Historical and Ecological Factors in the Biogeography of Aposematic Neotropical Butterflies

SYNOPSIS. Quantitative analysis of low-level (mostly subspecific)geographic differentiation of aposematic color patterns in threegroups of forest butterflies (Heliconiini, Ithomiinae, and Troidini),in 1,550 half-degree quadrants throughout the Neotropics, indicatesfour principal species-endemicity regions, 44 principal subspecies-endemicitycenters, and 300 quadrants of subspecies hybridization. Theendemism centers are different in outline but nearly identicalin position for each of the three ecologically different groups.Basic data on present and past physical environments (climate,soils, geomorphology, and vegetation structures), when integratedinto maps, show 1) regions of favorable ecological conditionsfor forest organisms in the present, 2) regions of environmentalconformities and rapid transitions in the present, and 3) regionsof high probability for humid forest persistence during themajor landscape changes at the end of the last glacial period,13,000–20,000 yr ago. Species diversity (a local phenomenon)is readily related to favorable modern ecological conditionsand environmental microheterogeneity, promoted by unpredictablemild disturbance. Biogeographical patterns of evolution at thelevel of regional subspecies correlate very well with presumedpaleoecological conditions. The biogeographical data also supportan hypothesis of differentiation resulting from areas of rapidenvironmental change; most of the hybridization quadrants fallwithin transition zones. There is lower correlation betweencenters of endemism and zones of en vironmental conformity,but some individual cases of differentiation in the butterfliesmay be adequately explained by modern ecological factors. Speciespresently undergoing differentiation in isolated habitat islands(Amazonian savannas and high-altitude Andean forests and paramos)may offer the best opportunities for observation of evolutionaryprocesses in the present.     

Stomatal responses to humidity and temperature in darkness

Stomatal responses to leaf temperature (T_l) and to the mole fractions of water vapour in the ambient air (w_a) and the leaf intercellular air spaces (w_i) were determined in darkness to remove the potential effects of changes in photosynthesis and intercellular CO₂ concentration. Both the steady‐state and kinetic responses of stomatal conductance (g_s) to w_a in darkness were found to be indistinguishable from those in the light. g_s showed a steep response to the difference (Δw) between w_a and w_i when w_a was varied. The response was much less steep when w_i was varied. Although stomatal apertures responded steeply to T_l when Δw was held constant at 17 mmol mol^?1, the response was much less steep when Δw was held constant at about zero. Similar results were obtained in the light for Δw = 15 mmol mol^?1 and Δw ≈ 0 mmol mol^?1. These results are discussed in the context of mechanisms for the stomatal response to humidity.     

Detection of aphid remains in predatory insects and spiders by ELISA

An ELISA was developed which would detect and quantify ingested aphids in predators found in and around cereal crops. The detection limit of the assay was less than one hundredth of an homogenised adult aphid. Tests with 13 species of aphid showed that those which had been used as the principal immunogens reacted most strongly in the assay. Nearly a hundred species of invertebrates, both predators and alternative prey, have been tested in the assay and no evidence of significant cross-reaction was found with any of these species or with a number of samples of plant material on which aphids may be found. Aphid material could still be detected in predators which had been stored for up to 7 days in 4% formalin or 70% ethanol.     

Elevated volatile concentrations in high‐nutrient plants: do insect herbivores pay a high price for good food?

1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.     

Phagocytosis in Dictyostelium: Nibbling, Eating and Cannibalism

ABSTRACT. Phagocytosis is a highly conserved biological process that serves numerous functions in a wide variety of organisms. Over the past few decades Dictyostelium has proven to be an excellent organism for investigations in cell biology and this is certainly no less the case for a study of phagocytosis. This review examines three distinct phagocytic activities which have been characterized in Dictyostelium. The first, "vegetative phagocytosis," represents the classical eukaryotic microbial uptake of food particles (bacteria). The second, a predatory form of phagocytosis, arises when one species such as Dictyostelium caveatum attacks another species of slime mold, engulfing small pieces of the target prey. This has been termed "cell nibbling." The third phagocytic process is "sexual cannibalistic phagocytosis." In this situation a zygote giant cell, having arisen from the fusion of gametic amoebae, attracts unfused nonzygotic amoebae of the same species and engulfs them as a food source. While cell nibbling has not been actively studied, vegetative and sexual cannibalistic phagocytosis have received varying amounts of attention leading to the idea that some of the elements (e.g., glycoprotein receptors and a G_αs subunit) involved in certain of these phagocytic events may be the same. On the other hand, some unique events (e.g., filopodial induction in prey by D. caveatum ) are also worthy of further investigation. Among other things, the presence of self-nonself recognition, the existence of opsonin-like substances and the presence of signal transduction elements (e.g., an A2-like receptor that negatively modulates sexual phagocytosis) once considered to be extant only in higher organisms suggest that much can be learned about phagocytosis in general by further studies in the classic, eukaryotic microbe Dictyostelium discoideum and related species.