Primary site and initial products of ammonium assimilation in the symbiotic sea anemone Anemonia viridis

Invertebrates containing endosymbiotic dinoflagellate algae (zooxanthellae) retain excretory nitrogen, and many are able to take up ammonium from the surrounding seawater. However, the site of assimilation and role of nitrogen recycling between symbiont and host remains unclear. In the present study, ammonium uptake by the symbiotic sea anemone Anemonia viridis (Forskål) was examined by following the pathway of assimilation using ¹⁵N-enriched ammonium. Since zooxanthellae became enriched with ¹⁵N from ammonium at up to 17 times the rate of the host, they appear to be the primary site of assimilation. In the light, the rate of zooxanthellae enrichment at 20?M was twice that at 10?M, whereas the rate of host enrichment was not significantly affected by ammonium concentration. When anemones were incubated with [¹⁵N]ammonium in the dark, after 12?h without light the rate of enrichment was lowered in both zooxanthellae and host. However, while the enrichment of the host was significantly reduced when the light level was lowered from 300 to 150?μmol photons m^?2?s^?1, zooxanthellae enrichment was unchanged. Low molecular weight material from the zooxanthellae became enriched at 20 times the rate of that from the host, and enrichment was detected in the amino acids glutamate, glutamine, aspartate, alanine, glycine, phenylalanine, threonine, valine, tyrosine, and leucine from zooxanthellae. In the zooxanthellae, amino acids accounted for 65% of the total enrichment of low molecular weight material. Of the amino acids detected in zooxanthellae, over 90% of the enrichment was accounted for by glutamate, glutamine and aspartate. The enrichment of the amide group of glutamine was greater than that of the amine group of glutamate or glutamine, consistent with the glutamine synthetase/glutamine 2-oxoglutarate amidotransferase cycle as the mechanism of ammonium assimilation. To examine the flux of ¹⁵N from zooxanthellae to host, anemones were pulse-labelled with [¹⁵N]ammonium and then transferred to an unlabelled chase. Over a 2?h period there was no evidence for a flux of nitrogen from zooxanthellae to host. However, during the chase period, the enrichment of low molecular weight material declined and that of high molecular weight material increased in both zooxanthellae and host, indicating that protein was synthesized using ¹⁵N from ammonium in both components of the symbiosis. Again by using a pulse-chase system, it was found that glutamate was metabolised most rapidly by zooxanthellae, followed by (in order of decreasing rate of turnover) aspartate, alanine, glycine and valine (no data are available for glutamine). Unlike these amino acids, nitrogen was transferred to the essential amino acids phenylalanine and threonine, increasing their enrichment during the chase period. While recycled nitrogen is clearly important to this symbiosis, the mechanism by which it is cycled remains to be resolved.     

Effects of Pollinator Loss on Endemic New Zealand Mistletoes (Loranthaceae)

Abstract: The endemic mistletoes Peraxilla colensoi and P. tetrapetala (Loranthaceae) have declined considerably in New Zealand since 1840, reputedly because of introduced herbivores but coincident with a major decline in native bird densities. We show that at two South Island sites ( Craigieburn and Ohau) there are too few bird pollinators visiting the flowers to allow full fruit set. We studied pollination rates in P. colensoi at Wakefield and P. tetrapetala at Craigieburn over four flowering seasons and P. tetrapetala in one season at Ohau. Supplemental hand pollination increased fruit production 1.25–5.3 times at Craigieburn and Ohau but not at Wakefield. Excluding birds by covering mistletoes with mesh bags decreased fruit set significantly at Wakefield but had little effect at Craigieburn and Ohau. Bellbirds ( Anthornis melanura ) and Tuis (   Prosthemadera novaeseelandiae ) visited flowers significantly more often at Wakefield than at Craigieburn. A lack of pollen tubes in the style, not self-incompatibility or resource shortage, caused the low fruit production in unmanipulated flowers at Craigieburn. Thus, at the two P. tetrapetala sites (Craigieburn and Ohau) fruit set was chronically pollen limited, whereas P. colensoi at Wakefield was not pollen-limited. Data from other Peraxilla sites also suggest pollination failure. Our study suggests that the conservation of Peraxilla species will require maintenance of native bird populations. Tuis and Bellbirds are important pollinators and dispersers of many other New Zealand plants, and the breakdown of such mutualistic relationships may have widespread consequences.     

Landscape assessment of side channel plugs and associated cumulative side channel attrition across a large river floodplain

Determining the influences of anthropogenic perturbations on side channel dynamics in large rivers is important from both assessment and monitoring perspectives because side channels provide critical habitat to numerous aquatic species. Side channel extents are decreasing in large rivers worldwide. Although riprap and other linear structures have been shown to reduce side channel extents in large rivers, we hypothesized that small “anthropogenic plugs” (flow obstructions such as dikes or berms) across side channels modify whole-river geomorphology via accelerating side channel senescence. To test this hypothesis, we conducted a geospatial assessment, comparing digitized side channel areas from aerial photographs taken during the 1950s and 2001 along 512 km of the Yellowstone River floodplain. We identified longitudinal patterns of side channel recruitment (created/enlarged side channels) and side channel attrition (destroyed/senesced side channels) across n?=?17 river sections within which channels were actively migrating. We related areal measures of recruitment and attrition to the density of anthropogenic side channel plugs across river sections. Consistent with our hypothesis, a positive spatial relationship existed between the density of anthropogenic plugs and side channel attrition, but no relationship existed between plug density and side channel recruitment. Our work highlights important linkages among side channel plugs and the persistence and restoration of side channels across floodplain landscapes. Specifically, management of small plugs represents a low-cost, high-benefit restoration opportunity to facilitate scouring flows in side channels to enable the persistence of these habitats over time.     

Correction to: Status and trends of circumpolar peregrine falcon and gyrfalcon populations

While collating contributions and comments from 36 researchers, the coordinating authors accidentally omitted Dr. Suzanne Carrière from the list of contributing co-authors. Dr. Carrière’s data are described in Tables 1 and 3, Figure 2 and several places in the narrative. The new author list is thus updated in this article.     

Surplus territory contenders in male red-winged blackbirds: where are the desperados?

Summary We tested whether payoff asymmetries could explain why floater red-winged blackbirds seldom escalate contests to acquire territories. We removed territorial male \ldowners\rd and allowed floater replacements to claim territories. We then released owners to see how three currencies of payoff asymmetries (replacement occupancy) owners' likelihood and speed of reclaiming their territories (owner success). Neither the duration of an owner's internment nor the amount of time that a floater replacement had held the territory affected owner success (Figs. 1 and 2). Owner success was also not affected by the number of neighbors that they had (Fig. 3). Finally, owner success was the same irrespective of whether or not he was the likely sire of offspring on the territory, or the size of his harem (Fig. 4). Although these results are consistent with the proposal that payoff asymmetries will be irrelevant in contests for valuable resources, they are inconsistent with the proposal's corollary that excluded individuals should become \lddesperados\rd and escalate or even fight to the death in contests for those resources. Expected payoffs for passive acquisition of territories in this species may be higher than from a more aggressive desperado strategy.Correspondence to: P.J. Weatherhead     

Prenatal diagnosis of trisomy for the distal two-thirds of the long arm of chromosome 14 (q21→qter)

A de novo case of ‘pure’ trisomy 14q21 → qter is described which was detected at amniocentesis following an abnormal ultrasound scan of a 25–year-old woman. This is apparently the largest distal 14q duplication reported in a case surviving beyond the first trimester. The infant apipeared to have an association of clinical abnormalities previously observed in distal 14q trisomy and proximal 14q trisomy/mosaic trisomy 14.     

A Multidisciplinary Study of Spatial and Temporal Scales Containing Information in Turbulent Chemical Plume Tracking

This report describes the results of a multidisciplinary study of turbulent chemical plume tracking of blue crabs and autonomous agents. The study consists of a coordinated investigation of animal behavior, fluid mechanics, strategy simulations, and chemical sensing. The objective is to provide a comprehensive understanding of chemical plume tracking in a single biological system and to prescribe strategies that are effective for autonomous agents. The consensus of the study is that spatial variation in the plume, measured by sampling at multiple locations simultaneously, yields information that is useful for plume tracking. Behavioral investigations reveal that blue crabs demonstrate the ability to detect the chemical plume and use lateral movements to avoid losing contact with the odor. Blue crabs move rapidly towards the source, strongly suggesting that temporal comparisons of odor properties are not employed during navigation. Analysis of the concentration fields reveals that a spatial correlation between spanwise-separated sensors indicates the relative direction of the plume centerline over short time periods provided the sensor spacing is scaled appropriately relative to the plume. Similarly, simulations of tracking strategies reveal an optimal separation for the sensors at a distance roughly equal to the plume width; both smaller and larger sensor spans degrade tracking performance. The simulations further reveal an optimal sensor size above which the fine details of the concentration distribution are obscured and below which there is insufficient contact with the odor to enable effective navigation. Finally, analysis of the chemical signal shows that the frequency dependent correlation function between two (or more) sensors indicates the relative position of the source.     

A survey of drinking water supplies in the Province of Ontario for dioxins and furans

A survey of drinking water supplies in the Province of Ontario was initiated in 1983 to determine the extent of their contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). This drinking water survey arose from concerns regarding the discovery of PCDDs and PCDFs in sport fish from western Lake Ontario in the early 1980's.A total of 49 water supplies throughout all Regions of Ontario have been examined to date. Water supplies in the vicinity of chemical industries and pulp and paper mills were sampled more frequently; as many as 20 times. Detection limits were in the low parts per quadrillion (ppq) range for all tetra- to octachlorinated PCDDs and PCDFs.As of February 1989, 4, 347 results were received for 399 raw and treated water samples. Only 37 positive results were reported, constituting less than 1 percent of the total number of results. The O₈CDD congener accounted for 36 of the 37 positive results. The 2,3,7,8- TCDD isomer was not detected in any sample.     

Effects of ozone on foliar leaching in Norway spruce (Picea abies L. Karst): confounding factors due to NOx production during ozone generation

Previous experiments with conifers fumigated with O(3), produced by air-operated electric discharge ozonators, have provided evidence that O(3) increases the leaching of NO(3)(-), NH(4)(+), K(+), Ca(2+), Mg(2+) and some other cations from needles, when the trees are treated with acid mist. This evidence has provided the foundation of the ozone-acid mist hypothesis of spruce decline. We report experiments with Norway spruce saplings fumigated with purified and unpurified O(3). The results show that the accumulation of NO(3)(-) in the needles arises from the rapid deposition of N(2)O(5) and HNO(3) formed from N(2) in the ozonator. An increase in removal of NH(4)(+), Na(+), Ca(2+), Mg(2+), Zn(2+) and Mn(2+) from the needles during soaking in H(2)SO(4), pH3, was also observed, which was related to the increase in NO(3)(-) but was independent of O(3) concentration. It is concluded that results of previous experiments cited in support of the ozone-acid mist hypothesis arose from effects which were at least partly caused by N(2)O(5) produced as a contaminant, and were incorrectly attributed to ozone. Other effects, such as growth stimulations, visible symptons, enhanced frost sensitivity, and infestation by pests or pathogens, which have been attributed to O(3) generated by electric discharge in air, should be interpreted with caution. Future experiments with ozone must eliminate this problem by either using O(2)-driven ozonators, or by purifying the output from air-driven ozonators using cold and/or water traps.