107 research outputs found
Olfactory information use for foraging in "Microplitis mediator", a parasitoid of the cabbage moth "Mamestra brassicae"
No full textMy PhD project was at the interface between behavioural ecology and biological control, two disciplines that do not easily intertwine because of their divergent aims. On one hand, behavioural ecology is a fundamental science that seeks to understand animal behaviour from an evolutionary perspective and generally works from the point of view of the individual. On the other hand, as an applied science, biological control seeks to elaborate concrete strategies to improve pest control and works from population and community perspectives. However, the success of biological control methods depends on the behaviour of biological control agents, i.e. natural enemies of target pests, which creates a perfect opportunity for behavioural ecology and biological control to work hand in hand. In this work, I studied the foraging behaviour of the larval parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) with the idea that my findings could contribute to the improvement of the control of its host the cabbage moth Mamestra brassicae (Linnaeus) (Lepidoptera: Noctuidae), which is an important cabbage pest distributed throughout Europe and Asia. Information about the biology, the life cycle and the rearing method of M. mediator and M. brassicae is reviewed in chapter 1.
In a first study (chapter 2), I tested the olfactory attractiveness of flowers/inflorescences of five wildflowers species (bishop’s weed, cornflower, buckwheat, candytuft, and oregano) to naive female M. mediator. I conducted choice tests in a Y-tube olfactometer to test the olfactory attractiveness of flowers/inflorescences against air and the relative attractiveness of the flower species offered in paired choice. I showed that all the flower species were highly attractive to female M. mediator when tested against air, but that in paired choice tests cornflower and candytuft were as attractive as each other and both more attractive than buckwheat. This indicates that M. mediator is able to use olfactory cues to identify potential food sources and has evolved preferences that could be exploited in biological control. In particular, this study has shown that cornflower is a very promising floral subsidy.
However, in a patchy and unpredictable environment, not all food sources are equally abundant and/or near, and parasitoids are expected to have evolved capacities to detect the most promising food sources in terms of proximity and/or abundance. In a second study (chapter 3), I tested whether female Microplitis mediator foraging for food sources, i.e. flowers of cornflower and inflorescences of buckwheat, were able to use quantitative olfactory information to orient themselves towards the most promising (i.e. most abundant and/or closest) food sources. I conducted behavioural assays in a 6-arm olfactometer where groups of six wasps were released and faced with a gradient of volatile concentration created by using different numbers of flowers/inflorescences as odour sources. I also collected and analyzed the volatiles emitted by different numbers of flowers/inflorescences of the two flower species. The results showed that female M. mediator were able to use quantitative olfactory information. In general, they were most attracted to the highest numbers of flowers/inflorescences, which also emitted the highest volatile quantities. However, the response of the wasps towards the two flower species differed. The contrast between the different numbers of flowers/inflorescences was important for the wasps to be able to discriminate and had to be higher with cornflower than with buckwheat. With cornflower, the flower species emitting both substantially higher absolute volatile quantities and more potentially attractive types of volatile compounds (e.g. benzenoïds), the response of the wasps to single flowers was very strong already and showed saturation with increasing numbers of flowers. Conversely, with buckwheat, the flower species emitting low volatile quantities, the response of the wasps to few inflorescences was weak but accelerated with increasing numbers of inflorescences. This would suggest that a higher sensitivity at low volatile quantities than at high volatile quantities could have been selected in M. mediator, which would be adaptive. These results highlight the importance of taking flower density into account to optimize the use of floral subsidies for biological control purposes. In particular, these results suggest that cornflower should be attractive at low densities whereas higher densities of buckwheat could be needed to attract M. mediator in the field.
To conclude, my work has shown that M. mediator is well adapted for food foraging, because it can detect both the quality and the quantity of olfactory information to localize potentially rewarding food sources. I also demonstrated that studying the foraging behaviour of a parasitoid provides relevant information that can be exploited to improve its use for biological control
Maternal care and interactions within and between families : how the environment and chemical communication shape family life in a social insect
No full textThe evolution of parental care represents an important step in the evolution of sociality and is widespread across different species and different taxa. Parental care is a trait that shows a wide diversity regarding duration and forms of care within and between species and is an important field of research both in evolutionary biology and behavioral ecology. However, its importance in these fields has only been recognized relatively recently. Environmental effects influence condition and individuals will choose distinct behavioral strategies to maximize their fitness. Condition can be communicated through chemicals and such condition-dependent cues can be used by conspecifics to adjust their own behavior. The focus of my dissertation was the investigation of environmental effects and chemical signaling on maternal care and within and between family interactions. I used the European earwig (Forficula auricularia) as a model system for my experimental work.
As an introductory chapter, I have written a review article about the evolution of parental care in insects (Chapter 1). Here, I summarized present hypotheses about the roles of ecology and life history from the literature and combined them with new suggestions regarding the influence of social interactions on parental care.
In my first experiment (Chapter 2), I investigated the influence of maternal nutritional condition on mother-offspring interactions. Female condition was manipulated through a high-food and a low-food treatment. I could show that the period and amount of maternal food provisioning was dependent on the condition of the female. Females in poor condition provided food to fewer nymphs and for a shorter period of time compared to females in good condition. Offspring attendance remained at a constantly high level independent of female condition and was maintained by both the female and the nymphs, suggesting strong benefits of living in a (family) group.
In my second experiment (Chapter 3), I investigated effects of nymph condition and food availability on brood mixing in F. auricularia. Females provide care for foreign nymphs that join their brood. This however increases brood size and thus competition between the offspring. Previous work showed that cannibalism is directed primarily against unrelated nymphs under conditions of low food availability. My results showed that the brood mixing dynamics are influenced by the condition of the nymphs, but are independent of the food availability in the environment. The overall degree of brood mixing was high, suggesting again benefits of living in groups.
Furthermore, my third experiment (Chapter 4) tested the presence of family specific cuticular hydrocarbon profiles. Insects mainly use cuticular hydrocarbons as means of communication and individual recognition. Previous results from our group show that there are significant negative effects of inbreeding, which makes kin recognition important in this species. I could show that cuticular hydrocarbon profiles are indeed family specific and that the earwigs have the potential to use them to discriminate kin from non-kin. This allows to direct social behaviors to the appropriate individuals and to avoid inbreeding and the associated fitness losses.
In a fourth experiment (Chapter 5), I tested the effect of maternal condition-dependent cues on nymph selfishness and survival. In species where parental care is provided, offspring could use cues of parental condition to adjust their begging behavior and their selfishness by varying the degree of sibling competition. My results show that maternal condition cues influence offspring survival depending on the time of breeding, and further suggest that offspring use these maternal condition-dependent cues to adjust their degree of selfishness, which changes during the breeding season. Together with former evidence on maternal sensitivities to condition-dependent nymph chemical cues, my study shows context-dependent reciprocal information exchange about condition between earwig mothers and their offspring, mediated by cuticular hydrocarbons.
My last experiment (Chapter 6) investigated the effects of high and low food availability during the juvenile and early adult development and its influences on development, maternal care and egg production. Females of the European earwig represent two distinct phenotypes. One type produces only one clutch, the other type produces two clutches during its life. Previous experiments have shown that the phenotype is not purely inherited genetically, but likely to be condition-dependent. My results revealed that especially restriction in the late juvenile development has negative effects on development and the probability of second clutch production. Environmental conditions experienced early in an individual’s lifetime can have detrimental effects once individuals become adult and need to be considered to understand individual variation in reproductive success and life-history trade-offs.
All in all my results show that behavioral strategies are driven by the condition of the individuals involved. I demonstrated that condition is reflected in the cuticular hydrocarbon profiles of the earwigs. Such condition-dependent chemical cues allow individuals to adjust their behavior according to their own state and to the state of interacting conspecifics. I showed how the environment and chemical communication shape family life in a social insect and revealed how this affects not only maternal care and social interactions within and between families, but also reproductive success of individuals. Thus, my work shows how individual condition affects not only parent-offspring interactions, but also major life history traits like reproductive success
Maternal behaviour and the evolution of chemical signalling by offspring in the European earwig (Forficula auricularia)
No full textParental 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
Consistent cooperation in a cichlid fish is caused by maternal and developmental effects rather than heritable genetic variation.
No full textThis is the author accepted manuscript. The final version is available from Royal Society via the DOI in this record.Studies on the evolution of cooperative behaviour are typically confined to understanding its adaptive value. It is equally essential, however, to understand its potential to evolve, requiring knowledge about the phenotypic consistency and genetic basis of cooperative behaviour. While previous observational studies reported considerably high heritabilities of helping behaviour in cooperatively breeding vertebrates, experimental studies disentangling the relevant genetic and non-genetic components of cooperative behaviour are lacking. In a half-sibling breeding experiment, we investigated the repeatability and heritability of three major helping behaviours performed by subordinates of the cooperatively breeding fishNeolamprologus pulcherTo experimentally manipulate the amount of help needed in a territory, we raised the fish in two environments differing in egg predation risk. All three helping behaviours were significantly repeatable, but had very low heritabilities. The high within-individual consistencies were predominantly due to maternal and permanent environment effects. The perceived egg predation risk had no effect on helping, but social interactions significantly influenced helping propensities. Our results reveal that developmentally plastic adjustments of provided help to social context shape cooperative phenotypes, whereas heritable genetic variation plays a minor role.Funding was provided by the ‘ProDoc’ program of the Swiss National Science Foundation (SNF, projects PDFMP3_137196 and 31003A_156881 to B.T.), and the ‘120% support grant’ to C.K. of the University of Bern
Differential food allocation by male and female great tit, Parus major, parents : are parents or offspring in control?
No full textInteractions in families of the European earwig (Forficula auricularia) - behavioural dynamics and conflicts
No full textInteractions in families and their stability are often discussed on an evolutionary background only. However, the evolutionary stability of an interaction tells only half of the story. It is further necessary to have knowledge about the behavioural stability of such an interaction in a family. What is the value of an evolutionarily stable strategy (ESS) when the behavioural dynamics that actually happens does not allow the interaction to reach or to be expressed at the evolutionary optimum? It is therefore important to know whether a behavioural interaction has an equilibrium and if so, whether and how this equilibrium can be attained behaviourally. To know whether an interaction has an equilibrium and whether this equilibrium is behaviourally attainable or not provides information about the behavioural stability of an interaction. This knowledge is important for behaviours where the behavioural stability is questioned, for example in siblicide. The knowledge of how the equilibrium is reached allows to draw conclusions about who has the behavioural control in an interaction.
In the first part of my thesis (chapter 2) I investigated the stability of behavioural interactions and whether they are compatible with ESS. In a basic two player model with repeated sequential interactions I found, that only half of the behavioural interactions lead to stability and therefore represent a behaviourally stable strategy (BSS). Testing the compatibility of BSS and ESS I found, that indeed a considerable number of ESS were not compatible with any BSS.
In the second and in the third part of my thesis (chapters 3, 4 & 5) I performed lab experiments with earwigs to assess how behavioural interactions can be influenced by external (environmental) and internal (individual) factors. In a first experiment I manipulated the nutrition levels of nymphs and females and hence also their hunger states. Combining nymphs and females from different or equal nutrition levels (cross-fostering) allowed me to conclude how nymphs and females react to the hunger state of the other (environment) and how this reaction is influenced by their own hunger state. Results showed, that the behaviour of the female depends on their own hunger state only and that the behaviour of the nymphs is influenced by their own hunger state and the hunger state of the female. In a second experiment I investigated whether nymphs can recognise related individuals and how relatedness influences the killing (siblicide) and cannibalism behaviour in nymphs. I found that individuals can recognise kin and that the killing and cannibalism behaviour is influenced by the relatedness of two interacting individuals.
All three parts of my thesis point out, that the interactions between individuals of a family are important, because they affect their behavioural and evolutionary stability. Over the course of time the stability of behavioural interactions rules the evolutionary stability of a strategy. Selection can only act on BSS because only these strategies have an attainable equilibrium which is necessary for evolutionary stability. It is therefore absolutely necessary to have knowledge about the behaviour (how interact two individuals, who has the behavioural control) and its stability (e.g., siblicide) to draw any conclusions about evolutionary stability.
Zusammenfassung
Interaktionen in Familien und deren Stabilität werden oft nur in evolutionärem Zusammenhang diskutiert. Die evolutionäre Stabilität enthält jedoch nur die halbe Wahrheit. Es ist ebenfalls notwendig über die Verhaltensstabilität solcher Interaktionen innerhalb von Familien Bescheid zu wissen. Was ist der Nutzen einer evolutiv stabilen Strategie (ESS = evolutionarily stable strategy), wenn die zu Grunde liegende Verhaltensdynamik der Interaktion es nicht erlaubt das evolutive Optimum zu erreichen oder auszudrücken? Es ist daher auch wichtig zu wissen ob eine Verhaltensinteraktion ein Gleichgewicht hat und falls ja, ob und wie dieses Gleichgewicht über Verhalten erreicht werden kann. Zu wissen ob eine Interaktion ein Gleichgewicht hat, und ob dieses Gleichgewicht über Verhalten erreicht werden kann oder nicht, liefert Informationen über die Verhaltensstabilität der Interaktion. Dieses Wissen ist wichtig für Verhalten bei denen die Verhaltensstabilität in Frage gestellt werden kann, zum Beispiel bei Brudermord (engl. siblicide). Das Wissen darüber wie ein Gleichgewicht erreicht wird erlaubt es Rückschlüsse zu ziehen, wer die Kontrolle über die Verhaltensinteraktion besitzt.
Im ersten Teil meiner Arbeit (Kapitel 2) untersuchte ich die Stabilität von Verhaltensinteraktionen und ob diese mit ESS kompatibel sind. In einem einfachen Zwei-Spieler Modell mit wiederholten, nacheinander abfolgenden Interaktionen habe ich herausgefunden, dass nur die Hälfte der Verhaltensinteraktionen zu Stabilität führen und damit auch eine verhaltensstabile Strategie (BSS = behaviourally stable strategy) repräsentieren. Bei Kompatibilitätstest zwischen BSS und ESS fand ich heraus, dass tatsächlich eine beträchtliche Anzahl von ESS mit keiner BSS kompatibel waren.
Im zweiten und dritten Teil meiner Arbeit (Kapitel 3, 4 & 5) führte ich Laborexperimente mit Ohrwürmern durch, um abzuschätzen wie Verhaltensinteraktionen durch externe (umweltbedingte) und interne (individuelle) Faktoren beeinflusst werden können. In einem ersten Experiment manipulierte ich das Nahrungsniveau von Nymphen und Weibchen und damit einhergehend deren Hungerzustand. Kombinierung von Nymphen und Weibchen aus verschiedenen und gleichen Nahrungsniveaus (Vertauschungsexperiment; engl. cross-fostering) erlaubte es mir Rückschlüsse zu ziehen wie Nymphen und Weibchen auf den Hungerzustand des Anderen (Umwelt) reagieren, und wie stark diese Reaktion durch den eigenen Hungerzustand beeinflusst wird. Die Resultate zeigten auf, dass das Verhalten der Weibchen nur auf ihrem eigenen Hungerzustand beruht und dass das Verhalten der Nymphen sowohl von ihrem eigenen als auch vom Hungerzustand des Weibchens abhängt. In einem zweiten Experiment untersuchte ich ob Nymphen verwandte Nymphen erkennen können und ob Verwandtschaft das Tötungs- und Kannibalismusverhalten der Nymphen beeinflusst. Ich fand heraus, dass Nymphen verwandte Nymphen erkennen können und dass sowohl Tötungs- als auch Kannibalismusverhalten von der Verwandtschaft zweier interagierender Nymphen beeinflusst wird.
Alle drei Teile meiner Arbeit zeigen auf, dass Interaktionen zwischen Angehörigen einer Familie wichtig sind, weil diese ihre eigene Verhaltensstabilität und evolutive Stabilität beeinflussen. Im Verlaufe der Zeit können Verhaltensinteraktionen die evolutionäre Stabilität von Strategien bestimmen. Selektion kann nur auf BSS wirken, weil diese ein über Verhalten erreichbares Gleichgewicht besitzen, welches für evolutive Stabilität notwendig ist. Es ist daher von grundlegender Wichtigkeit Wissen über Verhalten (auf welche Art und Weise interagieren zwei Individuen, wer hat die Kontrolle über das Verhalten) und dessen Stabilität (z.B. beim Brudermord) zu haben um Rückschlüsse über dessen evolutionäre Stabilität ziehen zu können
Developmental changes in the BDNF-induced modulation of inhibitory synaptic transmission in the Kölliker-Fuse nucleus of rat
No full textThe Kolliker-Fuse nucleus (KF), part of the pontine respiratory group, is involved in the control of respiratory phase duration, and receives both excitatory and inhibitory afferent input from various other brain regions. There is evidence for developmental changes in the modulation of excitatory inputs to the KF by the neurotrophin brain-derived neurotrophic factor (BDNF). In the present study we investigated if BDNF exerts developmental effects on inhibitory synaptic transmission in the KF. Recordings of inhibitory postsynaptic currents (IPSCs) in KF neurons in a pontine slice preparation revealed general developmental changes. Recording of spontaneous and evoked IPSCs (sIPSCs, eIPSCS) revealed that neonatally the gamma-aminobutyric acid (GABA)ergic fraction of IPSCs was predominant, while in later developmental stages glycinergic neurotransmission significantly increased. Bath-application of BDNF significantly reduced sIPSC frequency in all developmental stages, while BDNF-mediated modulation on eIPSCs showed developmental differences. The eIPSCs mean amplitude was uniformly and significantly reduced following BDNF application only in neurons from rats younger than postnatal day 10. At later postnatal stages the response pattern became heterogeneous, and both augmentations and reductions of eIPSC amplitudes occurred. All BDNF effects on eIPSCs and sIPSCs were reversed with the tyrosine kinase receptor-B inhibitor K252a. We conclude that developmental changes in inhibitory neurotransmission, including the BDNF-mediated modulation of eIPSCs, relate to the postnatal maturation of the KF. The changes in BDNF-mediated modulation of IPSCs in the KF may have strong implications for developmental changes in synaptic plasticity and the adaptation of the breathing pattern to afferent inputs
Scent-marking behaviour and social dynamics in a wild population of Eurasian lynx Lynx lynx.
No full textScent-marking is widespread among mammals and has been observed in many felid species. Although the behaviour is well-described, little is known about its function in wild felid populations. We investigated patterns of scent-marking and its role in intra- and intersexual communication among resident and non-resident Eurasian lynx Lynx lynx by observing interactions among wild lynx at natural marking sites by means of infrared camera traps. Marking activity of resident animals showed a peak during the mating season and was lowest during the time when females gave birth and lactated. Both sexes scent-marked, but male lynx visited marking sites much more often than females and marked relatively more often when visiting a site. Most visits to marking sites were by residents but we also observed scent-marking by non-residents. Juveniles were never observed marking. We found no evidence of lynx regularly renewing scent-marks after a certain 'expiry date' but the presence of a strange scent-mark triggered over-marking. Males responded similarly to the presence of another individual's scent-mark, irrespective of whether it was the top- or the underlying scent-mark in a mixture of scent-marks they encountered. Our results suggest that marking sites could serve as 'chemical bulletin boards', where male lynx advertise their presence and gain information on ownership relationships in a given area. Females placed their urine marks on top of the ones left by resident males, but further studies are needed to explain the functions of over-marking in females
Sociogenomics of maternal care and parent-offspring coadaptation in the European earwigs (Forficula auricularia)
No full textConflict and cooperation are ubiquitous in nature and in animal families where parents and offspring reciprocally influence each other's behavior and fitness. Evolutionary models predict selection for parent-offspring coadaptation that strike balance between parents pursuing self-fitness versus offspring demanding parental investment. Ultimately, it facilitates well-coordinated parenting and optimized cooperation with their offspring in the face of sexual reproduction and genetic recombination which cause genetic conflict. However, the genomic basis of parent-offspring coadaptation is poorly understood. My dissertation focused on the sociogenomics of materanl care and parent-offspring coadaptation in the European earwig (Forficula auricularia), a facultative uni-parental female care insect.
In the first chapter, we sequenced the transcriptome of the European earwig from various tissues and developmental stages of female and male applying Roche 454 pyrosequencing and Illumina HiSeq. The reads were de novo assembled independently and screened for possible microbial contamination and repeated elements. Hybrid assembly of these data yield comprehensive transcriptome with a low level of fragmentation comparing to the eukaryotic core gene dataset. More than 8,800 contigs of the hybrid assembly show significant similarity to insect-specific proteins and those were assigned for Gene Ontology terms. Finally, I validated the transcriptome and established a quantitative PCR method and applied it to homologs of five known sex-biased genes of the honeybee. The qPCR pilot study confirmed sex specific expression and also revealed significant expression differences between the brain and antenna tissue samples. The transcriptome presented here offers new opportunities to study the molecular bases and evolution of parental care and sociality in arthropods.
In the second chapter, I identified two parent-offspring coadapted genes, PebIII and Th, in the European earwig, based on comparative transcriptomics from experimentally manipulated mother-offspring interactions. Functional study applying RNAi revealed that PebIII in offspring enhances survival, in mothers enhances their relative investment in future reproduction and indirectly delayed offspring development; Th in mothers enhanced food provisioning, in offspring indirectly enhanced the likelihood of maternal future reproduction. These results suggested PebIII being reciprocally selfish while Th being reciprocally altruistic in both mothers and offspring. Metabolic pathway analyses further indicated the role of Th-restricted dopaminergic reward, PebIII mediated chemical perception and regulations between insulin signaling, juvenile hormone and vitellogenin in parent-offspring coadaptation and social evolution.
In the third chapter, I manipulated the interaction between earwig mothers and offspring over two generation and investigated transgenerational effects of maternal care on the expression of the two parent-offspring coadapted genes found in chapter2 and the fitness consequences in mothers and offspring. Significant transgenerational effects were found for the expression of PebIII and Th in the head of mothers. The expression of PebIII in the whole body of offspring showed significant effects of transgeneration treatment, current generation treatment and current generation by transgeneration treatments interaction. Significant transgenerational effect was found for relative maternal investment in future reproduction and offspring growth rate. Maternal future reproduction and latency for maternal future reproduction showed significant effects of current generation parental care treatment. Our results indicates an epigenetic regulation of gene expressions underlying parent-offspring coadaptation.
In the last chapter, the expressions of parent-offspring coadapted genes were validated using Fluidigm gene expression dynamic array. An additional treatment was included to control for time effect. We found the regulation of Th and PebIII were not influenced by the interaction between parent and offpsirng per se, but rather controlled by the reproductive stage of mothers suggesting preprogrammed expression in earwig. Such regulation of parenting genes in the sub-social species might be ancestral to the age-dependent division of labor in eusocial system.
These four chapters of my thesis were a series of continuous work and provided significant insights into the genomic basis of parent-offspring coadaptation. I established qPCR method to validate the de novo hybrid assembled transcriptome of the European earwig. I identified candidate parent-offspring coadapted genes using comparative trascriptomics. I established the method of Fluidigm gene expression dynamic array for earwigs to validate the RNA-Seq results. I established the RNAi techonology for earwigs to manipulate gene expressions and to study the social function of candidate genes. I demonstrated that PebIII and Th are two parent-offspring coadapted genes, which are co-regulated in mothers and offspring during active post-hatching parental care. Their expression were preprogrammed in mothers, reflecting the reproductive stage of females. Both genes showed causal effects on the behavior and fitness of earwig mothers and nymphs, coordinating the selfishness and altruism in family life. I showed transgenerational effects of maternal care on the expression of PebIII and Th, and opened the door for future studies of the epigenetic mechanisms regulating gene expression over generations and maintaining parent-offspring coadaptation in earwigs
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