Differential effects of mercurial compounds on excitable tissues.

Sarcoplasmic reticulum (SR), Ca2+ plus Mg2+-ATPase, and Ca2+-ionophore were obtained from white rabbit skeletal muscles. Methylmercury inhibited the Ca2+ plus Mg2+-ATPase and Ca2+-transport but had no effect on the Ca2+-ionophore. Mercuric chloride inhibited all three functions (i.e., ATPase, transport and ionophoric activity). The mechanism of HgCl2 inhibition of the Ca2+-ionophore was by competition with Ca2+ for Ca2+-ionophoric site whereas its inhibition of the enzyme and Ca2+-transport was due to the blockage of essential sulfhydryl (--SH) groups. Ca2+ plus Mg2+-ATPase and Ca2+-transport were more sensitive to methylmercury than to HgCl2. Acetylcholine receptor (AChR) was obtained for the electric organ of T. californica. Methylmercury inhibited the ACh binding to AChR WITH Ki = 5.7 - 10(-6) M. This effect was not due to mercuric ion alone since mercuric chloride up to 10(-4) M did not affect ACh binding to AChR. It is concluded that: the Ca2+ plus Mg2+-ATPase and Ca2+-transport contain --SH groups essential for their activity, and that the two functions are tightly coupled; the Ca2+-ionophore contains no --SH groups essential for its activity; CH3HgCl inhibition of Ca2+ plus Mg2+-ATPase and Ca2+-transport is partly due to its reactivity with --SH groups in hydrophobic environment; the Ca2+-transport is inhibited by HgCl2 through two processes, one which is the blockage of --SH groups and another which is the inhibition of the Ca2+-ionophoric site; and the inhibition of ACh binding to AChR is due to the blockage of --SH groups in hydrophobic environment, which is inaccessible to Hg2+. Our data present for the first time a molecular basis for the myopathy associated with mercurial compounds toxicity.     

Activity of phosphorylase in Solanum tuberosum during low temperature storage

Changes in the activity of phosphorylase were measured during storage of potatoes at + 2° when the sugar content rises rapidly and subsequently at + 10° when the accumulated sugar is converted mainly to starch. The observed changes were relatively small and could not be related to any of the components of the phosphorylase system, which was shown to be complex.     

Biotransformation of pregnenolone - 7alpha-3H, progesterone - 7alpha-3H and dehydroepiandrosterone - 7alpha-3H by porcine fetal and maternal adrenal homogenate preparations.

The biotransformation of pregnenolone-7alpha-3H and of progesterone-7alpha-3H by porcine fetal and maternal adrenal homogenates at 56 and 112 days of pregnancy and of dehydroepiandrosterone-7alpha-3H by fetal adrenal homogenates has been investigated in vitro. Both pregnenolone-7alpha-3H and progesterone-7alpha-3H were metabolized extensively by maternal adrenal preparations, the principal radioactive metabolites isolated being cortisol, corticosterone, 11-deoxycortisol, deoxycorticosterone, 11beta-hydroxyprogesterone and androstenedione. In addition, 17alpha-hydroxyprogesterone, 20alpha-dihydroprogesterone and cortisone were formed from both substrates and 17alpha-hydroxypregnenolone and progesterone were formed from pregnenolone. Although essentially the same radioactive metabolites were isolated after incubation of fetal adrenal glands with pregnenolone-7alpha-3H or progesterone-7alpha-3H, a greater proportion of the radioactivity was associated with corticosteroids at 112 days of pregnancy than at 56 days. 11beta-Hydroxyandrostenedione and androstenedione were isolated and identified together with an unknown polar metabolite, after incubation of fetal adrenal tissue with dehydroepiandrosterone-7alpha-3H. These results are discussed in relation to feto-placental steroid biosynthesis and metabolism and the role of the fetal adrenal in the initiation of parturition in the pig.     

Testing the precision and sensitivity of density estimates obtained with a camera‐trap method revealed limitations and opportunities

The use of camera traps in ecology helps affordably address questions about the distribution and density of cryptic and mobile species. The random encounter model (REM) is a camera‐trap method that has been developed to estimate population densities using unmarked individuals. However, few studies have evaluated its reliability in the field, especially considering that this method relies on parameters obtained from collared animals (i.e., average speed, in km/h), which can be difficult to acquire at low cost and effort. Our objectives were to (1) assess the reliability of this camera‐trap method and (2) evaluate the influence of parameters coming from different populations on density estimates. We estimated a reference density of black bears (Ursus americanus) in Forillon National Park (Québec, Canada) using a spatial capture–recapture estimator based on hair‐snag stations. We calculated average speed using telemetry data acquired from four different bear populations located outside our study area and estimated densities using the REM. The reference density, determined with a Bayesian spatial capture–recapture model, was 2.87 individuals/10km² [95% CI: 2.41–3.45], which was slightly lower (although not significatively different) than the different densities estimated using REM (ranging from 4.06–5.38 bears/10km² depending on the average speed value used). Average speed values obtained from different populations had minor impacts on REM estimates when the difference in average speed between populations was low. Bias in speed values for slow‐moving species had more influence on REM density estimates than for fast‐moving species. We pointed out that a potential overestimation of density occurs when average speed is underestimated, that is, using GPS telemetry locations with large fix‐rate intervals. Our study suggests that REM could be an affordable alternative to conventional spatial capture–recapture, but highlights the need for further research to control for potential bias associated with speed values determined using GPS telemetry data.     

Wind-sensitive interneurones in the spider CNS (Cupiennius salei ): directional information processing of sensory inputs from trichobothria on the walking legs

Spiders can use air particle movements to localize moving prey. We studied the responses of 32 wind-sensitive interneurones in the hunting spider Cupiennius salei to prey stimuli. Stimulation with a tethered flying fly or with artificial air pulses activated plurisegmental interneurones that responded to changes in air movement velocity and were thus well suited to represent the highly fluctuating air stream typical of prey stimuli. In most interneurones (n = 18) the responses to the stimulation of different legs were not significantly different from each other. Different interneurones had different response characteristics and their latencies largely overlapped suggesting that there is parallel processing of the signals by populations of interneurones with different response characteristics. In two interneurones the number of spikes and the spiking pattern elicited by stimulation of each of the eight legs markedly differed depending on the leg stimulated. These neurones may play an important role in directional information processing. Stimulation of the adjacent legs from front to back or from back to front revealed two interneurones sensitive to the direction of successive stimulation of the legs. These neurones may be able to detect the motion of an air movement source in a preferred direction and thus act as nearfield motion detectors to localize a moving prey item. Accepted: 28 September 1996     

Individually mark–mass release–resight study elucidates effects of patch characteristics and distance on host patch location by an insect herbivore

1. How organisms locate their hosts is of fundamental importance in a variety of basic and applied ecological fields, including population dynamics, invasive species management and biological control. However, tracking movement of small organisms, such as insects, poses significant logistical challenges. 2. Mass‐release and individual–mark–recapture techniques were combined in an individually mark–mass release–resight (IMMRR) approach to track the movement of over 2000 adult insects in an economically important plant–herbivore system. Despite its widespread use for the biological control of the invasive thistle Carduus nutans, the host‐finding behaviour of the thistle head weevil Rhinocyllus conicus has not previously been studied. Insects were released at different distances from a mosaic of artificially created host patches with different areas and number of plants to assess the ecological determinants of patch finding. 3. The study was able to characterize the within‐season dispersal abilities and between‐patch movement patterns of R. conicus. Weevils found host plant patches over 900 m away. Large patches, with tall plants, situated close to the nearest release point had the highest first R. conicus resights. Patch area and plant density had no effect on the number of weevils resighted per plant; however, R. conicus individuals were more likely to disperse out of small patches and into large patches. 4. By understanding how R. conicus locates host patches of C. nutans, management activities for the control of this invasive thistle can be better informed. A deeper mechanistic understanding of host location will also improve prediction of coupled plant–herbivore spatial dynamics in general.