Re-structuring of marine communities exposed to environmental change: a global study on the interactive effects of species and functional richness

Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research.     

Reward-related behavioral paradigms for addiction research in the mouse: performance of common inbred strains

The mouse has emerged as a uniquely valuable species for studying the molecular and genetic basis of complex behaviors and modeling neuropsychiatric disease states. While valid and reliable preclinical assays for reward-related behaviors are critical to understanding addiction-related processes, and various behavioral procedures have been developed and characterized in rats and primates, there have been relatively few studies using operant-based addiction-relevant behavioral paradigms in the mouse. Here we describe the performance of the C57BL/6J inbred mouse strain on three major reward-related paradigms, and replicate the same procedures in two other commonly used inbred strains (DBA/2J, BALB/cJ). We examined Pavlovian-instrumental transfer (PIT) by measuring the ability of an auditory cue associated with food reward to promote an instrumental (lever press) response. In a separate experiment, we assessed the acquisition and extinction of a simple stimulus-reward instrumental behavior on a touch screen based task. Reinstatement of this behavior was then examined following either continuous exposure to cues (conditioned reinforcers, CRs) associated with reward, brief reward and CR exposure, or brief reward exposure followed by continuous CR exposure. The third paradigm examined sensitivity of an instrumental (lever press) response to devaluation of food reward (a probe for outcome insensitive, habitual behavior) by repeated pairing with malaise. Results showed that C57BL/6J mice displayed robust PIT, as well as clear extinction and reinstatement, but were insensitive to reinforcer devaluation. DBA/2J mice showed good PIT and (rewarded) reinstatement, but were slow to extinguish and did not show reinforcer devaluation or significant CR-reinstatement. BALB/cJ mice also displayed good PIT, extinction and reinstatement, and retained instrumental responding following devaluation, but, unlike the other strains, demonstrated reduced Pavlovian approach behavior (food magazine head entries). Overall, these assays provide robust paradigms for future studies using the mouse to elucidate the neural, molecular and genetic factors underpinning reward-related behaviors relevant to addiction research.     

Olfactory Predator Discrimination in Yellow‐Bellied Marmots

The mechanism underlying olfactory predator identification may be relatively experience‐independent, or it may rely on specific experience with predators. A mechanism by which prey might identify novel predators relies on the inevitable creation of sulfurous metabolites that are then excreted in the urine of carnivorous mammals. We tested whether free‐living, yellow‐bellied marmots (Marmota flaviventris) and mid‐sized herbivores that fall prey to a variety of carnivorous mammals could discriminate herbivore (elk—Cervus elephas) urine from predator (red fox—Vulpes vulpes, coyote—Canis latrans, mountain lion—Felis concolor, wolf—Canis lupus) urine, a novel herbivore (moose—Alces alces), and a distilled water control. We further asked how specific this assessment was by testing whether marmots responded differently to predators representing different levels of risk and to familiar vs. unfamiliar predators. We found that marmots responded more to urine from coyotes (a familiar predator on adults), mountain lions (a potentially unfamiliar predator that could kill adults) and wolves (a locally extinct predator that could kill adults) than to elk urine (a non‐predator). Red fox (a predator that poses a risk only to recently emerged marmot pups) urine elicited a less substantial (but not significantly so) response than coyote urine. Marmots can identify predators, even novel ones, using olfactory cues, suggesting that experience with a specific predator is not required to identify potential threats.     

The distribution of divergent mitochondrial DNA lineages of threespine stickleback (Gasterosteus aculeatus) in the northeastern Pacific Basin: post-glacial dispersal and lake accessibility

Aim This study furthers the documentation of the geographical distribution of two divergent (c. 3%) mitochondrial DNA clades in the threespine stickleback (Gasterosteus aculeatus) and tests the hypotheses that the northeastern Pacific distribution has been influenced by post‐glacial colonization and lake elevation and that clade identity is associated with certain morphological attributes such as reduction in body armour. Location Lakes and nearshore marine environments of the eastern Pacific Basin from southcentral Alaska to southeastern British Columbia, (BC) Canada. Methods Restriction enzyme analysis of polymerase chain reaction‐amplified mitochondrial DNA fragments (cytochrome b) from a total of 45 new populations combined with existing data for a further 45 populations. Lake elevation data were collected for 78 localities and tested for an association with mtDNA clade by contingency table analyses. Morphological data were collected on sticklebacks from eight samples representing four lake‐stream systems and tested for differentiation among populations with different mtDNA clade identities using analyses of variance. Results We extend the known distribution of the haplotypes diagnostic of the Trans‐North Pacific Clade (TNPC) southward to mid‐Vancouver Island and, for the first time, on mainland BC, in other island populations far from putative refugia, and in nearby anadromous populations. A morphological analysis indicated that the mainland population with the TNPC was not characterized by reduced spine or lateral plate (‘armour’) traits that characterize some putative relict populations on the Queen Charlotte Islands. We found a significant association between lake elevation and the presence of the TNPC; the TNPC was present more often in lakes located at or lower than 42 m than in higher elevation lakes. Main conclusions Our data support the hypothesis that post‐glacial colonization by TNPC‐bearing marine sticklebacks and aspects of lake ‘accessibility’ were important in determining the distribution of mtDNA clades in the eastern Pacific Ocean basin. More generally, our study demonstrates how processes acting both across immense geographic scales (e.g. pan‐Pacific dispersal) and local scales (lake accessibility contingent on timing and extent of isostatic rebound) may interact to explain biogeographical patterns.     

Contextual Information and Differential Responses to Alarm Whistles in California Ground Squirrels

In the field, we videotaped the reactions of squirrels to playbacks of 1, 3 and 5 whistle vocalizations at two sound intensities differing by 10 dB. The squirrels reacted by running to boulders or burrows and freezing. As time progressed following playbacks, freezing declined and squirrels resumed feeding, locomotion and grooming. With increasing numbers of whistles, squirrels were more likely to run and less likely to mount a boulder. With more high intensity whistles, squirrels froze quadrupedally more and bipedally less. Freezing postures did not vary as a function of the number of low-intensity whistles. Walking was suppressed least by 1 and 3 whistles at low intensity, and inhibited most by all high-intensity whistles as well as by the low-intensity 5-whistle playback. When the squirrel was on a boulder, quadrupedal freezing was more common than bipedal freezing. Off the boulder, the two freezing postures were equally likely. We propose that squirrels assessed risk from information encoded in the whistle(s) and contextual to it, and varied their reactions as a function of apparent risk.     

H3 lysine 9 methylation is maintained on a transcribed inverted repeat by combined action of SUVH6 and SUVH4 methyltransferases

Transcribed inverted repeats are potent triggers for RNA interference and RNA-directed DNA methylation in plants through the production of double-stranded RNA (dsRNA). For example, a transcribed inverted repeat of endogenous genes in Arabidopsis thaliana, PAI1-PAI4, guides methylation of itself as well as two unlinked duplicated PAI genes, PAI2 and PAI3. In previous work, we found that mutations in the SUVH4/KYP histone H3 lysine 9 (H3 K9) methyltransferase cause a loss of DNA methylation on PAI2 and PAI3, but not on the inverted repeat. Here we use chromatin immunoprecipitation analysis to show that the transcribed inverted repeat carries H3 K9 methylation, which is maintained even in an suvh4 mutant. PAI1-PAI4 H3 K9 methylation and DNA methylation are also maintained in an suvh6 mutant, which is defective for a gene closely related to SUVH4. However, both epigenetic modifications are reduced at this locus in an suvh4 suvh6 double mutant. In contrast, SUVH6 does not play a significant role in maintenance of H3 K9 or DNA methylation on PAI2, transposon sequences, or centromere repeat sequences. Thus, SUVH6 is preferentially active at a dsRNA source locus versus targets for RNA-directed chromatin modifications.     

AT1-receptor antagonism reverses the blood pressure elevation associated with diet-induced obesity

Previous studies in our laboratory demonstrated that rats exhibiting obesity in response to a moderately high-fat (MHF) diet developed hypertension associated with activation of the local and systemic renin-angiotensin system. In this study, we examined the effect of the angiotensin type 1 (AT(1))-receptor antagonist, losartan, on blood pressure in obesity-prone (OP) and obesity-resistant (OR) rats fed a MHF diet. Using telemetry monitoring, we characterized the evolution of blood pressure elevations during the development of obesity. Male Sprague-Dawley rats were implanted with telemetry transducers for chronic monitoring of blood pressure, and baseline measurements were obtained. Rats were then switched to the MHF diet (32% kcal as fat) and were segregated into OP and OR groups at week 5. At week 9 on the MHF diet, OP rats exhibited significantly greater 24-h mean arterial blood pressure compared with OR rats (OP: 105 +/- 4 mmHg, OR: 96 +/- 2 mmHg; P < 0.05). Elevations in blood pressure in OP rats were manifest as an increase in systolic pressure. Administration of losartan to all rats at week 9 resulted in a reduction in blood pressure; however, losartan had the greatest effect in OP rats (percent decrease in mean arterial pressure by losartan; OP: 19 +/- 4, OR: 10 +/- 2%; P < 0.05). These results demonstrate that elevations in blood pressure occur subsequent to established obesity in rats fed a high-fat diet. Moreover, these results demonstrate the ability of losartan to reverse the blood pressure increase from diet-induced obesity, supporting a primary role for the renin-angiotensin system in obesity-associated hypertension.     

Mapping of the functional microcirculation in vital organs using contrast-enhanced in vivo video microscopy

A functional microcirculation is vital to the survival of mammalian tissues. In vivo video microscopy is often used in animal models to assess microvascular function, providing real-time observation of blood flow in normal and diseased tissues. To extend the capabilities of in vivo video microscopy, we have developed a contrast-enhanced system with postprocessing video analysis tools that permit quantitative assessment of microvascular geometry and function in vital organs and tissues. FITC-labeled dextran (250 kDa) was injected intravenously into anesthetized mice to provide intravascular fluorescence contrast with darker red blood cell (RBC) motion. Digitized video images of microcirculation in a variety of internal organs (e.g., lung, liver, ovary, and kidney) were processed using computer-based motion correction to remove background respiratory and cardiac movement. Stabilized videos were analyzed to generate a series of functional images revealing microhemodynamic parameters, such as plasma perfusion, RBC perfusion, and RBC supply rate. Fluorescence contrast revealed characteristic microvascular arrangements within different organs, and images generated from video sequences of liver metastases showed a marked reduction in the proportion of tumor vessels that were functional. Analysis of processed video sequences showed large reductions in vessel volume, length, and branch-point density, with a near doubling in vessel segment length. This study demonstrates that postprocessing of fluorescence contrast video sequences of the microcirculation can provide quantitative images useful for studies in a wide range of model systems.     

AT2 receptors contribute to acute blood pressure-lowering and vasodilator effects of AT1 receptor antagonism in conscious normotensive but not hypertensive rats

The aims of this study were to determine the contribution of the AT2 receptor to the antihypertensive and regional vasodilatory effects of AT1 receptor blockade in adult spontaneously hypertensive rats (SHR), 2-kidney, 1-clip hypertensive (2K1C) rats, and sham-operated normotensive rats. Several studies have provided evidence to support the notion that the AT2 receptor may have opposing effects to those mediated by the AT1 receptor. We therefore tested the hypothesis that the depressor and vasodilator effects of acute AT1 receptor blockade are dependent on AT2 receptor activation. Heart rate, mean arterial pressure, and regional hemodynamics were measured over a 4-day protocol in rats that received the following treatments in randomized order: saline vehicle, the AT1 receptor antagonist candesartan (0.1 mg/kg iv bolus), the AT2 receptor antagonist PD-123319 (50 microg.kg(-1).min(-1)), or both antagonists. Intravenous candesartan reduced mean arterial pressure in all groups of rats, and this was accompanied by renal and mesenteric vasodilation. Neither saline nor PD-123319 significantly affected these variables. Concomitant PD-123319 administration partially reversed the depressor and mesenteric vasodilator effects of candesartan in sham-operated normotensive rats but not in SHR or 2K1C rats. These data indicate that the AT2 receptor contributes to the blood pressure-lowering and mesenteric vasodilator effects of AT1 receptor blockade in the acute setting in conscious normotensive but not hypertensive rats.