The influence of environmental factors on the abundance and recruitment of the sand crab Emerita analoga (Stimpson 1857): source-sink dynamics?

The sandcrab Emerita analoga is the dominant species inhabiting sandy beaches along the Pacific coast of the American continent. In our study, 10 sandy beaches were sampled seasonally from 2006 to 2011, including coastal planktonic sampling from 2006 to 2008. Two major population cores were detected, the first one in the northern part of the study area and the second in the area immediately to the south of the Itata River mouth. Zoeal stages were found along the entire coastal zone. Highest densities and recruitment were found during spring and summer of each year. PLS regression indicated that source-sink habitat proxies correlated positively with morphodynamic parameters; while beach slope and total organic matter were negatively correlated. These results agree with the source-sink hypothesis, finding higher densities of adults, recruits and cohort recurrence on open coast beaches with milder physical dynamics. Furthermore, a hypoxic event and a mega-earthquake/tsunami negatively affected recruitment at the inter-annual scale.

Geographical variation in the use of intertidal rocky shores by the lizard Microlophus atacamensis in relation to changes in terrestrial productivity along the Atacama Desert coast.

1. The movement of materials and organisms between ecosystems is a common process in nature. 2. In the present study we investigate the hypothesis that the movement of consumers between ecosystems depends not only on the differences in productivity between ecosystems and prey availability, but also on these animals' biological characteristics. 3. To address this hypothesis we investigated the changes in abundance, habitat utilization and diet of the lizard Microlophus atacamensis along its geographical range on the coast of the Atacama Desert. Within this range, intertidal rocky shore communities do not show important variations in their species composition and abundance, but terrestrial communities show a steep gradient of productivity associated with the increase in rainfall from north to south. 4. Our results show that the use of intertidal habitats and the consumption of intertidal prey by M. atacamensis change within its geographical range: in the North, the species uses intertidal areas and behaves as an herbivore consuming mostly algae, whereas in the South it expends most of the time in terrestrial habitats as a carnivore mainly of arthropods. 5. Our study gives new evidence for cross-ecosystem connections created by consumer movement between habitats of contrasting but variable productivity levels.

Temporal variation in the diversity and cover of sessile species in rocky intertidal communities affected by copper mine tailings in northern Chile.

Several coastal rocky shores in the northern Chile have been affected by the discharges of copper mine tailings. In spite of this, the temporal and spatial variation on the diversity and composition of their intertidal benthic communities has scarcely been studied. The objectives of the present study were to analyse and to compare quantitatively the temporal variation on the diversity, cover and composition of sessile species in rocky intertidal benthic communities of the northern Chilean coast, in relation to the presence of copper mine tailings. The results show that the drastic reduction on the sessile species diversity and the monopolization of the substrate exerted by the green algae Enteromorpha compressa, are common and permanent features of the intertidal rocky shores affected by copper mine tailings. Such spatial (between sites) and temporal (seasonal) variation of these changes has been associated with the relative concentrations of trace metals and inorganic particles of the mining wastes. Our results suggest that the mechanical effects of resuspended and settling tailings are a more likely cause.

Effect of neurotensin on glucose and insulin portal blood levels in hyperglycemic rats.

A new multiple sampling technique for obtaining blood from the portal vein has been used to investigate the effects of neurotensin on insulin and glucose portal blood levels in rats rendered hyperglycemic by a constant glucose infusion. The peptide has been first injected acutely (2 microgram/rat iv), and then constantly infused (0.5 microgram/min for 55 min). The preliminary results indicate that no effect of the acute injection could be observed, but hyperglycemia and hyperinsulinemia were induced by the constant infusion of the peptide. It is suggested that neurotensin may stimulate the release of insulin probably through a direct mechanism.

Studies on the dynamics and mechanism of glibenclamide-induced insulin secretion.

Sustained, 60-minute perfusion of glibenclamide (0.5, 1.5 and 10 mug/ml) elicits a one-phase insulin release profile, formed by a rapid secretion peak followed by a second peak with lower insulin levels than the former. Basal insulin secretion values are observed during the period comprised between 13 and 60 minutes of perfusion. Concurrent stimulation with glucose (100, 150, 200 and 300 mg%) plus glibenclamide (1 mug/ml) causes a marked rise in both phases of insulin secretion. The addition of glibenclamide does not modify the biphasic secretion pattern caused by maximal glucose concentration (400 mg%). The maximal values of both phases of secretion in the dose-response curve elicited by different glucose concentrations shift to the left when glibenclamide is added to the perfusate. The increase in insulin secretion caused by glibenclamide is not inhibited by puromycin. Both theophylline and phentolamine modify and increase the glibenclamide-induced insulin release pattern. Propranolol and imidazole inhibit glibenclamide-induced insulin release. Our results suggest that: 1. Glibenclamide increases beta cell sensitivity to glucose stimulation. 2. Glibenclamide and glucose induce secretion of insulin originating in the same compartment. 3. Modification of alpha and beta adrenergic receptors may modify glibodulate the beta cell response to glibenclamide.

Evidence for a hypophyseal factor that stimulates insulin secretion by the pancreas (insulotrophine?)

The continuous infusion of glucose (1 mg/kg/min) via the carotid artery in anesthetized dogs produced a biphasic pattern of insulin secretion. The first peak reached a maximum 3 min after glucose infusion and decreased to basal level at 7 min. As long as glucose infusion persisted a slow and maintained increase in insulin level in the pancreatico-duodenal vein was observed. The same amount of glucose infused in to the carotid arteries of hypophysectomized dogs, failed to induce any change in plasma insulin level. Plasma sample obtained from the jugular vein of dogs receiving glucose via the carotid arteries were infused into a second dog via the pancreatico-duodenal artery. One minute after the onset of infusion a rise in insulin was observed in the pancreatico-duodenal vein. The stimulating effect was not due to the high blood glucose level present in the jugular vein of dogs undergoing the cephalic glucose infusion. Infusion through the pancreatico-duodenal artery of a glucose solution at a concentration equal to the highest blood glucose level observed in the jugular vein did not evoke insulin secretion. Plasma samples obtained from the jugular vein of dogs receiving saline via the carotid arteries did not evoke insulin secretion when receiving into the pancreatico-duodenal arteries of dogs. Pancreatic infusion of plasma obtained from the jugular vein of hypophysectomized dogs infused glucose through the carotid arteries did not evoke any pancreatic response. These findings are demonstrative of the presence of a hypophyseal humoral insulin stimulating factor in the jugular vein of dogs receiving a cephalic glucose load.

Effect of cephalic glucose infusion on insulin secretion.

The continuous infusion of glucose (1 mg/kg/min) via the carotid artery in anesthetized dogs produces a biphasic pattern of insulin secretion. The first peak reaches a maximum 3 min after glucose infusion and drops to basal level at 7 min. As long as the glucose infusion persists a slow and mantained increase in insulin level in the pancreaticoduodenal vein can be observed. The same amount of glucose infused in the general circulation via the jugular vein provoked a different pattern of insulin secretion. Cerebral glucose infusion to vagotomized dogs also produced a two phase response to insulin secretion, but the levels reached in the first phase were lower that those observed in the normal dogs. The infusion of glucose, via the jugular vein, in vagotomized dogs, failed to induce any change in plasma insulin levels. Our data suggest that a glucose load to the brain induces pancreatic insulin secretion mediated partially by the vagus nerves. These results are also compatible with the hypothesis that a humoral factor could be involved in the pancreatic response.