Nutrients are assimilated efficiently by Lymantria dispar caterpillars from the mature leaves of trees in the Salicaceae

The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71–81%) but significantly lower PAE from their mature leaves (45–52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68–76% and 72–92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high‐quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available.     

A speculative model of affective illness cyclicity based on patterns of drug tolerance observed in amygdala-kindled seizures

In this article, we discuss molecular mechanisms involved in the evolution of amygdala kindling and the episodic loss of response to pharmacological treatments during tolerance development. These phenomena allow us to consider how similar principles (in different neurochemical systems) could account for illness progression, cyclicity, and drug tolerance in affective disorders. We describe the phenomenon of amygdala-kindled seizures episodically breaking through effective daily pharmacotherapy with carbamazepine and valproate, suggesting that these observations could reflect the balance of pathological vs compensatory illness-induced changes in gene expression. Under certain circumstances, amygdala-kindled animals that were initially drug responsive can develop highly individualized patterns of seizure breakthroughs progressing toward a complete loss of drug efficacy. This initial drug efficacy may reflect the combination of drug-related exogenous neurochemical mechanisms and illness-induced endogenous compensatory mechanisms. However, we postulate that when seizures are inhibited, the endogenous illness-induced adaptations dissipate (the “time-off seizure” effect), leading to the re-emergence of seizures, a re-induction of a new, but diminished, set of endogenous compensatory mechanisms, and a temporary period of renewed drug efficacy. As this pattern repeats, an intermittent or cyclic response to the anticonvulsant treatment emerges, leading toward complete drug tolerance. We also postulate that the cyclic pattern accelerates over time because of both the failure of robust illness-induced endogenous adaptations to emerge and the progression in pathophysiological mechanisms (mediated by long-lasting changes in gene expression and their downstream consequences) as a result of repeated occurrences of seizures. In this seizure model, this pattern can be inhibited and drug responsivity can be temporarily reinstated by several manipulations, including lowering illness drive (decreasing the stimulation current.), increasing drug dosage, switching to a new drug that does not show crosstolerance to the original medication, or temporarily discontinuing treatment, allowing the illness to re-emerge in an unmedicated animal. Each of these variables is discussed in relation to the potential relevance to the emergence, progression, and suppression of individual patterns of episodic cyclicity in the recurrent affective disorders. A variety of clinical studies are outlined that specifically test the hypotheses derived from this formulation. Data from animal studies suggest that illness cyclicity can develop from the relative ratio between primary pathological processes and secondary endogenous adaptations (assisted by exogenous medications). If this proposition is verified, it further suggests that illness cyclicity is inherent to the neurobiological processes of episode emergence and amelioration, and one does not need to postulate a separate defect in the biological clock. The formulation predicts that early and aggressive long-term interventions may be optimal in order to prevent illness emergence and progression and its associated accumulating neurobiological, vulnerability factors.     

Infiltration of a facultative ant–plant mutualism by the introduced Argentine ant: effects on mutualist diversity and mutualism benefits

1. Ant–plant mutualisms have been the focus of considerable empirical research, but few studies have investigated how introduced ants affect these interactions. Using 2 years of survey data, this study examines how the introduced Argentine ant [Linepithema humile (Mayr)] differs from native ants with respect to its ability to protect the extrafloral nectary‐bearing coast barrel cactus (Ferocactus viridescens) in Southern California. 2. Eighteen native ant species visited cacti in uninvaded areas, but cacti in invaded areas were primarily visited by the Argentine ant. The main herbivore of the coast barrel cactus present at the study sites is a leaf‐footed bug (Narnia wilsoni). 3. Herbivore presence (the fraction of surveys in which leaf‐footed bugs were present on individual cacti) was negatively related to ant presence (the fraction of surveys in which ants were present on individual cacti). Compared with cacti in uninvaded areas, those in invaded areas were less likely to have herbivores and when they did had them less often. 4. Seed mass was negatively related to herbivore presence, and this relationship did not differ for cacti in invaded areas versus those in uninvaded areas. 5. Although the Argentine ant might provide superior protection from herbivores, invasion‐induced reductions in ant mutualist diversity could potentially compromise plant reproduction. The cumulative number of ant species on individual cacti over time was lower in invaded areas and was associated with a shortened seasonal duration of ant protection and reduced seed mass. These results support the hypothesis that multiple partners may enhance mutualism benefits.     

Identification of a 13-kDa protein associated with the polyhydroxyalkanoic acid granules from Acinetobacter spp.

Abstract Transferrin-binding proteins from Neisseria meningitidis vary among different isolates. We have identified and studied a hypervariable region adjacent to the carboxyl-end of the transferrin-binding domain of the Tbp2 molecule. The tbp2 genes from six strains of N. meningitidis were cloned and sequenced in this particular region. Sequence analysis of these regions along with five other sequences available from pathogenic Neisseria showed a common organisation of seven highly variable nucleotide stretches interspersed with six conserved nucleotide stretches. The variable regions correlated with the location of immunoreactive epitopes in polyclonal antisera raised to transferrin-binding proteins identified by peptide pin technology. Sequence analysis suggested a mosaic-like organisation of the tbp2 genes. Taken together, these data suggest that the antigenic variation in this part of the protein may result from a strong host immune pressure.