The evolution and ecology of multiple antipredator defences

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such “defence portfolios” that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.     

Genes expressed during sexual differentiation of Chlamydomonas reinhardtii

Four genes specifically expressed during gametogenesis of Chlamydomonas reinhardtii have been cloned and their expression patterns analyzed. mRNAs encoded by these gamete-specific genes (gas) were absent or present only at very low levels in vegetative cells and mature zygotes. In young zygotes 2 h after gamete fusion, the mRNAs of three gas genes still persisted. The gas mRNAs accumulated during gametic differentiation. The temporal patterns of accumulation of individual mRNAs differed; some started to increase early during gametogenesis, others accumulated in the late phase. The accumulation of one of the late mRNAs (gas28) was stricly light-dependent. To illustrate the utility of the genes cloned in the analysis of sexual differentiation in Chlamydomonas reinhardtii we show that in a gametogenesis-defective mutant, the expression of late genes is prevented while that of early genes is normal.     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

Skeletal troponin I as a marker of exercise-induced muscle damage

Sorichter, Stephan, Johannes Mair, Arnold Koller, WalterGebert, Daniel Rama, Charles Calzolari, Erika Artner-Dworzak, and BerndPuschendorf. Skeletal troponin I as a marker of exercise-inducedmuscle damage. J. Appl. Physiol.83(4): 1076-1082, 1997.The utility of skeletal troponin I (sTnI)as a plasma marker of skeletal muscle damage after exercise wascompared against creatine kinase (CK), myoglobin (Mb), and myosin heavychain (MHC) fragments. These markers were serially measured in normalphysical education teacher trainees after four different exerciseregimens: 20 min of level or downhill (16% decline) running(intensity: 70% maximal O₂uptake), high-force eccentric contractions (70 repetitions), orhigh-force isokinetic concentric contractions of the quadriceps group(40 repetitions). Eccentrically biased exercise (downhill running andeccentric contractions) promoted greater increases in all parameters.The highest plasma concentration were found after downhill running{median peaks: 309 U/l CK concentration ([CK])}, 466 µg/l Mb concentration([Mb]), 1,021 µU/l MHC concentration ([MHC]),and 27.3 µg/l sTnI concentration ([sTnI]). Level running produced a moderate response (median peaks: 178 U/l [CK],98 µg/l [Mb], 501 µU/l [MHC], and 6.6 µg/l [sTnI]), whereas the concentric contraction protocoldid not elicit significant changes in any of the markers assayed. sTnIincreased and peaked in parallel to CK and stayed elevated (>2.2µg/l) for at least 1-2 days after exercise. In contrast to MHC,sTnI is an initial, specific marker of exercise-induced muscle injury,which may be partly explained by their different intracellularcompartmentation with essentially no (MHC <0.1%) or a small solublepool (sTnI: median 3.4%).

     

Effects of surfactant proteins SP-B and SP-C on dynamic and static mechanics of immature lungs

Kobayashi, Tsutomu, Katsumi Tashiro, Ken Yamamoto, ShunichiNitta, Shigeo Ohmura, and Yasuhiro Suzuki. Effects of surfactant proteins SP-B and SP-C on dynamic and static mechanics of immature lungs. J. Appl. Physiol. 83(6):1849-1856, 1997.To investigate the effects of surfactantproteins B (SP-B) and C (SP-C) on lung mechanics, we compared tidal andstatic lung volumes of immature rabbits anesthetized with pentobarbitalsodium and given reconstituted test surfactants (RTS).With a series of RTS having various SP-B concentrations (0-0.7%)but a fixed SP-C concentration (1.4%), both the tidal volume with25-cmH₂O insufflation pressure and the static volume deflated to5-cmH₂O airway pressure increased, significantly correlating with the SP-B concentration: the former increased from 6.5 to 26.0 ml/kg (mean), and the latter increased from6.4 to 31.8 ml/kg. With another series of RTS having afixed SP-B concentration (0.7%) but various SP-C concentrations(0-1.4%), the tidal volume increased from 5.1 to 24.8 ml/kg,significantly correlating with the SP-C concentration, whereas thestatic volume increased from 3.4 to 32.0 ml/kg, the ceiling value, inthe presence of a minimal concentration of SP-C (0.18%). Inconclusion, certain doses of SP-B and SP-C were indispensable foroptimizing dynamic lung mechanics; the static mechanics, however,required significantly less SP-C.

     

Inhibitory effects of carcinogenic mycotoxins on deoxyribonucleic acid-dependent ribonucleic acid polymerase and ribonuclease H.

Fourteen mycotoxins were tested for inhibitory effects on ribonucleic acid polymerase of rat liver and Escherichia coli and nuclear ribonuclease H of rat liver and Tetrahymena pyriformis. These enzymes were strongly inhibited by (-)-luteoskyrin, (+)-rugulosin, patulin, and PR toxin.     

Water relation parameters of the CAM plant Kalanchoë daigremontiana in relation to diurnal malate oscillations

Summary In the CAM plant Kalanchoë daigremontiana, kept in an environmental rhythm of 12 h L: 12 h D in a growth chamber at 60% relative humidity and well watered in the root medium, decreasing water potentials and osmotic potentials of the leaves are correlated with malate accumulation in the dark. In the light increasing water and osmotic potentials ( _W and _S ) are associated with decreasing malate levels. Transpiratory H₂O loss is high in dark and low in light.In continuous light, the CAM rhythm rapidly disappears in the form of a highly damped endogenous oscillation. Malate levels, and water and osmotic potentials of the leaves remain correlated as described above. However, transpiration is very high as malate levels decrease and water and osmotic potentials increase.It can concluded, that water relation parameters like total water potential ( _W ) and osmotic potential ( _S ) change in close correlation with changes of malic acid levels. As an important osmotically active solute in CAM plants, malic acid appears to affect water relations independently of and in addition to transpiration. The question remains open, whether turgor ( _P ) is involved in CAM regulation in intact plants in a similar way as it determines malate fluxes in leaf slices.Abbreviations CAM Crassulacean Acid Metabolism - L Light - D Dark