Social networks and individual behaviour variation in wild crickets

David Newton Fisher's thesis post correctionsIndividuals engage in competitive and cooperative interactions with conspecifics. Furthermore, within any population of interacting individuals there are typically consistent differences among-individuals in behavioural traits. Understanding the importance of both these types of individual-specific behaviours allows us to understand why populations are structured as they are, why individuals show apparently limited behavioural flexibility, and how these elements link to population-level properties. I used extensive video camera monitoring of a population of wild field crickets (Gryllus campestris) to study the interactions and behaviours of uniquely identified individuals. I studied the shyness, activity and exploration of individuals of this population across contexts: from young to old and between captivity and the wild. This allowed me to confirm that individuals were relatively consistent across their adult lifetimes for all three traits, but only consistent between captivity and the wild for activity and exploration. I then found that high activity levels were positively related to high mating rates and short lifespans. Crucially, lifetime mating success was not related to activity level, indicating that the trade-off between lifespan and mating success was sufficient to allow variation in activity level to persist across generations. I also found that cricket social network structure is stable across generations despite the complete turnover of individuals every year. This social network structure influences sexual selection, with some male crickets heavily involved in networks of both pre- and post-copulatory competition, yet males are unable to use pre-copulatory competition to avoid post-copulatory competition. Additionally, positive assortment by mating rate between males and females may reduce the fitness of males with high mating rates, as they face stronger sperm competition. Finally, I used actor-based models to determine the factors predicting cricket social network structure and to test and reject the social-niche hypothesis for the maintenance of among-individual variation in behaviour. I also demonstrated that little else is needed in a stochastically changing network aside from positive assortment by mating rate to simulate a population with a similar skew in mating success to the one observed in the real cricket population. These results give insights into the importance of trade-offs and stochasticity in maintaining the extensive variation in the natural world.Natural environment research counci

Tarsal intersegmental reflex responses in the locust hind leg

Locomotion is vital for vertebrates and invertebrates to survive. However, the mechanisms for locomotion are partially unknown. Central Pattern Generators and reflex systems have been shown to be the basis of most movements performed by arthropods. Much has been investigated lately on Central Pattern Generators, but little work has been done in reflex systems. Locomotion and motor output in feet (or tarsus in arthropods) has also been disregarded in research. Despite that feet are responsible for stability and agility in most animals, research on feet movements is scarce.In this thesis the tarsal intersegmental reflex of the locust hind leg is investigated. The tarsal reflex consists of a response in the tarsus when there is a change in the femoro-tibial joint. The main objective of the thesis is to describe the system and to develop mathematical and experimental methods to study, model and analyse it. Through a set of experiments is shown that as the knee joint is extended, the tarsus is depressed, and as the knee joint flexes, the tarsus levates. The experiments demonstrated that there is a purely neuronal link between the femoro-tibial joint position and the tibio-tarsal joint position. Moreover, it also reveals the effect of neuromodulatory compounds, such as dopamine, serotonin or octopamine. The tarsal reflex responses are fairly consistent across individuals, although significant variability across animals was found.To model a system where variability is an issue, a mathematical model with strong generalisation abilities is used: Artificial Neural Networks (ANNs). To design the ANNs, a metaheuristic algorithm has been implemented. The resulting ANNs are shown to be as accurate as other mathematical models used in physiology when used in a well known reflex system, the FETi responses. This results showed that ANNs are as good as Wiener methods in predicting responses and they outperform them in prediction of Gaussian inputs. Furthermore, they are able to predict responses in different animals, independently of the variability, with a more limited performance.New experimental methods are also designed to obtain accurate recordings of tarsal movements in response to knee joint changes. These experimental methods facilitate the data acquisition and its accuracy, reducing measurement errors. Using the mathematical methods validated, these responses are modelled and studied, showing responses to Gaussian and sinusoidal inputs, variability across individuals and effects of neuromodulators.With the tarsal reflex described and modelled, it can be used as a tool for further research in disciplines such as medicine, in the diagnose and treatment of euromuscular dysfunction or design of prosthesis and orthoses. This model can also be implemented in robotics to aid in stability when walking on irregular terrain

Serotonergic modulation of the ventral pallidum by 5HT1A, 5HT5A, 5HT7 AND 5HT2C receptors

Introduction: Serotonin's involvement in reward processing is controversial. The large number of serotonin receptor sub-types and their individual and unique contributions have been difficult to dissect out, yet understanding how specific serotonin receptor sub-types contribute to its effects on areas associated with reward processing is an essential step. Methods: The current study used multi-electrode arrays and acute slice preparations to examine the effects of serotonin on ventral pallidum (VP) neurons. Approach for statistical analysis: extracellular recordings were spike sorted using template matching and principal components analysis, Consecutive inter-spike intervals were then compared over periods of 1200 seconds for each treatment condition using a student’s t test. Results and conclusions: Our data suggests that excitatory responses to serotonin application are pre-synaptic in origin as blocking synaptic transmission with low-calcium aCSF abolished these responses. Our data also suggests that 5HT1a, 5HT5a and 5HT7 receptors contribute to this effect, potentially forming an oligomeric complex, as 5HT1a antagonists completely abolished excitatory responses to serotonin application, while 5HT5a and 5HT7 only reduced the magnitude of excitatory responses to serotonin. 5HT2c receptors were the only serotonin receptor sub-type tested that elicited inhibitory responses to serotonin application in the VP. These findings, combined with our previous data outlining the mechanisms underpinning dopamine's effects in the VP, provide key information, which will allow future research to fully examine the interplay between serotonin and dopamine in the VP. Investigation of dopamine and serotonins interaction may provide vital insights into our understanding of the VP's involvement in reward processing. It may also contribute to our understanding of how drugs of abuse, such as cocaine, may hijack these mechanisms in the VP resulting in sensitization to drugs of abuse

The changing roles of Hox3 genes in insect evolution: characterizing the zen paralogues in the beetle Tribolium castaneum

Hox genes encode transcription factors responsible for the determination of axial patterning of all bilaterian embryos. However, insect Hox3 orthologues, named zerknüllt (zen), have changed their function multiple times, which led to the abandonment of the canonical Hox function, and subsequent switch of their functional domain from embryonic to extraembryonic tissue. To date, in fact, all described zen genes play role in extraembryonic membranes (EEMs). The EEMs protect the embryos from the insults of the outer environment and their formation allowed insects to oviposit in various niches, ultimately allowing them to colonize land. The evolution of the EEMs is tightly linked to the evolution of Hox3/zen. Concurrently with the origin of EEMs, Hox3 has gradually switched from embryonic role to zen´s function in the EEMs. However, it is only within winged insect that the complete transition from Hox3 to zen and complete EEMs are observed. Further, besides switching to extraembryonic tissue, in this new domain, zen genes have also acquired two different functions: one in early tissue specification and the other in late morphogenesis. However, little is known about the causes triggering the switch from Hox3 to zen, and the subsequent functional divergence of zen. Here, in order to get insight into what has triggered the functional divergence of zen, I focused on the holometabolous beetle Tribolium castaneum, as two functionally diverged paralogues were described: one with the function during early embryogenesis (Tc-zen1) and the second one with the function during late embryogenesis (Tc-zen2). In order to decipher how the two diverged functions of Tc-zen1 and Tc-zen2 were acquired, I investigated transcriptional and translation regulation of both Tc-zen genes during early and late embryogenesis. I showed that, although the early function was described only for Tc-zen1, both paralogues reach their expression peak during early embryogenesis. To reveal the degree of divergence in transcriptional targets between the paralogues during early development, I knocked down (via parental RNA interference, pRNAi) the Tc-zen genes and performed RNA-sequencing (RNA-seq). Differential expression (DE) analysis and the subsequent comparative analysis of the identified targets of Tc-zen1 and Tc-zen2 suggest that the paralogues do not share substantial number of transcriptional targets during early embryogenesis. Additionally, principal component analysis revealed that despite the early expression of both paralogues, the impact of Tc-zen2 knockdown on early transcriptional control was significantly lower than for Tc-zen1, which is consistent with Tc-zen2 having a late function. Nonetheless, the analysis of expression levels of each zen gene in knockdown samples of its paralogue revealed a subtle regulatory function of Tc-zen2 during early embryogenesis, particularly in repression of Tc-zen1. To further investigate transcriptional regulation by Tc-zen2 during late embryogenesis, I have first showed that after the Tc-zen2 expression peak is reached during early embryogenesis, the low transcript expression persists until the late development. Consistent with the timing of the transcript expression, I showed that Tc-Zen2 protein is present until the late developmental stage, where its function takes place. To identify transcriptional targets of Tc-zen2 during late embryogenesis, I performed the second RNA-seq after pRNAi experiment. DE analysis revealed much higher impact of Tc-zen2 on transcriptional control during late embryogenesis than during early embryogenesis. The functional profile of candidate target genes of Tc-zen2 during late embryogenesis was obtained by thorough gene ontology (GO) term analysis. Consistent with the phenotypic manifestation of the morphogenesis function of Tc-zen2 during late embryogenesis, many of the identified candidate targets were assigned to GO terms with function in epithelial morphogenesis. In conclusion, the results obtained within the presented project suggest that acquirement of the two distinct functions of Tc-zen paralogues might be partially explained by two different transcriptional signatures they attained. While the function of Tc-zen1 temporally correlates with its expression peak and transcriptional regulation of its downstream targets, Tc-zen2, although expressed early, has very low impact on the downstream transcriptional regulation during early embryogenesis. Moreover, the fact that Tc-zen paralogues share very few targets during early embryogenesis suggests only subtle early regulatory roles of Tc-zen2 and separation of its morphogenesis function to late embryogenesis. This result was further endorsed by observation of Tc-zen2 transcript and protein expression throughout embryogenesis until the Tc-zen2 late function takes place. In addition, I identified a much higher number of Tc-zen2 candidate transcriptional targets during late embryogenesis, of which many likely play roles in epithelial morphogenesis. These diverse lines of evidence suggests that the diverged functions of Tc-zen1 and Tc-zen2 might have been acquired by regulation of different downstream transcriptional targets, which could have ultimately allow for separation of Tc-zen paralogues functions to early and late development