Diving muskrats (Ondatra zibethica) invoke a series of cardiovascular and respiratory adjustments in response to stimulation of the nares with water. This dive response is characterized by apnoea, a decrease in cardiac output and an increase in peripheral resistance. The result is that blood flow is maintained to those organs most susceptible to oxygen deprivation, the heart and the brain. The initiation of the dive response in mammals is primarily the result of nasal stimulation with water. In addition, the baroreceptors acting via the baroreflex have been suggested to be involved in either the initiation or the maintenance of this response. The chemoreceptors, acting via the chemoreflex, have also been implicated in the maintenance of the dive response, although the importance of this contribution is controversial. The purpose of this thesis was to examine the role of the baroreceptors and chemoreceptors in the diving response of the muskrat. Changes in input from these receptors recorded from the cut carotid sinus nerve and their modulation by the carotid sinus efferent activity during nasal stimulation may have important implications for the role of the baroreceptors and chemoreceptors in the diving response. In the initial part of the dive, baroreceptor activity decreased, while chemoreceptor activity did not change. Subsequently, baroreceptor and chemoreceptor activity increased, exceeding pre-dive levels. This increase was not due to a change in receptor threshold or sensitivity induced by the nasal stimulation, but was a reflection of the increase in the usual stimulus modality of both receptor groups. The efferent activity recorded from the central end of the cut carotid sinus nerve was of two types, both of which responded to nasal stimulation. This change in the efferent discharge has the potential to modify afferent activity. Nasal stimulation caused one type of efferent activity (type A) to stop. The second type of efferent activity (type B) responded with an initial increase in discharge, returning to pre-dive levels after 6.6 seconds. Based-on the similar characteristics of these efferents to those of previous work it is postulated that the actions of the efferents would be to inhibit the baroreceptors and chemoreceptors during the initiation of the nasal stimulation, but to be less effective as the dive progressed. It is concluded that there is no contribution from the baroreceptors to the initiation of the diving bradycardia, although the lack of baroreceptor activity may contribute to the increase in peripheral resistance. Later in the dive, both heart rate and arterial blood pressure increase, despite a concomitant elevation in baroreceptor activity. The baroreceptors therefore have no role in the maintenance of the diving response. The initial inhibition of the chemoreceptors may be important to permit the full expression of the dive response, including a decrease in central respiratory output. Later in the dive the chemoreceptors may contribute to the maintenance and termination of the diving response. / Science, Faculty of / Zoology, Department of / Graduate

Heart rate was found to be significantly lower in unrestrained diving muskrats than in those which were forced to dive. The response in the unrestrained animal represents a heart rate of about 9% of the resting rate and is similar to the cardiac responses recorded in freely diving pinnipeds. Apnea and bradycardia were initiated by water lapping the nares of the conscious animal. Anaesthesia abolished this narial reflex to submersion. In anaesthetized muskrats water was drawn into the nasal cavity causing transient apnea and prominent bradycardia by stimulating receptors located principally in the glottal and pharyngeal areas. Nerve blockade by reversible cooling and section demonstrated that these nasal receptors are innervated by the maxillary and inferior, laryngeal nerves. In the conscious animal trigeminal neurotomy failed to affect the course of the response confirming that the muskrat has a number of external sensory mechanisms capable of initiating the diving reflexes. Respiratory activity was shown to have a marked effect on heart rate when the muskrat was at rest and when water was passed through the nares. Cardioacceleration during nasal stimulation resulted from a central component and from neural input originating in fast adapting pulmonary receptors. Artificial ventilation not only increased heart rate but often tended to restore normal respiratory activity. Pulmonary deafferentation by steaming eliminated the Hering-Breuer reflex to maintained lung inflation as well as the cardioacceleration seen in response to artificial ventilation during nasal stimulation. The loss of the Hering-Breuer reflex occurred first suggesting that different receptors are involved. Lung deflation per se caused a reflex bradycardia but it appears that this does not potentiate the narial reflex since nasal bradycardia was not reduced when lung inflation was maintained. Central and peripheral components arising from respiratory activity have their greatest effect during the recovery period. Elimination of the carotid bodies delayed but did not abolish chemoreceptor driven bradycardia demonstrating that these are the most chemosensitive units but not the only ones responding to changes in blood gas tensions. No role however, has been found for the arterial baroreceptors. The barostatic reflex brought on by drug induced hypertension was triggered at a lower pressure than that found in the seal but it appears that this pressure would not be exceeded in the muskrat if heart rate remained low during a dive. It is concluded that the cardiac response to submersion in the muskrat results from at least three reflex arcs. These reflexes originate from the nares, the lungs and from peripheral chemoreceptors. Although the chemoreceptors act to maintain the prevailing diving responses, it is likely that the external narial reflex accounts for almost all of the cardiovascular adjustment brought about in normal foraging dives since these are usually of short duration. The chemoreflex could play a significant role in dives exceeding one minute by prompting the animal to resurface when oxygen stores are depleted. / Science, Faculty of / Zoology, Department of / Graduate

Abstract In order to examine the prevalence of Cryptosporidium in wild Arvicolinae in the Czech Republic and understand the role that wild rodents play in the transmission of this parasite to humans and livestock, 152 faecal samples from 129 common voles (Microtus arvalis) and 23 bank voles (Clethrionomys glareolus) were collected on 9 localities in 2012. All samples were examined for presence of Cryptosporidium sp. using both the aniline-carbol-methyl violet staining method and molecular tools. The age, sex and faecal consistency were noted at the time of sampling. Microscopical examination revealed the presence Cryptosporidium sp. oocysts in 2 samples originated from common voles and 2 samples from bank voles. Genotyping was done through PCR amplification and characterization of the SSU rRNA and actin loci. Cryptosporidium specific DNA was detected in 10 samples (4 from common voles and 6 from bank voles) including those microscopically positive. Cryptosporidium infection was not linked to diarrhoea. Sequence and following phylogeny analyses revealed two new Cryptosporidium genotypes originated from bank voles and two new genotype from common vole, phylogeneticaly distinct from known species and genotypes. The host specificity needs to be verified by experimental infection in the future.

Cranial and external measurements in 422 museum specimens of the common vole, Microtus arvalis, from Switzerland were examined to determine whether they varied with altitude in accordance with either (1) Bergmann's Rule, or (2) subspeciation. Correlation coefficients between altitude and size were calculated on 32 dimensions, each of which had been divided into sex segregated age groups. In not one of the 108 tests was correlation significant. The lack of adherence to Bergmann's Rule was investigated by (1) reviewing the basic concepts of the Rule, as applied to homeotherms; (2) identifying the major abiotic and biotic selection pressures that might affect growth in Microtus arvalis, including climate and competition with sympatric congenerics; and (3) indicating deficiencies in data derived from museum specimens which might have influenced the computations. There were several references in the literature to the occurrence of two subspecies of Microtus arvalis in Switzerland - the nominate subspecies M. a. arvalis (Pallas, 1779) and a montane subspecies called either M. a. incertus (Selys-Longchamps, 1841) or M. a. rufescentefuscus (Schinz, 1845). The lack of evidence in this study for the existence of two phenotypically and distributionally distinct subspecies was considered by (1) examining the general appropriateness of discussing variation in Microtus arvalis in terms of subspeciation; and (2) reviewing the literature on the diagnostic characters and distribution attributed to the montane morph. Two major conclusions were drawn. The first was that Bergmann's Rule should not be considered a "rule" until firm definitions are established on at least two of its founding precepts - the groups of animals to which it applies and the taxonomic level at which it applies - and until it is found to apply to a majority of the cases for which it is intended. The second conclusion was that for species like Microtus arvalis, in which growth is highly variable and distribution is by and large continuous, the usefulness of formal recognition of in-fraspecific populations is questionable until an overview of the geographic variability of the species as a whole is well documented. / Science, Faculty of / Zoology, Department of / Graduate

L'acquisition, en laboratoire, des génomes mitochondriaux complets de plusieurs espèces de rongeurs Arvicolinae permet la définition de l'histoire évolutive du groupe dans un cadre évolutif et temporel. Ces relations phylogénétiques sont inférés sur un grand nombre de caractères (16000 pb), grâce à des méthodes d'analyses statistiques novatrices.La base de données moléculaires constituée représente un échantillon de génomes mitochondriaux à évolution dite "rapide", ouvrant des perspectives quant à la description des points chauds mutationnels dans des études de génomique comparative, et permettant d'identifier plus globalement la source de l'hétérogénéité des taux de substitution mitochondriale au sein des génomes mitochondriaux des Mammifères. / Experimental acquisition of complete mitochondrial genome for several Arvicolinae species allows defining evolutionary history of the group in evolutionary and temporal frames. These phylogenetic relationships are inferred on a great number of characters (16000 bp), thanks to innovator statistical analysis methods.Constituted molecular data set represents a sample of "fast evolving" mitochondrial genomes, and allows describing mutational hots spots in comparative genomic studies, and identifying globally the origin of mitochondrial substitution rate heterogeneity detected in Mammalian mitochondrial genomes.

L’évolution de la dentition des mammifères se caractérise par d’importantes innovations morphologiques comme la mise à occlusion et l’hétérodontie. Parmi rongeurs, dont la formule dentaire est fortement réduite, les arvicolinés possèdent une dentition hautement dérivée, avec des molaires prismatiques et hypsodontes. L’objectif de cette thèse est d’explorer les différentes innovations morphologiques de la dentition au travers des aspects développementaux et adaptatifs. Les méthodes de morphométrie géométrique sont utilisées sur les molaires, les incisives et les mandibules afin d’explorer les dynamiques de développement et d’évolution de la dentition. Un modèle développemental permettant de prédire les proportions de molaires inférieures est examiné et validé à l’échelle de l’ordre des rongeurs ; il peut également être étendu à la prémolaire. De plus, le lien entre la morphologie dentaire, notamment les proportions de molaires, et le régime alimentaire est complexe, un caractère morphologique ne reflétant pas directement une alimentation. Cependant les covariations entre les molaires marquent le mouvement de mastication et ainsi la fonction. Nos résultats confirment une imbrication complexe des contraintes historiques, fonctionnelles et développementales dans l’interprétation des morphologies. Les différentes composantes de la mandibule présentent une organisation hiérarchique complexe. Le développement de la dentition des mammifères est gouverné par des processus similaires mais des mécanismes tels que l’hétérochronie ont pu conduire à une diversification des phénotypes au cours du temps. / The evolution of mammalian dentition is defined by profound morphological modifications as occlusion and heterodonty. Among rodents, characterized by a reduced dental formula, arvicolines have a highly derived dentition, with prismatic and hypsodont molars. The aim of this Ph.D thesis is to explore various morphological innovations through developmental and adaptive aspects. Geometric morphometric methods were used on molars, incisors and mandibles to investigate the dynamics of development and evolution of dentition. A developmental model predicting molar proportions is tested and confirmed for the rodent order; it could be also extended to the premolar. The relationship between dental morphology, in particular molar proportions, and diet is complex, diet being not directly inferred from one morphological trait. Yet, covariations between molars inform on masticatory movement and thus on function. Our results confirmed that morphologies could be understood from a complex combination of historical, functional and developmental constraints. The various structures of the mandible have a complex hierarchical organization. The development of mammalian dentition is controlled by similar processes but through times, mechanisms as heterochrony may lead to a diversification of phenotypes.

Force dived animals undergo cardiovascular changes characterized by bradycardia, increased total peripheral resistance, and changes in blood flow distribution. Since these changes occur in decerebrated animals, the dive response must be a brainstem reflex. However, in voluntary dives, animals may show anticipatory bradycardia and may also adjust their cardiovascular responses according to anticipated dive duration, indicating suprabulbar influences upon dive responses. Studies of heart rate using telemetry have shown that there can be substantial differences in the dive response of voluntarily and force dived animals. Furthermore, some animals show a "fear bradycardia" when trapped in a stressful situation, leading some researchers to suggest that bradycardia during forced submersion is an artifact of the stress of the situation. Muskrats (Ondatra zibethica) were observed freely diving for food in an indoor tank using a video camera and VCR unit. EKG was telemetered from the animals and recorded on the audio channel of the VCR tape. Heart rate responses to voluntary dives were analyzed and compared with those from escape and forced dives. Heart rate responses were also recorded from decorticate and sham operated muskrats to elucidate the role that the cerebral cortex plays in the dive response. In all types of dives, muskrats exhibited a rapid and large bradycardia upon submergence (heart rate declined by greater than 55% of the predive heart rate). Obviously diving bradycardia in the muskrat was not due to fear or stress, but occurred as a response to submersion per se. There was no evidence of post-dive tachycardia or anticipatory immersion bradycardia. Disturbing the animal in a non-diving situation resulted in only a 13% decrease in heart rate. In intact animals voluntary, escape, and forced submergence resulted in progressively greater decreases in heart rate. Heart rate fell by 56% in voluntary dives, 65% in escape dives, and 73% in forced dives. Intensification of the bradycardia to a lower heart rate than that seen in voluntary dives was mediated by the cerebral cortex, as heart rate in decorticate muskrats in escape and forced dives did not fall below that seen in voluntary dives. This indicates that the final adjustment of dive heart rate is dependent upon an intact cerebral cortex. However, in decorticate muskrats there appeared to be a recovery of cortical function, as intensification of bradycardia in forced dives was dependent upon the time that had elapsed after surgery. This study shows that there is a cortical influence upon the cardiovascular system during diving. It also indicates that in experiments with unanesthetized animals, the degree of stress of the situation must be taken into account, as this may affect physiological responses. / Science, Faculty of / Zoology, Department of / Graduate

The topic of the presented thesis is evolution of the arvicoline rodents (Cricetidae) using the phylogenetic approach. Phylogenetic relationships within the Arvicolinae were examined based on two genes (mitochondrial cytb, nuclear GHR exon 10) and approx. 470 morphological, developmental, behavioural, ecological and cytogenetic characters. The thesis consists of four related topics: (i) Phylogeny of arvicoline rodents (Robovský et al. 2008: Zool. Scr. 37: 571-590); (ii) Fossils, phylogeny and morphological evolution in the Arvicolinae (Rodentia: Cricetidae); (iii) Enamel, diet and habitat evolution in arvicoline rodents (Cricetidae); and (iv) Vole population cycles: evolutionary history or actual life histories?.