Indirect effects of metal contamination on energetics of yellow perch (Perca flavescens) resulting from food web simplification

1. Benthic invertebrate community composition and yellow perch (Perca flavescens) diet, growth and activity levels from lakes along a metal‐contamination gradient were used to assess the importance of a naturally diverse prey base for maintaining energy transfer to growing fish, and how this transfer is disrupted by metal contamination. 2. Zoobenthic communities had lower diversity in metal‐contaminated lakes, with a notable absence of large bodied invertebrate taxa. 3. The average mass of non‐zooplankton prey items was significantly greater for 2+ and 3+ perch from the reference lake, and increased significantly with age in all except the most contaminated lakes where prey choice was limited. 4. Benthivorous perch from all contaminated lakes exhibited slowed growth. Perch from one of the contaminated lakes exhibited faster growth during piscivory, indicating slowed growth only while benthivorous. 5. Estimates of fish activity, using the activity of the glycolytic enzyme Lactate dehydrogenase in perch white muscle tissue as a proxy, suggested that shifts in diet to larger prey (in reference and intermediately contaminated lakes) lowered activity costs, which may explain how diet shifts maintain growth efficiency as perch grow larger.     

Ultrastructural Observations on the Infection of Rat Liver by Plasmodium berghei Sporozoites In Vivo1

The invasion of liver parenchymal cells by sporozoites of Plasmodium berghei Vincke & Lips, 1948, was studied in vivo using transmission electron microscopy. Livers of Brown Norway rats were examined 30 and 60 min after intraportal injection of 15 million sporozoites each. Sporozoites found after incorporation into vacuoles in hepatocytes were often located near a bile canaliculus at the lateral cell surface, surrounded by hepatocyte lysosomal structures; however, degradation of sporozoites caused by lysosomal digestion inside hepatocytes was never observed. Due to the crescent shape of sporozoites, serial sections were necessary to demonstrate the actual process of invasion of the hepatocyte. The hepatocyte's plasmalemma appeared to invaginate due to the sporozoite's action, thereby creating a parasitophorous vacuole. It was suggested that the sporozoite actively penetrated the hepatocyte; however, no visible depletion of rhoptries and micronemes was observed.     

Endocrinology of the Amphibian Pineal

McCord and Allen (1917) found that extracts of mammalian pinealglands contain a potent contracting agent of larval amphibianmelanophores. Lerner and his co-workers determined the chemicalstructure of this principle and named it melatonin. This agentcontracts dermal melanophores at a concentration as low as 10^–10g/ml. Both intact and eyeless larval amphibians blanch whenplaced in the dark, and the melanophore contraction which causesthis lightening response is abolished by pinealectomy. The amphibianpineal contains photoreceptive elements similar to those foundin the vertebrate lateral eyes, and these elements are inhibitedby light but are stimulated in its absence. There is evidencefor the presence of both HIOMT and melatonin the amphibian pineal.It has been proposed that the body-blanching response resultsfrom a direct stimulation of the pineal under conditions ofdarkness leading to a release of melatonin into the generalcirculation which is then responsible for a direct contractingeffect on dermal melanophores. The cytophysiological effectsof melatonin mimic those that take place in the body-blanchingresponse. Since no other hormone or pharmacological agent duplicatesthis response, this is strong evidence that melatonin is a hormonethat normally regulates body blanching. Other evidence for thesupport of this hypothesis is presented. Cytological features of both normal and melatonin-induced lighteningindicate that the effects of melatonin are at the effector celllevel rather than at either the hypothalamus or the pituitary.An inhibition of MSH-release by melatonin is not involved. Melatoninplays a normal role in young larvae to regulate the lighteningresponse that takes place in darkness (the primary chromaticresponse). Neither melatonin nor the pineal play a role in thelater (secondary stage) adaptive background responses of amphibians.As McCord and Allen first noted, the pineal may contain othersubstances which may have other physiological roles in amphibiansas well as other vertebrates. These have been little studied.     

The Structure and Development of the Dorsal Bristle Complex of Oxytricha fallax and Stylonychia pustulata*

SYNOPSIS. Oxytricha fallax and Stylonychia pustulata possess 6 rows of dorsal bristle units. Each dorsal bristle unit consists of a pair of kinetosomes; the anterior kinetosome has a cilium and the posterior kinetosome a ciliary stub. The kinetosome pair, located at the bottom of a cortical pit surrounding the cilium and ciliary stub, is surrounded by an asymmetrical fibrillar mass. Future rows 1-4 are formed from 2 sets of primordia originating within mature dorsal rows 1-3. Rows 5 and 6 originate from the anterior regions of both right marginal cirral primordia. Old dorsal bristle units utilized in formation of primordia are presumably maintained in the new rows of the proter and opisthe; those outside the primordia are resorbed. The morphogenetic pattern of the Oxytrichidae is similar to those of the Urostylidae and Holostichidae, but quite different from that of the Euplotidae.     

DISTANCE METHODS: A REPLY TO FARRIS

Abstract— Farris (1985) claimed that my assertions about unbiasedness and consistency of estimates of a phylogeny obtained by least squares fitting are in error. The counterexample he constructed violates the assumptions of additivity and independence of distances which were clearly stated in my earlier paper. As such it is not a valid counterexample. It is argued, contrary to Farris's claims, that one need not avoid nonmetric distances, and that one should avoid negative branch lengths in estimates of phylogenies from distance data. Statistical tests of clockness, and, to a limited extent, of alternative phylogenies can be constructed, and these are demonstrated by example. A computer program to infer phylogenies from distance matrices has been in free distribution by me for several years; it seems as effective as the program recently announced by Farris. Information on phylogenies is present in distance data, as in other kinds of data, and statistical methods can be developed to extract it.     

Maintenance Respiration and Carbon Balance of Plants at Low Levels of Sodium Chloride Salinity

The daily course of carbon influx and efflux was measured inyoung plants of Phaseolus vulgaris, Xanthium strumarium, Zeamays, and Atriplex halimus, exposed to low levels of salinity(NaCl) and varying daytime light intensities. Maintenance respiration(R_M) was calculated. In Phaseolus, Xanthium, and Atriplex, R_Mrose with increasing salinity, approximately up to those levelsof salinity above which apparent signs of toxicity appear. Athigher levels of salinity R_M declined. There was no responseof R_M to salinity in Zea. At the levels of salinity tested,salinity did not affect the ratio of growth respiration to photosynthesis. At –5 x 10⁵ Pa of NaCl salinity, the increase in R_M inXanthium was calculated to account for 24% of the growth reductioncaused by salt. The remainder could be ascribed to reduced photosynthesis.The increase of R_M is considered to be indicative of an adaptivemechanism, not present in the very salt-sensitive Zea.     

Hemocyanins Relationships in Their Structure, Function and Assembly

Hemocyanins are high molecular weight oxygen-carrying proteinsthat occur in the molluscs and arthropods. The oxygen-bindingsite in these proteins is a pair of copper atoms bound directlyto ammo acid side chains. The biscopper sites of these proteinsbind single molecules of dioxygen or carbon monoxide. In arthropodsthere are two copper atoms per approximately 70 000 daltonsof protein. This corresponds to the molecular weight of theminimum polypeptide chain. In molluscs however there are twocopper atoms per 50,000 daltons of protein. This does not correspondto the minimum polypeptide chain although it does correspondto the minimal functional unit. The minimal polypeptide chainin molluscan hemocyanins is approximately 400,000 daltons andappears to be composed of eight or more 50 000 dalton unitslinked together like a string of pearls. In the molluscs, thenative hemocyanins found in the hemolymph generally occur asgiant cylindrical molecules 350 Å in diameter, 380 Ålong, with molecular weights of 9 000,000. These large moleculesare composed of approximately 20 polypeptide chains. In thehemolymph of the arthropods depending upon the species, hemocyaminsoccur as hexamers dodecamers 24-mers and 48-mers. The molecularweight of the 48-mers is about 3 600,000. The respiratory functionsof hemocyamns show a wide range of allosteric properties. Thelarge molecules commonly show cooperativity in oxygen binding.The number of interacting subunits is in some cases dependentupon external conditions of pH and ionic composition. The oxygenaffinity is usually sensitive to pH and to low molecular weightcofactors like chloride, calcium and magnesium ions. The intrinsicoxygen binding properties of an organism s hemocyanin and itsallosteric control by modulators allow organisms possessingthese giant molecules to adapt to their environmental conditions.     

Variation in the Competence of Tobacco Pith Cells for Cytokinin-Habituation in Culture

Pith parenchyma tissues of tobacco sometimes lose their exogenous requirement for a cell division factor such as the cytokinin, kinetin. This process, known as cytokinin habituation, appears to involve epigenetic changes since it is a heritable change in cell phenotype which is directed, regularly reversible, and leaves the cell totipotent. In this report, we show that pith cells in culture consist of at least two types of cytokinin-requiring cells. The first type habituates rapidly under inductive conditions. The second type continues to express the cytokinin-requiring phenotype for many cell generations in culture but retains the capacity for habituation. These findings suggest that pith cells differ in their competence to habituate and that different states of competence are inherited by individual cells.     

Gene regulation of shell banding in a land snail from Israel

The Israeli land snail, Xeropicta vestalis, offers a particularly clear example of gene regulation in relation to natural selection, in that within each population the appropriate phenotype is generated only at the correct part of the animals life cycle, and a contrasting phenotype develops when the forces of natural selection change. In the mountains of Jerusalem, where the winter is cold, the shells are dark. Westwards, towards the coastal plain where the winter is warmer, the shells gradually become paler. As dark shells absorb more radiation than pale ones, this clinal variation in morph frequencies can be explained in thermal terms. (Banded shells are also more cryptic than non-banded shells, so that in the mountains visual selection by predators may be an additional force which favours dark shells.) Xeropicta vestalis is an annual, semelparous species: the snails hatch in winter, become mature within one year, reproduce, and then die. In the coastal plain the snails are active throughout most of the year, and they have a long period in which to grow to reach adult size. In the mountains and hills, on the other hand, the snails are active for only a very short period. They spend most of their lives as small snails, in a state of aestivation. Xeropicta vestalis must be dark in mountains because when it finally awakens, it must very rapidly and hastily reach reproduction size. A dark shell, by speeding up temperature-dependent processes in this critical stage, assists the snail to mature rapidly. Shell darkness varies with age: in the mountains and hills the shells are moderately dark when they hatch, but become darker whilst growing in early winter. In the coastal plain also, the snails are moderately dark when they hatch; but here they become paler, whilst growing in winter and spring. In both cases, each snail is darker in the colder months and paler in the hot ones. A strategy of gene regulation of shell colour is thus favoured when the subsequent forces of the environment are very contrasting in their direction, very severe—yet also very predictable.