Landscape-scale patterns of shrub-species abundance in California chaparral – The role of topographically mediated resource gradients

We examine the degree to which landscape-scale spatial patterns of shrub-species abundance in California chaparral reflect topographically mediated environmental conditions, and evaluate whether these patterns correspond to known ecophysiological plant processes. Regression tree models are developed to predict spatial patterns in the abundance of 12 chaparral shrub and tree species in three watersheds of the Santa Ynez Mountains, California. The species response models are driven by five variables: average annual soil moisture, seasonal variability in soil moisture, average annual photosynthetically active radiation, maximum air temperature over the dry season (May–October), and substrate rockiness. The energy and moisture variables are derived by integrating high resolution (10 m) digital terrain data and daily climate observations with a process-based hydro-ecological model (RHESSys). Field-sampled data on species abundance are spatially integrated with the distributed environmental variables for developing and evaluating the species response models.The species considered are differentially distributed along topographically-mediated environmental gradients in ways that are consistent with known ecophysiological processes. Spatial patterns in shrub abundance are most strongly associated with annual soil moisture and solar radiation. Substrate rockiness is also closely associated with the establishment of certain species, such as Adenostoma fasciculatum and Arctostaphylos glauca. In general, species that depend on fire for seedling recruitment (e.g., Ceanothous megacarpus) occur at high abundance in xeric environments, whereas species that do not depend on fire (e.g., Heteromeles arbutifolia) occur at higher abundance in mesic environments. Model performance varies between species and is related to life history strategies for regeneration. The scale of our analysis may be less effective at capturing the processes that underlie the establishment of species that do not depend on fire for recruitment. Analysis of predication errors in relation to environmental conditions and the abundance of potentially competing species suggest factors not explicitly considered in the species response models.     

Restriction enzyme analysis of mitochondrial DNA of the Aspergillus flavus group: A. flavus, A. parasiticus, and A. nomius

Mitochondrial DNA restriction fragment length polymorphisms were identified that clearly distinguish Aspergillus flavus, A. parasiticus, and A. nomius. Mitochondrial DNAs of A. flavus and A. parasiticus were found to be circular, and their size was estimated size to be 32 kilobases. A restriction map was constructed for the mitochondrial genome of an A. parasiticus isolate by using four restriction endonucleases. Four genes tested were found to have the same order as in the mitochondrial genome of A. nidulans. The mitochondrial genome of A. nomius was estimated to be 33 kilobases.     

Elevated glutamate and NMDA disrupt production of the second messenger cyclic GMP in the early postnatal mouse cortex

The second messenger cyclic guanosine monophosphate (cGMP) plays many roles during nervous system development. Consequently, cGMP production shows complex patterns of regulation throughout early development. Elevated glutamate levels are known to increase cGMP levels in the mature nervous system. A number of clinical conditions including ischemia and perinatal asphyxia can result in elevated glutamate levels in the developing brain. To investigate the effects of elevated glutamate levels on cGMP in the developing cortex we exposed mouse brain slices to glutamate or N‐methyl D ‐aspartate (NMDA). We find that at early postnatal stages when the endogenous production of cGMP is high, glutamate or NMDA exposure results in a significant lowering of the overall production of cGMP in the cortex, unlike the situation in the mature brain. However, this response pattern is complex with regional and cell‐type specific exceptions to the overall lowered cGMP production. These data emphasize that the response of the developing brain to physiological disturbances can be different from that of the mature brain, and must be considered in the context of the developmental events occurring at the time of disturbance. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009     

Inhibition of nicotinamide nucleotide transhydrogenase in rat liver submitochondrial particles by dicyclohexylcarbodi-imide and butanedione

Nicotinamide nucleotide transhydrogenase in rat liver submitochondrial particles is inhibited by treatment with NN'-dicyclohexylcarbodi-imide or butane-2,3-dione. Both inhibitions are pseudo-first-order with respect to enzyme activity. The reaction order with respect to inhibitor is close to unity for butanedione, but is significantly lower than unity for dicyclohexylcarbodi-imide.     

Use of leuprolide to treat endometriosis in a rhesus macaque.

Endometriosis was diagnosed in an aged dysmenorrheic rhesus monkey (Macaca mulatta) after biopsy of a 7 cm abdominal mass which could not be completely resected due to extensive adhesions. A 6-month course of treatment with leuprolide, a gonadotropin-releasing hormone agonist, resulted in cessation of menstrual cycles and marked clinical improvement. Dysmenorrhea and hypovolemic shock occurred 2 months after therapy was completed. Despite supportive treatment and resumption of leuprolide, the primate's clinical deterioration and abdominal mass enlargement necessitated euthanasia. To our knowledge, this is the first report of a case of endometriosis in a rhesus macaque treated with a gonadotropin-releasing hormone agonist. Although prolonged leuprolide therapy was clinically effective, its cost and the difficulty in early diagnosis of endometriosis may limit its use in nonhuman primate medicine.     

Is there Ca2+(Sr2+)-3-hydroxybutyrate symport in rat-liver mitochondria? A reappraisal

The observation in this laboratory that respiration and Sr2+ import were stimulated by the addition of 3-hydroxybutyrate to suspensions of N-ethylmaleimide-treated mitochondria respiring in state 6, after the addition of Sr2+, in a sucrose medium containing choline as substrate, led to the proposal by Moyle and Mitchell [(1977) FEBS Lett. 84, 135-140] that there is a Ca2+(Sr2+)-3-hydroxybutyrate symporter in rat liver mitochondria. However, experiments described in the present paper support a different interpretation. Under the conditions of the experiments by Moyle and Mitchell, the rate of respiration and the poise of Sr2+ accumulation are mainly limited, not by delta mu H+, but by lack of respiratory substrate. Even though N-ethylmaleimide is a potent inhibitor of 3-hydroxybutyrate dehydrogenase, we have found that, somewhat surprisingly, under the special conditions of these experiments, sufficient 3-hydroxybutyrate dehydrogenase activity remains available to account for the 3-hydroxybutyrate-dependent respiratory stimulation and Sr2+ import.     

Functional,Non-Clonal IgMa-Restricted B Cell Receptor Interactions with the HIV-1 Envelope gp41 Membrane Proximal External Region

The membrane proximal external region (MPER) of HIV-1 gp41 has several features that make it an attractive antibody-based vaccine target, but eliciting an effective gp41 MPER-specific protective antibody response remains elusive. One fundamental issue is whether the failure to make gp41 MPER-specific broadly neutralizing antibodies like 2F5 and 4E10 is due to structural constraints with the gp41 MPER, or alternatively, if gp41 MPER epitope-specific B cells are lost to immunological tolerance. An equally important question is how B cells interact with, and respond to, the gp41 MPER epitope, including whether they engage this epitope in a non-canonical manner i.e., by non-paratopic recognition via B cell receptors (BCR). To begin understanding how B cells engage the gp41 MPER, we characterized B cell-gp41 MPER interactions in BALB/c and C57BL/6 mice. Surprisingly, we found that a significant (∼7%) fraction of splenic B cells from BALB/c, but not C57BL/6 mice, bound the gp41 MPER via their BCRs. This strain-specific binding was concentrated in IgM^hi subsets, including marginal zone and peritoneal B1 B cells, and correlated with enriched fractions (∼15%) of gp41 MPER-specific IgM secreted by in vitro-activated splenic B cells. Analysis of Igh^a (BALB/c) and Igh^b (C57BL/6) congenic mice demonstrated that gp41 MPER binding was controlled by determinants of the Igh^a locus. Mapping of MPER gp41 interactions with IgM^a identified MPER residues distinct from those to which mAb 2F5 binds and demonstrated the requirement of Fc C_H regions. Importantly, gp41 MPER ligation produced detectable BCR-proximal signaling events, suggesting that interactions between gp41 MPER and IgM^a determinants may elicit partial B cell activation. These data suggest that low avidity, non-paratopic interactions between the gp41 MPER and membrane Ig on naïve B cells may interfere with or divert bnAb responses.     

Predation drives morphological convergence in the Gambusia panuco species group among lotic and lentic habitats

Fish morphology is often constrained by a trade‐off between optimizing steady vs. unsteady swimming performance due to opposing effects of caudal peduncle size. Lotic environments tend to select for steady swimming performance, leading to smaller caudal peduncles, whereas predators tend to select for unsteady swimming performance, leading to larger caudal peduncles. However, it is unclear which aspect of performance should be optimized across heterogeneous flow and predation environments and how this heterogeneity may affect parallel phenotypic evolution. We investigated this question among four Gambusia species in north‐eastern Mexico, specifically the riverine G. panuco, the spring endemics G. alvarezi and G. hurtadoi, and a fourth species, G. marshi, found in a variety of habitats with varying predation pressure in the Cuatro Ciénegas Basin and Río Salado de Nadadores. We employed a geometric morphometric analysis to examine how body shapes of both male and female fish differ among species and habitats and with piscivore presence. We found that high‐predation and low‐predation species diverged morphologically, with G. marshi exhibiting a variable, intermediate body shape. Within G. marshi, body morphology converged in high‐predation environments regardless of flow velocity, and fish from high‐predation sites had larger relative caudal peduncle areas. However, we found that G. marshi from low‐predation environments diverged in morphology between sub‐basins of Cuatro Ciénegas, indicating other differences among these basins that merit further study. Our results suggest that a morphological trade‐off promotes parallel evolution of body shape in fishes colonizing high‐predation environments and that changing predation pressure can strongly impact morphological evolution in these species.