     

Cytological aspects of in vitro androgenesis in wheat (Triticum aestivum L.) using fluorescent microscopy

Summary Two winter wheat genotypes (Diószegi 200 and Mv 15) were compared for their in vitro androgenic capacity. On average, the induction frequency of embryogenic structures was 71.7% in Diószegi 200 and only 4.3% in Mv 15. The haploid induction ability of the two genotypes differed considerably, with Diószegi 200 being much higher. The difference in the in vitro inductability of the microspores may result from genetic differences which are manifested in the survival rate of the microspores during the culture period and their adaptability to in vitro conditions. Special DNA fluorochrornes were suitable for studying the different pathways of in vitro androgenesis. Our data indicate that the repeated equal divisions of the microspore nucleus might lead to pollen embryo formation, and subsequent divisions of the vegetative portion of the pollen grain after the first asymmetric microspore mitosis can result in pollen callus formation.