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.     

Pattern of conodont reworking in the Upper Devonian of the Alps: palaeoenvironmental and palaeotectonic implications

Transfer of sediments from shallow shelf to basin usually implies vertical (stratigraphic) reworking of fossils, but in a few instances produces only lateral reworking (actually within the time span of a subzone). An Upper Devonian (Frasnian) pelagic carbonate sequence with allodapic intercalations and thick intraclast parabreccias triggered by seismic shocks and related tsunami and turbidity currents has been studied. Here, the standard biozone sequence is undisturbed at the zonal as well as the subzonal level. However, distribution of conodonts is discontinuous, and ranges of some important species are altered; mature specimens are commonly broken, whereas complete specimens are mostly juvenile forms. Maxima and minima of element frequency and anomalous thickening or thinning of subzones are recognized. Such distribution patterns of conodonts are compared with the four main facies distinguished and related to the environmental interpretation (a platform-basin system, the original gentle slope of which was fragmenting in fault-controlled blocks). The mean frequency of shallow-water, proximal conodonts is 10% whereas transitional to distal deeper-water genera dominate throughout the entire section. In the dominant biofacies, conodonts settled vertically, in the subordinate one they were transported laterally. The 'intraclast parabreccia' is interpreted as a peculiar type of seismitc. The anomalous thickness variation of biozones is related to the step topography of the slope in a fault-controlled carbonate basin.     

Epidemiology of apple proliferation (AP) in northwestern Italy: evaluation of the frequency of AP-positive psyllids in naturally infected populations of Cacopsylla melanoneura (Homoptera: Psyllidae)

Adults of Cacopsylla melanoneura, vector of the apple proliferation (AP) phytoplasma, were collected every 2 weeks from January until May in 2000 and 2001 by the beating tray method in eight apple orchards of the Aosta Valley (northwestern Italy). Total DNA was extracted from batches of five insects and amplified with the universal phytoplasma primers P1/P7 in direct PCR. A nested PCR assay was then performed on P1/P7 amplicons using the primers fO1/rO1, specific for the AP‐ phytoplasma group. The digestion of fO1/rO1 amplicons with Ssp I restriction endonuclease confirmed that C. melanoneura adults harboured the AP phytoplasma. The data obtained with PCR were used to estimate the proportion of AP‐positive insects in over wintered and offspring adults. Percentages of AP‐positive insects of 3.6% and 0.8% were estimated in 2000 among over wintered and offspring psyllids respectively. In 2001 only the over wintered insects were found infected, with an estimated proportion of 2.8%. The seasonal abundance of the vector was measured using yellow sticky traps. C. melanoneura was always present at a low population level, and the highest density was recorded from mid‐February until mid‐March in both years. The results show that the overwintered population is higher and spends a longer period in apple orchards, suggesting the crucial role of the overwintered adults in vectoring AP.     

Species‐specific influences of shrubs on the non‐dormant soil seed bank of native and exotic plant species in central‐northern Monte Desert

Deserts shrubs are well known to facilitate vegetation aggregation, mostly through seed trapping, and stress amelioration during and after plant establishment. Because vegetation aggregation effects are a by‐product of shrub presence, beneficiary species may not only be native, but also exotic. However, despite the high risk that exotic invasive species pose to ecosystem services, little is known of the role of desert shrubs on plant invasions. We assessed the influence of two shrub species on the non‐dormant soil seed bank (i.e. the number of seeds that readily germinate with sufficient water availability) of an invasive annual grass (Schismus barbatus) and of coexisting native species in a central‐northern Monte Desert (Argentina). Soil samples were collected beneath the canopies of two dominant shrub species (Bulnesia retama and Larrea divaricata) and in open spaces (i.e. intercanopies) in May 2001. Overall, the density of germinated seedlings of Schismus and that of the native species were negatively associated across microsite types. Schismus density was similar to that of all native species pooled together (mostly annuals), and was highest in Larrea samples (with no significant differences between Bulnesia and intercanopies). On the contrary, the density of all native species pooled together was highest in Bulnesia samples. Our results suggest that shrubs may contribute to plant invasions in our study system but, most importantly, they further illustrate that this influence can be species specific. Further research is needed to assess the relative importance of in situ seed production (and survival) and seed redistribution on soil seed bank spatial patterns.     

Wolbachia endosymbiont in a species of the Anastrepha fraterculus complex (Diptera: Tephritidae)

Summary

In Anastrepha sp.2 aff. fraterculus, the egg-cell harbours a large population of endosymbionts. The bacteria were identified as belonging to genus Wolbachia by PCR assay using primers of the ftsZ gene followed by sequencing of the amplified band. Newly deposited eggs stained in toto by Hoechst show that the bacteria are unevenly dispersed throughout the egg-cell, with a higher accumulation at the posterior pole, and that the degree of infestation varies from egg to egg. Analysis by transmission electron microscopy shows that bacteria are present in the female germ line of embryonic and larval stages, as well as in the different cell types of the ovaries at the adult stage. Mature ova within the follicles harbour a large population of the symbionts. The results indicate the existence of a transovarian transmission of the endosymbionts in this fly.     

Spermatogenesis and sperm—spermatheca relations in Spirorbis spirorbis (L.)

The differentiation from early spermatid to spermatozoon is described with special emphasis on the formation of the helix of chromatin and mitochondrial junctions. The role of microtubules in morphogenesis is discussed.

New observations on the role of the recently described spermatheca are presented; phagocytosis and digestion of spermatozoa are proven, and the various origins of the sperm found in the spermatheca are specified.     

Floral traits and reproduction of Avicennia schaueriana Moldenke (Acanthaceae): a generalist pollination system in the Lamiales

Pollination systems may vary in their degree of specialization from generalist to specialist and this is associated with the frequency and efficiency of pollinators. Self‐compatibility and a generalist pollination system appear to be adaptations that enhance the ability for colonizing new areas, which is typical of mangrove species. Avicennia schaueriana is a western mangrove species included in Acanthaceae, Lamiales, an order known to have specialized pollination. We aimed to describe the floral morphology and analyze the pollination and reproductive systems of A. schaueriana in a mangrove area on the northern coast of the state of Pernambuco, Brazil, to analyze the possible adaptations of this species to the environment. Avicennia schaueriana is self‐compatible; however, pollination activity is essential because there is no spontaneous formation of fruit. Reproductive efficacy was high, indicating pollinator efficiency. Some floral attributes of A. schaueriana suggest specialization; however, the broad spectrum of pollinators observed suggests that it has a generalist pollination system. The way in which pollinators interact with flowers and the environmental conditions may have exerted a selective force on the floral attributes of A. schaueriana, characterizing an adaptive generalized pollination system, which is somewhat specialized.     

An early winged crown group stick insect from the Early Eocene amber of France (Insecta,Phasmatodea)

The new stick insect family Gallophasmatidae, based on Gallophasma longipalpis gen. et sp.n. , from the Earliest Eocene French amber has a pattern of tegmina venation typical of Archaeorthoptera, also present in at least some Mesozoic ‘Phasmatodea’. On the other hand, Gallophasma displays in its body anatomy some apomorphies of the extant Euphasmatodea, e.g. fusion of metatergum and abdominal tergum 1, correlated with the reduction of abdominal sternum 1 to lateral triangular sclerites. A unique autapomorphy of Gallophasma is the presence of annulated and apparently multi‐segmented or pseudo‐segmented cerci; all other Phasmatodea have one‐segmented cerci. The venation of the tegmina of Gallophasma differs from that of extant winged Phasmatodea in the plesiomorphic absence of a knob‐like dorsal eversion. This and other differences in the wing venation between extant and extinct Phasmatodea might have been caused by the loss of wings at some point in the evolutionary history of the order and their secondary gain in a subclade of the extant phasmids.     

Spatial patterns in the distribution of European springtails (Hexapoda: Collembola)

Using a large database on the spatial distribution of European springtails (Collembola) we investigated how range sizes and range distribution across European countries and major islands vary. Irrespective of ecological guild, islands tended to contain more endemic species than mainland countries. Nestedness and species co‐occurrence analysis based on country species lists revealed latitudinal and longitudinal gradients of species occurrences across Europe. Species range sizes were much more coherent and had fewer isolated occurrences than expected from a null model based on random colonization. We did not detect clear postglacial colonization trajectories that shaped the faunal composition across Europe. Our results are consistent with a multiregional postglacial colonization. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 498–506.     

Hygroreception in olfactometer studies

Abstract In olfactometric studies, a technique used to measure insect behavioural bias towards airborne chemicals, many of the factors that could affect the bioassay outcome other than the volatiles themselves are carefully controlled (e.g. lighting conditions, temperature, spatial position, physiological state of the insects, time of day when the bioassay is performed) but one factor, namely humidity, is overlooked frequently when studying responses to plant volatiles. Many insect species respond positively and negatively to changes in humidity and, during bioassays, differences arising from odour choices with different water vapour release rates might have confounding effects versus the original intent of the behavioural study. The present study aims to assess the effect of different substrates on the water vapour content of air in an olfactometer‐like set‐up. The results show that airflow humidity is affected by the odour source used in the olfactometer air flow. In addition, the response of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) is studied towards different humidities and plant material in an olfactometer. The present study suggests that humidity needs to be controlled in olfactometric studies.