Thermoregulatory responses of dystrophic hamsters to changes in ambient temperatures

The ability of dystrophic hamsters to maintain their body temperature despite abnormal muscle and brown adipose tissue, two organs involved in thermoregulation, was evaluated. Dystrophic hamsters (CHF 146) between the ages of 30 and 160 days kept at 21 degrees C had core (rectal) temperatures (TR) that were 0.5-1.5 degrees C lower than Golden Syrian controls. The reduced core temperatures of dystrophic hamsters were unlikely the result of an incapacity to generate heat since the dystrophic hamsters were able to maintain their TRs during 3 h of acute cold stress (4 degrees C) and to adapt to prolonged cold exposure. However, TRs of cold-acclimated dystrophic hamsters were still 1 degree C below TRs of cold-acclimated control animals. By contrast, increasing the ambient temperature raised TRs of both normal and dystrophic hamsters. When kept at 32 degrees C overnight, the TRs of dystrophic hamsters remained significantly below those of control animals. When heat-exposed dystrophic hamsters were returned to 21 degrees C, their TRs returned to values significantly lower than those of control hamsters. Thus, dystrophic hamsters showed a capacity to thermoregulate, like control hamsters, but appeared to do so at a lower temperature. The reduced core temperatures of dystrophic hamsters kept at 21 degrees C cannot be explained by a reduction in metabolic activity since newborns and 30- and 140-day-old dystrophic hamsters had rates of oxygen consumption (VO2) and carbon dioxide production (VCO2) that were similar to those of controls. These results suggest that the thermoregulatory set point may be altered in dystrophic hamsters.     

Species distribution profiles of the neotropical orchids Masdevallia and Dracula (Pleurothallidinae,Orchidaceae); implications for conservation

The orchid genera Masdevallia and Dracula bear very strange and bizarre flowers. They are, however, very popular with plant enthusiasts and there is a fair amount of commercial trade in these genera. The genera belong to a sub-tribe of the orchids, the Pleurothallidinae, which otherwise mostly have small and insignificant flowers. The majority of the species of Masdevallia and Dracula have been reported from single localities and approximately two thirds of all species are found at three or fewer sites. Most genera in the sub-tribe have similar distribution patterns. Using published deforestation rates and species distribution profiles we calculate that 402 of the total 3405 pleurothallid species may have been driven to extinction by random deforestation events. It is possible that as many as 46 Masdevallia species and 14 Dracula species have already been lost and that annual extinction rates for the two genera are 1 and 0.3 species per year respectively. It has been suggested that the two genera should be protected, by listing them in CITES Appendix I. It is unlikely that embargoes on trade would change extinction rates caused by forest conversion. Such embargoes might actually hamper ex situ conservation efforts.     

Bilateral symmetry and sexual selection: a meta-analysis

A considerable body of primary research has accumulated over the last 10 yr testing the relationship between developmental instability in the form of fluctuating asymmetry and performance of individuals in mating success itself or sexual attractiveness. This research comprises 146 samples from 65 studies of 42 species of four major taxa. We present the results of a meta-analysis of these studies, which demonstrates that there is indeed an overall significant, moderate negative relationship: for studies, the overall mean Pearson's r or effect size = -.42, P <.0005; for species, the overall mean r = -.34, .01 < P < .025. Based on calculated fail-safe numbers, the effect-size estimates are highly robust against any publication or reporting bias that may exist. There is considerable evidence that the magnitude of the negative correlation between fluctuating asymmetry and success related to sexual selection is greater for males than for females, when a secondary sexual trait rather than an ordinary trait is studied, with experimentation compared with observation, and for traits not involved with mobility compared with traits affecting mobility. There is also limited evidence that higher taxa may differ in effect size and that intensity of sexual selection negatively correlates with effect size.     

Stretch activation and nonlinear elasticity of muscle cross-bridges.

When active insect fibrillar flight muscle is stretched, its ATPase rate increases and it develops "negative viscosity," which allows it to perform oscillatory work. We use a six-state model for the cross-bridge cycle to show that such "stretch activation" may arise naturally as a nonlinear property of a cross-bridge interacting with a single attachment site on a thin filament. Attachment is treated as a thermally activated process in which elastic energy must be supplied to stretch or compress the cross-bridge spring. We find that stretch activation occurs at filament displacements where, before the power stroke, the spring is initially in compression rather than in tension. In that case, pulling the filaments relieves the initial compression and reduces the elastic energy required for attachment. The result is that the attachment rate is enhanced by stretching. The model also displays the "delayed tension" effect observed in length-step experiments. When the muscle is stretched suddenly, the power stroke responds very quickly, but there is a time lag before dissociation at the end of the cycle catches up with the increased attachment rate. This lag is responsible for the delayed tension and hence also for the negative viscosity.     

MECHANISMS OF FEMALE CHOICE IN RED JUNGLE FOWL

We examined mate preference behavior in red jungle fowl, Gallus gallus, to determine if the mechanism of mate preference used by females was relative or absolute. Under a relative model, females compare males and prefer the one with the most exaggerated form of secondary sex character, regardless of where the proffered males lie along the population distribution of the trait. Under an absolute or threshold model, females have a threshold for the character, above which they will exert a preference and below which they will not. Female red jungle fowl preferred roosters with longer combs and redder irises, but this preference was exerted only when hens mated quickly; females mating slowly mated at random. The threshold model was supported in two ways: i) chosen males from the fast-mating group had larger combs than chosen males in the slow-mating group; ii) when the same female was presented with two pairs of males in two different trials, one large-combed pair and one small-combed pair, hens mated significantly more slowly, and often refused to mate, when only short-combed roosters were available. Hens thus alter their behavior depending on the males they see, and they may not exert a preference at all if both males fall below the threshold. Further corroborating evidence comes from a set of mate choice trials using underdeveloped roosters, in which males had small combs and females mated slowly or did not mate. The method of choice used by females could affect the speed with which correlations develop between the genes for male traits and genes for female preferences. Sexual selection for good genes may be more consistent with an absolute than a relative method of female choice.     

Truncation of thermal tolerance niches among Australian plants

Aim

Despite recognition that realized distributions inherently underestimate species' physiological tolerances, we are yet to identify the extent of these differences within diverse taxonomic groups. The degree to which species could tolerate environmental conditions outside their observed distributions may have a significant impact on the perceived extinction risk in ecological models. More information on this potential error is required to improve our confidence in management strategies.

Location

Australia.

Time Period

1983–2012.

Major Taxa Studied

Plants.

Methods

To quantify the scale and spatial patterns of this disparity, we estimated the existing tolerance to thermal extremes of 7,124 Australian plants, more than one‐third of the native continental flora, using data from cultivated records at 128 botanical gardens and nurseries. Hierarchical Bayesian beta regression was used to assess whether factors such as realized niches, traits or phylogeny could predict the incidence or magnitude of niche truncation (underestimation of thermal tolerances), while controlling for sources of collection bias.

Results

Approximately half of the cultivated species analysed could tolerate temperature extremes beyond those experienced in their native range. Niche truncation was predictable from the breadth and extremes of their realized niches and by traits such as plant growth form. Phylogenetic relationships with niche truncation were weak and appeared more suited to predicting thermal tolerances directly.

Main conclusions

This study highlights a widespread disparity between realized and potential thermal limits that may have significant implications for species' capacity to persist in situ with a changing climate. Identifying whether thermal niche truncation is the result of biotic interactions, dispersal constraints or other environmental factors could provide significant insight into community assembly at macroecological scales. Estimating niche truncation may help to explain why certain ecological communities are more resilient to change and may potentially improve the reliability of model projections under climate change.     

The relationship between codon boundaries and multiple reading-frame preferences: coding organization of bacterial insertion sequences

Theoretical considerations have shown that the five possible overlapping reading-frame configurations differ significantly in their coding flexibility and thus in their information content (Siegel and Fitch 1980; Smith and Waterman 1980). Contrary to expectation, the overlapping frame configuration allowing the greatest coding flexibility is rarely seen, whereas one of the most constraining is common. We point out here that this overlapping reading-frame paradox and an observed but unexplained preference in coding regions for a pyrimidine-purine at codon boundaries (Shepherd 1981; Jones and Kafatos 1982; Smith et al. 1983) are intimately linked. The codon boundary preference, which may be related to translation efficiency or accuracy, places constraints on the evolution of overlapping coding regions. These considerations may help identify actual coding regions in DNA sequences. We have analyzed five sequenced (enteric) bacterial insertion sequences for codon boundary incidences and reading-frame configurations and find that they are consistent with these proposed constraints.      

Lateral cerebral ventricle and preoptic-anterior hypothalamic area infusion and perfusion of beta-endorphin and ACTH to unrestrained rats: core and surface temperature responses

Both beta-endorphin and ACTH have been found in high concentrations within the hypothalami of mammals and each neuropeptide has been proposed to play a physiological role in regulating body temperature. In an attempt to determine how these peptides may alter thermoregulation, small, microgram concentrations of beta-endorphin and ACTH were injected either into lateral cerebral ventricle (ICV) or directly into the preoptic-anterior hypothalamic area (POAH) or perfused into the POAH of unrestrained rats. Core (rectal) and surface (tail) temperatures were recorded before and after ICV and POAH injection of 1 microgram of beta-endorphin or ACTH or perfusion (10 ng/microL) of either neuropeptide. POAH perfusion of naloxone HCl following the neuropeptide perfusion was tested to determine the specificity of the temperature responses. Regardless of the route of central administration, beta-endorphin, in the concentrations used, consistently evoked a hyperthermic core temperature response, that could be antagonized by naloxone. Increased core temperatures may, in part, have been due to peripheral vasoconstriction, as suggested by the decreases seen in tail temperature. The same concentrations of ACTH failed to show any prominent core temperature changes. Results suggest that beta-endorphin is a more potent modulator than ACTH in altering core temperatures of unrestrained rats. Whether beta-endorphin and ACTH act physiologically in an antagonistic manner to maintain a constant body temperature remains to be proven.     

Factors influencing the release of proteins by cultured schwann cells

Cultured rat schwann cells grown in association with sensory neurons when labeled with [(3)H]leucinem, [(3)H]glucosamine, or [(35)S]methionine release labeled polypeptides into the culture medium. Analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the culture medium reveals a reproducible pattern of more than 20 polypeptides with molecular weights ranging from 15,000 to more than 250,000. Five major polypeptides (apparent molecular weights 225,000, 210,000, 90,000, 66,000, 50,000, and 40,000) account for approximately 40 percent of the leucine or methionine radioactivity in medium polypeptide. Schwann cells grown in a serum-free defined medium, in which schwann cells do not relate normally to axons, release approximately four times less labeled medium polypeptides tha cultures grown in medium supplemented with serum and chick embryo extract. In addition, there is a qualitative difference in the pattern of medium polypeptides resolved by SDS-PAGE, so that a single polypeptide (mol wt 40,000) accounts for nearly all of the label in medium polypeptides. Switching of cultures grown in defined medium to supplemented medium for 2 d results in a fourfold increase in the amount of labeled polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides as resolved by SDS-PAGE. This change in the pattern of polypeptides release by schwann cells is accompanied by changes in the association between schwann cells and axons. An early step in the establishment of normal axon-schwann cell relations appears to be an inward migration of schwann cells into axonal bundles and spreading of schwann cells along neurites. These changes are evident within 48 h after medium shift. Our results thus suggest that the release of proteins by schwann cells may be important for the development of normal axonal ensheathment.     

Arginine vasotocin,an endogenous neuropeptide of Aplysia,suppresses the gill withdrawal reflex and reduces the evoked synaptic input to central gill motor neurons

The superfusion (15 min) of arginine vasotocin (AVT; 10^?9–10^?12M) over the abdominal ganglion of Aplysia californica suppressed the amplitude of the gill withdrawal reflex evoked by tactile stimulation of the siphon, increased the rate of gill reflex habituation, and decreased the evoked synaptic activity to central gill motor neurons. The suppressive effects of AVT on gill reflex behaviors were not due to toxic effects of the hormone since the effects were completely reversible following washout and 3 h rest. The results obtained with AVT were similar to those previously found using the mammalian neuropeptide arginine vasopressin. AVT may act by increasing the activity of central neurons which exert suppressive control over both gill reflex behaviors and evoked activity to central gill motor neurons.