Declining acceptability of a food plant for the polyphagous grasshopper Schistocerca americana: the role of food aversion learning

ABSTRACT Successive contacts with a food that was initially acceptable to the acridid Schistocerca americana (Drury) (Orthoptera: Acrididae) were monitored. It was found that acceptability, as measured by meal length, declined with experience until the food, spinach, was completely rejected. Reduced acceptability of spinach was maintained even after feeding for three meals on a fully acceptable and suitable food, a period of 2–3 h. Experiments with spinach-filled capsules placed in the gut suggested that the decline in acceptability was not due to direct feedback from the gut or haemolymph on the sensory or feeding control systems. Food aversion learning is indicated as the mechanism underlying the decline in acceptability.     

Mechanisms influencing changes in lake area in Alaskan boreal forest

During the past ～50 years, the number and area of lakes have declined in several regions in boreal forests. However, there has been substantial finer‐scale heterogeneity; some lakes decreased in area, some showed no trend, and others increased. The objective of this study was to identify the primary mechanisms underlying heterogeneous trends in closed‐basin lake area. Eight lake characteristics (δ¹⁸O, electrical conductivity, surface : volume index, bank slope, floating mat width, peat depth, thaw depth at shoreline, and thaw depth at the forest boundary) were compared for 15 lake pairs in Alaskan boreal forest where one lake had decreased in area since ～1950, and the other had not. Mean differences in characteristics between paired lakes were used to identify the most likely of nine mechanistic scenarios that combined three potential mechanisms for decreasing lake area (talik drainage, surface water evaporation, and terrestrialization) with three potential mechanisms for nondecreasing lake area (subpermafrost groundwater recharge through an open talik, stable permafrost, and thermokarst). A priori expectations of the direction of mean differences between decreasing and nondecreasing paired lakes were generated for each scenario. Decreasing lakes had significantly greater electrical conductivity, greater surface : volume indices, shallower bank slopes, wider floating mats, greater peat depths, and shallower thaw depths at the forest boundary. These results indicated that the most likely scenario was terrestrialization as the mechanism for lake area reduction combined with thermokarst as the mechanism for nondecreasing lake area. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the growing season, thereby increasing plant growth, floating mat encroachment, transpiration rates, and the accumulation of organic matter in lake basins. The transition to peatlands associated with terrestrialization may provide a transient increase in carbon storage enhancing the role of northern ecosystems as major stores of global carbon.     

Coexistence theory in the Cape Floristic Region: revisiting an example of leaf niches in the Proteaceae

Competition in plant communities is often a contentious issue because the mechanisms of competitive interactions are not obvious. We sought evidence that Proteaceae communities are competing along two leaf niche axes as observed in a previous study. Two functional characters, leaf size and leaf shape were measured on numerous individuals per species per plot of six communities from two different regions. Patterns of overdispersion along these leaf trait axes between species were observed, similar to the earlier study. The observed results were compared with the patterns expected under a null model using standard and novel indices to test the significance of trait dispersion between species within a plot. Competition and niche differentiation in the observed plots were not supported as the observed trait overlaps were not significantly different from the null expectation. Our results do not support the theory that Proteaceae communities compete along the two proposed functional leaf traits.     

Do we have any solid evidence of clinical utility about the pathophysiology of schizophrenia?

A diagnosis of schizophrenia, as in most of psychiatric practice, is made largely by eliciting symptoms with reference to subjective, albeit operationalized, criteria. This diagnosis then provides some rationale for management. Objective diagnostic and therapeutic tests are much more desirable, provided they are reliably measured and interpreted. Definite advances have been made in our understanding of schizophrenia in recent decades, but there has been little consideration of how this information could be used in clinical practice. We review here the potential utility of the strongest and best replicated risk factors for and manifestations of schizophrenia within clinical, epidemiological, cognitive, blood biomarker and neuroimaging domains. We place particular emphasis on the sensitivity, specificity and predictive power of pathophysiological indices for making a diagnosis, establishing an early diagnosis or predicting treatment response in schizophrenia. We conclude that a number of measures currently available have the potential to increase the rigour of clinical assessments in schizophrenia. We propose that the time has come to more fully evaluate these and other well replicated abnormalities as objective potential diagnostic and prognostic guides, and to steer future clinical, therapeutic and nosological research in this direction.     

Evidence for rodent pollination in Erica hanekomii (Ericaceae)

Pollination by rodents, originally discovered in Cape Proteaceae, is known from a handful of plant lineages and may be more widespread than current data suggest. Here, we demonstrate the occurrence of this mode of pollination in Erica, the largest plant genus in the Cape flora of South Africa. The localized endemic Erica hanekomii appears to be adapted for pollination by rodents, on account of its low, mat‐forming habit with many dull‐coloured, pendulous flower heads, large volumes (up to c. 30 µL per inflorescence) of sucrose‐dominated nectar, hook‐shaped styles and late winter flowering phenology. Rodents trapped in the vicinity of E. hanekomii plants had many thousands of Erica tetrads in their droppings. Nocturnal laboratory observation showed that Acomys subspinosus (Cape spiny mouse) is adept at manipulating E. hanekomii inflorescences and lapping nectar without destroying gynoecia. During terrarium experiments, pollen was deposited mainly on the rostrum, but also on the chest area and forelegs of A. subspinosus. No birds or insects were seen to visit E. hanekomii in the field. Whereas natural fruit set was 73%, inflorescences from which rodents, but not insects, were excluded using mesh cages, had fruit set of just 3.3%. Exclusion of all visitors resulted in zero seed production. Broken anther rings (a sign of flower visitation in Erica) were observed in 90.1% of flowers in the field and 92% of flowers exposed to rodents in the laboratory, but in virtually none of the flowers from which rodents were selectively excluded. This first record of a non‐flying mammal pollination syndrome in Ericaceae raises interesting new questions about the origins of the rodent pollination system and the selective factors that lead to its evolution. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 163–170.