Complex Structure of Lasiopodomys mandarinus vinogradovi Sex Chromosomes, Sex Determination, and Intraspecific Autosomal Polymorphism.

The mandarin vole, Lasiopodomys mandarinus, is one of the most intriguing species among mammals with non-XX/XY sex chromosome system. It combines polymorphism in diploid chromosome numbers, variation in the morphology of autosomes, heteromorphism of X chromosomes, and several sex chromosome systems the origin of which remains unexplained. Here we elucidate the sex determination system in Lasiopodomys mandarinus vinogradovi using extensive karyotyping, crossbreeding experiments, molecular cytogenetic methods, and single chromosome DNA sequencing. Among 205 karyotyped voles, one male and three female combinations of sex chromosomes were revealed. The chromosome segregation pattern and karyomorph-related reproductive performances suggested an aberrant sex determination with almost half of the females carrying neo-X/neo-Y combination. The comparative chromosome painting strongly supported this proposition and revealed the mandarin vole sex chromosome systems originated due to at least two de novo autosomal translocations onto the ancestral X chromosome. The polymorphism in autosome 2 was not related to sex chromosome variability and was proved to result from pericentric inversions. Sequencing of microdissection derived of sex chromosomes allowed the determination of the coordinates for syntenic regions but did not reveal any Y-specific sequences. Several possible sex determination mechanisms as well as interpopulation karyological differences are discussed.

Age-related differences in physiology and survival of northern red-backed voles (Myodes rutilus) in captivity.

Age-related deterioration of physiological functions is one of the most evident manifestations of ageing. In wild populations of some species, including murid rodents, lifespans are substantially modified by environmental signals that affect an individual's response to such challenges as unfavourable climatic conditions, parasitic load etc. But the real impact of ageing on natural mortality of most species remains obscure. To clarify how age affects the responsiveness of organisms to environmental challenges, we performed longitudinal laboratory observations of wild-derived northern red-backed voles (Myodes rutilus). We fixed individual longevity and measured metabolic indexes (basal and maximal metabolic rates), ability to maintain body temperature under acute cooling, plasma corticosterone, indexes of acquired and innate immunity in the same individuals of 3-4, 6-7 and 9-10 months old. The maximum estimated lifespan was about 2 years 8 months, which is considerably older than in nature, but less than 30% of individuals passed the one-year milestone. Regardless of the intense mortality, in the first year of life, animals did not demonstrate any age-related deterioration in physiological functions, except leucocyte number. No consistency in any individual physiological index was found. As the individual longevity of red-backed voles varied between years of captivity, we suggest that the welfare and lifespan of wild animals in captivity may be affected by the environmental conditions in the period preceding removal of the animal from the wild.

Fathers and sons: Physiological stress in male Zaisan mole voles, Ellobius tancrei.

The social environment can be stressful for at least some group members, resulting in elevated levels of glucocorticoid stress hormones (GC). Patterns of the relationships between social rank and GC levels vary between species. In carnivores, primates and birds that live in permanent cooperative groups, helpers do not usually display physiological indicators of stress. Very little is known about status-related GC differences within cooperative groups of rodents. In this laboratory study, we compared GC concentrations in dominant (fathers) and subordinate (natal sons) males of a cooperative subterranean vole, Ellobius tancrei. The assessment of adrenocortical activity by measuring urine glucocorticoid metabolites (UGM) was previously validated for this species through an ACTH challenge test. We observed clear peaks of UGM in the second or third urine samples taken after the administration of ACTH (lag time equal to 2.5-3 h). Thus, UGM is suitable to estimate physiological stress in Ellobius. Postpubertal sons living in natal groups had significantly higher UGM concentrations than their fathers. The average UGM levels of sons were positively associated with their ages and paternal body masses, and negatively associated with paternal ages. Hence, son-father interactions rather than just younger ages of sons appear to contribute to GC differences. The revealed pattern was not consistent with that reported for most cooperative species from other taxa, highlighting the importance of comparative studies.