Differential effects of offspring condition-dependent signals on maternal care regulation in the European earwig

Parent-offspring conflict theory predicts the evolution of offspring solicitation signals that can influence the amount and/or the duration of parental investment. Short-term effects of offspring solicitation signals on parental food provisioning have been widely demonstrated, but persistent effects of offspring signals on the maintenance of parental care have been rarely studied. Also, the relation between the amount of care provided to the brood and how it is distributed among individual offspring within a brood is not well enough understood. Here, we investigated in the European earwig (Forficula auricularia) the effects of offspring condition-dependent chemical signals on the maintenance of maternal care among broods and the distribution of maternal food within broods. Mothers were isolated from their brood for 3days and continuously exposed to chemical signals extracted from broods of experimentally manipulated nutritional state. After re-introducing mothers to their brood, a range of maternal behaviours were quantified. We found that earwig mothers groomed their offspring significantly more after exposure to chemical extract from high-food brood in comparison with mothers exposed to extract from low-food brood, which in turn displayed significantly more aggressive behaviour. Furthermore, we manipulated offspring individual nutritional condition within the brood to evaluate the effect of offspring state on the within-brood food distribution. Within broods, poorly fed individuals received significantly more food than well-fed individuals, probably due to scramble competition. These results show that earwig nymphs express multi-component condition-dependent signals and behaviours differentially affecting maternal care provisioned to the brood and the distribution of care within brood

Smyd3 regulates cancer cell phenotypes and catalyzes histone H4 lysine 5 methylation

Smyd3 is a lysine methyltransferase implicated in chromatin and cancer regulation. Here we show that Smyd3 catalyzes histone H4 methylation at lysine 5 (H4K5me). This novel histone methylation mark is detected in diverse cell types and its formation is attenuated by depletion of Smyd3 protein. Further, Smyd3-driven cancer cell phenotypes require its enzymatic activity. Thus, Smyd3, via H4K5 methylation, provides a potential new link between chromatin dynamics and neoplastic disease

Maternal behaviour and the evolution of chemical signalling by offspring in the European earwig (Forficula auricularia)

Parental care provided to current offspring such as food and/or protection increases offspring development and survival which contributes to the parent’s fitness. However parental investment by means of time and energy may also reduce future chance to reproduce and therefore entails parent’s lifetime reproductive success. We expect parents to adjust their parental investment equally among their different offspring within and between broods in order to maximise their fitness. From the point of view of one current offspring, parental care should be rather positively biased towards itself compared to current or future siblings. Thus the different genetic interest over the duration and amount of parental investment is expected to lead to parent-offspring conflict. Resolution of this conflict may be achieved by the evolution of an offspring solicitation signal that regulates parental care as predicted by various theories and models. Although several empirical studies have supported the presence of offspring solicitation signals, mostly in birds, the origin and driving forces for the evolved signalling function have not been clearly demonstrated. The European earwig, Forficula auricularia, displays facultative maternal care, i.e. offspring can survive in absence of a caring mother but have significantly higher survival when attended by a mother. Thus one can test the on-going selection for an offspring cue to evolve a function of solicitation signal, which is predicted to be condition-dependent and regulating maternal care. Chemical cues are the main means of communication in insects (i.e. pheromones), which also regulate reproductive physiology (i.e. hormones). Therefore I decided for my thesis to explore the possible evolution of chemical signalling by offspring in the context of maternal care in the European earwig. In a first experiment, I manipulated the nutritional condition (low-food, LF, versus high-food, HF) of earwig first instar nymphs and extracted their cuticular hydrocarbons (CHCs). Caring mothers were presented to these different extracts or a solvent control (C) and their effects on maternal foraging as well as food provisioning to their brood were measured. By gas-chromatography coupled with mass-spectrum analysis, I found that nymphs of different nutritional state produce similar total amount of CHCs but they differ in the relative abundance of specific chemical compounds, particularly long-chain CHCs. Mothers exposed to offspring condition-dependent CHCs adjusted their maternal care behaviours. They foraged and later provisioned significantly more food to their brood when exposed to extract from HF. This first result demonstrated that CHCs of offspring are used as solicitation signals and that mothers may select for an offspring chemical signal of quality. In a second experiment, I investigated the effects of offspring condition-dependent chemical signals on the maintenance of maternal care among broods and the distribution of maternal food within broods. Mothers were isolated from their 1st instar brood for 3 days and continuously exposed to chemical signals extracted from broods of experimentally manipulated nutritional state (HF, LF). After re-introducing mothers to their brood, a range of maternal behaviours were quantified. I found that earwig mothers groomed their offspring significantly more after exposure to chemical extract from HF brood in comparison with mothers exposed to extract from LF brood, which in turn displayed significantly more aggressive behaviour. Furthermore, I manipulated offspring individual nutritional condition within the brood to evaluate the effect of offspring state on the within-brood food distribution. Within broods, poorly fed individuals received significantly more food than well-fed individuals. These contrasting results of offspring condition-dependent signals observed at the brood and individual levels suggest various selective pressures, such as scramble competition within brood and maternal selection among broods, shaping offspring solicitation signals. Finally, to test whether offspring chemical signals can per se manipulate the lifetime reproductive success of mothers, I measured long term consequences of exposure to offspring chemical signals on mothers’ residual fecundity. The probability to have a second clutch by females was not affected by offspring chemical signals. However, the predictability for females to lay a second clutch within a certain interval was significantly affected by the condition-dependent chemical signals produced by offspring. The date of laying a second clutch was highly related to date of first clutch laying/hatching and strongly predictable when females were exposed to extract from HF offspring. The importance of timing of the second clutch may be critical for seasonal species like F. auricularia in order to ensure offspring survival. This last result confirms the potential for offspring chemical signals to manipulate maternal future fecundity, yet mothers may actively select for this offspring signal of quality in their best interest in order to optimally adjust their investment between current and future broods. In conclusion, I showed that earwig first instar nymphs produce CHCs that vary in their relative abundances depending on offspring nutritional state. Earwig mothers adjust their maternal care behaviours (food provisioning, grooming vs. aggressiveness) according to these condition-dependent . Higher food provisioning and more grooming by mothers exposed to HF brood extract suggest maternal selection for offspring chemical cues of quality. Finally, the potential of offspring chemical cues per se to influence future maternal fecundity confirms their evolving function as solicitation pheromone in the context of maternal care

An offspring signal of quality affects the timing of future parental reproduction

Solicitation signals by offspring are well known to influence parental behaviour, and it is commonly assumed that this behavioural effect translates into an effect on residual reproduction of parents. However, this equivalence assumption concerning behavioural and reproductive effects caused by offspring signals remains largely untested. Here, we tested the effect of a chemical offspring signal of quality on the relative timing and amount of future reproduction in the European earwig (Forficula auricularia). We manipulated the nutritional condition of earwig nymphs and exposed females to their extract, or to solvent as a control. There were no significant main effects of exposure treatment on 2nd clutch production, but exposure to extracts of well-fed nymphs induced predictable timing of the 2nd relative to the 1st clutch. This result demonstrates for the first time that an offspring signal per se, in the absence of any maternal behaviour, affects maternal reproductive timing, possibly through an effect on maternal reproductive physiology

Automated Surveillance of Lepidopteran Pests with Smart Optoelectronic Sensor Traps

Several lepidopterans are pests in horticulture and pose biosecurity risks to trading countries worldwide. Efficient species-specific semiochemical lures are available for some of these pests, facilitating the implementation of surveillance programmes via trapping networks. These networks have a long history of success in detecting incursions of invasive species; however, their reliance on manual trap inspections makes these surveillance programmes expensive to run. Novel smart traps integrating sensor technology are being developed to detect insects automatically but are so far limited to expensive camera-based sensors or optoelectronic sensors for fast-moving insects. Here, we present the development of an optoelectronic sensor adapted to a delta-type trap to record the low wing-beat frequencies of Lepidoptera, and remotely send real-time digital detection via wireless communication. These new smart traps, combined with machine-learning algorithms, can further facilitate diagnostics via species identification through biometrics. Our laboratory and field trials have shown that moths flying in/out of the trap can be detected automatically before visual trap catch, thus improving early detection. The deployment of smart sensor traps for biosecurity will significantly reduce the cost of labour by directing trap visits to the locations of insect detection, thereby supporting a sustainable and low-carbon surveillance system

A chemical signal of offspring quality affects maternal care in a social insect

Begging signals of offspring are condition-dependent cues that are usually predicted to display information about the short-term need (i.e. hunger) to which parents respond by allocating more food. However, recent models and experiments have revealed that parents, depending on the species and context, may respond to signals of quality (i.e. offspring reproductive value) rather than need. Despite the critical importance of this distinction for life history and conflict resolution theory, there is still limited knowledge of alternative functions of offspring signals. In this study, we investigated the communication between offspring and caring females of the common earwig, Forficula auricularia, hypothesizing that offspring chemical cues display information about nutritional condition to which females respond in terms of maternal food provisioning. Consistent with the prediction for a signal of quality we found that mothers exposed to chemical cues from well-fed nymphs foraged significantly more and allocated food to more nymphs compared with females exposed to solvent (control) or chemical cues from poorly fed nymphs. Chemical analysis revealed significant differences in the relative quantities of specific cuticular hydrocarbon compounds between treatments. To our knowledge, this study demonstrates for the first time that an offspring chemical signal reflects nutritional quality and influences maternal care

Coefficients table of GLM for carrot phenology.

<p>Variety: E = excellent, M = medium, P = poor. Line: male sterile (♀) and male fertile (♂). The intercept condition is the male-sterile, excellent line.</p

Seed set amongst the three carrot varieties.

<p>E = excellent, M = medium, P = poor. Boxes represent middle 50% of data, lines within boxes are the median.</p