Native parasitoids and a novel invasive host:Linking evolutionary ecology and biological pest control

The use of natural enemies to control pests is of increasing importance in agriculture because pesticide application has become restrictive. One of the major challenges within biological pest control is to find natural enemies that have the right combination of traits to efficiently find and kill the pest in the field/greenhouse. This is especially difficult for new invasive pest species, because existing enemies in the invaded areas are nog always effective to attack the exotic species. In this thesis we focused on the biological control of the Suzuki fruit-fly (Drosophila suzukii) to determine if and how native natural enemies, parasitoids, can adapt to the new host by evolution and apply this knowledge to improve biological pest control. Through behavioural experiments and cross-breeding experiments in the laboratory we show that there is large variation within native parasitoid species to kill the invasive Suzukii pest and show that this trait is partly genetically determined. In addition, we show how we can improve parasitoids by artificial selection for biological control. This dissertation demonstrates the importance of evolutionary biology in halting the impact of invasive species: (1) for developing sustainable biological control methods and (2) for preserving and promoting genetic diversity between and within species in order to increase the resilience of species to changing environments

Reciprocal predicates: a prototype model

Many languages have verbal stems like hug and marry whose intransitive realization is interpreted as reciprocal. Previous semantic analyses of such reciprocal intransitives rely on the assumption of symmetric participation. Thus, 'Sam and Julia hugged' is assumed to entail both 'Sam hugged Julia' and 'Julia hugged Sam'. In this paper we report experimental results that go against this assumption. It is shown that although symmetric participation is likely to be preferred by speakers, it is not a necessary condition for accepting sentences with reciprocal verbs. To analyze the reciprocal alternation, we propose that symmetric participation is a typical feature connecting the meanings of reciprocal and binary forms. This accounts for the optionality as well as to the preference of this feature. Further, our results show that agent intentionality often boosts the acceptability of sentences with reciprocal verbs. Accordingly, we propose that intentionality is another typical semantic feature of such verbs, separate from symmetric participation

Effects of age, gender and educational background on strength of motivation for medical school

The aim of this study was to determine the effects of selection, educational background, age and gender on strength of motivation to attend and pursue medical school. Graduate entry (GE) medical students (having Bachelor’s degree in Life Sciences or related field) and Non-Graduate Entry (NGE) medical students (having only completed high school), were asked to fill out the Strength of Motivation for Medical School (SMMS) questionnaire at the start of medical school. The questionnaire measures the willingness of the medical students to pursue medical education even in the face of difficulty and sacrifice. GE students (59.64 ± 7.30) had higher strength of motivation as compared to NGE students (55.26 ± 8.33), so did females (57.05 ± 8.28) as compared to males (54.30 ± 8.08). 7.9% of the variance in the SMMS scores could be explained with the help of a linear regression model with age, gender and educational background/selection as predictor variables. Age was the single largest predictor. Maturity, taking developmental differences between sexes into account, was used as a predictor to correct for differences in the maturation of males and females. Still, the gender differences prevailed, though they were reduced. Pre-entrance educational background and selection also predicted the strength of motivation, but the effect of the two was confounded. Strength of motivation appears to be a dynamic entity, changing primarily with age and maturity and to a small extent with gender and experience

Evolution of parasitoid host preference and performance in response to an invasive host acting as evolutionary trap

The invasion of a novel host species can create a mismatch in host choice and offspring survival (performance) when native parasitoids attempt to exploit the invasive host without being able to circumvent its resistance mechanisms. Invasive hosts can therefore act as evolutionary trap reducing parasitoids' fitness and this may eventually lead to their extinction. Yet, escape from the trap can occur when parasitoids evolve behavioral avoidance or a physiological strategy compatible with the trap host, resulting in either host-range expansion or a complete host-shift. We developed an individual based model to investigate which conditions promote parasitoids to evolve behavioral preference that matches their performance, including host-trap avoidance, and which conditions lead to adaptations to the unsuitable hosts. The model was inspired by solitary endo-parasitoids attacking larval host stages. One important aspect of these conditions was reduced host survival during incompatible interaction, where a failed parasitization attempt by a parasitoid resulted not only in death of her offspring but also in host killing. This non-reproductive host mortality had a strong influence on the likelihood of establishment of novel host-parasitoid relationship, in some cases constraining adaptation to the trap host species. Moreover, our model revealed that host-search efficiency and genetic variation in host-preference play a key role in the likelihood that parasitoids will include the suboptimal host in their host range, or will evolve behavioral avoidance resulting in specialization and host-range conservation, respectively. Hence, invasive species might change the evolutionary trajectory of native parasitoid species, which is important for predicting biocontrol ability of native parasitoids towards novel hosts