Dietary cadmium induces histopathological changes despite a sufficient metallothionein level in the liver and kidneys of the bank vole (Clethrionomys glareolus)

The objective of this study was to correlate hepatic and renal cadmium (Cd) accumulation, Cd-binding capacity of metallothionein (MT) and lipid peroxidation with the tissue injury in the male bank voles raised under short (8 h light/16 h dark) and long (16 h light/8 h dark) photoperiods that affect differently Cd accumulation and MT induction in these rodents. The animals were exposed to dietary Cd (0, 40 and 80 microg/g) for 6 weeks. The accumulation of Cd in the liver and kidneys appeared to be dose-dependent in bank voles from the two photoperiod groups; however, the short-photoperiod animals exhibited significantly higher concentrations of Cd in both organs than the long-photoperiod bank voles. Cd-Binding capacity of MT in the liver and kidneys of bank voles from the long photoperiod was sufficiently high to bind and detoxify all Cd ions, while in the animals fed 80 microg Cd/g under the short photoperiod, the concentrations of Cd in both organs exceeded (by about 10 microg/g) the MT capacity. However, similar histopathological changes in the liver (a focal hepatocyte swelling and granuloma) and kidneys (a focal degeneration of proximal tubules) occurred in Cd-80 bank voles from the two photoperiods. Likewise, in either photoperiod group, dietary Cd brought about a similar, dose-dependent decrease in the hepatic and renal lipid peroxidation, which paralleled closely that of the iron (Fe) concentrations. These data indicate that: (1) MT does not protect the liver and kidneys against Cd-induced injury in the bank vole exposed to the higher level of dietary Cd; and (2) lipid peroxidation cannot be responsible for the tissue damage. It is hypothesized that dietary Cd produces histopathological changes indirectly, through depressing the tissue Fe and Fe-dependent oxidative processes.     

Melatonin increases tissue accumulation and toxicity of cadmium in the bank vole (<Emphasis Type="Italic">Clethrionomys glareolus</Emphasis>)

Recent study has shown that a short photoperiod increases the accumulation and toxicity of cadmium (Cd) in the bank vole as compared to a long photoperiod. Since many of the effects of photoperiod on physiological processes in small mammals are transduced by the pineal gland and its hormone melatonin, in this study the effect of subchronic melatonin injection (7 mol/kg/day for 6 weeks) on the hepatic, renal and intestinal Cd accumulation in the bank voles raised under a long photoperiod and exposed to dietary Cd (0.9 mol/g) was examined. Simultaneously, histological examinations of the liver and kidneys, and analyses of metallothionein (MT) and lipid peroxidation were carried out. Melatonin co-treatment brought about a significant increase in the hepatic (61%), renal (79%) and intestinal (77%) Cd concentrations as compared to those in the Cd alone group. However, the concentrations of MT in the liver and kidneys of the Cd + melatonin co-treated bank voles did not differ from those in the Cd alone group. Also, histopathological changes in the liver (infiltration of leukocytes) and kidneys (glomerular swelling and a focal tubular cell degeneration) as well as an increase (2-fold) in the renal lipid peroxidation occurred only in animals from the Cd + melatonin group. These data indicate that (1) subchronic melatonin injection has similar effect on the tissue accumulation and toxicity of Cd to that produced by a short photoperiod and (2) the Cd-induced toxicity in the liver and kidneys of melatonin co-treated bank voles is probably due to increased Cd accumulation and decreased synthesis of MT.     

Low ambient temperature decreases cadmium accumulation in the liver and kidneys of the bank vole (Clethrionomys glareolus)

The importance of photoperiod and ambient temperature on the accumulation of cadmium in the liver and kidneys of bank voles was determined in the present study. Males and females, aged 1 month, were given 3.0 g Cd ml^–1 drinking water and divided into four groups according to photoperiod (16 h light/8 h dark and 8 h light/16 h dark) and ambient temperature (20 or 5°C); liver and kidneys were removed for cadmium as well as copper, iron and zinc analyses at the end of 6 weeks. Bank voles exposed to 5°C in both photoperiods consumed approximately 30% less water containing cadmium than those kept at 20°C. However, the total accumulation of cadmium in the liver and kidneys of males and females exposed to the low temperatures was 4.3–4.8 and 2.2–3.3 times less than that in animals maintained at room temperature in the long and short photoperiod, respectively. Simultaneously, the low temperature brought about an increase in the copper concentrations in the liver (12–43%) and kidneys (47–78%), giving rise to an inverse correlation between the cadmium accumulation and the tissue copper concentration. In contrast to cadmium and copper, the concentrations of iron and zinc were affected primarily by photoperiod. These findings indicate that ambient temperature is an important determinant of cadmium retention in the bank vole. It appears that low temperature decreases tissue cadmium accumulation not only by reducing cadmium intake but also through changes in copper metabolism.     

Photoperiodic elevation of testicular zinc protects seminiferous tubules against fluoride toxicity in the bank vole Clethrionomys glareolus

Recent work has shown that a high fluoride (F) intake in rodents leads to histopathologic changes in the germinal epithelium of testes and to zinc deficiency in the testis and several other organs. The purpose of the present study was to determine whether an elevation of testicular zinc concentration during fluoride exposure could protect the testes of bank vole from damage. The elevation of testicular zinc was achieved by exposing the bank voles to a long photoperiod (16 hr light/8 hr dark). The zinc concentration in the testes of bank voles kept under the long photoperiod was 38% higher than that in animals exposed to a moderate photoperiod (12 hr light/12 hr dark). Fluoride exposure (200 μg F/ml drinking water) during 4 months decreased additionally p > 0.05 zinc concentration in the testes of bank voles kept under the moderate photoperiod. The same animals also exhibited histopathologic changes in the germinal epithelium. By contrast, these disturbances were not observed in animals maintained in the long photoperiod. This experiment suggests that an increase in testicular zinc due to a long photoperiod prevents seminiferous tubules from a damage induced by fluoride in bank voles. The protective effects of zinc (or a long photoperiod) did not appear to be related to a decrease in testicular fluoride accumulation or lipid peroxidation.     

Seasonal Changes of Body Iron Status Determine Cadmium Accumulation in the Wild Bank Voles

The objective of this study was to examine relations between body iron (Fe) status and cadmium (Cd) accumulation in a small rodent, the bank vole, caught from the wild population in late autumn (November) and early spring (March). The concentrations of Fe in the liver, kidneys, and duodenum in the bank voles from the spring were only 30%, 60%, and 70%, respectively, of those found in the animals from the autumn. An analysis of hematocrit and hemoglobin content of blood showed no significant effect of the season, suggesting that the animals from the spring were not anemic. The exposure to dietary Cd (10 μg/g) for 7 days resulted in 70% higher accumulation of Cd in the liver and kidneys of the spring than autumn bank voles, and the concentration of Cd in the duodenum was 3.5 times higher in the spring animals, despite the fact that relative Cd intake was significantly higher in the autumn bank voles. The data indicate that seasonal changes of body Fe status occurring in the wild bank voles may influence tissue accumulation of Cd.     

Cellular acidosis in rodents exposed to cadmium is caused by adaptation of the tissue rather than an early effect of toxicity

Proton (¹H) Nuclear Magnetic Resonance (NMR) spectroscopy was used to investigate the biochemical response of bank voles and wood mice (two wild rodent species frequently found on metal-contaminated sites) to chronic cadmium (Cd) insult. Similar effects, in terms of both metabolic changes (consistent with cellular acidosis) and induced metallothionin (MT) production were observed in all animals. These changes appeared to be an adaptation of the liver to toxic insult rather than onset of a toxic effect, and, in common with previous studies, were more marked in bank voles than wood mice. This may have reflected the greater Cd intake and assimilation of the former but was not explained by differences in concentrations of free (non MT-bound) Cd; concentrations of which were negligible in both voles and mice. Responses to Cd insult were detected in both species even though their bodies contained cadmium concentrations well below the World Health Organisation critical renal concentration of 200 μg/g dry mass.     

Testicular toxicity induced by dietary cadmium is associated with decreased testicular zinc and increased hepatic and renal metallothionein and zinc in the bank vole <Emphasis Type="Italic">(Clethrionomys glareolus)</Emphasis>

Mechanism of testicular toxicity induced by dietary cadmium (Cd) has been less investigated than that following acute Cd injection. In the present study we characterized testicular injury in a small rodent, the bank vole, exposed subchronically to dietary Cd in a quantity of 0.9 mol/g, and determined the importance of some factors (Cd accumulation, metallothionein (MT), oxidative stress, and zinc (Zn)) in the injury. Dietary Cd induced moderate histopathological changes (hemorrhage in interstitium, necrosis and apoptosis in seminiferous tubule epithelium) in young (1 month old) bank voles fed, for 6 weeks, Fe-adequate (1.1–1.4 mol/g) and Fe-enriched (4.5–4.8 mol/g) diets. In contrast, adult (5 months old) bank voles appeared to be resistant to the toxic effects of dietary Cd, despite the fact that testicular Cd contents were higher and MT levels lower than those in the young animals. The Cd-induced histopathological changes and apoptosis were accompanied by increased testicular lipid peroxidation, decreased testicular Zn concentration and elevated levels of hepatic and renal MT and Zn. Supplemental dietary Zn (1.7–1.8 mol/g) prevented the Cd-induced testicular Zn depletion and injury. The data indicate that dietary Cd produces testicular lesions indirectly, through decreasing testicular Zn, which seems to be due to the sequestration of this element by the Cd-induced hepatic and renal MT.     

Seasonal Changes in Scents and Responses to them in Meadow Voles: Evidence for the Co-evolution of Signals and Response Mechanisms

Relatively little is known about the mechanisms of communication during the non-breeding season in species that are seasonal breeders. Previous work with meadow voles, Microtus pennsylvanicus, housed under long photoperiods, has shown that they prefer the odors of opposite-sex conspecifics. In this paper, we investigated the effects of short photoperiod on preferences for sex-specific odors and the production of such odors. Short-photoperiod females preferred anogenital and fecal scents of other short-photoperiod females over those of males, but did not show sexual preferences for three other scents. Short-photoperiod males did not exhibit sexual preferences for any of the odors. Furthermore, scents from short-photoperiod voles did not elicit sex-specific preferences in long-photoperiod voles, and scents from long-photoperiod voles did not elicit preferences from short-photoperiod voles. These and previous results indicate that both the odors and responses to odors change seasonally and that long-photoperiod voles respond selectively to scents from long-photoperiod voles and short-photoperiod voles respond selectively to scents from short-photoperiod voles. Taken together, these results suggest the co-evolution of seasonal changes in scents and in perceptual or other response mechanisms.     

Melatonin and the wintering strategy of the tundra vole,Microtus oeconomus

Short photoperiod induces physiological changes connected to the wintering of the tundra vole, Microtus oeconomus. The aim of the present study was to investigate the effects of continuous melatonin treatment on selected hormones and enzyme activities associated with energy metabolism in the species. Liver, kidney, and muscle glycogen concentrations and glycogen phosphorylase activities, as well as liver and kidney glucose-6-phosphatase and lipase esterase activities were determined. Plasma leptin, ghrelin, thyroxine, testosterone, cortisol, and melatonin concentrations were also measured. Exogenous melatonin stimulated gluconeogenesis, increased glycogen stores, and reduced fat mobilization in kidneys. Melatonin treatment also increased the food intake of the voles. This may have been mediated via elevated ghrelin levels of the melatonin-treated animals, as ghrelin is known to increase appetite of rodents. Winter metabolism of the species does not seem to require accumulation of fat or extra stores of liver or muscle glycogen. On the contrary, successful wintering of the tundra vole presumably depends on continuous food availability.     

内蒙古草原布氏田鼠代谢率与身体器官的关系

动物代谢率存在差异的原因及其意义是进化生理学的一个核心问题。为了解代谢率的影响因素和功能意义, 我们测定了不同驯化条件下布氏田鼠(Microtus brandti) 的基础代谢率(basal metabolic rate , BMR) 、日能量消耗(daily energy expenditure , DEE) 和冷诱导的最大代谢率(maximum metabolic rate , MMR) , 分析了动物体内11 种器官、组织的重量与代谢率的关系。结果显示, 排除温度、光照、食物质量和体重的影响后, BMR 与心脏、肝脏、肾脏、胃和盲肠相关; DEE与心脏、肾脏、胃和盲肠相关; MMR 与脑重显著负相关。这表明: 在布氏田鼠体内存在着代谢活性器官, 主要包括心脏、肝脏、肾脏、胃和盲肠, 这些器官对BMR 有较大的贡献。动物的能量周转水平与体内“代谢机器” (metabolic machinery) 的大小相关连, 主要受到心脏、肾脏、胃和盲肠的影响。最大代谢率受脑重的影响。BMR 与MMR 的相关性不显著, 而BMR 与DEE 的相关性显著, 说明较高的BMR 有助于维持较高的DEE , 但不能维持较高的MMR。     

Short photoperiod influences energy intake and serum leptin level in Brandt's voles (Microtus brandtii)

Photoperiod cues play important roles in the regulation of seasonal variations in body mass (BM) and energy balance for many small mammals. The present study was designed to examine the effects of photoperiod acclimation on BM, energy intake, and serum leptin levels in Brandt's voles (Microtus (Lasiopodomys) brandtii). After 4 weeks of acclimation to either long (LD; light:dark, 16:8) or short (SD; 8:16) photoperiod, SD voles had lower BM, body fat mass, and dry mass of liver and kidneys, but higher digestible energy intake in comparison to LD voles. SD voles also showed a lower level of serum leptin than did LD voles. Furthermore, the level of serum leptin was correlated positively with body fat mass and negatively with gross energy intake. Together, these data suggest that Brandt's voles employ a strategy of minimizing body growth, increasing energy intake, and mobilizing fat deposition in response to cues associated with short photoperiod. Furthermore, leptin seems to be involved in the regulation of BM and energy balance mediated by photoperiod.     

Expression patterns of clock genes in the hypothalamus and eye of two Lasiopodomys species

ABSTRACT

To investigate the relationship between light sensing systems in the eye and circadian oscillators in the hypothalamus of subterranean rodents, we studied subterranean Mandarin voles (Lasiopodomys mandarinus) that spend their entire lives under dark conditions with degenerated eyes, and compared oscillatory expression patterns of clock genes in the hypothalamus and eye between Mandarin voles and their aboveground relatives, Brandt’s voles (L. brandtii). Individuals of both vole species were kept under a 12-h light/12-h dark condition or continuous dark condition for 4 weeks. In both species, the expressions of most genes showed significant cosine rhythmicity in the hypothalamus but relatively weak rhythmicity in the eye. The number of rhythmic genes in the eye of Mandarin voles increased under the dark condition, but the opposite trend was observed in the eye of Brandt’s voles. The expression levels of most clock genes in the hypothalamus of both vole species did not significantly differ between the two conditions, but unlike in Mandarin voles, these expression levels significantly decreased in the eye of Brandt’s voles kept under the dark condition. In both vole species, the peak phase of most clock genes exhibited advanced or invariant change in the hypothalamus under the dark condition, and the peak phase of most clock genes showed consistent changes between the eye and hypothalamus of Mandarin voles. However, most clock genes in the eye showed a delayed phase in Brandt’s voles kept under the dark condition. In conclusion, the hypothalamus plays an important role in both vole species irrespective of the light condition. However, the expression patterns of clock genes in the eye differed between the vole species, indicating that each species adapted differently to their environments.     

光周期对雄性布氏田鼠种内个体气味辨别的影响

本文研究了成年雄性布氏田鼠对不同光照周期下(长光照: LD; 短光照: SD) 的陌生雌鼠和陌生雄鼠气味的行为表现。实验发现: 所有被试雄鼠对LD 雄鼠、雌鼠气味比SD 雄鼠、雌鼠气味有更多的社会探究行为。LD 雄鼠比SD 雄鼠对同性或异性陌生个体气味的嗅闻和挖掘行为要多, 而且差异显著。在探究LD 动情雌鼠气味源时, LD 雄鼠比SD 雄鼠表现出更多的嗅闻和挖掘行为; 在探究SD 动情雌鼠气味源时, LD 和SD 雄鼠的行为反应没有明显差别。所有被试雄鼠在LD 雄鼠气味源箱中的停留时间都显著多于在SD 雄鼠气味源箱中的停留时间。LD 雄鼠在LD 雌鼠气味源箱中的停留时间显著多于在SD 雌鼠气味源箱中的停留时间; 而SD 雄鼠在LD 和SD 雌鼠气味源箱中的进入频次和停留时间没有明显差别。同时, LD 雄鼠对LD 动情雌鼠的气味在嗅闻频次和嗅闻时间上多于非动情LD 雌鼠, 而对SD 动情和非动情雌鼠的气味没有表现出明显的偏好; SD 雄鼠对LD 和SD 动情雌鼠的嗅闻行为仅在频次上显著多于对非动情雌鼠的嗅闻, 而在时间上没有显著差别。结果表明: 布氏田鼠嗅觉通讯中的个体气味及其对气味进行辨别过程中的行为反应都随着光照周期的不同而发生变化。动物的个体气味带有季节性信息, 来源于长光照下的气味比短光照下的气味更具有性吸引; 短光照在一定程度上可能抑制了雌鼠的动情和雄鼠的性行为反应。其嗅觉通讯行为的适应意义可能在于: 减少秋季短日照环境下的繁殖活动, 提高雄性个体之间的社会容忍性以利于集群越冬。     

Reproductive effort of female bank voles in a risky environment

In cyclically fluctuating vole populations, strong intraspecific competition and intense predation simultaneously or separately increase the costs of reproduction and so may set the framework for the optimal breeding tactic of voles. In a factorial experiment, we manipulated two factors in the breeding environment of bank vole (Clethrionomys glareolus) pairs, each with two treatment levels: no predation risk or high risk of specialist predators and low or high density of voles. In the manipulation, we used odours of conspecific voles and/or mustelid predators. Both over-wintered and young, summer-born, wild-caught bank vole females and males in breeding condition were used. Each female—male pair of voles was placed in a cage and the cages were distributed in large outdoor enclosures. All animals were fed ad libitum. Under predation risk, both old and young females suppressed breeding significantly. The density of conspecific voles did not affect overall breeding. However, there was some evidence that population density stimulated breeding of old females but suppressed breeding of young ones. Both risk factors appeared to increase litter sizes of those individuals who decided to breed. Our results indicate that the risk of predation may be an important factor determining reproductive tactics of bank vole females. In risky environments, females seemed to choose between two totally opposite tactics: they suppressed breeding, which may increase their own survival to the next breeding event, or they continued to breed in spite of expected high survival costs. Females seemed to compensate the latter costs with a higher effort to the current and probably the last reproduction.     

Seasonality and seasons out of time--the thermoregulatory effects of light interference

The change in photoperiod is the main environmental cue for seasonal function of the reproductive, thermoregulatory, and immune systems in rodents existing outside of the tropics. In Israel, the social vole Microtus socialis breeds mainly under short photoperiod (SP) conditions. Previous studies showed that exposing voles to light interference (LI) in the field during the winter resulted in death. The aim of the current study was to determine the thermoregulatory response of SP-acclimated voles to LI. Therefore, heat production (VO2) at different ambient temperatures (Ta) and nonshivering thermogenesis (NST) were measured. Results show that LI of 15 min every 4h during the dark period significantly (p < 0.02) decreased VO2 at Ta = 15 degrees C and significantly (p < 0.05) decreased NST-capacity. These results can at least partly explain why LI-voles died during the winter under field conditions, through eliminating winter acclimatization of the thermoregulatory system, or what is considered as "seasons out of time."     

Seasonal and photoperiodic effects on lipid droplet size and lipid peroxidation in the brown adipose tissue of bank voles (<Emphasis Type="Italic">Myodes glareolus</Emphasis>)

Seasonal changes in lipid droplet size and lipid peroxidation in the brown adipose tissue (BAT) of wild bank voles were examined. In addition, a role of photoperiod in these changes was studied; bank voles were held from the birth under long photoperiod (LP) for 12 weeks, and then half of them was transferred to short photoperiod (SP) for 6 weeks and another one remained under LP. In the wild bank voles the absolute BAT weight was seasonally constant, while the significant differences in the lipid droplet size were observed. The smallest lipid droplets (mean, 11 μm²) were seen in winter; they increased by 30 % in spring and reached the highest size (24 μm²) in summer. Lipid peroxidation in the BAT did not differ significantly between the seasons, although high intraseason variation of this process was noted. The laboratory experiment revealed that the size of lipid droplets was determined by photoperiod; SP induced 13-fold decrease, and continuous exposure to LP brought about a further 2.5-fold increase in the size of lipid droplets. Conversely, a significant decrease in lipid peroxidation was seen in LP bank voles in comparison with the SP animals. The data indicate that short photoperiod is responsible for the small size of lipid droplets in the BAT of bank voles during winter, which may be a necessary requirement for high thermogenic capacity of the tissue. Photoperiod appears also to affect lipid peroxidation in the BAT of these animals.     

光周期对布氏田鼠和长爪沙鼠体重和能量代谢的影响

本文测定了光周期对雄性布氏田鼠和长爪沙鼠的体重、基础代谢率和能量代谢的影响。动物从长光照(16L∶8D , LD) 转入短光照(8L∶16D , SD) 条件下驯化6 周(田鼠) 和7 周(沙鼠) 。结果显示: (1) 无论在LD还是SD 条件下, 两种动物的体重都趋于增加, 但反应程度不同也具有种间差异性。两种动物的体重对光周期的反应有时段性, 约14 d 前两种动物的体重增加迅速, 而后增加缓慢, 3 周左右趋于稳定。短光照条件下布氏田鼠和长爪沙鼠的体重分别增长了37 %和11 % , 均低于长光照组(分别为47 %和25 %) , 说明短光照条件下布氏田鼠和长爪沙鼠的体重增长较长光照缓慢; (2) 光照对两种动物的摄入能、消化能和可代谢能均没有显著影响,摄入能与体重的增长无关; (3) 光照对两种动物的基础代谢率无显著影响。这些结果表明: 布氏田鼠和长爪沙鼠在自然环境中, 可能以光周期作为一种信号, 当环境温度降低、食物质量变劣时, 采取降低体重以减少绝对能量需求的策略而适应环境。     

Aromatization and antioxidant capacity in the testis of seasonally breeding bank voles: Effects of LH, PRL and IGF-I

Aromatization and antioxidant strategies in the male gonads are important processes, which are involved in control of normal fertility. The objective of this study was to show whether luteinizing hormone (LH), prolactin (PRL), and insulin-like growth factor-I (IGF-I) as well as the length of photoperiod are able to exert an effect on aromatase expression, steroid hormone levels, and antioxidant concentrations in testes of bank voles, seasonally breeding rodents. Mature bank voles that were kept under short light cycles or long light cycles served as the animal model. Testicular sections were used for immunohistochemical visualization of aromatase expression, whereas testicular homogenates were used for radioimmunological measurement of steroids, biochemical determination of superoxide dismutase activity, total antioxidant status (TAS) and protein content. In the testes of hormone-treated voles a stronger immunostaining for aromatase was concurrent with the increase in testosterone and estradiol levels, and total antioxidant status compared with the controls. In contrast, there was a decrease in superoxide dismutase (SOD) activity. The strongest effect on aromatase immunoexpression and steroid hormone levels was detected after combined doses of LH and IGF-I, indicating a stimulatory role of these hormones on estrogen synthesis in the bank vole. An increase in total antioxidant status in testes of hormone-treated bank voles suggests the presence of testicular defense, whereas a decrease in superoxide dismutase activity indicates a protective role of administered hormones against toxic oxygen radicals. The present study also demonstrates a significant, photoperiod-dependent relationship between aromatization and antioxidant capacity in the testis of the bank vole.     

Predation rate, prey preference and predator switching: experiments on voles and weasels

We studied the predation rate and prey selection of the least weasel ( Mustela nivalis nivalis ) on its two most common prey species in boreal environments, the bank vole ( Clethrionomys glareolus ) and the field vole ( Microtus agrestis ), in large outdoor enclosures. We also studied the response of weasels to odours of the two species in the laboratory. The enclosure experiment was conducted using constant vole densities (16 voles/ha) but with varying relative abundance of the two species. Weasels showed higher predation rates on bank voles, and males had higher predation rate than females. Females killed disproportionately more of the more abundant prey species, but they preferred bank voles to field voles when both were equally available. Overall, the predation rate also increased with increasing abundance of bank voles. Therefore our results are in agreement with earlier laboratory results showing preference for bank voles, even if no intrinsic preference for odours of either species was observed in our laboratory study. We suggest that the least weasel hunts according to prey availability, prey aggregation and suitability of hunting habitat, and that this causes the observed dependence of least weasels on field voles and emphasises the role of the field vole in the vole-weasel interaction in cyclic vole populations. Furthermore, our results suggest that predation by weasels may facilitate the coexistence of the two vole species via predator switching, and that it may cause the observed synchrony in dynamics between vole species.     

Gene conversion in the mitochondrial genome on interspecific hybridization in voles of the <Emphasis Type="Italic">Clethrionomys</Emphasis> genus

The phenomenon of interspecific hybridization accompanied by transfer of the mitochondrial genome from the northern red-backed vole (Clethrionomys rutilus) to the bank vole (Cl. glareolus) in northeastern Europe is well known already for 25 years. However, the possibility of recombination between homologous segments of maternal and paternal mtDNAs of the voles during fertilization was not previously studied. Analysis of data on variability of nucleotide sequences of the mitochondrial gene for cytochrome b in populations of red-backed and bank voles in the area of their sympatry has shown that as a result of interspecific hybridization, the mitochondrial gene pool of bank voles contains not only mtDNA haplotypes of red-backed vole females, but also mtDNA haplotypes of bank voles bearing short nucleotide tracts of red-backed vole mtDNA. This finding supports the hypothesis that an incomplete elimination of red-backed vole paternal mtDNA during the interspecific hybridization between bank vole females and red-backed vole males leads to the gene conversion of bank vole maternal mtDNA tracts by homologous ones of mtDNA of red-backed vole males.