M. A. Potapov

Effects of selection for olfactory preferences in an inbred mouse strain.

Sexual reproduction, a major evolutionary advantage, ensures an increase in the latent mutation reserve and, in addition, improves the overall population gene pool by testing the adaptive value of new mutations and stabilizing their advantageous combinations [1]. Since individual organisms ceased to be self-reproducing units, interindividual relatedness became more important, and “the population level” appeared, manifesting itself as a family, which is a new, triune reproductive unit (male, female and their offspring). As population biology developed starting with Darwin’s works [2], it became increasingly evident that the formation of the reproductive “cells” is not accidental in natural populations, because the advantages of combinatorial variability proved to be actually beneficial for the species’ evolutionary fate. Both the “latent” genetic features and physiological state of mates are known to be distinguished by animals and determine their mating preferences [3]. Gradual progress in the phenotypical expression of vitally important traits is thus supported [1, 4, 5]. In any case, when a female has an opportunity to choose the mate, reproduction is optimized (a higher fecundity and better offspring development are observed [6, 7]). In inbred animals, the range of phenotypical variability is similar to that observed in heterogeneous populations and influences the mating preferences. Several hypotheses were put forward to explain this phenomenon by an a priori preserved genetic variability or “phenotypical instability” [8, 9]. Because of genetic and/or phenotypical variability, discrimination is possible between the potential sexual partners, as well as mating preferences and the effects of epigamic selection. In this study, we attempted to determine the ethological and physiological effects of the odorous choice of a male by females of inbred strains, because the “chemical sense” is the leading one in mammalian communications [10]. The BALB/c mice from the Laboratory of Biomedical Modelling (Tomsk), which are maintained at the Institute of Animal Systematics and Ecology, Russian Academy of Science, were used. Two weeks prior to the experiments, each male was placed into an individual cage to smooth out the differences caused by the behavioral and physiological effects of the keeping in groups [10]. When testing for mating preference as described earlier [6, 7], it was determined what time it takes estrous females to examine the bedding from two males. Formation of a mating pair was considered to be completed when the stimulus from one of the males was examined for a longer time and repeated preference was displayed by the female. Then, both male and female were kept in one cage to obtain about three litters of young mice, which were weaned at the age of three weeks. Next day after the young mouse birth, the fathers were tested for parental care [7]. For this purpose, they were removed from the cage, in which the young mice were replaced from the nest into the opposite corner. Then, the father was returned to the nest, and, if it did not carry any of the young mice into the nest for 10 min, it was considered to exhibit no paternal care, and vise versa. After each of eight selection cycles, ten pairs were selected to form the “preferential olfactory stimulus” (POS) experimental group (the selection rate being 50%). Ten control (C) pairs were formed from animals bred without the selection for the POS; some of these were brother–sister pairs.

Localization of ASV Integrase-DNA Contacts by Site-Directed Crosslinking and their Structural Analysis

Background We applied crosslinking techniques as a first step in preparation of stable avian sarcoma virus (ASV) integrase (IN)-DNA complexes for crystallographic investigations. These results were then compared with the crystal structures of the prototype foamy virus (PFV) intasome and with published data for other retroviral IN proteins. Methodology/Results Photoaffinity crosslinking and site-directed chemical crosslinking were used to localize the sites of contacts with DNA substrates on the surface of ASV IN. Sulfhydryl groups of cysteines engineered into ASV IN and amino-modified nucleotides in DNA substrates were used for attachment of photocrosslinkers. Analysis of photocrosslinking data revealed several specific DNA-protein contacts. To confirm contact sites, thiol-modified nucleotides were introduced into oligo-DNA substrates at suggested points of contact and chemically crosslinked to the cysteines via formation of disulfide bridges. Cysteines incorporated in positions 124 and 146 in the ASV IN core domain were shown to interact directly with host and viral portions of the Y-mer DNA substrate, respectively. Crosslinking of an R244C ASV IN derivative identified contacts at positions 11 and 12 on both strands of viral DNA. The most efficient disulfide crosslinking was observed for complexes of the ASV IN E157C and D64C derivatives with linear viral DNA substrate carrying a thiol-modified scissile phosphate. Conclusion Analysis of our crosslinking results as well as published results of retroviral IN protein from other laboratories shows good agreement with the structure of PFV IN and derived ASV, HIV, and MuLV models for the core domain, but only partial agreement for the N- and C-terminal domains. These differences might be explained by structural variations and evolutionary selection for residues at alternate positions to perform analogous functions, and by methodological differences: i.e., a static picture of a particular assembly from crystallography vs. a variety of interactions that might occur during formation of functional IN complexes in solution.

Stabilizing function of sexual selection in relation to male aggressiveness in rodents.

A series of experiments on water voles ( Arvicola terrestris L.) and outbred (Swiss) and inbred (BALB/c and C57BL/6) strains of house mice was performed to estimate the dependence of the attractiveness of male rodents on their aggressiveness. The results showed that females preferred males with intermediate aggressiveness indices, which proved to have higher reproductive capacity. The aggressiveness (aggressiveness index) was measured as the mean ratio of aggressive acts to the total number of social interactions between males placed in the same cage. The males were divided into four groups according to their aggressiveness indices: low-aggressive (with aggressiveness indices varying in different series from 0.00‐0.20, M = 0.13), mediumaggressive (0.45‐0.65, M = 0.55), aggressive (0.65‐0.85, M = 0.75), and high-aggressive (0.85‐1.00, M = 0.93). Olfactory attractiveness was estimated by attractiveness index calculated as the proportion of tests in which the stimulus of the given male (the bedding from its cage) was preferred by a female. The stimulus was considered preferred if a receptive female (at the late proestrus or estrus stage) explored it for a longer time than other stimuli. From 17 to 112 males were studied in individual experimental series. The dependence of the olfactory attractiveness of males on their aggressiveness was not monotonic (figure). Low-aggressive males were the least attractive for females (their mean attractiveness index was M = 0.14), and aggressive males were the most attractive ( M = 0.86). The attractiveness of high-aggressive males ( M = 0.51) was significantly lower than that of aggressive and about the same as that of medium-aggressive ( M = 0.49). Although linear approximation can be applied to the observed dependence of attractiveness on aggressiveness ( r 14 = 0.63, R 2 = 0.40, t = 3.07, p = 0.001), which explains the widespread opinion that it is monotonic, a fourth-degree polynomial approximation considerably better fits the observed dependence ( r 14 = 0.93, R 2 = 0.87, t = 9.81, p < 0.000001).

Male sexual attractiveness and aggressiveness in rodents having different mating systems

Male aggressiveness can affect male reproductive success both directly by increasing competitiveness and indirectly through female preference. Assuming that significance of male aggressiveness in species having different mating systems can be different, we studied how male aggressiveness relates to sexual attractiveness in polygynous rodents, the water vole (Arvicola terrestris) and the house mouse (Mus musculus), and in a monogamous species, the steppe lemming (Lagurus lagurus). Our analysis revealed that the relation between odor attractiveness and aggressiveness is nonlinear. In polygynous species, males are more aggressive, so females opt for aggressive, albeit not too aggressive, males. In the monogamous steppe lemming, males show low level of intermale aggressiveness, and the most attractive are slightly aggressive males who have greater reproductive potential.

The effect of habitat hydrology on intraspecific competition, settlement structure, and reproduction in the water vole (Arvicola terrestris).

Analysis of long-term monitoring of the water vole population in Northern Baraba Lowland (Ubinskii raion, Novosibirsk oblast) has revealed correlation between flow intensity of the Om’ River in the study area and population numbers and population dynamics (estimated May through August), average number of live embryos in overwintered females, and percentage of mature young-of-the-year females in different years of study.

Interstrain Odor Preferences and Factors Influencing Growth Rates of Two Strains of Mice and Their Hybrids

We used C57BL/6J (B6) and BALB/cLac (C) mice strains to examine whether inter-strain odor preferences are correlated with differences in pup growth caused by the combination of genotypes of mothers and young. In our study, C females preferred B6 male odor (soiled bedding) over C male odor; C females raising such hybrid pups had improved milk quality (protein and lipid content). B6 females preferred B6 male odor and their milk quality did not change during gestation of hybrid pups. On the other hand, pup development may be influenced by the “graft-versus-host” reaction (GVHR) that is induced by maternal lymphocytes that are naturally transferred via milk. At weaning, weight indices of the spleen in hybrid pups raised by C dams were lower than in hybrids raised by B6 females. As a result of the inter-strain differences in these physiological mechanisms, hybrid pups grew faster if their mother was a C female than if she was a B6 female. Thus, preference of C females for dissimilar B6 males is supported by the long-term positive effects on hybrid pup development during lactation. B6 females have no effective mechanisms giving advantages for the hybrids and they do not prefer dissimilar males.

ATTRACTIVENESS OF MALE VOLE ODOR IS POSITIVELY CORRELATED WITH PUP VIABILITY

The aim of this study was to determine whether pup weight and growth rate are correlated with the “attractiveness” of the odor of the male that the female mated with. To determine male attractiveness, receptive water vole (Arvicola terrestris L.) females were exposed to odor stimuli from triads of males. The odor stimulus from each male was presented to 1-5 different females. The average time of odor investigation served as a measure of male attractiveness. For breeding, male-female pairs were chosen randomly. It was found that the attractiveness of a male’s odor was positively correlated with the mean birth weight of his progeny and their growth rate to weaning. A relationship between pup characteristics and father’s social rank or body weight was not observed. Because the measured attractiveness of the male odor was not based only on the preference of his mate or on the male’s social/physical status, we suggest that some mechanisms other than genetic dissimilarity, kinship or dominance are involved in odor attractiveness.

Mating systems in the steppe lemming (Lagurus lagurus) and narrow-skulled vole (Microtus gregalis) from the Northern Kulunda Steppe

A comparative analysis of reproductive behavior has been performed in the steppe lemming (Lagurus lagurus) and narrow-skulled vole (Microtus gregalis). The results show that the species are similar in certain behavioral features indicative of the stability of mating pairs. However, in the narrow-skulled vole, unlike in the steppe lemming, mature males in olfactory tests show preference for receptive sibling females versus non-kin females. Probably, it is the absence of the incest taboo that allows the involvement of young of the year in reproduction within growing family groups and accounts for “coloniality” of the species.

Variable Social Rank of White-Spotted Male Water Voles: The Effect of the Presence of Females

Western Siberia is inhabited by cyclic populations of the water vole Arvicola terrestris that are polymorphic for white spotting (WS). This trait is known to occur in other regions of the species range [1–3] and in other mammalian species [4–7]. Different types of WS vary in the mode of inheritance. Genes responsible for WS act either on neural crest cells (from which melanoblasts originate) or on the cellular environment of melanoblasts through which they migrate to the site of differentiation [4]. The rate of their migration and the level of WS expression depend on both environmental and genotypic factors [5, 8]. The genes that control WS often pleiotropically affect reproductive and behavioral traits of animals [4, 5, 7].

Amicable and aggressive behavior as factors of formation of species-specific family-group relations in rodents

53 Formation of family groups in mammals, including rodents, is primarily based on the type of mating rela tions [11], such as promiscuity, monogamy, or polyg amy. In rodents, the last type of mating relations is rep resented by polygyny, with polyandry only found in the naked mole rat (Heterocephalus glaber) [3]. An ele mentary unit of population is a family triad comprising a female, a male, and their offspring [6, 12]. As a whole, this unit represents a “simple” family, which is typical of monogamy. When descendants continue their life in this family and engage in breeding, then a “complex” family is formed. In the case of promiscu ity or polygyny, when males do not participate in parental care, a family remained being “incomplete.”