Molecular and ecological signs of mitochondrial adaptation: consequences for introgression?

The evolution of the mitochondrial genome and its potential adaptive impact still generates vital debates. Even if mitochondria have a crucial functional role, as they are the main cellular energy suppliers, mitochondrial DNA (mtDNA) introgression is common in nature, introducing variation in populations upon which selection may act. Here we evaluated whether the evolution of mtDNA in a rodent species affected by mtDNA introgression is explained by neutral expectations alone. Variation in one mitochondrial and six nuclear markers in Myodes glareolus voles was examined, including populations that show mtDNA introgression from its close relative, Myodes rutilus. In addition, we modelled protein structures of the mtDNA marker (cytochrome b) and estimated the environmental envelopes of mitotypes. We found that massive mtDNA introgression occurred without any trace of introgression in the analysed nuclear genes. The results show that the native glareolus mtDNA evolved under past positive selection, suggesting that mtDNA in this system has selective relevance. The environmental models indicate that the rutilus mitotype inhabits colder and drier habitats than the glareolus one that can result from local adaptation or from the geographic context of introgression. Finally, homology models of the cytochrome b protein revealed a substitution in rutilus mtDNA in the vicinity of the catalytic fraction, suggesting that differences between mitotypes may result in functional changes. These results suggest that the evolution of mtDNA in Myodes may have functional, ecological and adaptive significance. This work opens perspective onto future experimental tests of the role of natural selection in mtDNA introgression in this system.

Sex-specific selection on energy metabolism--selection coefficients for winter survival.

Selection for different fitness optima between sexes is supposed to operate on several traits. As fitness-related traits are often energetically costly, selection should also act directly on the energetics of individuals. However, efforts to examine the relationship between fitness and components of the energy budget are surprisingly scarce. We investigated the effects of basal metabolic rate (BMR, the minimum energy required for basic life functions) and body condition on long-term survival (8 winter months) with manipulated densities in enclosed populations of bank voles (Myodes glareolus). Here, we show that survival selection on BMR was clearly sex-specific but density-independent. Both the linear selection gradient and selection differential for BMR were positive in females, whereas survival did not correlate with male characteristics. Our findings emphasize the relative importance of individual physiology over ecological factors (e.g. intra-specific competition). Most current models of the origin of endothermy underline the importance of metabolic optima in females, whose physiology evolved to fulfil demands of parental provisioning in mammals. Our novel findings of sex-specific selection could be related to these life history differences between sexes.

[Experimental studies of the location of neural centers in the bovine uterus]. / Badania doswiadczalne nad lokalizacja osrodków nerwowych macicy u krowy.

Three cows of the black-and-white breed were used for the studies. In cow N.1 the ovary, oviduct and the uterus were excised. In cow N.2 the uterus cornua were excised. The control was cow N.3. The animals were slaughtered after 21 days from the operation and the following material was taken: medulla oblongata, the thoraco-lumbosacral segment of the spinal cord together with bilateral spinal ganglia and the sympathetic trunk ganglia, as well as nerve ganglia and plexi of the abdominal and pelvic cavities. The material was fixed in alcohol, embedded in paraffine and cut into 15 micron thick clises which were stained according to Nissel'a modified method. The analysis of the preparations ahowed that the central nervous system sends directly to the uterus a small number of nerve fibres from the following nuclei; of the vagus nerve (medulla oblongata), intermediolateralis, intermedio-medialis and of the cerebello-spinal tract (spinal cord). Most fibres innervating the uterus of the cow come from the ganglia and plexi of the peripheral vegetative system; mesenteric anterior, hypogastric, pelvic, visceral, mesenteric posterior and also form ganglia of the sympathetic trunk and spinal ganglia.

[Nucleus motorius lateralis in the lumbosacral segment of the spinal cord in horses]. / Nucleus motorius lateralis w odcinku ledzwiowo-krzyzowym rdzenia kregowego u konia.

Two medullae oblongatae of horses were cut into 15 microns cross-sections and stained according to the modified method of Nissel. The lateral motor nucleus lies in the lateral and median part of the ventral column of spinal cord grey matter. It adjoins medially nucleus motorius medialis of the spinal ventral column. Cells of this nucleus occur both along the whole lumbar and sacral segment of the spinal cord. In the lateral motor nucleus three cell groups are distinguished-median, basal and lateral. The latter is divided in some segments into subgroups-dorsal and ventral. Along the nucleus quite numerous constrictions and intervals are found, which are caused by various numbers of cells in particular cross-sections. Nucleus motorius lateralis is formed mainly of large and medium multipolar or single spindle cells.

[Nucleus motorius medialis in the lumbosacral segment of the spinal cord in horses]. / Nucleus motorius medialis w odcinku ledzwiowo-krzyzowym rdzenia kregowego u konia.

The studies carried out on 2 spinal cords of horses showed that cells of the medial motor nucleus (nucleus motorius medialis) are present in all neuromers of the lumbar and sacral segment of the spinal cord. It lies in the medial part of grey matter of the ventral column, neighbouring laterally and ventrally with cells of the lateral motor nucleus, whereas dorsally with cells of the nucleus of the ventral commissural horn. Along the nucleus numerous constrictions and intervals are found, which are connected with various numbers of nerve cells in particular cross-sections.

[Lateral motor nucleus in the lumbosacral segment of the spinal cord of the horse]. / Nucleus motorius lateralis w odcinku ledzwiowo-krzyzowym rdzenia kregowego u konia.

Two medullae oblongatae of horses were cut into 15 microns cross-sections and stained according to the modified method of Nissel. The lateral motor nucleus lies in the lateral and median part of the ventral column of spinal cord grey matter. It adjoins medially nucleus motorius medialis of the spinal ventral column. Cells of this nucleus occur both along the whole lumbar and sacral segment of the spinal cord. In the lateral motor nucleus three cell groups are distinguished - median, basal and lateral. The latter is divided in some segments into subgroups - dorsal and ventral. Along the nucleus quite numerous constrictions and intervals are found, which are caused by various numbers of cells in particular cross-sections. Nucleus motorius lateralis is formed mainly of large and medium multipolar or single spindle cells.

[Medial motor nucleus in the lumbosacral segment of the spinal cord of the horse]. / Nucleus motorius medialis w odcinku ledzwiowo-krzyzowym rdzenia kregowego u konia.

The studies carried out on 2 spinal cords of horses showed that cells of the medial motor nucleus (nucleus motorius medialis) are present in all neuromers of the lumbar and sacral segment of the spinal cord. It lies in the medial part of grey matter of the ventral column, neighbouring laterally and ventrally with cells of the lateral motor nucleus, whereas dorsally with cells of the nucleus of the ventral commissural horn. Along the nucleus numerous constrictions and intervals are found, which are connected with various numbers of nerve cells in particular cross-sections.

[Experimental studies of the localization of neural centers in the ovaries and fallopian tubes in cows]. / Eksperymentalne badania nad lokalizacja osrodków nerwowych jajnika i jajowodu u krowy.

For the studies 4 sexually mature cows were used, in which ovaria and oviducts were cut out bilaterally or unilaterally. The fourth cow was the control of the experiment. The operated animals were kept alive for 21 days and then slaughtered. For studies were taken: the brain stem, spinal cord from the segments Th9 - Th13 and L1 - S4, bilateral spinal ganglions, bilaterally the sympathetic chain from the segment Th10 - S4, and also ganglions and visceral-plexi, anterior mesenteric, intermesenteric, posterior mesenteric, hypogastric and pelvic. The material was fixed in alcohol, embedded in paraffin and cut into 15 micron sections. The sections were stained by Nissel's method. For examinations subsequent sections were taken. Due to the operations performed degeneration changes occurred in nervous cells in the central and peripheral nervous system. They were the basis for determination of the localization of the nervous centres for ovarium and oviduct. The source of preganglionic sympathetic visceromotor fibres for these organs is nucleus intermediolateralis in the segment L2 - L3. The sympathetic postganglionic fibres originate from cells of the sympathetic chain from L1 to L3 and from the posterior mesenteric ganglion and hypogastric plexus. The source of parasympathetic fibres for ovarium and oviduct are cells of nucleus parasympathicus nervi vagi in the segment located somewhat posteriorly from obex. The source of viscerosensory fibres for the discussed parts of the sexual organs in the cow are cells of the spinal ganglions in the segment Th9 - Th13 and cells of nucleus tractus spinocerebellaris dorsalis localized in neuromers L2 and L3.

[Changes in the central and peripheral nervous system in cows after laparotomy]. / Zmiany w osrodkowym i obwodowym ukladzie nerwowym po laparotomii u krowy.

Two sexually mature cows were used for the studies in which operations were performed, consisting in cutting the abdominal tunics at a length of 30 cm in the left iliac region. The cows were kept alive for 21 days after the operation. Then they were slaughtered, taking the following material for studies: The spinal cord, bilateral spinal ganglions, bilateral subvertebral sympathetic ganglions and autonomous ganglions of abdominal and pelvic cavities. The material was embedded in paraffin and cut into 15 n sections, which were stained with methylene blue according to Nissel. Regressive changes in cells of many nervous centres due to the operations performed were found. They were found in: spinal ganglions of the lumbar and sacral segment, nuclei of spinal grey matter (nucleus motorius, nucleus dorsalis, nucleus intermediomedialis, nucleus intermediolateralis) in the lumbar and sacral segment and in the sympathetic subvertebral ganglions of the lumbar and sacral segment. Degeneration changes of the cells were observed only on the operated side.

[Structure and topography of nucleus dorsalis in the spinal cord of horses]. / Budowa i topografia nucleus dorsalis w rdzeniu kregowym konia.

The material for the study was taken from 2 spinal cords of sexually mature horses. Preparations obtained from this material were stained according to Nissl and with the use of cresyl violet. The nucleus dorsalis of the horse extends from the 8th cervical neuromere to the 3rd lumbar neuromere of the spinal cord. The cells which form this nucleus lie in the grey matter of the spinal cord, dorsolaterally of the central canal. The nucleus dorsalis is made out of large and medium-size round and oval cells. The characteristic feature of the structure and configuration of this nucleus in the horse is the occurrence of numerous discontinuities over a considerable part of its length. The nucleus is continuous only over a short distance contained between Th17 and 2/3 of the anterior L2. The nucleus dorsalis shows great variation with regard to the number of cells which form it in the individual neuromeres of the spinal cord. In this respect, the best developed segment of the nucleus in the horse is contained between Th17 and L2.

[Structure and topography of the nucleus intermediomedialis in the equine spinal cord]. / Budowa i topografia nucleus intermediomedialis w rdzeniu kregowym u konia.

In this paper, structure and position of the centers of the parasympathetic nervous system in the horse spinal cord were presented. Studies were carried out on 2 horse spinal cordis. After sampling, the material was dehydrated in alcohol, embedded in paraffin and cut into 15 micron thick sections. The sections were stained according to Nissl's method. Every third section was studied. Nucleus intermediomedialis in the horse spinal cord is an intermittent tract of nervous cells passing from the I cervical neuromere to the V sacral segment. The cells of this nucleus form round, horizontally--oval concentrations on the transversal sections or its cells are situated loosely in the pars intermedia of the spinal cord grey substance in a small distance from the central canal. Nucleus intermediomedialis is constructed of round, oval, spindle-shaped, small cells of average size along its whole length. This nucleus is best developed in the sacral segment, a little weaker in the cervical and lumbar parts and the weakest in the thoracic part of the spinal cord.