Evolution of talking plants in a tritrophic context: conditions for uninfested plants to attract predators prior to herbivore attack

Herbivory induces plants to emit volatile chemicals that attract enemies of the herbivores (bodyguards of plants). In this way, the plant acquires protection and the bodyguards gain food. These plant signals cause neighboring plants, not under attack, to release signals as well. We hypothesize that such "secondary" signals help to reduce damage from future herbivore attacks by the protection received from the bodyguards. By modeling we explore the conditions for such secondary signals to evolve. Three kinds of strategies are considered: plants of the first strategy always emit a signal, those of the second strategy emit a signal only when infested, and those of the third strategy emit a signal not only when infested, but also when a certain number of neighbors are infested (i.e. secondary signaling). When signaling is much less (much more) costly than damage from herbivory, the first (second) strategy will be favored by selection, whereas for intermediate costs the third strategy, i.e. secondary signaling, will evolve. However, secondary signaling will not evolve when the primary signals lure the bodyguards too effectively. This is because the undamaged plant gains associational defense when the infested individual is defending very well; therefore, the need for secondary signaling decreases.     

Alien predators are more dangerous than native predators to prey populations

Alien predators are widely considered to be more harmful to prey populations than native predators. To evaluate this expectation, we conducted a meta-analysis of the responses of vertebrate prey in 45 replicated and 35 unreplicated field experiments in which the population densities of mammalian and avian predators had been manipulated. Our results showed that predator origin (native versus alien) had a highly significant effect on prey responses, with alien predators having an impact double that of native predators. Also the interaction between location (mainland versus island) and predator origin was significant, revealing the strongest effects with alien predators in mainland areas. Although both these results were mainly influenced by the huge impact of alien predators on the Australian mainland compared with their impact elsewhere, the results demonstrate that introduced predators can impose more intense suppression on remnant populations of native species and hold them further from their predator-free densities than do native predators preying upon coexisting prey.     

NGF causes TrkA to specifically attract microtubules to lipid rafts

Membrane protein sorting is mediated by interactions between proteins and lipids. One mechanism that contributes to sorting involves patches of lipids, termed lipid rafts, which are different from their surroundings in lipid and protein composition. Although the nerve growth factor (NGF) receptors, TrkA and p75(NTR) collaborate with each other at the plasma membrane to bind NGF, these two receptors are endocytosed separately and activate different cellular responses. We hypothesized that receptor localization in membrane rafts may play a role in endocytic sorting. TrkA and p75(NTR) both reside in detergent-resistant membranes (DRMs), yet they responded differently to a variety of conditions. The ganglioside, GM1, caused increased association of NGF, TrkA, and microtubules with DRMs, but a decrease in p75(NTR). When microtubules were induced to polymerize and attach to DRMs by in vitro reactions, TrkA, but not p75(NTR), was bound to microtubules in DRMs and in a detergent-resistant endosomal fraction. NGF enhanced the interaction between TrkA and microtubules in DRMs, yet tyrosine phosphorylated TrkA was entirely absent in DRMs under conditions where activated TrkA was detected in detergent-sensitive membranes and endosomes. These data indicate that TrkA and p75(NTR) partition into membrane rafts by different mechanisms, and that the fraction of TrkA that associates with DRMs is internalized but does not directly form signaling endosomes. Rather, by attracting microtubules to lipid rafts, TrkA may mediate other processes such as axon guidance.     

Selective signalling by cuttlefish to predators

Rather than simply escaping, prey animals often attempt to deter an attack by signalling to an approaching predator, but this is a risky strategy if it allows time for the predator to draw closer (especially when the signal is a bluff). Because prey are vulnerable to multiple predators, the hunting techniques of which vary widely, it could well be beneficial for a prey animal to discriminate predators and to signal only to those that are likely to be deterred. Higher vertebrates make alarm calls that can identify the type of predator to the signaller's conspecifics, and a recent study shows that squirrels direct an infrared deterrent signal specifically at infrared-sensitive pit-vipers and not at other snakes. We show here that na?ve juvenile cuttlefish (Sepia officinalis L.) use a visual signal selectively during encounters with different predatory species. We analysed sequences of defensive behaviours produced by cuttlefish, to control for effects of relative threat level (or 'response urgency'). This showed that a high contrast 'eyespot' signal, known as the deimatic display, was used before flight against visually oriented teleost fish, but not crabs and dogfish, which are chemosensory predators.     

Psychiatrists campaign to attract colleagues to treat HIV-disease patients.

The shortage of psychiatrists willing to treat patients with HIV infection has become so severe the Canadian Psychiatric Association has launched a campaign to try and encourage more specialists to enter the field. At the heart of the campaign is a booklet, Consultant/Mentor Directory for HIV Disease and Psychiatry, that provides a network of 40 psychiatrists across the country who regularly deal with HIV-infected patients. They want to encourage colleagues to do the same. "There aren''t a lot of psychiatrists seeing people with HIV disease," maintains Dr. Allan Peterkin, chair of the CPA Working Group on HIV Disease and Psychiatry. He worries that the shortage has led to some "ghettoization" of treatment.     

Marine nutrient contributions to freshwater apex predators

Recent investigations into the nutrient cycling of coastal ecosystems have suggested that migratory or anadromous fish could be important vectors of marine nutrients. Anadromous fish have assimilated marine nutrients that would contribute to the nutrient budgets of freshwater systems by excretion, gamete release, or the decay of post-reproductive carcasses. However, the extent to which freshwater predators utilize marine material is not well understood. In systems where anadromous fish temporarily constitute a major portion of the fish community, they may contribute substantially to the diet of piscivorous fish and other predators. Here we show the contribution of anadromous blueback herring, shad, and alewife (Alosa) to diets of large, non-indigenous piscivorous catfish (Ictalurus furcatus) using δ³⁴S and δ¹³C. The spawning anadromous Alosa, captured in tidal freshwater, had enriched δ³⁴S and δ¹³C values compared to resident, native freshwater species. As a result of consuming the anadromous Alosa, the I. furcatus isotope signature shifted towards the marine signal. The isotope analysis revealed that anadromous fish contribute substantially to the diet of most captured I. furcatus. The percentage of anadromous Alosa carbon and sulfur that was incorporated into I. furcatus (≥38 cm total length) ranged from 0 to 84% and 10 to 69%, and had means (±SD) of 42 (±24) and 43 (±16)%, respectively. Although the δ¹⁵N signal of marine-derived biomass is enriched by approximately 3‰ relative to terrestrial or freshwater biomass, it was not as useful as δ³⁴S and δ¹³C for nutrient source owing to trophic fractionation. This study demonstrates that anadromous fish may be a significant source of nutrients to tidal freshwater apex predators. Received: 19 March 1999 / Accepted: 26 October 1999     

Orchids mimic green-leaf volatiles to attract prey-hunting wasps for pollination

An outstanding feature of orchids is the diversity of their pollination systems [1]. Most remarkable are those species that employ chemical deceit for the attraction of pollinators [2]. The orchid Epipactis helleborine is a typical wasp flower, exhibiting physiological and morphological adaptations for the attraction of pollinating social wasps [3]. As noted by Darwin [1], this species is almost entirely overlooked by other potential pollinators, despite a large nectar reward. Therefore, the mechanism for the attraction of pollinating social wasps was something of a mystery. By using a combination of behavioral experiments, electrophysiological investigations, and chemical analyses, we demonstrate for the first time that the flowers of E. helleborine and E. purpurata emit green-leaf volatiles (GLVs), which are attractive to foragers of the social wasps Vespula germanica and V. vulgaris. GLVs, emitted by damaged plant tissues, are known to guide parasitic wasps to their hosts [4]. Several E. helleborine GLVs that induced response in the antennae of wasps were also emitted by cabbage leaves infested with caterpillars (Pieris brassicae), which are common prey items for wasps [5]. This is the first example in which GLVs have been implicated in chemical mimicry for the attraction of pollinating insects.     

Flybrella: a device to attract and kill house flies

Flybrella is a lightweight inexpensive trap that can be suspended like an upside-down umbrella in prominent locations where house flies, Musca domestica L., rest. It consists of a solid, cylindrical backbone to which is attached a perforated transparent tube, or baffle, with a commercial sugar/toxicant strip affixed inside. Centered directly beneath the tube and also attached to the backbone is a 10-cm-diameter inverted opaque plastic cone. House flies readily enter the tube, feed on the fast-acting toxicant, and then fall directly down the tube where they are collected in and concealed by the cone. The cone may be emptied easily through a capped opening in the bottom. In paired indoor tests, the efficacy of the commercial sugar/toxicant strip was increased significantly by the individual addition of several other attractant materials. Variants of the original design were tested, including a more efficient design featuring two concentric tubes with offset perforations. The toxicant strip may be easily removed and/or replaced when desired.