Phylogeny of the Dipus sagitta Species Complex by Nuclear Gene Sequences

The northern three-toed jerboa Dipus sagitta had long been considered to be a single polytypic species. High genetic diversity of D. sagitta was earlier revealed on the basis of several mitochondrial and nuclear genes, and several separate species were hypothesized to occur within the taxon. However, the relationships between phylogenetic lineages have not been established because of the small sample size of nuclear genes. In the present work, a far larger set of nuclear DNA loci was used, and thus, a higher resolution of the phylogenetic tree was achieved for ten D. sagitta forms. The structure revealed for the species mainly confirmed the topology and relationships of the mtDNA lineages. Yet the mitochondrial and nuclear phylogenies were not completely consistent. Some of the D. sagitta genetic lineages were therefore assumed to be a product of reticular evolutionary processes. The taxon was concluded to be the diverse species complex D. sagitta sensu lato, in which long-diverged lineages are not always reproductively isolated.

[Female mate choice, male-male competition, and male sexual traits: Experimental study of sexual selection directedness in Campbell's dwarf hamster (Phodopus campbelli Thomas 1905)]

We studied the relationship between female mate choice and male-male competition in Campbell's dwarf hamster. Sexually motivated (SM) females chose between two tethered male siblings that differed in expression of sexual traits. Males were unrelated to the female and able to contact and copulate with her. The same males were used in encounter experiment with the following free access of competing male to another SM female. We measured males' sex-related morphology of body mass, mid-ventral specific skin gland, ano-genital distance, and external testicular diameter. We also estimated levels of blood testosterone and cortisol, specific T- and B-cell immune responses to antigens, as well as aggressive and sexual dominance. We found out that female mate choice was not dependent on male aggressive and sexual dominance estimated through encounter experiments. Both in female mate choice and male-male competition experiments (encounter of males and free excess of males to receptive female) successful males did not differ from unsuccessful males in expression of sexual traits (ST). Among males with higher expression of ST mate choice by the female was not associated with aggressive dominance and sexual dominance of a male. There were no significant differences between successful and unsuccessful males in variables treated as potential predictors of male's success, both in female mate choice and male-male competition experiments. Variables explaining female's preference and male's aggressive dominance, which were revealed by General Regression Model analysis, did not coincide. Our results suggest that there are no reasons to discuss the expression of ST in Campbell dwarf hamster males in terms of intersexual or intrasexual selection mechanisms or in terms of their interaction. At the same time, our study demonstrates that testing theoretical models such as "Handicap hypothesis" or "Immunity handicap hypothesis" may face difficulties, which are discussed in the text.

[Testosterone and Induced Humoral Immunity in Male Campbell Dwarf Hamsters (Phodopus campbelli, Thomas, 1905, Rodentia, Cricetidae): Experimental Manipulation of Testosterone Levels]

In this paper we report the results of testosterone manipulation in the blood of male Campbell dwarf hamsters Phodopus campbelli Thomas, 1905 through castration, followed by testosterone treatment. Under these conditions, we studied antibody production rates in response to injection with sheep red blood cells (SRBC). It was shown that castration induced a dramatic decrease in blood testosterone but had no effect on the humoral response to SRBC. Males that received a testosterone compound with a long-lasting action (omnadren) exhibited a poor response to SRBC following re-exposure in the context of elevated testosterone compared to castrated males inoculated with an oil base of the drug.

Mitochondria-targeted antioxidant SkQ1 accelerates maturation in Campbell dwarf hamsters (Phodopus campbelli)

We tested two hypotheses. 1) SkQ1 positively affects postnatal development of hamsters in litters born to parents receiving long-term SkQ1 treatment. 2) SkQ1 accelerates maturation of juvenile females receiving the antioxidant treatment from 10 days of age. Parental pairs were kept in an outdoor vivarium under conditions close to natural. At the age of 25 days, juvenile males in litters born to parents treated daily with SkQ1 (50 nmol/kg per os) had higher epididymis mass. Both the size of a litter and SkQ1 affected epididymis mass in young males. Both the litter size and SkQ1 affected uterus mass in 25-day-old females. Juvenile females who received SkQ1 treatment from 10 days of age demonstrated earlier opening of the vagina. This experiment was replicated with the same result. At the age of 2.5 months, virgin females treated with SkQ1 from the early age demonstrated higher ovary mass.

Effects of mitochondria-targeted plastoquinone derivative antioxidant (SkQ1) on demography of free-breeding Campbell dwarf hamsters (Phodopus campbelli) kept in outdoor conditions. reproduction and lifespan: explanation in the framework of ultimate loads

We studied demographic effects of the mitochondria-targeted antioxidant SkQ1 on free-breeding Campbell dwarf hamsters (Phodopus campbelli, Thomas, 1905, Rodentia, Cricetidae) in an outdoor vivarium with seasonally varying day length and temperatures. The animals were kept in pairs from their young age. We removed litters from parental cages at their age of 25 days. Experimental hamsters received daily 50 nmol/kg SkQ1 with water by oral dosing, whereas control animals received water. SkQ1 had no effect on the lifespan of either males or females in reproductive pairs. Mortality among females was higher than among males irrespective of SkQ1 treatment, this being related to higher costs of reproduction in females. However, SkQ1 accelerated breeding in pairs in the first half of the reproductive period of a year. Although there were no statistical differences in body mass of males and females between experimental and control animals during most of their life, SkQ1-receiving males had higher body mass at the end of their life. The opposite tendency was characteristic for old females. One-year-old males and females of the experimental and control groups showed no difference in intensity of immune response to sheep red blood cells. The dermal hypersensitivity response to phytohemagglutinin (test for T-cell immunity) was significantly higher in SkQ1-treated 1- and 1.5-year-old males. This was not true for females. There was a tendency toward increased density of the neutrophil population in blood in 1-year-old SkQ1-treated males. However, experimental males showed no difference from control males in the activity of the "peroxidase-endogenous hydrogen peroxide system" of neutrophils. The background level of stress estimated by the concentration of cortisol in blood serum was significantly lower in the SkQ1-treated males during autumn adaptive adjustment of the organism. A similar trend was also observed during the January frosts, when the background level of stress was rather high. We observed no differences between cortisol concentration in experimental and control animals during the reproductive period in early spring and mid-summer. We tend to interpret the absence of geroprotective effect of SkQ1 on free-breeding dwarf hamsters by its ability to intensify breeding. We previously demonstrated the ability of SkQ1 to increase the lifespan of non-breeding females.

[Immunocompetence and reproductive characteristics of male Campbell dwarf hamsters selected for low and high humoral immune response to SRBC: testing the immunocompetence handicap hypothesis]

We selected Campbell dwarf hamsters (Phodopus campbelli Thomas, 1905) for low and high humoral immune response to the sheep red blood cells (SRBC) challenge in three generations (P, F1, F2). Non-specific innate immunity and acquired T-cell immunity, resting metabolic rate, testosterone, and cortisole hormone levels, reproductive characteristics, including maturation related morphological traits, and aggressive behavior were studied within sets of males:with low (LI) and high (HI) immune response to SRBC. We found no difference between LI and HI males in cutaneous response to injection of phytohemagglutinin, (DTH test for T-cell immunity), in activity of Peroxidase - Endogenous Hydrogen Peroxide System of Neutrophils , in the white blood count, in resting metabolic rate, in body mass and ano-genital distance at the age of two months, in the blood level of testosterone before and after recurrent immunization by SRBC and in the blood level of cortisole in response to the social stressor (10 min encounter in the neutral arena). At that, LI males had significantly higher basal level of blood cortisole, were less aggressive in response to stranger male and had smaller testosterone-dependent mid-ventral specific skin gland at the age of two months. Males of two groups did not differ in the initial mating success with intact young females (time since pair formation until first litter born), although females of LI males born fewer number of pups. In fact, our results do not support the Handicap Immunocompetence Hypothesis (Folstad, Karter, 1999) which is based on the assumption of trade-off between immunocompetence and reproductive effort.

[Spontaneous tumors in the Campbell hamster: a possible new model of experimental oncology]

The spectrum of spontaneous tumors in the Campbell hamsters has not been described yet. 152 Campbell hamsters (110 females and 42 males), spontaneously died by ordinary death, underwent the necropsy and the histopathological examination. Tumors were found in 50% of males and in 48% of females dead after the achievement of the first tumor development age (430 and 260 days respectively). The main type of tumors in Campbell hamsters was thymoma of B1 type which is known in human, but unusual in laboratory animals. The thymomas had low grade of malignancy, did not induce the wasting syndrome and did not metastasize. It is probable that thymoma B1 kills the animals by the dislocation of mediastinal organs. Frequency of this tumor was 40% in males and 40% in females dead after the achievement of the first tumor development age. Any sex differences were not found although males dead with thymoma had significantly more evident reproductive success in comparison with animals without this tumor. Besides, thymomas, squamous carcinomas of forestomach (in males and females), skin carcinomas (in males and females), adenocarcinomas of reproductive system, kidney and lung (in females only) and small-cell lymphomas (in males only) were found. Hence, spontaneous tumors in Campbell hamsters could be useful as a model for research in the experimental oncology, especially as unique model of human thymoma of B1 type which has not been observed in laboratory mice and rats yet.

[Resting metabolic rate, stress, testosterone, and induced immune response in "spring" and "fall" males of Campbell dwarf hamsters. Rearing under the long day conditions]

We have studied morphological and physiological traits of even-young males of Campbell dwarf hamsters (Phodopus campbelli Thomas, 1905) born at the end of summer ("fall males") and at the end of winter ("spring males") in a vivarium with constant 14-hour day length (14D:10N). After removal from parental cages at the age of one month, males were kept in isolation under the same light conditions. The results obained signify the statistical difference between "fall" and "spring" males in resting metabolic rate, morphological traits associated with sexual activity, some endocrine and immunologic characteristics. Spring males had higher resting metabolic rate, higher body mass in the middle of experiment, bigger testes, seminal vesicles, higher concentration of testosterone in blood and more intensive T-cell immune response to the intracutaneous injection of phytohemagglutinin. They did not differ significantly in basal level of blood cortisole and antibodies production in response to sheep red blood cells (SRBC) antigen challenge, but possessed lower adrenocortical response to the social stressor and adrenocorticotropic hormone. GLM analysis showed that cortisol level in blood after 10 min encounter of males in the open arena, and resting metabolic rate were the only factors significantly influenced humoral immune response to SRBC. When intensity of T-cell immune response was considered as dependent variable, season turned out to be the only factor in the final model that caused a significant effect.

[Specific immunity and polymorphism of breeding plumage in pied flycatcher (Ficedula hypoleuca) males (Aves: passeriformes)]

The relationship between the type of melanin-based plumage coloration and the strength of experimentally induced immune response was studied using as an example a pied flycatcher population from the Moscow Region. The plumage of pied flycatcher males exhibits the full spectrum of transitions from contrasting black-and-white to cryptic brownish, the latter being very similar to the coloration of females. In spite of numerous studies, the nature of this polymorphism still remains vague. Unlike many other avian species with monocyclic breeding, a considerable fraction of pied flycatchers combines two energy-consuming productive processes, breeding and molt. During the main experimental treatment we activated the humoral immunity of free-living males in chick-rearing period by injection of nonpathogenic multigenic antigen (sheep red blood cells, SRBC) and estimated the strength of the immune responses after repeated captures in 6-8 days. In addition, after each capture we estimated the numbers of leucocytes (WBC), heterophil to lymphocyte ratios (H/L) and measured night time basal metabolic rates (BMR). Non-molting males of different color types showed the same immune responses. Among molting birds, the strength of the immune response was significantly higher in pale males (morphs 4-7 by Drost's scale) than in bright males with rich melanin-based coloration (morphs 2-3). This difference resulted from two opposite processes. During molting, pale males heightened the antibody titer after immunization, while bright males tended to reduce the strength of immune response. Possibly such an asymmetry in immunocompetence at the first stage of molt reflects the different life strategies of pied flycatcher males - conspicuous birds less commonly combine breeding with molt than cryptic ones.

[Autoregulation in mammalian populations and stress: an old theme revisited]

We consider the current state of four hypotheses explaining the auto-regulation of population numbers in mammals: 1. Density -- and frequency-dependent selection of genetically determined stereotypes of behavior (Chity, 1960, 1967). 2. Physiological effects of stress conditioned by redundant density (Christian, 1950, 1963; Christian, LeMunyan, 1958). 3. Maternal effects on offspring (Ward, 1984; Lee, MacDonald, 1985). 4. Kin hypothesis based on assumption of temporal variation in relatedness of neighbors (Charnov, Finerty, 1980). All four hypotheses consider the density of individuals or their signals (visual, acoustic, or chemical) to be the main factor of regulation, and are based on an assumption of density-dependent variation in spacing behavior. The local density is considered to be derived from the ability of individuals to disperce. This ability appears to be determined by internal (including genetic), as well as external limiting factors. The above hypotheses are not quite alternative. In fact, all four hypotheses imply stress (directly or indirectly) as a regulatory mechanism within the population, although its role is usually associated with J. Christian's hypothesis. Besides the direct density-dependent, physical exclusion of competitors, social behavior may activate and control neuroendocrine regulatory mechanisms which lead to a reduction in breeding intensity and maturation, and increased mortality due to functional disorders and immunity syppression. To date we cannot reject any of these hypotheses. We believe that progress in understanding the role of physiological stress in the regulation of population density in mammals will depend on attention to the following factors: 1. Abundance (availability) of feeding resources, predators and parasites are real factors affecting levels of physiological stress in wild mammals. Population density depends on these factors, and their role in the stress dynamic in the population can be decisive. 2. Social conflicts (density-dependent behavior) are usually considered to be the main factor of physiological stress and a keystone of autoregulation mediated by stress. We still pay little attention to the role of stress hormones and neurotransmitters in the regulation of animal behavior. Both hormones and neurotransmitters can greatly affect individual behavior, including interactions between individuals in the population. 3. A common viewpoint is that stress negatively influences ontogenesis, reproduction, and survival. At the same time, in nature we often observe a positive relationship between stress and reproduction, or stress and survival, and we must pay more attention to this phenomenon. 4. In spite of a well developed theory about the role of stress in the regulation of reproduction and survival in mammalian populations, we still do not pay much to species-specific characteristics of the neuroendocrine mechanism of stress and its effects on population demography.

[Long-term dynamic of fecal corticosterone and its ecological and social correlates in males of great gerbil (Rhombomys opimus Licht.). Non-invasive approach in studies of stress in natural populations]

The relationship between fecal corticosterone concentrations and characteristics of the environment and population demography were studied in adult male gerbils (Rhombomys opimus Licht.) at the southern border of Kyzylkum desert (Reserve "Ecocentre Dzeiran", Bukhara region, Republic Uzbekistan) in spring and fall seasons from 1999 to 2004. We extracted hormones from air-dried fecal samples and analyzed their concentrations by radioimmunoassay (Gerlinskaya et al., 1993). An analysis for year-specific relationships between hormone concentrations and environmental variables of temperature and precipitation using Pearson's r statistic revealed that corticosterone concentrations correlated positively with total precipitation in January and February and negatively with precipitation during March and April. There was also a significant negative relationship between fecal corticosterone and the number of hot days in March (>20 degrees C). Demographic variables that characterized population densities (percent of burrow systems occupied, mean and maximum number of burrow systems/1 ha, number of females in the burrow system) correlated positively with corticosterone concentrations in feces in the beginning of spring, but these relationships were small compared with mean concentrations of corticosterone for the entire spring season that were strongly and positively correlated with number of gerbils, including all pups emerged, in burrow systems owned by one male (within its home range). In contrast, correlation coefficients of corticosterone concentrations with characteristics of feeding resources in the spring were low and negative. In the long-term perspective (interannual comparison), mortality among adult males was highly negatively correlated with mean corticosterone concentrations in the beginning of spring, which is within the period of maximum reproductive effort and potential stress. Body mass was independent of corticosterone concentrations in males in either the beginning of spring, or during the whole spring. In the fall, mean concentrations of fecal corticosterone in males was positively correlated with the number of days from June to October with mean daily temperatures exceeding 30 degrees C, and with percent of burrow systems where at least one adult, > or = 1 year old gerbil had survived. Mortality from fall to spring of the next year and the fall body mass did not correlate with concentrations of corticosterone in feces collected in the fall. When we analyzed corticosterone concentrations in spring seasons of all years combined using a stepwise regression analysis of a sampling of individual males (we analyzed residuals after withdrawal of year effect) on a set of variables representing habitat resources, distances between nearest neighbor males, and variables representing group demography we found low R2 values not exceeding 0.17. Within the six-year period, concentrations of corticosterone in the spring related negatively with abundance of annual herbs and positively with number of females in a male's social group. When only years of high density were analyzed, fecal corticosterone concentrations in males in the spring were again negatively determined by abundance of herbs, as well as by the nearest neighbor distance, and positively determined by the number of females within a male's home range. At the beginning of spring the only determinants were distance to the nearest neighbor male and number of females. In years of low density none of the variables were found to affect corticosterone levels during the whole spring, while in the beginning of spring only partial regression coefficients of abundance of herbs were negative and significant. Stepwise logistic regression analysis revealed positive dependence (P = 0.05) of disappearance of adult males during summer drought on concentrations of fecal corticosterone in the spring, but only when burrow systems with at least one adult (male or female) surviving after the summer were considered. Our results provide evidence ground for the assumption that in a desert rodent with non-regular population fluctuations such as the great gerbil, density may be more suppressed by external factors and not by density dependent mortality mediated by stress. Density dependent increases of stress caused by intense reproductive effort occurred when feeding and climatic conditions were favorable to compensate for negative effects on survival. However, in individual gerbils mortality mediated by stress can take place because we found higher stress in the beginning of spring in males, which did not occur in the population after the summer drought.

[Social environment and morpho-physiological status of young males in the fall groups of great gerbil (Rhombomys opimus Licht). Effect of adults' presence]

The dependence of stress and sex hormone levels, size of mid-ventral skin gland, and body mass of young males on the presence in social groups of adult gerbils (>1 year old) were studied during the fall of 1999 in the non-breeding high density population of the great gerbil (Rhombomys opimus Licht; Bukhara region, Uzbekistan). Contents of corticosterone and testosterone in fecal samples collected from young males in the field were analyzed by non-invasive radioimmunoassay. The fall gerbil groups with adults were of larger size than those without adults. The total number of individuals in a group is positively correlated with concentration of corticosterone in feces of young males. Presence of adult male and especially of adult female suppresses maturation of juvenile males indicated by size of the androgene-dependent mid-ventral gland, but accelerates their total growth. Thus, the social environment influences morpho-physiological characters of young males, effecting rate of their maturation directly or indirectly through the density dependent stress.

[The correlation of the size of the pinna and the auditory bulla in specialized desert rodents]

Relation between size of pinna and auditory bulla in specialized desert rodents (families Allactagidae, Dipodidae, Gerbillidae, Heteromyidae, and genus Selevinia) is statistically significant and described by hyperbola. The empirical distribution of respective sizes can be interpreted as a total of two main trends. One is enlargement of the pinna, the bulla remains small (most of Allactagidae), another is enlargement of the bulla, the pinna remains small (Gerbillidae, Heteromyidae, Selevinia, most Dipodidae). A few species display moderate enlargement of both pinna and bulla, while in Euchoreutes they both are hypertrophied. Biomechanical preconditions are supposed to be following. Enlargement of the pinna is responsible for increasing of both sensitivity and locatory abilities of the hearing organ, while enlargement of the bulla is responsible for the first function only. So, the two main trends are results of selection of development of the hearing organ at the level of either pinna or bulla. It is shown by dispersion and correlation analyses that size of the parts of the hearing organ under investigation are correlated mostly with mobility and escaping mode. It is concluded therefore that the rodents characterized by active and speedy escaping from predation display the first of the above trends, while the rodents characterized by passive escaping from predation display the second trend.

[The ecology of communities of related animal species (research approaches and methods exemplified by terrestrial vertebrates)]

The review is dedicated to some old and modern problems in studying of the assemblages of phylogenetically related species among terrestrial vertebrates. The classical approach by Robert Mac-Arthur, discussed elsewhere summarized briefly. Although an explanative potential of competition theory seems exhausted there is no new paradigm that can simply explain species diversity in natural communities. From the beginning of 90's community ecology became very complex and controversial discipline. At the same time it is still a pioneering science. We have not enough comparative data on geo2 graphically distinct communities studied under the unified methods of data collection and analysis. Some recent results of intercontinental comparisons signify to the high degree of individualism in structure of geographically isolated communities. This makes doubtful any extrapolation from one region to another. Examination and explanation of processes is still the most contradictory field in community ecology. Confusion of causes and effects is continuing to be serious methodological problem. Much of attention was paid recently to the macroecological approach. A desire for reconsideration of some "old rules" of biodiversity is explained by advances in paleozoology, biogeography and systematic, as well as by some unsatisfactory explanations within the framework of competition theory.

[The dynamics of the spatial organization of communities of small mammals (exemplified by rodents of the trans-Altai Gobi of Mongolia)]

Between-year variation of rodent population densities was studied in the central part of trans-Altai Gobi, Mongolia, in summers of a nine year period. Variation in spatial structure of the desert rodent community in 1982-84 and in 1992 was examined by the use of discriminant function analysis. Although population densities, breadth and positions of niches of many species tended to vary independently, the positive conjunct variation was found for the most ecologically distinctive species. This can be explained by limitations of the climate. Although a guild structure of the community was pronounced each year, there were significant between year shifts in niche breadth and niche centres along certain axes of ecological space. Within year nearest neighbours in niche overlap (high seasonal overlap) differed in between year variation in abundance. It is supposed that interspecific competition could contribute to development of community structure.

[Vegetation as a factor in species diversity in communities of desert rodents]

Diversity of rodent species was studied in relation to the abundance of grass vegetation, projection cover of arboreal and semi-arboreal vegetation, and mechanical soil composition in the Kyzyl Kum desert (Bukhara Province, Uzbekistan) and in the Chihuahua desert (Bolsón de Mapimí, Durango, Mexico). Species diversity indices for rodent communities in 1-hectare plots significantly varied in both deserts in similar environmental conditions. Nevertheless, the obtained data agree with the data on the hill-shaped relationship between species diversity and productivity of the environment. Stepwise regression analysis of the linear component links suggests that the abundance of grass and the projection cover of arboreal and semi-arboreal perennials, rather than the type of soil surface, exert a significant influence on the diversity of rodent species. At a given projection cover of arboreal and semi-arboreal plants (or an abundance of grass), the diversity of rodent species in Bukhara decreases with an increase in grass abundance (or projection cover of arboreal and semi-arboreal plants). By contrast, in Mapimí the diversity increases. The difference is probably due to both specific environmental conditions and particular fauna genesis.

Comparison of Niche-Packing and Community Organization in Desert Rodents in Asia and North-America

We compared patterns of species diversity, locomotory morphology, feeding modes, and spatial organisation for rodent communities in four Asian deserts (Kyzylkum, Gobi, ?Thar, Negev) and one North American (Chihuahuan) desert. Deserts were similar in gamma and alpha diversity. A positive relationship between regional species diversity (and biomass) and mean annual precipitation was found. The Asian deserts showed a greater degree of divergence and specialisation between bipedal and quadrupedal forms. The range of feeding modes was similar in deserts on both continents, but the Negev was the only Asian desert in which granivory was as important as in the Chihuahuan. Temperate Asian desert rodents were organised into spatial guilds, separated primarily by characteristics of the soil and perennial vegetation. North American desert rodent species overlapped more extensively in habitat use. The similarities and differences between these deserts can be explained by their biogeographic histories.