Seasonal declines in reproductive success of the common tern Sterna hirundo: timing or parental quality?

Reproductive success declines over the course of the breeding season in many bird species. Two categories of hypothesis have been evoked to explain this decline. The “timing” hypothesis suggests that seasonal declines in breeding success are attributable to the date of laying. The “parental quality” hypothesis suggests that seasonal declines result from the fact that young, inexperienced, or low quality birds breed later in the season. To evaluate the relative importance of timing and parental quality, egg exchanges and removals were used to manipulate hatching dates of common terns Sterna hirundo. Indices of quality, attendance, provisioning rates, and reproductive success of birds in three experimental groups (delayed hatch pairs, advanced hatch pairs, and pairs induced to relay) were compared to those of date‐matched controls. Pairs that hatched chicks early raised more chicks than pairs hatching chicks late in the season, regardless of initial laying date. This suggests that hatching chicks early is advantageous in itself. Our results, however, also support the parental quality hypothesis. There was a significant negative relationship between natural laying date and fledging success, independent of hatching date. Differences in chick growth and survival suggest that higher quality adults may be able to compensate for the disadvantages of late hatching dates and achieve similar reproductive success to that of pairs hatching chicks early. We found that pairs hatching chicks late in the season were subject to more incidents of kleptoparasitism than those hatching chicks early. This may be a proximate factor contributing to seasonal declines in reproductive success for common terns, although such a mechanism would not be likely in non‐colonial species. Failure to control for egg quality may have biased the results of some prior egg exchange experiments. Additionally, altered cost of incubation may be an unavoidable confounding factor in studies designed to manipulate timing of breeding.     

Separation and properties of leaf aspartate aminotransferase and alanine aminotransferase isoenzymes operative in the C4 pathway of photosynthesis

Isoenzymes of aspartate and alanine aminotransferases believed to have a specific role in C₄-photosynthesis in Atriplex spongiosa leaves have been separated and their properties examined. The identity of isoenzymes separated by ammonium sulfate fractionation and DEAE-cellulose chromatography was established by comparing mobilities of these fractions on acrylamide gels with the bands in tissue and cell extracts. Consistent with earlier findings, both aspartate aminotransferase and alanine aminotransferase activities in leaves were separable into two major isoenzyme species. One of the two alanine aminotransferase isoenzymes lost all activity during chromatography on DEAE-cellulose but this was restored by incubating with pyridoxal phosphate. The Michaelis constants, maximum velocities, and pH optima for both the forward and reverse directions of the reactions catalysed by each isoenzyme were determined. The relationship between the physical and kinetic characteristics of these enzymes and their intracellular location and possible role in photosynthesis was considered.     

Effects of Burning and Grazing on a Coastal California Grassland

We tested the effects of fall burning and protection from livestock grazing as management to enhance native grasses on a coastal grassland in central California. Plants from the Mediterranean, introduced beginning in the late 1700s, have invaded and now dominate most of California's grasslands. Coastal grasslands are generally less degraded than those inland and have higher potential for restoration and conservation. Productivity of the experimental plots varied annually and declined over the course of the study because of rainfall patterns. Foliar cover of the native Danthonia californica (California oatgrass) increased more under grazing than grazing exclusion and did not respond to burning. Two other natives, Nassella pulchra (purple needlegrass) and Nassella lepida (foothill needlegrass), responded variably to treatments. The response of N. pulchra differed from that reported on more inland sites in California. Restoring these grasslands is complicated by differing responses of target species to protection from grazing and burning. The current practice of managing to enhance single species of native plants (e.g., N. pulchra) may be detrimental to other equally important native species.     

Acylation of monolysocardiolipin in rat heart.

Cardiolipin is a major mitochondrial membrane glycerophospholipid in the mammalian heart. In this study, the ability of the isolated intact rat heart to remodel cardiolipin and the mitochondrial enzyme activities that reacylate monolysocardiolipin to cardiolipin in vitro were characterized. Adult rat heart cardiolipin was found to contain primarily linoleic and oleic acids. Perfusion of the isolated intact rat heart in the Langendorff mode with various radioactive fatty acids, followed by analysis of radioactivity incorporated into cardiolipin and its immediate precursor phosphatidylglycerol, indicated that unsaturated fatty acids entered into cardiolipin mainly by deacylation followed by reacylation. The in vitro mitochondrial acylation of monolysocardiolipin to cardiolipin was coenzyme A-dependent with a pH optimum in the alkaline range. Significant activity was also present at physiological pH. With oleoyl-coenzyme A as substrate, the apparent K(m) for oleoyl-coenzyme A and monolysocardiolipin were 12.5 microm and 138.9 microm, respectively. With linoleoyl-coenzyme A as substrate, the apparent K(m) for linoleoyl-coenzyme A and monolysocardiolipin were 6.7 microm and 59.9 microm, respectively. Pre-incubation at 50 degrees C resulted in different profiles of enzyme inactivation for the two activities. Both activities were affected similarly by phospholipids, triacsin C, and various lipid binding proteins but were affected differently by various detergents and myristoyl-coenzyme A. [(3)H]cardiolipin was not formed from monolyso[(3)H]cardiolipin in the absence of acyl-coenzyme A. Monolysocardiolipin acyltransferase activities were observed in mitochondria prepared from various other rat tissues. In summary, the data suggest that the isolated intact rat heart has the ability to rapidly remodel cardiolipin and that rat heart mitochondria contain coenzyme A-dependent acyltransferase(s) for the acylation of monolysocardiolipin to cardiolipin. A simple and reproducible in vitro assay for the determination of acyl-coenzyme A- dependent monolysocardiolipin acyltransferase activity in mammalian tissues with exogenous monolysocardiolipin substrate is also presented.     

Cyclooxygenase expression is elevated in retinoic acid-differentiated U937 cells

Cyclooxygenase (COX) is the rate-limiting enzyme for the biosynthesis of prostaglandins in monocytes/macrophages. The COX-1 is constitutively expressed in most tissues and may be involved in cellular homeostasis, whereas the COX-2 is an inducible enzyme that may play an important role in inflammation and mitogenesis. When U937 monocytic cells were incubated with retinoic acid (RA) for 48 h, cell differentiation took place with concomitant increases in prostaglandin E₂ (PGE₂) production and COX activity. In this study, the mechanism of RA (all-trans- or 9-cis-RA)-induced enhancement of PGE₂ biosynthesis in U937 cells was examined. Treatment of cells with all-trans- or 9-cis-RA up to 48 h caused an increase in PGE₂ production in a time- and dose-dependent manner. Both RA isomers caused the enhancement of PGE₂ production and the up-regulation of COX-1 expression at the protein and mRNA levels. The increase in COX-1 mRNA was found to precede the increase in COX-1 protein expression. Interestingly, the COX-2 protein and COX-2 mRNA were not detected in U937 cells, and their levels remained undetectable during the entire course of RA treatment. We conclude that treatment of U937 cells by RA for 48 h caused the initiation of cell differentiation, which was found to be concomitant with a significant increase in PGE₂ production mediated via the up-regulation of COX-1 mRNA and protein expression.     

Regulation of cardiolipin biosynthesis by fatty acid transport protein-1 IN HEK 293 cells

Cardiolipin (CL) is a major phospholipid involved in energy metabolism mammalian mitochondria and fatty acid transport protein-1 (FATP-1) is a fatty acid transport protein that may regulate the intracellular level of fatty acyl-Coenzyme A's. Since fatty acids are required for oxidative phosphorylation via mitochondrial oxidation, we examined the effect of altering FATP-1 levels on CL biosynthesis. HEK-293 mock- and FATP-1 siRNA transfected cells or mock and FATP-1 expressing cells were incubated for 24 h with 0.1 mM oleic acid bound to albumin (1:1 molar ratio) then incubated for 24 h with 0.1 mM [1,3-³H]glycerol and radioactivity incorporated into CL determined. FATP-1 siRNA transfected cells exhibited reduced FATP-1 mRNA and increased incorporation of [1,3-³H]glycerol into CL (2-fold, p < 0.05) compared to controls indicating elevation in de novo CL biosynthesis. The reason for this was an increase in [1,3-³H]glycerol uptake and increase in activity and mRNA expression of the CL biosynthetic enzymes. In contrast, expression of FATP-1 resulted a reduction in incorporation of [1,3-³H]glycerol into CL (65%, p < 0.05) indicating reduced CL synthesis. [1,3-³H]Glycerol uptake was unaltered whereas activity of cytidine-5′-diphosphate-1,2-diacyl-sn-glycerol synthetase (CDS) and CDS-2 mRNA expression were reduced in FATP-1 expressing cells compared to control. In addition, in vitro CDS activity was reduced by exogenous addition of oleoyl-Coenzyme A. The data indicate that CL de novo biosynthesis may be regulated by FATP-1 through CDS-2 expression in HEK 293 cells.     

Development of a macrophyte-based index of biotic integrity for Minnesota lakes

Traditional approaches for managing aquatic resources have often failed to account for effects of anthropogenic disturbances on biota that are not directly reflected by chemical and physical proxies of environmental condition. The index of biotic integrity (IBI) is a potentially effective assessment method to integrate ecological, functional, and structural aspects of aquatic systems. A macrophyte-based IBI was developed for Minnesota lakes to assess the ability of aquatic plant communities to indicate environmental condition. The index was developed using quantitative point intercept vegetation surveys for 97 lakes that represent a range of limnological and watershed characteristics. We followed an approach similar to that used in Wisconsin to develop the aquatic macrophyte community index (AMCI). Regional adaptation of the AMCI required the identification of species representative of macrophyte communities in Minnesota. Metrics and scaling methods were also substantially modified to produce a more empirically robust index. Regression analyses indicated that IBI scores reflected statewide differences in lake trophic state (R² = 0.57, F = 130.3, df = 1, 95, p < 0.005), agricultural (R² = 0.51, F = 83.0, df = 1, 79, p < 0.005), urban (R² = 0.22, F = 23.0, df = 1, 79, p < 0.005), and forested land uses (R² = 0.51, F = 84.7, df = 1, 79, p < 0.005), and county population density (R² = 0.14, F = 16.6, df = 1, 95, p < 0.005). Variance partitioning analyses using multiple regression models indicated a unique response of the IBI to human-induced stress separate from a response to natural lake characteristics. The IBI was minimally affected by differences in sample point density as indicated by Monte Carlo analyses of reduced sampling effort. Our analysis indicates that a macrophyte IBI calibrated for Minnesota lakes could be useful for identifying differences in environmental condition attributed to human-induced stress gradients.