A. V. Surov

Field Studies of Chemical Signalling: Direct Observations of Dwarf Hamsters (Phodopus) in Soviet Asia

Chemical signals are vital sources of information in the lives of most, if not all, vertebrates. Considerable success has been achieved in experimentally determining the context, regulatory mechanisms and biochemical bases of vertebrate chemical signalling, particularly in rodent species. While the microtine and cricetine rodents are amenable to rearing under laboratory conditions, in the wild the majority are small, cryptic, nocturnal and virtually impossible to study by direct observation. What is missing is an integrated picture of the use of scent marking by free-ranging individuals, and the perception of those signals by other individuals at later times. This study reports the results of a direct, observational, field study of scent marking behavior in wild, free-ranging population of a small, nocturnal rodent — the Djungarian hamster, Phodopus campbelli.

Differences in Endogenous Activity within the Genus Phodopus

Timing, distances, and durations of above-ground activity were monitored during three successive years in wild populations of dwarf hamsters ( Phodopus ). Both P. campbelli (Djungarian hamsters) and P. sungorus (Siberian hamsters) were nocturnal. However, P. campbelli arose earlier (before dark or soon after dark versus well after dark) and remained above ground 2.5 times longer than P. sungorus . Longer expeditions allowed female P. campbelli to travel farther than both sexes of P. sungorus at the same speed. In contrast, P. campbelli males were active for the same amount of time as females but travelled almost three times faster, covering much greater distances and larger areas. Patterns of wheel running by females in the laboratory confirmed the earlier onset and longer duration of activity in P. campbelli , demonstrating that differences between species in the wild were not simply responses to different environmental stimuli. Activity before and after dark and prolonged activity throughout the dark are interpreted as evidence that resource acquisition in the colder, drier, more seasonal habitat of P. campbelli requires more energy and time than resource acquisition in habitat of P. sungorus . As such, constraints on energy and time during the breeding season may have been important in the evolution of biparental care in P. campbelli but not P. sungorus .

Ecological and physiological characteristics of seasonal biology of the mongolian hamster, Allocricetulus curtatus allan 1940 (Cricetinae, Rodentia)

Analysis of the seasonal dynamics of body weight and steroid hormones (cortisol, progesterone, and testosterone), the pattern of hypothermia, and basic reproductive parameters has been performed in the Mongolian hamster (Allocricetulus curtatus), a poorly studied rodent species inhabiting areas with a sharply continental climate. The results show that torpor bouts take place in wintering animals. Changes in body weight during the autumn-winter season are insignificant. The pattern of fluctuations in the levels of sex steroids and cortisol is similar to that in dwarf hamsters of the genus Phodopus. Seasonal features in the dynamics of basal cortisol level differentiate A. curtatus from the closely related Eversmann’s hamster (A. eversmanni), which may be due to differences in the social structure of these species.

Genetic structure of urban population of the common hamster (Cricetus cricetus)

Over the past half-century, the common hamster (Cricetus cricetus), along with range-wide decline of natural populations, has actively populated the cities. The study of the genetic structure of urban populations of common hamster may shed light on features of the habitation of this species in urban landscapes. This article is focused on the genetic structure of common hamster populations in Simferopol (Crimea), one of the largest known urban populations of this species. On the basis of the analysis of nucleotide sequences of the cytochrome b gene and mtDNA control region, and the allelic composition of ten microsatellite loci of nDNA, we revealed that, despite the fact that some individuals can move throughout the city at considerable distances, the entire population of the city is represented by separate demes confined to different areas. These demes are characterized by a high degree of the genetic isolation and reduced genetic diversity compared to that found for the city as a whole.

Superspecies Complex Cricetulus barabensis sensu lato: Karyotype Divergence and Interrelation in Natural Contact Zones

Three different chromosomal forms of striped hamsters that belong to the superspecies complex Cricetulus barabensis sensu lato (Cricetidae, Rodentia), namely, “barabensis”, “pseudogeiseus”, and “griseus”, were studied to determine their relationships based on different biological and genetic species concepts and using the morphological, karyomorphs, molecular, and hybridization data. The results of craniometry suggest that differences between these karyotypes are rather of subspecies level. Cytogenetic differences also proved to be insignificant and correspond to the level of chromosomal races within a single species. An analysis of cytochrome b mitochondrial gene (cytb) differences of about 2.3–4.1% between the forms studied, which suggest intraspecific distinctions or those between allied species. Hybridization experiments, which produced various litters from mating between three karyomorphs, also confirmed both male and female fertility. In nature, there are several zones where contact is possible between the “barabensis” and “pseudogeiseus” karyomorphs. In one of these zones, in Central Mongolia, atypical karyotypes were found in two male specimens using chromosomal analysis. Taking into account the chromosome number and shape, this karyotype could be attributed to a hybrid between the second and subsequent generations. However, typing the cytb gene and intron localized to Y chromosome (DBY1) did not reveal any traces of recent or ancient hybridization. In another zone, in South Buryatia, where the contact could be expected between the karyomorphs studied, the “barabensis” and “pseudogeiseus” populations are separated by the Chikoi River and the distance between them does not exceed 5 km. Nevertheless, neither karyological nor molecular analysis detected any hamsters with nonstandard karyotypes or any traces of gene flow. An analysis of the entire cytb nucleotide sequence, as well as the Tajima’s test, the distribution of pairwise differences, and the level of nucleotide diversity suggest that both contact zones have formed long ago; the absence of gene flow cannot be explained by their recent formation. Thus, the evolutionary formation of each of the three karyomorphs that were the subject of our study appears to be independent.

Daily torpor in hamsters (Rodentia, Cricetinae)

Study of ecological adaptations, including torpor, related to survival through the adverse conditions of the autumn-winter season is important for both the estimation of the body reserves in mammals in general and the search for the ways to increase the cold-stress resistance in humans. The changes in the body temperature during the period from October to May were studied in hamsters of six species under the natural photoperiod and temperature conditions. Incidental winter torpor (a drastically decreased physiological activity) was detected in all species except Cricetulus griseus; in three of them, it had not been observed before. No specific combination of conditions causing torpor was identified. Apparently, it is determined by individual characteristics of the animal. Torpors were the most frequent in January, at temperatures from −15 to −5°C; their depth was positively correlated with the ambient temperature. Since torpor is a rare event, it is assumed to be a stored resource of the body allowing animal to save energy and occurring only in extreme situations.

A record of hibernation on the surface of incisor teeth in the hamster Mesocricetus raddei (Nehring, 1894)

The surface of the lower incisor teeth was studied in an adult male Mesocricetus raddei hamster with a temperature logger implanted into its peritoneal cavity in June 2010. From July 2010 to March 2011, the hamster lived under natural conditions in an enclosure and overwintered in a self-made burrow. Logger data showed that, beginning from mid-August, the animal body temperature periodically dropped and then returned to the norm, with the duration and depth of hypothermia (torpor bouts) increasing and those of nor-mothermia (arousals) decreasing with time. Growth increments on the incisor surface (presumably, daily increments) were unclear in the apical and middle tooth parts but very distinct in the basal part. The number and width of basal increments generally corresponded to the number and duration of arousals. The growth of the incisors apparently continued throughout the winter season, with every arousal after a torpor bout being marked by the formation of a distinct increment on the incisor surface. Thus, it appears that the pattern of increments on the incisor surface can be used to evaluate the course of wintering in hibernating hamsters. Experiments with vital markers are needed to confirm this assumption.

New data on the distribution of chromosomal races in the supraspecies complex Cricetulus barabensis sensu lato (Rodentia, Cricetidae) and analysis of reproductive barriers among them

The taxonomy of striped hamsters from the supraspecies complex Cricetulus barabensis sensu lato (Rodentia, Cricetidae) is still controversial. The morphological and genetic differences between them are insufficient. In laboratory hybridization experiments, we obtained F1 and F2 hybrids from different combinations of mating between three chromosomal races. We found no evidence of reduced viability and fertility in the hybrids. In order to specify the distribution and detect natural hybridization, we analyzed the chromosomes of animals from potentially contacting populations of “barabensis” and “pseudogriseus” in southern Buryatia and central Mongolia. Two specimens with an abnormal karyotype were found in the “barabensis” population from the vicinity of Kharkhorin (central Mongolia), which can be considered as a result of distant hybridization. Karyological analysis of the hamster populations in southern Buryatia revealed parapatricity of the two chromosomal races, but regular hybridization between them was not found. In general, our data suggest that there is no intensive genetic interchange between the two chromosomal races.

Molecular phylogenetics and taxonomy of dwarf hamsters Cricetulus Milne-Edwards, 1867 (Cricetidae, Rodentia): description of a new genus and reinstatement of another

The taxonomy of the genus Cricetulus has been controversial. The phylogenetic relationships both within the genus and among Cricetulus lineages and other genera were examined using a set of five nuclear and two mitochondrial genes. The results demonstrate that Cricetulus in its current treatment is a polyphyletic assemblage because the subgenus Urocricetus is phylogenetically unrelated to all other Cricetulus and is a distant sister group to Phodopus. The grey hamster (C. migratorius) proved to be closer to Cricetus and Allocricetulus than to Cricetulus proper, which includes C. barabensis C. sokolovi and C. longicaudatus. Based on these results Urocricetus is elevated to the rank of a full genus and a new genus Nothocricetulus gen.nov. is described for the grey hamster.

Microsatellite loci variation and investigation of gene flow between two karyoforms of Cricetulus barabensis sensu lato (Rodentia, Cricetidae)

We examine the diversity of six microsatellite loci and partial RAG1 exon of “barabensis” and “pseudogriseus” karyoforms in Cricetulus barabensis sensu lato species complex. A total of 435 specimens from 68 localities ranging from Altai to the Far East are investigated. The results of the population structure analysis (factor analysis and NJ tree based on Nei genetic distances) support subdivision into two well-differentiated clusters corresponding to the two karyoforms. These karyoforms are also well differentiated by the level of microsatellite variability. In several “barabensis” specimens, we found microsatellite alleles that are common in “pseudogriseus” populations but are otherwise absent in “barabensis.” Most of these specimens originate from a single population in one of the zones of potential contact between karyoforms, Kharkhorin in Central Mongolia. These molecular results are consistent with previously published karyological data in suggesting that rare hybridization events between the two chromosomal races occur in nature.