Antipredator behaviours of a spider mite in response to cues of dangerous and harmless predators.

Prey are known to invest in costly antipredator behaviour when perceiving cues of dangerous, but not of relatively harmless predators. Whereas most studies investigate one type of antipredator behaviour, we studied several types (changes in oviposition, in escape and avoidance behaviour) in the spider mite Tetranychus evansi in response to cues from two predatory mites. The predator Phytoseiulus longipes is considered a dangerous predator for T. evansi, whereas Phytoseiulus macropilis has a low predation rate on this prey, thus is a much less dangerous predator. Spider mite females oviposited less on leaf disc halves with predator cues than on clean disc halves, independent of the predator species. On entire leaf discs, they laid fewer eggs in the presence of cues of the dangerous predator than on clean discs, but not in the presence of cues of the harmless predator. Furthermore, the spider mites escaped more often from discs with cues of the dangerous predator than from discs without predator cues, but they did not escape more from discs with cues of the harmless predator. The spider mites did not avoid plants with conspecifics and predators. We conclude that the spider mites displayed several different antipredator responses to the same predator species, and that some of these antipredator responses were stronger with cues of dangerous predators than with cues of harmless predators.

Breaking and entering: predators invade the shelter of their prey and gain protection.

Many herbivorous arthropods construct shelters on their host plant that offer protection against natural enemies. This has resulted in selection on natural enemies to enter these shelters, where they can feed on prey that are inaccessible for competing predators and parasitoids. The spider mite Tetranychus evansi produces a shelter consisting of a dense web that is impenetrable for most predators; the only known natural enemy that can penetrate the web and can forage efficiently on this pest is Phytoseiulus longipes. We show that this predator preferentially foraged and oviposited in the web of its prey. Moreover, intraguild predation on juveniles of these predators was significantly higher outside this web and in the less dense web of a closely related prey species (T. urticae) than inside the web of T. evansi. Although the production of shelters by herbivores may be profitable at first, their adapted natural enemies may reap the benefit in the end.

Interações simbióticas entre Escherichia coli e seres humanos: a instabilidade de uma relação / Symbiotic interactions between Escherichia coli and humans: the instability of a relationship

Relações simbióticas podem ser interações altamente instáveis. Uma série de fatores pode alterar drasticamente o perfil de uma relação, causando prejuízos ou benefícios ao hospedeiro. Essas mudanças estão intimamente ligadas ao custo/benefício por trás dessas interações. Tais fatos nos levam a questionar quais são as possíveis condições que favorecem o comportamento parasitário, comensal ou mutualista? E em que condições cada estratégia tornam-se mais vantajosas para o simbionte? A bactéria Escherichia coli é um exemplo de simbionte que pode apresentar as três estratégias em único hospedeiro, causando desde graves infecções a benefícios defensivos e nutricionais. Nesse contexto, discutiremos nesse trabalho as características da relação simbiótica entre essa bactéria e o ser humano, demonstrando sua complexidade, abordando os possíveis fatores que atuam como determinantes no perfil da relação e as vantagens e desvantagens de cada estratégia

Symbiotic interactions can be highly unstable. A series of factors can dramatically alter the relationship, leading to costs or benefits to the host. These facts lead us to question: what are the possible conditions that promote parasitism, mutualism or commensalism? And under what conditions does each strategy become more advantageous for the symbiont? The bacterium Escherichia coli is an example of symbiont that may have the three strategies in a single host, it may cause serious infections or defensive and nutritional benefits. In this context, we discuss the characteristics of the symbiotic relationship between this bacterium and human hosts, demonstrating its complexity and addressing the possible factors that act as determinants in the profile of the relationship and the advantages/disadvantages of each strategy

Spider mite web mediates anti-predator behaviour.

Herbivores suffer significant mortality from predation and are therefore subject to natural selection on traits promoting predator avoidance and resistance. They can employ an array of strategies to reduce predation, for example through changes in behaviour, morphology and life history. So far, the anti-predator response studied most intensively in spider mites has been the avoidance of patches with high predation risk. Less attention has been given to the dense web produced by spider mites, which is a complex structure of silken threads that is thought to hinder predators. Here, we investigate the effects of the web produced by the red spider mite, Tetranychus evansi Baker & Pritchard, on its interactions with the predatory mite, Phytoseiulus longipes Evans. We tested whether female spider mites recognize predator cues and whether these can induce the spider mites to produce denser web. We found that the prey did not produce denser web in response to such cues, but laid more eggs suspended in the web, away from the leaf surface. These suspended eggs suffered less from predation by P. longipes than eggs that were laid on the leaf surface under the web. Thus, by altering their oviposition behaviour in response to predator cues, females of T. evansi protect their offspring.