Sibling inhibition of hoarding in postweaning hamster pups (Mesocricetus auratus)

If hamster pups are placed in individual cages at weaning (21 days of age) they begin to hoard food immediately; within 2-6 days, they hoard 90% of the food they take from their food dish in the course of a 1-hr test, consuming only 10% of it. Pups that remain with their littermates after weaning in large group cages do not hoard food until they are placed in individual cages, when hoarding starts immediately. The inhibitory effect of littermates is just as pronounced in hamsters that have been allowed to hoard food in individual cages for 14 days after weaning and are then regrouped into litters. If litters are housed in divided cages that prevent physical interactions among littermates, but allow the interchange of olfactory, auditory, and some visual cues, hoarding is suppressed to an intermediate level. These results show that the presence of siblings inhibits the expression of hoarding, partly as a result of direct physical interactions and partly through the agency of sensory cues. The onset of hoarding following the dispersal of young from the nest cannot be explained as a motivational consequence of the young no longer having access to the mother's food hoard.     

Behavioral development in mice: Effects of maternal environment and the albino locus

We examined the interaction of the albino locus with the maternal environment on the behavioral development of two coisogenic strains of mice. Subjects of the pigmented C57BL/6 strain (=B6^+/+) and of the albino C57BL/6^c2J strain (=B6^c/c) were either fostered by a mother of their own strain or cross-fostered at birth to an F₁ hybrid dam. They were compared for the amount and daily distribution of activity displayed during 48 h in a seminatural device at weaning and when 75 days old. Food hoarding in the nest and food consumption at the food-search place were also recorded in adult subjects. When animals were fostered by a mother of their own strain, albino mice were more active and less nocturnal than pigmented mice at both ages. They hoarded less food in the nest and ate more at the food-search place. Most of these differences disappeared when both strains were fostered by an F₁ dam. The amount of activity displayed during 48 h increased between 21 and 75 days of age. This increase was affected by cross-fostering to an F₁ dam in B6^c/c mice only. The developmental pattern of daily distribution of activity was changed by F₁ dams in B6^+/+ mice only. Whereas these influences of F₁ dams produced subjects resembling the mother's phenotypic score, maternal effects on hoarding behavior in B6^c/c mice produced subjects which did not resemble their foster mother. The results are discussed in terms of different possible ways of hereditary transmission of behavior and some methodological consequences are emphasized.     

Diet self-selection and food hoarding after food deprivation by Siberian hamsters

Siberian hamsters (Phodopus sungorus) increase food hoarding, but not food intake, after a fast. Because the physiological mechanisms underlying these changes in food hoarding are virtually unknown, we sought insight into these mechanisms by allowing hamsters to self-select their diet from food sources varying in macronutrient composition and caloric density ("dietary wisdom"). Therefore, the effects of food deprivation length on diet self-selection were tested in adult female hamsters after adaptation to three composite diets: sunflower seeds (SS), pellet chow (PC), and rabbit chow (RC). One group initially was fasted for 32 h, the other for 56 h, and then each was refed. The remaining nonexperienced fast was instated after prefast body mass, food intake, and hoarding were recovered. Food hoarding, but not food intake, was increased regardless of fast length or sequence; moreover, the largest increase in food hoarding was on the first day of refeeding and was primarily reflected as increased SS hoarding. When the longer fast occurred first body mass loss was greater and the increased food hoard size was maintained for more days than when the longer fast came second. The order of food intake and hoarding preferences was not changed after a fast (SS > PC > RC), but the degree of food hoarding preference for SS was exaggerated. Collectively, these results support the notion that food hoarding increases with decreases in lipid stores, and show that when internal lipid stores are decreased, external lipid stores are preferentially increased.     

Genetics of spike-wave discharges in the electroencephalogram (EEG) of the WAG/Rij inbred rat strain: A classical mendelian crossbreeding study

The WAG inbred strain might be an animal model for human absence epilepsy. To study the inheritance pattern of absence epilepsy, WAG rats were crossbred, in a classical Mendelian way, with inbred ACI rats which show no signs of epilepsy. In the parental strains, reciprocal F₁ hybrids, F₂, B₁, and B₂ generations, the number and duration of spikewave discharges were determined. One hundred percent of the F₁ animals showed spike-wave discharges, while the percentages for the F₂, B₁ and B₂ generations were 79, 95, and 37%, respectively. These results suggest that the occurrence of spike-wave discharges is determined by one gene with a dominant mode of inheritance. Cavalli's least-squares fitting procedure suggested different genetic models for the two parameters (number and duration) during the two periods (dark and light). These results confirm our previous findings (Peeterset al., Behav. Genet. 20, 453–460, 1990) that a number of genes are involved in absence epilepsy. One dominant gene appears to determine the occurrence, however, while others manipulate the number and duration of epileptic phenomena during the two periods dark and light.To whom correspondence should be addressed.     

Maternal effects in mice: Influence of parents' and offspring's genotypes

Different backcrosses between the F₁ and two inbred parental strains (C and B6) were compared for swimming speed in a water escape task and for swimming ability in a water channel. Results showed maternal effects, mice from an F₁ dam swimming faster than mice from an inbred dam. Albino mice appear to be more sensitive to these effects than pigmented ones. The degree of expression of these effects could also be related to the inbreeding level of the offspring, the reciprocal backcrosses showing differences, whereas the two reciprocal F₁'s did not. Maternal effects appear to be greater in the water escape task than in the water channel situation.     

NON-H-2-LINKED GENETIC CONTROL OF RESISTANCE TO BALB/c FIBROSARCOMA METH-A

The genetic control of hybrid resistance to BALB/c fibrosarcoma Meth-A was investigated. A Meth-A tumour grew slower in (BALB/c X C57BL/6)F₁ and reciprocal hybrid mice than in syngeneic BALB/c mice and was also found to grow slower in females than in males. Significant F₁ resistance was demonstrated after both subcutaneous and intraperitoneal injection of tumour cells. However, (BALB/c X DBA/2)F₁ mice did not show any significant resistance to Meth-A. In H-2 linkage studies of [BALB/c X (BALB/c X C57BL/6)] backcross mice, no statistically significant differences in the resistance of H-2 heterozygotes and homozygotes to Meth-A were observed. These results indicated that F₁ hybrid resistance to Meth-A was controlled by non-H-2-linked resistance factor(s). No linkage was observed between resistance to Meth-A and coat colour c- and b-loci.     

Fasting-induced increases in food hoarding are dependent on the foraging-effort level

Two strategies that have evolved to help animals meet energy demands are increases in body fat and in hoarded food. Reliance on each varies, but both are characterized by energy stored in excess of current demands for future use. Fasted Siberian hamsters decrease their lipid stores and, upon refeeding, food hoarding rather than food intake increases. Here, we tested the effect of foraging-effort level on fasting-induced increases in food hoarding and whether decreases in total body fat or individual fat pad masses were associated with the hoarding increases. This was accomplished by housing female Siberian hamsters in a foraging/hoarding system where they earned food pellets upon completion of a programmed number of wheel revolutions (10, 75 or 200 per 75-mg pellet), or had no foraging requirement (free food and an active or blocked running wheel). After baseline, half the hamsters in each group were food deprived for 32 h and then refed (control hamsters were killed after the fast without refeeding). Fasted-refed hamsters increased foraging and food hoarding, especially at the lowest foraging effort, but not food intake, with few exceptions. These responses became progressively smaller as foraging effort increased. Fasting induced similar losses in carcass lipid across foraging efforts, but the lipid loss was not uniform across the fat pads and was not clearly related to hoard size. Collectively, the fasting-induced, increased food hoarding may be triggered by an overall change in energy metabolism rather than by a general or fat-pad-specific decrease in lipid stores.     

Geographic variation in the territorial success ofDrosophila melanogaster males

Drosophila melanogaster males defend food against other males to increase their access to females on food. The territorial behavior of stocks collected from Townsville, Corindi, and Melbourne on the east coast of Australia were compared. Males from these stocks showed the same incidence of territorial encounters. However, Melbourne males were more successful at obtaining territories in competition with Townsville or Corindi males. This difference could be accounted for largely by variation in body weight, although territorial success was also determined by other factors because Townsville and Corindi males that held territories were not heavier than Melbourne males. In reciprocal crosses between the populations there was directional dominance for increased territorial success. F₁ males were of intermediate weight and F₁ males that held territories tended to be lighter than territorial Melbourne males. Melbourne males were more successful than Townsville males because they tended to win escalated encounters, resulting in displacement of territory residents.     

Xenotropic type C virus expression in murine thymomas induced by radiation or 3-methylcholanthrene

Thymic lymphoma incidence and thymic expression of MuLV with xenotropic infectivity was monitored in AKR, RF, and reciprocal F₁ mice of the AKR × RF cross after treatment with either γ radiation or the chemical carcinogen 3-methylcholanthrene (MCA). These two inbred strains and the F₁ hybrids developed similarly high incidences of thymoma, and lymphomatous cells from AKR mice and (AKR♀ × RF♂)F₁ mice were observed to be expressing MuLV with xenotropic host range. However, lymphoma cells from RF mice and (RF♀ × AKR♂)F₁ mice did not shed xenotropic MuLV. Thymic xenotropic virus expression was therefore not correlated with a high incidence of radiation or chemically induced thymoma, but rather appeared to be a phenotype genetically transmitted by AKR mice to F₁ mice of the AKR × RF cross as a dominant trait in induced thymomas. In addition, a maternal effect on thymic xenotropic virus expression in induced thymomas was observed by the comparison of reciprocal F₁ hybrids in this cross.     

Daily variations of cerebral tyrosine in two inbred strains of mice and their F1 hybrids

The diurnal rhythms of endogenous cerebral tyrosine in 15 week-old mice from BALB/C/Orl and C57 BL/6/Orl strains and their reciprocal F₁ hybrids, placed on a fixed 12/12 h dark-light schedule, were determined over a 24 h period in the fore-brain and hind-brain. Significant inter-strain differences in mean tyrosine levels were described in both structures. The main finding was that BALB/C exhibited a significant 24 h rhythm whereas a 12 h rhythm was found in C57/BL. In F₁ hybrids, daily tyrosine rhythm appeared in both structures as a combination of the 2 parental ones. These findings support the suggestion that genetic factors may affect biological rhythms.     

A developmental genetic analysis of locomotor activity in mice: Maternal effects in the BALB/c and C57BL/6 strains and heredity in F1 hybrids

Continuous recording of locomotor activity of mice during 48 h in seminatural enclosures was performed at 21 and 75 days of age, on the same individuals. Four groups of inbred subjects were compared for amount of locomotor activity and its daily distribution: in both BALB/C ( = BALB) and C57BL/6 ( = C57) strains, pups were either fostered by a mother of their own strain or crossfostered to a mother of the other. In addition, two reciprocal F₁'s were compared to the parental strains. While no significant effect of crossfostering to a C57 dam appeared in BALB mice, 21-day-old C57 crossfostered to a BALB dam were more active and more nocturnal than those reared by a C57 dam. In C57 mice the change in activity level between 21 and 75 days was also affected by crossfostering. Reciprocal F₁ hybrids did not differ. A BALB pattern was dominant at 21 days for amount of activity and for change between 21 and 75 days. For daily distribution of activity, F₁ hybrids were BALB-like at weaning and C57-like (with heterosis) in adulthood.     

Genes on the X chromosome affect development of collagen-induced arthritis in mice

Susceptibility to collagen-induced arthritis (CIA) in mice is associated with a class II gene in MHC (A^q) but also with unknown genes outside MHC. Investigated here is the influence of genes on the X chromosome as well as the role of the X-linked immunodeficiency (xid) mutation. Reciprocal male F₁ hybrids, bred to be heterozygous or homozygous for A^q, showed a genetic influence in their susceptibility to develop CIA. Crosses were made between B10.G, B10Q, DBA/I, SWR/J, C3H.Q and CBA/Ca, and all F_i mice were castrated to avoid sex hormone modulation of the susceptibility. A differential timing of arthritis onset and severity were seen in the reciprocal F₁ males. An exception was the reciprocal F₁ male offspring from SWR/J and DBA/1 crosses which differed only in disease severity late in the course of the disease. The female F₁ crosses did not show the same pattern of differential susceptibility to CIA as the F₁ males. To exclude the possible influence the Y chromosome, F₁ males of reciprocal crosses were back-crossed to the parental strains creating offspring with equal X chromosomes but divergent Y chromosomes. No difference in development of arthritis was observed in these. The influence of the xid mutation was investigated next. The xid loci from the CBA/N mouse was bred into DBA/1 strain which is highly susceptible to CIA. The resulting congenic DBA/l-xid strain was resistant to induction of CIA and did not develop an antibody response to type II collagen. We conclude that polymorphic genes on the X chromosome modulate susceptibility to CIA. The results from the experiments with mice carrying xid mutations confirm that such immune modulating genes exist on the sex chromosomes.     

Genetic and environmental variability in lick rates of mice

The hypothesis of lick rate invariance was tested by comparing rates of licking among two inbred strains of mice and their F₁ hybrids across two different fluid regimens. DBA mice licked significantly faster than C57 mice, while the lick rate of both reciprocal F₁ groups was intermediate between that of the two parental strains. This ordered relationship held when either water or a morphine solution was the available fluid. C57 mice, but not others, also displayed transient changes in lick rate with changes in fluid regimens. Thus, rates of licking among mice are neither genetically nor environmentally invariant.     

Activity rhythms in inbred mice. I. Genetic analysis with recombinant inbred strains

Rhythm of activity of inbred mice was recorded automatically by a set of actographs. This rhythm was characterized by six indices in the temporal and frequency domains. Two methods of genetic analysis were applied to these indices using parental strains BALB/c and C57BL/6, the reciprocal F₁'s, and the seven recombinant inbred strains (RI). Findings on the F₁'s show no maternal effect but indicate dominance and heterosis. The RI method successfully rejects the hypothesis of a monogentic correlate for all measures. In line with F₁ data, it demonstrates the presence of a polygenetic correlate: at least one other locus is involved in each of the six outcome parameters.This study was supported by CNRS (URA 1294, affilieé Inserm), MEN (UFR Biomédicale des Saints-Pères, Paris V), Foundation pour la Recherche Medicale.     

Autosomal and maternal effects on pupation behavior inDrosophila melanogaster

This study demonstrates the importance of using a complete set of 16 reciprocal crosses (F₁, backcrosses, and F₂) to thoroughly investigate both genetic and nongenetic influences on patterns of inheritance of larval pupation behavior inDrosophila melanogaster. Larvae derived from natural populations show significant variation in pupal height, defined as the distance a larva pupates above the feeding substrate. Differences in the distance a larva pupates from fruit in nature is known to affect the fitness ofDrosophila populations. In this study the heredity of pupal height is analyzed by performing crosses between high- and low-pupating strains. We found that the inheritance of pupal height fit a classical additive polygenic model of inheritance, with intermediate F₁ pupal heights and greater variances in the F₂ generation. In addition, a significant maternal effect was also found by analyzing the reciprocal backcrosses. Progeny with low-pupating mothers had lower pupation heights than those with low-pupating fathers. Similarly, progeny with high-pupating mothers tended to have higher pupal heights than those with high-pupating fathers. This maternal effect was not attributable to strain differences in permanent cytoplasmic factors, sex chromosomes, or developmental time. Finally, we speculate upon the environmental conditions under which a transient maternal effect on pupation behavior would be expected to evolve in natural populations.This work was supported by a University Research Fellowship and Operating Grant from the Natural Sciences and Engineering Research Council to M. B. Sokolowski. S. J. Bauer was the recipient of an Ontario Graduate Scholarship.     

Inheritance of water-escape performance and water-escape learning in mice

Only two (C57BL, CBA) of six mouse strains improved their escape time in a simple water-escape task on five successive trials (days). The remaining four strains (BALB/c, C3H, 101, NMRI) did not learn in this test situation. The two most extreme inbred strains, C57BL (high escape performance, good learners) and BALB/c (low escape performance, nonlearners), were intercrossed to produce F₁, F₂, and two backcross (B₁, B₂) generations of both reciprocal crosses. The learning curves constructed by plotting log escape time against trial number were found to posses significant slopes and to fit straight lines for C57BL and CBA as well as for all four intercross generations. Accordingly, the inhertiance of learning ability to escape water could be explained in terms of an additive-dominance model without nonallelic interactions. Neither significant sex differences nor maternal influences were found in the six strains studied for the four strain crosses. F₁ mice escaped faster and their learning curves were significantly different from those of the other genotypes (F₂, B₁, B₂, parental strains), indicating behavioral heterosis. Albino mice of the segregating generations showed a poorer water-escape performance than their pigmented sibs.Dedicated to Prof. Dr. Ernst W. Caspari.     

Strain Difference and Mode of Inheritance of the Susceptibility to Passive Cutaneous Anaphylaxis Mediated by the Allogeneic IgE Antibody in the Mouse

The strain difference and mode of inheritance of the susceptibility to PCA (passive cutaneous anaphylaxis) were studied in mice. No marked strain differences were found in the susceptibility to PCA mediated by allogeneic IgG₁ monoclonal and xenogeneic IgG antibodies, although BALB/cCrj mice were somewhat less susceptible than the other strains. On the other hand, the susceptibility to PCA mediated by allogeneic IgE monoclonal antibodies differed greatly according to the strain; SJL/J, A.SW/J and DS/Shi mice being highly susceptible and C57BL/6JShi, BALB/cCrj, DBA/2Crj, C3H/HeShi and CBA/JNCrj mice insusceptible. Based on the marked difference between DS/Shi and C3H/HeShi strains, the mode of inheritance of the susceptibility to IgE PCA was studied using their F₁, F₂ and F₁ x parent backcross offspring. All the F₁ hybrids by reciprocal crosses between these two strains and F₁ x DS backcross mice were highly susceptible like DS/Shi mice. Backcross mice between F₁ and C3H/HeShi showed approximately 1:1 segregation into the susceptible and insusceptible. Segregation was also observed in the F₂ generation; 32% being insusceptible. These results suggest that the high susceptibility is a dominant phenotype controlled mainly by a single gene on an autosomal chromosome; this was statistically supported by tests of the segregation ratios obtained. However, in the PCA-positive recipients of F₁ x C3H backcross and F₂ generations, dye leakage into the skin was tended to be diffuse and less compact than in DS/Shi, F₁ and F₁ x DS backcross mice. This suggests the presence of some additional genes which modify the expression of the main gene.     

Diet choice exaggerates food hoarding, intake and pup survival across reproduction

Siberian hamsters increase food intake and hoarding during pregnancy and lactation, perhaps to compensate for large decreases in body fat (approximately 50%). We tested the effects of diet choice on these responses in pregnant, lactating and virgin hamsters housed in a simulated burrow system. Hamsters were offered pellet chow (PC) or a choice of sunflower seeds (SS), rabbit chow (RC) and PC. Pregnant or lactating PC-fed hamsters had increased food intake and hoard size compared with virgins, effects exaggerated by diet self-selection. The pregnancy-induced increases and lactation-induced decreases in body mass were enhanced and diminished by diet self-selection, respectively. Pregnant self-selecting hamsters ate relatively more carbohydrate and less fat and hoarded less carbohydrate and more fat than their virgin counterparts (protein not affected). Lactating and virgin self-selecting hamsters both ate and hoarded relatively more carbohydrate than protein or fat compared with PC-fed hamsters but were not different from each other. Litter and pup sizes were similar at birth, but pups from self-selecting mothers had decreased lipid content (50%) compared with pups from PC-fed mothers, whereas at weaning they were heavier but not fatter. Only lactating PC-fed mothers cannibalized their pups (approximately 60% eaten, 8/10 litters). The pregnancy-induced increased eating and hoarding of carbohydrate may have helped meet immediate energy needs sparing dwindling lipid reserves, whereas the decreased fetal lipid investment may have helped conserve energy in anticipation of the increased demands of lactation. The diet-induced exaggerated caloric intake and food hoard size of lactating hamsters may have promoted pup growth and survival.     

Courtship behavior and cotrol of reproductive isolation inDrosophila mojavensis: Genetic analysis of population hybrids

Drosophila mojavensis from the Sonora region and Baja California show asymmetrical sexual isolation in the laboratory: males from Sonora mate equally frequently with Sonora and Baja females, while the mating success of Baja males with Sonora females is reduced. This failure has been localized to three separate behavioral landmarks occurring during courtship. Genetic analysis was conducted using reciprocal F₁ hybrids of Sonora and Baja strains to examine inheritance patterns of the responsible courtship behaviors. Mating success and propensity of F₁ males were similar to Sonora males. F₁ females mated with males of Sonora and Baja races equally, although mating propensity of F₁ females was intermediate between that of Sonora and Baja females. Males of Baja strains presented with F₁ females showed a relatively high level of failure at attempted intromission. Genes for mating behaviors are located in the autosomes, but different loci responsible for the sexual isolation appear to act in males and females.This work was supported by NSF Grant BSR 8600105 to Theresa Markow.     

Body weight regulation with a proportional hoarding response in the rat

Female rats hoarded food when their body weight was reduced by fasting. The amount hoarded (H) was proportional to body weight according to the equation: H=a (W_o ? W_b) with W_o: ad lib food-body weight and W_b: actual body weight. Body weights prior to starvation and after recovery were not statistically different from regression line thresholds for hoarding. These results show the existence of a proportional regulation of body weight with a hoarding response below the body weight set point.