Biology subjects

Magalhaes, S.

Publications and source records attributed to Magalhaes, S..

8 recordsLinked to original sources

bioRxiv2018

Spider mites escape bacterial infection by avoiding contaminated food

To fight infection, arthropods rely on the deployment of an innate immune response but also upon physical/chemical barriers and avoidance behaviours. However, most studies focus on immunity, with other defensive mechanisms being relatively overlooked.\n\nWe have previously shown that the spider mite Tetranychus urticae does not mount an induced immune response towards systemic bacterial infections, entailing very high mortality rates. Therefore, we hypothesized that other defence mechanisms may be operating to minimize infection risk. Here, we test (a) if spider mites are also highly susceptible to other infection routes - spraying and feeding - and (b) if they display avoidance behaviours towards infected food. Individuals sprayed with or fed on Escherichia coli or Pseudomonas putida survived less than the control, pointing to a deficient capacity of the gut epithelium, and possibly of the cuticle, to contain bacteria. Additionally, we found that spider mites prefer uninfected food to food contaminated with bacteria, a choice that probably does not rely on olfactory cues.\n\nOur results suggest that spider mites may rely mostly on avoidance behaviours to minimize bacterial infection and highlight the multi-layered nature of immune strategies present in arthropods.

ecology↗

bioRxiv2018

Effect of cadmium accumulation on the performance of plants and of herbivores that cope differently with organic defences

Some plants can accumulate in their shoots metals that are toxic to most other organisms. This ability may serve as a defence against herbivores. Although both metal accumulation and the production of organic defences may be costly to the plant, the two mechanisms may interact on their effect on herbivores. However, this interplay between metal-based and classical organic defences remains overlooked.\n\nTo fill this gap, we studied the interactions between tomato (Solanum lycopersicum), a plant that accumulates cadmium, and two spider-mites, Tetranychus urticae and T. evansi that respectively induce and suppress organic plant defences, measurable via the activity of trypsin inhibitors. We exposed plants to different concentrations of cadmium and measured their effect on mites and plants. The oviposition of both spider-mite species was higher on plants exposed to low concentrations of Cd than on control plants but decreased at concentrations above 0.5 mM. Therefore, herbivores with contrasting responses to organic defences responded similarly to metal accumulation by the plants. On the plant, despite clear evidence for Cd accumulation, we did not detect any effect of Cd on traits that reflect the general response of the plant, such as biomass, water content and carbon/nitrogen ratio. Still, we found an effect of Cd supply upon the quantity of soluble sugars and leaf reflectance changes that may reflect structural modifications in the cells. In turn, these changes in plant traits interfered with the performance of spider mites feeding on those plants.\n\nAdditionally, we show that the induction and suppression of plant defences by spider mites was not affected by Cd supply to the plants. Furthermore, the effect of metal supply on spider-mite performance was not affected by previous infestation. Together, our results suggest no interaction between metal-based and organic plant defences, on our system. This may be useful for plants living in heterogeneous environments, as they may use one or the other defence mechanism, depending on their relative performance in each environment. This may be relevant to studies on the interactions between herbivores and plants, from physiology to ecology.

ecology↗

bioRxiv2018

Environments with a high probability of incompatible crosses do not select for mate avoidance in spider mites

Arthropods are often infected with Wolbachia inducing cytoplasmic incompatibility (CI), whereby crosses between uninfected females and infected males yield unviable fertilized offspring. Although uninfected females benefit from avoiding mating with Wolbachia-infected males, this behaviour is not present in all host species. Here we measured the prevalence of this behaviour across populations of the spider mite Tetranychus urticae. Females from five populations originally fully infected with Wolbachia showed no preference, possibly because they did not face the choice between compatible and incompatible mates in their environment. Hence, to determine whether this behaviour could be selected in populations with intermediate Wolbachia infection frequency, we performed 15 generations of experimental evolution of spider-mite populations under i) full Wolbachia infection, ii) no infection, or iii) mixed infection. In the latter selection regime, where uninfected females were exposed to infected and uninfected males at every generation, mating duration increased relative to the uninfected regime, suggesting the presence of genetic variation for mating traits. However, mate choice did not evolve. Together, these results show that CI-inducing Wolbachia alone does not necessarily lead to the evolution of pre-copulatory strategies in uninfected hosts, even at intermediate infection frequency.

evolutionary biology↗

bioRxiv2018

Costs and benefits of mating with fertilized females in a species with first male sperm precedence

Different patterns of sperm precedence are expected to result in specific mating costs and benefits for each sex, generating different selection pressures on males and females. However, most studies concern species with mixed paternity or last male sperm precedence, neglecting species with first male sperm precedence, in which only the first mating is effective.\n\nHere, we measured costs and benefits of multiple mating for both sexes of the spider mite Tetranychus urticae. First, we assessed the stability of the sperm precedence pattern, by mating females to one, two or several males, immediately after the first mating or 24 hours later. We found complete first male precedence, independently of the mating interval and the number of matings. Females paid a cost of polyandry, as multiply-mated females laid fewer eggs than once-mated females. However, while first males had reduced survival when exposed to an intermediate number of virgin females, second males paid no additional costs by matings with several mated females. Moreover, by mating multiply with mated females, males decreased the total number of offspring sired by first males, which suggests that these matings may entail a relative benefit for second males, despite being ineffective.\n\nOur results show that complex costs and benefits may arise in males in species with first male precedence. How these costs and benefits affect the maintenance of selection for polyandry remains an open question.

evolutionary biology↗

bioRxiv2018

Wolbachia both aids and hampers the performance of spider mites on different host plants

In the last decades, many studies had revealed the potential role of arthropod bacterial endosymbionts in shaping the host range of generalist herbivores and their performance on different host plants, which, in turn, might affect endosymbiont distribution in herbivores populations. We tested this by measuring the prevalence of endosymbionts in natural populations of the generalist spider mite Tetranychus urticae on different host plants. Focusing on Wolbachia, we then analysed how symbionts affected mite life-history traits on the same host-plants in the laboratory. Overall, the prevalences of Cardinium and Rickettsia were low, whereas that of Wolbachia was high, with the highest values on bean and eggplant and the lowest on purple, tomato and zuchini. Although most mite life-history traits were affected by the plant species only, Wolbachia infection was detrimental for egg hatching rate on purple and zucchini, and led to a more female-biased sex ratio on purple and eggplant. These results suggest that endosymbionts may affect the host range of polyphagous herbivores, both by aiding and hampering their performance, depending on the host plant and on the life-history trait that affects performance the most. Conversely, endosymbiont spread may be facilitated or hindered by the plants on which infected herbivores occur.

ecology↗

bioRxiv2018

The return of the trophic chain: fundamental vs realized interactions in a simple arthropod food web

The mathematical theory describing small assemblages of interacting species (community modules or motifs) has proved to be essential in understanding the emergent properties of ecological communities. These models use differential equations to study pairwise interactions between species. However, as community modules become more complex, it is not certain that all potential interactions will be effectively realized. Here, we use community modules to experimentally explore whether the number of trophic links among species scales with community complexity (i.e., by adding species known to feed on each other from pair-wise trials). To investigate this question, we used a simple mite community present in avocado orchards (Persea americana), composed of two predators (Euseius stipulatus and Neoseiulus californicus), one herbivore as shared prey (Oligonychus perseae), and pollen of Carpobrotus edulis as an alternative food resource. These configurations enabled the potential for (intraguild) predation and (apparent) competition to be expressed. Using a series of controls, we assessed whether the presence of one species affected the survival of another, or its conversion of food into offspring). We found that increasing the number of potential interactions did not result in more complex realized community modules. Instead, all communities were reduced to one or two linear trophic chains. Our results show that trophic links assumed to occur when species are assembled in pairs do not necessarily occur when other components of the community are present. Consequently, food-web structure may be unrealistic in theoretical community modules that are parameterized based on pair-wise interactions observed when alternative prey is absent. This further suggests the need for empirical research to work in concert with theoretical approaches to develop more realistic and predictive food-web models.

ecology↗

bioRxiv2017

Transgenerational cues about local mate competition affect offspring sex ratios in the spider mite Tetranychus urticae

In structured populations, competition for mates between closely related males, termed Local Mate Competition (LMC), is expected to select for female-biased offspring sex ratios. However, the cues underlying sex allocation decisions remain poorly studied. Here, we test for several cues in the spider mite Tetranychus urticae, a species that was previously found to adjust the sex ratio of its offspring in response to the number of females in an isolated population, i.e. a patch. We here investigate whether the offspring sex ratio of T. urticae females changes in response to 1) the current number of females in the same patch, 2) the number of females in the patches of their mothers and 3) their relatedness to their mate. Single females on patches produced similar sex ratios to those of groups of 15 females; their mothers had been in identical conditions of panmixia. The offspring sex ratios of females mated with their brother did not differ from those of females mated with an unrelated male. Females however produced a more female-biased offspring sex ratio if their mothers were alone on a patch compared to 15 other females. Thus, maternal environment is used as a cue for the sex allocation of daughters. We discuss the conditions under which the maternal environment may be a reliable predictor of LMC experienced by grand-sons.

evolutionary biology↗

bioRxiv2017

Despite reproductive interference, the net outcome of reproductive interactions among spider mite species is not necessarily costly

This preprint has been reviewed and recommended by Peer Community in Evolutionary Biology (http://dx.doi.org/10.24072/pci.evolbiol.100025). Reproductive interference is considered a strong ecological force, potentially leading to species exclusion. This supposes that the net effect of reproductive interactions is strongly negative for one of the species involved. Testing this requires a comprehensive analysis of interspecific reproductive interactions, accounting for the order and timing of mating events, and for their effects on either fertility or fecundity. To this aim, we measured reproductive interactions between a focal species, Tetranychus urticae, and an invasive (T.evansi) and a resident (T. ludeni) species, varying the mating sequence and interval, and measuring the effect of such crosses on fecundity and offspring sex ratio (a measure of fertility, as these species are haplodiploid). We found that mating with heterospecifics affected fecundity and sex ratio negatively, but also positively, depending on the species involved, and on the order and timing of mating events. Overall, the net effect of reproductive interactions was weak despite strong effects of particular events. In natural situations, the outcome of reproductive interactions will thus hinge upon the frequency of each event.

ecology↗