L. De Bruyn

Reversible frequency-dependent switches in male mate choice

Current sexual–selection theories predict that mating should occur preferentially with the highest–quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency–dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency–dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness.

Have Genetic Trade-Offs in Host Use been Overlooked in Arthropods?

A popular hypothesis to explain the high degree of host specialisation observed among mites and insects is the existence of host-associated fitness trade-offs. According to this theory, adaptation to a host results in a relatively poorer performance on alternative hosts due to the antagonistic pleiotropic action of one or more genes. Evidence in favour of the genetic trade-off hypothesis is however scarce. Recent ecological work has shown that the optimisation of adult performance drives the evolution of host choice in at least some phytophagous insects. Yet, most ecological and evolutionary studies on host choice assume that females maximise their fitness by optimising offspring performance. In this paper, we investigate whether a general lack of attention for the role of adult performance in host choice may have diminished the chance of detecting genetic trade-offs. We reviewed the literature on genetic trade-offs and showed that most studies neglected host specific variation in adult performance. Moreover, studies that considered both adult and offspring performance had a higher chance of detecting genetic fitness trade-offs. Our results also suggested that studies on asexual reproducing species tend to detect trade-offs more often than studies on obligate sexual reproducing species. We argue that future studies on genetic trade-offs should take all fitness parameters into account in order to be conclusive. This approach may reveal (i) that genetic trade-offs are more common than hitherto reported and/or (ii) that genetic trade-offs are more common, or more easily detected among asexual reproducing species like mites and aphids.

Plant stress and larval performance of a dipterous gall former

According to the plant vigour hypothesis, galling insects should respond positively and perform better on vigorous plants or plant parts, the opposite of the predictions of the plant stress hypothesis. I carried out field experiments to analyse the effects of sustained abiotic stress on the interactions between the common reed (Phragmites australis) and a gall-forming fly (Lipara lucens). The reed shoot diameter (a measure of plant vigour) is strongly affected by environmental conditions, where dry and/or nutrient-poor habitats produce thinner (stressed) shoots. L. lucens gall density is negatively correlated with shoot diameter. In a survival experiment with a wide range of shoot diameters, larval mortality was also highly correlated with shoot quality. Gall formation was higher on thinner, stressed shoots. An analysis of the gall tissues revealed that galls induced by L. lucens contain a high amount of a nutrient-rich feeding tissue. The impact of L. lucens is higher on thinner shoots. The results of this study showed that L. lucens performs better on stressed hosts, which contradicts the plant vigour hypothesis for galling insects. The low nutrient availability in the stressed shoots can be compensated by the production of galls with a nutrient-rich feeding tissue.According to the plant vigour hypothesis, galling insects should respond positively and perform better on vigorous plants or plant parts, the opposite of the predictions of the plant stress hypothesis. I carried out field experiments to analyse the effects of sustained abiotic stress on the interactions between the common reed (Phragmites australis) and a gall-forming fly (Lipara lucens). The reed shoot diameter (a measure of plant vigour) is strongly affected by environmental conditions, where dry and/or nutrient-poor habitats produce thinner (stressed) shoots. L. lucens gall density is negatively correlated with shoot diameter. In a survival experiment with a wide range of shoot diameters, larval mortality was also highly correlated with shoot quality. Gall formation was higher on thinner, stressed shoots. An analysis of the gall tissues revealed that galls induced by L. lucens contain a high amount of a nutrient-rich feeding tissue. The impact of L. lucens is higher on thinner shoots. The results of this study showed that L. lucens performs better on stressed hosts, which contradicts the plant vigour hypothesis for galling insects. The low nutrient availability in the stressed shoots can be compensated by the production of galls with a nutrient-rich feeding tissue.

Seasonal changes in leaf nutritional quality influence grass miner performance

1. The plant phenological age hypothesis predicts that phytophagous insects should prefer and perform better on phenologically young plants than on old plants because plant nutritional quality decreases with plant phenological age. This hypothesis was tested under field and laboratory conditions with the grass miner Chromatomyia milii on the free‐growth species Holcus lanatus.

Nutritional benefits of the leaf-mining behaviour of two grass miners: a test of the selective feeding hypothesis

1. The selective feeding hypothesis predicts that miners prefer tissues high in nutrient content and low in chemical and structural defence content. This hypothesis was tested for two dipteran grass miners, Chromatomyia milii and C. nigra, feeding on Holcus lanatus.

Reversible switches between male–male and male–female mating behaviour by male damselflies

For many animal groups, both sexes have been reported to attempt to mate with members of their own sex. Such behaviour challenges theories of sexual selection, which predict optimization of reproductive success. We tested male mate choice between opposite- and same-sex members in the damselfly Ischnura elegans. Binary choice experiments were conducted following exposure periods in insectaries with only males or with both sexes present. We show that switches in choice between the opposite sex and the same sex can be induced and reversed again by changing the social context. We argue that the observed reversibility in male–male- and male–female-directed mating behaviour is maladaptive and a consequence of strong selection on a males ability to alter choice between different female colour morphs.

Variation in flight morphology in a female polymorphic damselfly: intraspecific, intrasexual, and seasonal differences

In aerial animals, flight morphology needs to be designed to allow daily behavioural activities. Within species differences in behaviour can therefore be expected to relate to differences in flight morphology, not only between males and females but also between same-sex members when they use different behavioural strategies. In female polymorphic damselflies, one female morph is considered a male mimic that resembles the male’s body colour and behaviour (andromorph), whereas the other is dissimilar (gynomorph). Here, we questioned whether males, andromorphs, and gynomorphs of the damselfly Enallagma cyathigerum (Charpentier, 1840) differ in flight morphology, with andromorphs being more similar to males than gynomorphs. In addition, we evaluated whether differences in flight morphology are consistent or whether some morphs are more plastic in response to seasonal environmental fluctuations. Most morphometrics showed similar seasonal plasticity for males and both female morphs, which could only partly be e...

Seasonal feeding activity of the tree-hole tick, Ixodes arboricola.

Bird-specific ticks do not infest humans and livestock, but these ticks often share their avian hosts with generalist ticks that do. Therefore, their feeding activity may have an impact on the transmission of pathogens outside bird-tick transmission cycles. Here we examined the seasonal feeding activity of the tree-hole tick (Ixodes arboricola) in relation to the activity of its hole-breeding hosts (Parus major and Cyanistes caeruleus). We analysed data on ticks derived from birds, on the abundance of engorged ticks inside nest boxes, and on bird nests that were experimentally exposed to ticks. We observed a non-random pattern of feeding associated with the tick instar and host age. The majority of adult ticks fed on nestlings, while nymphs and larvae fed on both free-flying birds and nestlings. Due to their fast development, some ticks were able to feed twice within the same breeding season. The highest infestation rates in free-flying birds were found during the pre-breeding period and during autumn and winter when birds roost inside cavities. Except during winter, feeding of I. arboricola overlapped in time with the generalist Ixodes ricinus, implying that tick-borne microorganisms that are maintained by I. arboricola and birds could be bridged by I. ricinus to other hosts.

Comparison of different trapping methods in Agromyzidae (Diptera)

Trapping techniques are frequently used to monitor pest species. These trapping techniques have to provide reasonably precise estimates of densities and sex ratios of monitored species in order to apply appropriate insect pest control measures most efficiently. A broad range of trapping methods are applied to gather this basic ecological information. However, few studies question the reliability of trapping methods to obtain accurate data. Here, we investigate the usefulness of traps for the assessment of basic life‐history data in Agromyzidae. In this study, Malaise traps and coloured water traps are compared. Significant deviations of a 1♂: 1♀ sex ratio occurred both in Malaise and colour traps. The bias of these deviations of the sex ratio altered according to the trapping method. In the Malaise traps most significant deviations were female biased. All significant deviations observed in the colour traps were male biased. The overall sex ratio of all captured individuals was in every Malaise trap in favour of the females and in every colour trap in favour of the males. Different trapping methods also revealed intraspecific differences in phenology patterns. Agromyzid flies were trapped earlier in colour traps compared to Malaise traps. Possible explanations for the observed intraspecific differences in sex ratio and phenology pattern between traps are discussed. This study points out that a thorough analysis of the response of a target species to a certain trapping method is needed in order to ascertain the reliability of the collected data. The importance and consequences of these results for monitoring agromyzid pest species are emphasized.

Perfluorooctane sulfonic acid contamination reduced fitness in Drosophila hydei (Diptera: Drosophilidae).

ABSTRACT Studies on the effects of perfluorooctane sulfonic acid (PFOS) exposure on terrestrial invertebrates are very scarce. Here, we quantified the effects of PFOS on the number of offspring for two generations of Drosophila hydei Sturtevant 1921 (Diptera: Drosophilidae) reared in the laboratory. The first generation was exposed to a range of PFOS concentrations from 5 to 5,000 ng/ml and a control through their diet. For the second generation, offspring of the 50 ng/ml PFOS treatment and the control were further reared in a PFOS-free environment. For the first generation, the number of offspring decreased with increasing levels of PFOS contamination. Although the second generation was not exposed to PFOS, we still observed a reduction in the number of offspring when the parental flies were exposed to 50 ng/ml PFOS. The results of the current study indicate that the sensitivity to PFOS of D. hydei is several magnitudes higher than of the other terrestrial invertebrate species tested so far. This sensitivity falls within the concentration range detected in its natural food.