Browsing by Subject "allometry"

In recent years, the two-spotted field cricket Gryllus bimaculatus has emerged as a central model for studies on insect development, regeneration and physiology. At the moment, G.bimaculatus has the most extensive molecular toolkit within the Exopterygota, making it the foremost model for evolutionary developmental biology and comparative physiology within the field of entomology. However, the postembryonic development of G. bimaculatus has received considerably less attention than embryonic development. In this thesis, I have studied the postembryonic development of G. bimaculatus to better understand the evolution and physiology of the understudied Exopterygota. My thesis encompasses five parts: postembryonic morphology, wing development, appendage regeneration, allometry, and growth. The postembryonic stages, the nymphal stages, have never been properly characterised in G. bimaculatus. By following postembryonic development daily at 30 C, 8 nymphal stages (instars) were identified. Size, coloration, sclerotisation of the thorax, and morphology of the wings, the hind tibia and the ovipositor were useful characters in distinguishing the stages. The Dpp/BMP signalling pathway patterns the wing venation in the endopterygotan insects Drosophila melanogaster and Athaliae rosae, but nothing is virtually known about wing development in exopterygotan insects. The wings and the wing venation pattern in different nymphal stages of G. bimaculatus were studied using the hydrogen peroxide clearing protocol along with both brightfield and fluorescence microscopy, while the role of the Dpp/BMP signalling pathway was studied using immunohistochemistry (IHC), in situ hybridisation (ISH), and RNA interference (RNAi). The longitudinal veins are patterned in the 3rd and 4th nymphal stages, while the secondary veins in the 8th stage. The IHC and ISH experiments displayed only non-specific staining, while the RNAi experiments did not produce any change in the phenotype, possibly because of molecular redundancy. The nymphal legs of G. bimaculatus are known to be highly regenerative, and the Dpp/BMP signalling pathway has been shown to provide positional information in leg regeneration. However, nothing is known about the regeneration of the other appendages in G. bimaculatus. Antennae and cerci were amputated in different nymphal stages, and the degree of final regeneration depended on the nymphal stage. RNAi experiments did not produce any change in the phenotype, possibly because of molecular redundancy. The interrelationship between static, ontogenetic and evolutionary allometry in insects is poorly understood. The allometry of hind femur length with respect to body length has been shown to be negative in Orthoptera (i.e. evolutionary allometry), but nothing is known about corresponding ontogenetic and static allometry. By measuring hind femur length and body length in G. bimaculatus in different nymphal stages, the ontogenetic allometry was determined to be slightly positive or isometric, while the static allometries of different stages tended to be negative but highly variable. This may indicate that allometric relationships constrain development in the microevolutionary perspective, but are nevertheless evolvable in a macroevolutionary perspective of millions of years. The growth conditions and rearing of crickets and other insects have been widely reported, but the shape of the growth curve itself has been less investigated. The exponential, the von Bertalanffy (VBGF), the West, Brown and Enquist (WBE), and the dynamic energy budget (DBE) models have been proposed as continuous models for insect growth. These models were t to growth data from G. bimaculatus and the DBE and was shown to be optimal with parameter values α=0 and pAm = 0.69. The insects have been thought to follow Dyar's law, i.e. that the growth ratio or moulting increment (MI) is constant throughout development, although numerous other competing moulting models have been devised for the crustaceans. By fitting different moulting models to head width data from G. bimaculatus, the log-linear model (Mauchline's model) turned out to explain the MI the best. Lastly, the oxygen-dependent induction of moulting (ODIM) model has been proposed to explain moulting patterns in insects, but the model has never been applied to exopterygotan taxa. By fitting the ODIM model to growth data from G. bimaculatus, the model could predict moulting mass but not instar durations, probably because of high postembryonic plasticity in G. bimaculatus.

Physiologically based pharmacokinetic modelling (PBPK) can be used to predict pharmacokinetic behaviour of new drug molecules in human. PBPK model represents the body anatomically and physiologically with compartments connected to each other and combines those to drug specific parameters. PBPK modelling can be used to predict the absorption, disposition, and time-concentration profiles of drug molecules. The purpose of the study was to build a PBPK model for new drug molecule under research (compound A) and predict pharmacokinetics in human, to support the selection of dosing interval, formulation, and sampling time points for the first clinical trial. In this work it is described the building of the model in the ”bottom-up”-approach using in vitro parameters in GastroPlusTM-software. The modelling was done also for preclinical species (mouse, rat, dog) comparing the simulations to the observed in vivo data, which gave the confidence to the methods used in the modelling also for human. The model was first built for systemic kinetics and thereafter it was used for predicting pharmacokinetics after oral dosing. Parameters of systemic kinetics were compared also to the predictions from allometric scaling. Based on the preclinical species the most predictive method for the volume of distribution of compound A was the method by Lukacova, which predicted the volume of distribution to be moderate in human (1.7 l/kg). From the in vitro-to-in vivo -extrapolation methods the most predictive method to predict the clearance was the method by Poulin, which predicted low clearance in human (8.1-14.3 l/h). Empirical scaling factors based on the preclinical data were not needed, as the models predicted well the observed in vivo data. Allometric methods predicted the systemic kinetic parameters to be in the similar range. Advanced compartmental absorption transit -model (ACAT) integrated to GastroPlusTM-software predicted the absorption after oral dosing well in the preclinical species (predicted/observed ratio 0.8-1.3 for systemic exposure) despite the low solubility of the compound A. The model predicted the absorption in human to be sensitive to particle size and absorption rate to be clearly affected by the particle size. The feeding status was also predicted to affect on the absorption with larger particle sizes. The gut metabolism was not predicted to limit the oral exposure notably, whereas moderate bioavailability was predicted to be achievable. Compound A could be given in a capsule if the target particle size distribution could be achieved. The built PBPK-model can be used in the future to predict the first clinical doses by comparing the predicted plasma concentrations to in vitro pharmacodynamic parameters and to the plasma concentrations needed for efficacy in the pharmacodynamic models. The model can also be used to predict the drug-drug interactions.