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Little is known about the behavioural mechanisms facilitating kin-preferential communal breeding in wild house mice (Mus domesticus). We evaluated the effect of kinship and male availability on aggression, social structure and reproductive skew in groups of female mice freely interacting and reproducing in semi-natural indoor enclosures. Triplets of either sisters or non-sisters were established in enclosures provided with either one or three littermate males, which were unrelated and unfamiliar to the females. Sisters were more spatially associated and less aggressive than non-sisters, leading to higher incidences of communal breeding and reproduction. This is in agreement with theoretical considerations on kin selection in house mice. Reproductive success was highly skewed in favour of dominant females due to subordinate infertility or complete loss of first litters, which might have been caused by dominant females. In spite of this, subordinates only rarely dispersed from the enclosures, suggesting that perceived dispersal risk generally outweighed relatively reduced reproductive potentials. Aggression levels among females were significantly higher when one male was available, compared to when three males were available. We suggest that this might result from higher female-female competition for mates, due to the risk of missing fertilisation when synchronously oestrous females encounter limited numbers of males in a deme. Our results indicate that, first, communal nursing in house mice might have evolved to ‘make the best out of a bad job’ rather than to enhance offspring fitness; and, second, that female-female mate-competition might play an important role in shaping female social structure in this polygynous mammal.

To evaluate permanent effects of hippocampal and prefrontal cortex lesion on spatial tasks, lesioned and sham-operated female C57BL/6 mice were exposed to a series of conditioning schemes in IntelliCages housing 8–10 transponder-tagged mice from each treatment group. Sequential testing started at 51–172 days after bilateral lesions and lasted for 154 and 218 days in two batches of mice, respectively. Spontaneous undisturbed behavioral patterns clearly separated the three groups, hippocampals being characterized by more erratic hyperactivity, and strongly impaired circadian synchronization ability. Hippocampal lesions led to deficits in spatial passive avoidance, as well as in spatial reference and working memory tasks. Impairment was minimal in rewarded preference/reversal schemes, but prominent if behavioral responses required precise circadian timing or included punishment of wrong spatial choices. No differences between sham-operated and prefrontally lesioned subjects in conditioning success were discernible. These results corroborate the view that hippocampal dysfunction spares simple spatial learning tasks but impairs the ability to cope with conflicting task-inherent spatial, temporal or emotional cues. Methodologically, the results show that automated testing and data analysis of socially kept mice is a powerful, efficient and animal-friendly tool for dissecting complex features and behavioral profiles of hippocampal dysfunction characterizing many transgenic or pharmacological mouse models., Behavioural Brain Research, 352, ISSN:0166-4328, ISSN:1872-7549

Ribosomal s6 kinase 2 is a growth factor activated serine/threonine kinase and member of the ERK signaling pathway. Mutations in the Rsk2 gene cause Coffin-Lowry syndrome, a rare syndromic form of intellectual disability. The Rsk2 KO mouse model was shown to have learning and memory defects. We focused on the investigation of the emotional behavioral phenotype of Rsk2 KO mice mainly in the IntelliCage. They exhibited an anti-depressive, sucrose reward seeking phenotype and showed reduced anxiety. Spontaneous activity was increased in some conventional tests. However, KO mice did not show defects in place learning, working memory and motor impulsivity. In addition, we found changes of the monoaminergic system in HPLC and qRT-PCR experiments. Taken together, RSK2 not only plays a role in cognitive processes but also in emotional and reward-related behaviors.

Small mammals that inhabit arid and temporally unproductive environments use several methods to conserve energy. Here, we investigate the energetic role of sun basking in striped mice Rhabdomys pumilio from the Succulent Karoo desert in South Africa. We observed mice in front of their nests for 140 h and recorded the time they spent basking during the non-breeding (dry) and the breeding (wet) seasons. We measured temperature changes in model mice to provide an indication of the heat that can be absorbed from the sun. Finally, we measured the oxygen

Sex allocation theory is frequently applied to mammalian reproductive traits although the basic assumptions are rarely assessed. In particular, it has been proposed that the finding of negative correlations between sex ratio (percentage males) and litter size in a variety of mammals could ultimately be seen as an adaptation according to the Trivers-Willard hypothesis. Thereby it is supposed 1) that individual young of small litters are weaned at heavier weight than young of larger litters, 2) that this litter-size effect on individual weights persists into adulthood, and 3) that such small weight advantages increase male fitness more strongly than female fitness. In this study, during each of 4 trials, I introduced 4 male and 4 female mice from 8 different litters of wild-caught breeding pairs to a semi-natural enclosure and followed up the social and reproductive events for about 10 weeks. It appeared that small weight differences attributable to litter size variation had a significant positive effect on male fitness, but not on female fitness. As the sample size was small and the social development did vary considerably between trials, this result deserves further clarification.

Many birds are supreme long-distance navigators that develop their navigational ability in the first months after fledgling but update the memorized environmental information needed for navigation also later in life. We studied the extent of juvenile and adult neurogenesis that could provide such age-related plasticity in brain regions known to mediate different mechanisms of pigeon homing: the olfactory bulb (OB), and the triangular area of the hippocampal formation (HP tr). Newly generated neurons (visualized by doublecortin, DCX) and mature neurons were counted stereologically in 35 pigeon brains ranging from 1 to 168 months of age. At the age of 1 month, both areas showed maximal proportions of DCX positive neurons, which rapidly declined during the first year of life. In the OB, the number of DCX-positive periglomerular neurons declined further over time, but the number of mature periglomerular cells appeared unchanged. In the hippocampus, the proportion of DCX-positive neurons showed a similar decline yet to a lesser extent. Remarkably, in the triangular area of the hippocampus, the oldest birds showed nearly twice the number of neurons as compared to young adult pigeons, suggesting that adult born neurons in these regions expanded the local circuitry even in aged birds. This increase might reflect navigational experience and, possibly, expanded spatial memory. On the other hand, the decrease of juvenile neurons in the aging OB without adding new circuitry might be related to the improved attachment to the loft characterizing adult and old pigeons.

An assertion deeply rooted in the ornithological literature holds that sex-specific mortality causes a sex ratio disparity (SRD) between complete and incomplete broods. Complete broods are thought to reflect the primary sex ratio before any bias introduced by developmental mortality. Contrary to this view, however, complete and incomplete broods should exhibit identical sex ratio distributions even when the sexes experience differential mortality, as shown in the classic paper of Fiala (Am Nat 115: 442–444, 1980). Therefore, in partially unsexed samples, primary sex ratio biases cannot be distinguished from biases caused by differential mortality. In addition, complete broods do not represent primary sex ratio more accurately than incomplete ones and might even be misleading. Despite Fiala’s prediction, SRD does occur in some empirical studies. We show that this pattern could arise if (1) primary sex ratio affects chick mortality rates independently of sex (direct effect), (2) primary sex ratio covaries with a variable that also affects mortality rate, or (3) sex differential mortality covaries with overall mortality rate (indirect effects). Direct effects may cause stronger SRD than indirect ones with a smaller and opposite bias in the overall sex ratio and could also lead to highly inconsistent covariate effects on brood sex ratios. These features may help differentiate direct from indirect effects. Most interestingly, differences in covariate effects between complete and incomplete broods imply that influential variables are missing from the analysis.

Dispersal propensity, reflecting one of the most decisive mammalian life history traits, has been suggested to vary heritably and to locally adapt to prevailing dispersal conditions in wild house mouse populations. Because individual dispersal propensity highly significantly covaries with the developmental timing of the onset of agonistic interactions between littermate brothers, we used agonistic onset as an endophenotype to explore the potential genetic basis of dispersal-related behavioral variation in male house mice. We found significant covariation of microsatellite marker compositions with the probability of fraternal pairs to exhibit agonistic relationships before the age of 2 months. In particular, the presence of two alleles associated with a serotonin transporter protein gene (Slc6a4) and a testosterone dehydrogenase gene (Cyp3a11), respectively, strongly covaried with the probability of early agonistic onset. These results are congruent with recent findings of microsatellite length polymorphisms marking regulatory variation of gene expression that is relevant for social behavior, including dispersal propensity development, in other mammals. Genetic variability for ontogenetic timing of agonistic onset would be in agreement with genotypic differentiation of the dispersive behavioral syndrome in natural populations that could lead to local adaptation.

Deserts represent challenging, energy restricted environments for small mammals, but offer ample exposure to sunlight that might be used for energy saving during basking. The Succulent Karoo desert in southern Africa is a seasonal environment with cold moist winters, followed by maximum food availability in spring and dry hot summers with food shortage. The striped mouse (Rhabdomys pumilio) from the Succulent Karoo desert is diurnal and its activity is influenced by photoperiod in captivity. However, in contrast to standardized laboratory conditions, it can be expected that several factors other than photoperiod influence its activity pattern in the field. We expected that striped mice behave in a way that indicates that they use basking to passively warm up and thus reduce endogenous energy expenditure. We studied activity and basking patterns in 56 social groups of striped mice for a period of 4 yr, comprising 1534 observation sessions at their nests. Mice generally started activity around the time the sun illuminated their nest and terminated activity when their nest was no longer sunlit, i.e. they were strictly diurnal. The onset of activity was delayed on days when ambient temperature was colder and when group sizes were smaller. During the breeding season when food availability was high, striped mice usually left the nest before it was sunlit without basking. Outside the breeding season, they emerged and basked in front of nests mainly after nests were sunlit. These findings concur with the view that striped mice trade-off between active energy gain via foraging and passive energy acquisition by sun basking.

The physiological basis for population differentiation of dispersal timing during individual development in male wild house mice is still unknown. As major urinary proteins (MUPs) are known to convey information about competitive ability in male mice, we examined individual MUP profiles defined by isoelectric-focusing (IEF) patterns in relation to developmental timing of dispersive motivation. As an experimental paradigm marking the development of the dispersal propensity, we used agonistic onset between litter mate brothers when kept in pairs under laboratory conditions. Agonistic onset is known to reflect the initiation of dispersive motivation. Hence, we compared individual MUP IEF patterns between fraternal pairs that did or did not develop agonistic relationships before the age of 2 months. Urine was collected on the day of weaning and at the beginning of adulthood. We investigated whether there was a significant co-occurrence of particular MUP IEF patterns with the agonistic onset in male mice. We assumed that, based on this co-occurrence, particular MUP IEF patterns and/or a particular dynamic of MUP IEF expression from weaning to adulthood may be considered a physiological predictor of a specific behavioral strategy in male mice (i.e. submissive-philopatric or agonistic-dispersive strategy). We found that agonistic males expressed more MUP IEF bands than amicable ones at weaning, but these differences disappeared later on. The presence of two particular IEF bands at weaning was significantly associated with early agonistic onset. Our study suggests that MUPs could have a predictive value for the onset of aggressive behavior and dispersal tendency in male wild house mice.

The neonatal incidence rate of Down syndrome (DS) is well-known to accelerate strongly with maternal age. This non-linearity renders mere accumulation of defects at recombination during prolonged first meiotic prophase implausible as an explanation for DS rate increase with maternal age, but might be anticipated from chromosomal drive (CD) for trisomy 21. Alternatively, as there is selection against genetically disadvantaged embryos, the screening system that eliminates embryos with trisomy 21 might decay with maternal age. In this paper, we provide the first evidence for relaxed filtering stringency (RFS) to represent an adaptive maternal response that could explain accelerating DS rates with maternal age. Using historical data, we show that the proportion of aberrant live births decrease with increased family size in older mothers, that inter-birth intervals are longer before affected neonates than before normal ones, and that primiparae exhibit elevated levels of DS incidence at higher age. These findings are predicted by adaptive RFS but cannot be explained by the currently available alternative non-adaptive hypotheses, including CD. The identification of the relaxation control mechanism and therapeutic restoration of a stringent screen may have considerable medical implications.

The authors investigated implications of agonistic onset for anxiety and dispersive motivation in maturing wild house mouse males (Mus domesticus). Laboratory-kept fraternal pairs either developed agonistic dominance or stayed amicable during their first 2 months of life, when the authors assessed open-field behavior and dispersal propensity. State anxiety was lower in amicable than agonistic males and higher in subordinate than dominant ones. During subsequent dispersal trials, 1 dominant and 1 amicable male from 2 fraternal pairs were concomitantly introduced into seminatural enclosures containing 3 females. One male invariably became territorial. The defeated males, if previously dominant, dispersed at significantly higher rates than if previously amicable. The authors conclude that agonistic onset during development represents an adaptive behavioral switch from a submissive-philopatric to agonistic-dispersive coping strategy.

Female house mice (Mus domesticus) are known to perform communal breeding more often with kin than with non-kin partners. When mice are grouped in semi-natural enclosures, related females develop pre- reproductive alliances more frequently than unrelated ones. However, little is known about the behavioural mechanisms and the factors promoting kin preferential cooperative associations in female mice. Here we evaluate the relative importance of familiarity and age disparity on the pre-reproductive development of agonistic behaviour and spatial associations within groups of three related females, freely interacting in semi-natural indoor enclo- sures. We found that familiarity clearly promoted female alliance formation by reducing aggression and enhancing spatial cohabitation, while genetic relatedness per se did not alleviate the effects of unfamiliarity on female grouping. Older sisters clearly dominated younger ones, even if they had lower body weights, or if they had to confront two allied littermate sisters. Hence, our findings corroborate previous findings on familiarity as a proxy for kin-preferential alliance formation in female mice. More- over, we observed a strong impact of age stratification on female aggression-mediated dominance development. We suggest that this age effect could be expected from a queuing-for-reproduction view of younger house mouse females.

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

Divergence of dispersal regimens has been suggested to be the selective basis for the evolutionary differentiation of agonistic phenotypes found in natural populations of house mice. Dispersal propensity may, therefore, be expected to exhibit heritable variation in wild house mice, ultimately related to motivational differences causing observable differences in agonistic behaviour. To test for heritable components in dispersal propensity in wild house mice, father–offspring regressions of dispersal latencies from residential social groups were determined in standardized seminatural social settings. To evaluate potential motivational causes of phenotypic variation in dispersal behaviour, all test animals (fathers, sons, and daughters) were scored prior to the dispersal experiment in a standardized behavioural test, at 60 d of age. Activities were monitored in a 1 m 2 square test arena during 10-min observation periods. Test arenas exhibited four equidistant openings leading to cages containing fresh, own, sibling, or foreign bedding material. The apparatus allowed for scoring anxiety, exploratory activity, and kin preference. Subsequently, test animals were exposed to a resident population in a semi-natural enclosure providing a dispersal opportunity. Father–son regressions of dispersal latencies were significantly positive, but no significant relationship was found for daughters. Dispersal latency decreased with increasing exploratory activity scores in males, but increased in females. Anxiety as well as kin preferences did not affect dispersal propensity. Hence sex-linked, motivational components reflect heritable social behaviour variation in male house mice that may ultimately be caused by diverging dispersal regimens.

The debate over adaptive parental sex ratio adjustment in higher vertebrates appears neither to be resolvable by the current approach, nor does it necessarily make sense. It rests on the a priori supposition of parental manipulation, which is questioned here from first principle. It is considered an unlikely biological hypothesis if we extend our perspective to gametic and offspring optimal strategies, and to the potential mechanisms existing in the avian and mammalian reproductive systems. Evenness of primary sex ratios is expected to be optimal from the gametic point of view and is supposed here to be the more likely evolutionary outcome. Also, manipulations by sex-selective offspring mortality is argued to be unlikely as usually the benefits will be surpassed by the costs incurred. Furthermore, parents can adjust behavioural and energetic investment patterns to their offspring sex (ratio), thereby minimizing any costs of sex ratio control inability. Slight biases in offspring sex ratios are then viewed as resulting from physiological limitations ultimately relating to sex differences in embryonic development. Contrary to recent attempts to understand higher vertebrate sex ratio variation by further refinement of functional models (of parental optima) and data analysis, Bayesian logic precludes those approaches to gain useful new insights. To prove the basic assumption of parental manipulation, apart from defining gametic and offspring optima, the emphasis should lie on identifying control mechanisms by experimental verification.

Females of some bird species have a high degree of control over the sex ratio of their offspring at laying. Although several mechanisms have been put forward to explain how females might control the sex of their eggs, virtually nothing is known. As females are the heterogametic sex in birds, adjustment of the clutch sex ratio could arise either by pre- or post-ovulation control mechanisms. The Seychelles warbler (Acrocephalus sechellensis) exhibits extreme adaptive egg sex ratio bias. Typically, warblers produce only single-egg clutches, but by translocating pairs to vacant habitat of very high quality, most females were induced to produce two-egg clutches. Overall, females skewed clutch sex ratios strongly towards daughters (86.6%). This bias was evident in the first egg, but critically, also in the second eggs laid a day apart, even when all absent, unhatched, or unsexed second eggs were assumed to be male. Although a bias in the first egg may arise through either pre- or post-ovulation mechanisms, the skew observed in second eggs could only arise through pre-ovulation control. Post-ovulation adjustment may also contribute to skewed hatchling sex ratios, but as sex-biased release of gametes is likely to be a more efficient process of control, pre-ovulation mechanisms may be the sole means of adjustment in this species. High fitness differentials between sons and daughters, as apparent in the Seychelles warblers, may be necessary for primary sex ratio adjustment to evolve.

In a population of first-generation offspring from wild-caught house mice (Mus musculus domesticus), previous evidence suggested that male fitness is more strongly affected by an increase in body weight than female fitness. This paper shows that in these mice the young are weaned at heavier weights the smaller the litter and the better the maternal body condition. These effects persisted into adulthood and were less pronounced in female young. However, contrary to expectation from conventional sex ratio theory, maternal condition and litter size had no detectable effect on sex ratios. Also, litter size did not affect sex ratios in two populations of laboratory-kept, wild-caught western (M. m. domesticus) and eastern house mice (M. m. musculus). Wild house mice, therefore, appear not to adaptively manipulate the sex ratio of offspring. It is argued that this absence of sex ratio trends might not be maladaptive, but rather that models currently used to predict sex ratio trends in rodents may not be valid.

International audience; Social flexibility occurs when individuals of both sexes can change their social and reproductive tactics, which in turn can influence the social system of an entire population. However, little is known regarding the extent to which individuals of socially flexible species vary in their social behavior and in the underlying physiological mechanisms that support different social tactics. The present study in African striped mice modeled in captivity three male tactics described from the field: (a) philopatric males remaining in the family; (b) solitary roamers; or (c) group-living breeding males. Sixteen pairs and their offspring were kept in captivity, while one male offspring from the family remained as singly housed after he reached 21days of age. Differences in behavior, morphology, hormone and neuropeptide levels were tested, and physiological measurements were correlated with behavioral measurements. In standardized arena experiments group-living males (philopatrics and breeders) were significantly more aggressive than singly housed males, in agreement with previous data suggesting that group-living, but not roaming males, are territorial. Philopatric males showed signs of reproductive suppression, small testes, lower testosterone and higher corticosterone levels than their singly housed brothers. Higher levels of arginine vasopressin (AVP) were measured in the PVN and BNST of singly housed males compared to group-living males. Based on these findings we hypothesize that roamers are physiologically primed, and capable, if the opportunity to mate arises, to release AVP, form social bonds and become territorial, thus quickly adopting the tactic as breeding male which would yield a higher reproductive success.

The IntelliMaze allows automated behavioral analysis of group housed laboratory mice while individually assigned protocols can be applied concomitantly for different operant conditioning components. Here we evaluate the effect of additional component availability (enrichment) on behavioral and cognitive performance of mice in the IntelliCage, by focusing on aspects that had previously been found to consistently differ between three strains, in four European laboratories. Enrichment decreased the activity level in the IntelliCages and enhanced spatial learning performance. However, it did not alter strain differences, except for activity during the initial experimental phase. Our results from non-enriched IntelliCages proved consistent between laboratories, but overall laboratory-consistency for data collected using different IntelliCage set-ups, did not hold for activity levels during the initial adaptation phase. Our results suggest that the multiple conditioning in spatially and cognitively enriched environments are feasible without affecting external validity for a specific task, provided animals have adapted to such an IntelliMaze.

First generation laboratory-born descendants of wild-caught house mice (Mus musculus domesticus Rutty) were bred to produce litters of primipares and of dams that had conceived a second litter either after lactational anestrus or within the postpartum estrus. At the day of birth, pups were sexed and the number of implanted and resorbed embryos was determined to evaluate the influence of mode of reproduction on litter gender composition and its relation to fetal resorption. No significant deviations from an even sex ratio occurred in the sample. The results indicate that primipares produced litters with subnormal dispersion of the gender distribution, but this could not unequivocally be attributed to fetal resorption. No significant bias in the litter gender composition was detectable within litters conceived after lactational anestrus. In contrast, the dispersion of the gender distribution was significantly supernormal in the litters of dams inseminated at postpartum estrus. Within this group, fetal resorption had a significant effect upon the sex ratio, and this relationship was significantly affected by the number of implanted embryos: resorbing dams produced male-biased litters at small and intermediate numbers of implantation sites and female-biased litters when the number of implanted embryos was large. It is argued that this is most likely attributable to sex-selective fetal resorption.

Several environmental pollutants have been identified as antiandrogenic endocrine disrupting chemicals (EDC), with flutamide (FLU) being a model compound for this type of action. Despite impacts of EDC interfering with sexual differentiation and reproduction in amphibians, established information about suggested effects on sexual behavior is still lacking. In this study adult male Xenopus laevis were injected with human chorionic gonadotropin (hCG) to initiate mate calling behavior. After one day hCG-stimulated frogs were treated via aqueous exposure over three days without and with FLU at concentrations of 10(-8) and 10(-6) M in comparison to untreated frogs. Androgen controlled mate calling behavior was recorded during the 12h dark period. At the end of exposure circulating levels of testosterone (T) and 17beta-estradiol (E2) were determined and furthermore gene expression was measured concerning reproductive biomarkers such as hypophysial luteinizing hormone (LH), follicle-stimulating hormone (FSH), testicular aromatase (ARO), 5alpha reductase type 1 (SRD5alpha1) and 5alpha reductase type 2 (SRD5alpha2). Both concentrations of FLU caused a significant decrease in calling activity starting at the second day of exposure. HCG injected positive controls had elevated levels of T compared to negative control frogs while in parallel treatment with FLU did not affect significantly the hCG elevated sex steroid levels. Furthermore, hCG treatment led to significantly decreased levels of gene expression for ARO and SRD5alpha2 but no impacts were detected on LH, FSH or SRD5alpha1 mRNA levels compared to negative controls. In summary, the behavioral parameter mate calling is the most sensitive biomarker detecting antiandrogenic modes of action in this challenge-experiment indicating that this non-invasive method could markedly contribute for sensitive assessment of antiandrogenic EDC.

To evaluate the importance of lactational stress for sex ratio manipulation in postpartum inseminated house mice, 163 sexually inexperienced male and female BALB/c ABom inbred mice were mated and stud males were removed the day following the initial parturition. Randomly chosen dams were allowed to suckle their young for either one or 14 or 21 days. The results showed that two weeks of lactation enhance the incidence of total abortion of the litter conceived postpartum. If lactation continued another week, dams which gave birth to a second litter lost relatively more embryos during uterine development and the percentage of lost embryos was increased by the number of pups suckled. Among these dams, the number of embryos lost in utero correlated positively with viable litter sex ratios (percentage male pups) at second parturition, indicating that lactational stress enhances embryonic mortality and that this additional mortality predominantly affects female embryos.

Vertebrates obtain most of their energy through food, which they store mainly as body fat or glycogen, with glucose being the main energy source circulating in the blood. Basal blood glucose concentration (bBGC) is expected to remain in a narrow homeostatic range. We studied the extent to which bBGC in free-living African striped mice ( Rhabdomys pumilio ) is influenced by ecological factors with a bearing on energy regulation, i.e. food availability, abiotic environmental variation and social tactic. Striped mice typically form extended family groups that huddle together at night, reducing energetic costs of thermoregulation, but solitary individuals also occur in the population. We analysed 2827 blood samples from 1008 individuals of seven different social categories that experienced considerable variation in food supply and abiotic condition. Blood samples were taken from mice in the morning after the overnight fast and before foraging. bBGC increased significantly with food plant abundance and decreased significantly with minimum daily ambient temperature. Solitary striped mice had significantly higher bBGC than group-living striped mice. Our results suggest that adaptive responses of bBGC occur and we found large natural variation, indicating that bBGC spans a far greater homeostatic range than previously thought.

Wild house mouse populations have been suggested to locally adapt to varying dispersal regimes by expressing divergent aggressivity phenotypes. This conjecture implies, first, genetic polymorphism for dispersive strategies which is supported by the finding of heritable variation for male dispersal tendency in feral house mice. Secondly, aggressivity is assumed to translate into dispersal rates. This speculation is reinforced by experimental evidence showing that non-agonistic males display lower dispersal propensity than same-aged males that have established agonistic dominance. However, the actual ontogenetic behavioural pattern and its variability among populations remain unknown. Hence, in this study the timing of agonistic onset is quantified within laboratory-reared fraternal pairs, and compared between descendants from two different feral populations. Males from the two populations (G and Z) differed strongly in agonistic development, as Z fraternal pairs had a 50% risk of agonistic onset before 23.5+/-2.7 days of age, while this took 57.3+/-5.4 days in males from population G. This difference coincided with significant genetic differentiation between the males of the two populations as determined by 11 polymorphic microsatellite markers. Furthermore, in population G, males from agonistic and amicable fraternal pairs exhibited significant genetic differentiation. These results corroborate the supposition of genetic variability for dispersive strategies in house mice, and identify the ontogenetic timing of agonistic phenotype development as the potential basis for genetic differentiation. This opens a unique opportunity to study the genetic determination of a complex mammalian behavioural syndrome in a life history context, using a simple laboratory paradigm.

Summary Sex ratio variances can indicate control of sex allocation beyond the production of a certain mean. Furthermore, theory predicts that nonbinomial (nonrandom) offspring-group sex ratio distributions should be selectively favoured in some circumstances. Mechanisms of producing nonbinomial sex ratio variances include the allocation of sex to offspring in fixed or other nonrandom sequences. Variances and sequences are thus linked. In this chapter we review predictions of sex ratio models, consider constraints and expectations arising from particular sex-determination mechanisms and discuss statistical methods for variance and sequence analysis. Introduction In Chapters 3 and 4 variance was treated as a consideration necessary to ensure appropriate data analysis. However, variance of offspring-group sex ratios are of interest in themselves both because they may be under selection and because they can indicate parental control of sex allocation. We begin by reviewing predictions of sex ratio models (section 5.3) and considering constraints and expectations arising from particular sex-determination mechanisms (section 5.4). We then introduce sex ratio ‘precision’ and its measurement (section 5.5) and give methods for statistical analysis of sex ratio variance (section 5.6). Sequences of sex allocation, and their relationships with sex ratio variance, are considered in section 5.7. Variance expectations from optimality theory Optimal sex-allocation theory makes predictions not just about mean sex ratios but also about variances. When mating opportunities extend throughout large populations (panmixis) the sex ratio within a group of offspring is selectively neutral as long as the population sex ratio remains at equilibrium (Kolman 1960).

Generalized linear models (GLMs) are increasingly used in modern statistical analyses of sex ratio variation because they are able to determine variable design effects on binary response data. However, in applying GLMs, authors frequently neglect the hierarchical structure of sex ratio data, thereby increasing the likelihood of committing 'type I' error. Here, we argue that whenever clustered (e.g., brood) sex ratios represent the desired level of statistical inference, the clustered data structure ought to be taken into account to avoid invalid conclusions. Neglecting the between-cluster variation and the finite number of clusters in determining test statistics, as implied by using likelihood ratio-based χ2-statistics in conventional GLM, results in biased (usually overestimated) test statistics and pseudoreplication of the sample. Random variation in the sex ratio between clusters (broods) can often be accommodated by scaling residual binomial (error) variance for overdispersion, and using F-tests instead of χ2-tests. More complex situations, however, require the use of generalized linear mixed models (GLMMs). By introducing higher-level random effects in addition to the residual error term, GLMMs allow an estimation of fixed effect and interaction parameters while accounting for random effects at different levels of the data. GLMMs are first required in sex ratio analyses whenever there are covariates at the offspring level of the data, but inferences are to be drawn at the brood level. Second, when interactions of effects at different levels of the data are to be estimated, random fluctuation of parameters can be taken into account only in GLMMs. Data structures requiring the use of GLMMs to avoid erroneous inferences are often encountered in ecological sex ratio studies.

Habitat destruction and global climate change are two major threats to the persistence of ecosystems. The probability that a species survives such changes depends on its ability to track environmental shifts, either by moving between patches of habitat or by rapidly adapting to local conditions. This explains why the evolution of dispersal has become an integrative topic of paramount importance in evolutionary and behavioral ecology, as demonstrated by a recent conference*. A wide panel of researchers, who highlighted the recent major advances and the most promising lines of future research, were present at this meeting.

According to the developmental asynchrony hypothesis, changing the time of mating within the estrous cycle could alter the interval between completion of blastocyst development and uterine responsiveness for implantation. This may then lead to sex ratio skews in animals that exhibit sex-differential blastocyst development, because uterine stage may now benefit either slow (female) or fast (male) developing blastocysts. To test this hypothesis, the responses of two strains of mice to altered mating dynamics were compared. In a strain that exhibits higher male than female blastocyst developmental rates, sex ratios became significantly female-biased when mated late during the estrous cycle as opposed to early mating. However, timing of mating did not affect sex ratios in a strain with synchronous development of male and female preimplantation embryos. Hence, it is concluded that developmental asynchrony between male and female blastocysts on the one hand, and blastocysts and uterus on the other, are indeed responsible for the effect of timing of mating on litter sex ratios in mice.

We studied the effect of several variables (environmental and physiological) on web geometry in the garden cross spider Araneus diadematus. Variables were: web support, wind, temperature, humidity, and silk supply. All had an effect. The spiders generally attempted to fit their webs to the shape of the supporting frame (standard, small, vertical, or horizontal). Windy conditions (0.5 m s-1) during web construction caused spiders to build smaller and rounder webs, laying down fewer capture spirals while increasing the distances between capture-spiral meshes. Decreasing temperature from 24 degrees to 12 degrees C caused the capture spiral to have fewer and wider spaced meshes, which did not change overall capture area but reduced the length of capture-spiral threads laid down. Subsequent increase of temperature to 24 degrees C restored the number of meshes laid down, but the wider mesh was retained, causing the capture area to be increased over initial control values. Decreased humidity (from 70 to 20% rH) had the effect of reducing web and capture-spiral size, the latter by reducing mesh number while keeping mesh spacing constant. Subsequent increase of humidity to control level (70%) restored web and capture area. However, this was achieved by laying down capture meshes at larger distances, rather than returning to initial mesh numbers. Silk supply also had a strong effect. Webs built in unnaturally rapid succession by the same spider (4 in 24 h when 1 is the norm) became sequentially smaller, had fewer radii, shorter capture spirals, and were wider meshed.

This paper presents the hypothesis that developmental asynchrony between embryos of both sexes, on the one hand, and offspring development and responsiveness of maternal reproductive organs, on the other, may result in significant sex ratio biases at birth in mammals, and in birds. It is argued that the developmental asynchrony hypothesis may account for a significant proportion of findings on sex ratio skews, including the inconsistency of evidence and the lack of successful selection attempts. This mechanism could be used by the maternal organism adaptively to alter the sex ratio by control of the relative time of insemination within the oestrous cycle or by alteration of reproductive hormone levels around the time of ovulation and early embryonic development. However, the developmental asynchrony hypothesis may also imply that many of the sex ratio biases can be viewed as by-products of constraining selection on control of fertility and fecundity and on sexual dimorphic growth rates.

Breeding records from three inbred strains of mice (BALB/c ABom, C57BL/10ScSn, C3H/He/Kon) were examined with respect to the effects of parity and mode of conception upon litter size and sex ratio at birth. Litters from 3 modes of conception were considered: litters of primipares, litters of multipares conceived during postpartum oestrus and litters conceived after lactational anoestrus. Litters of multipares were assigned to one of these latter groups according to the inter-litter intervals. Parity had no significant effect upon the sex ratio but had a significant one upon the litter size, which did not vary between the strains when first litters were excluded from analysis. The expected variations in response to the mode of conception were found in BALB/c ABom mice but both the effects on the litter size as well as on the sex ratio varied significantly between the strains. Litter size reduction per se could be ruled out to be the cause of the sex ratio variations found. Rather, it is suggested that sex-specificity of embryonic loss depends upon the mode of conception.

Forbes[1xForbes, L.S. Trends Ecol. Evol. 1997; 12: 446–450Abstract | Full Text PDF | PubMedSee all References[1]suggests that the filtering efficiency of a proposed screening mechanism for defective embryos may adaptively decrease with maternal age in humans (adaptive-filtering hypothesis). However, neither the decreasing filtering ability nor any adaptive function are supported by the evidence cited. In fact, the well-known increase in chromosomal error rates in ova with maternal age (by-product hypothesis) perfectly predicts `the rising incidence of chromosomal abnormalities in live-births, the falling incidence of normal embryos in spontaneous abortions, and the increased incidence of spontaneous abortions with maternal age' (Ref. [1xForbes, L.S. Trends Ecol. Evol. 1997; 12: 446–450Abstract | Full Text PDF | PubMedSee all References[1], p. 446). These relationships would straightforwardly follow from an increased chromosomal aberration rate, given that such aberrations cause insufficient embryonic function which lead to pregnancy termination.The crucial point for the adaptive-filtering hypothesis would be, however, that this probability would decrease with age. There is a clear prediction here: the increase of the proportion of aberrant offspring with age should be steeper for live births than for abortions. Forbes[1xForbes, L.S. Trends Ecol. Evol. 1997; 12: 446–450Abstract | Full Text PDF | PubMedSee all References[1]erroneously suggests (p. 447) that his Box 5 implies that the adaptive-filtering hypothesis predicts increased proportions of abnormal embryos in abortions: reasonable alterations of the overlap of distributions and positioning of thresholds in Box 5(b) can obviously produce opposite trends!The other relevant tests reported by Forbes are conflicting or controversial. The proportion of maternal-origin trisomies does not increase with age according to a cytogenetic study, but does so according to molecular genetic findings. And the magnitude of increase in the proportion of defective ova does not meet the increase in chomosomal aberration rates in live births. However, the crucial finding of lower aberration rates in abortions is not mentioned.Even if one had evidence for alteration of the filtering mechanism, the adaptive value would be a matter of additional enquiry. While one can always construct the appropriate fitness scenarios (and such fitness effects need not exist in today's societies), testable predictions still emerge. For instance, the costs of bearing an aberrant embryo must be higher, the younger other dependent offspring are. Likewise, the benefit of additional children clearly diminishes with family size. Hence, the proportion of aberrant live births should decrease with increased family size and increase with increased age of the previous child.As long as one cannot provide evidence for predictions that differentiate between the hypotheses, the existence of an adaptive maternal screening mechanism in human pregnancies is bound to be a mere conjecture from the zeitgeist. This conjecture is not new[2xShepard, T.H. and Fantel, A.G. Clin. Perinatol. 1979; 6: 216–243See all References[2], but the persisting lack of decisive evidence (though relatively easy to compile) reveals the ambition still to be vaulting.

To determine the impact of concurrent pregnancy and lactation on reproduction in house mice, Mus musculus, the reproductive performances of primiparous inbred mice (Balb/c bom) were examined. Data on litter size and composition, and birth weights were recorded for 117 first litters and 29 second litters of dams, which were impregnated during postpartum oestrus. Twelve pregnant and 13 non-pregnant dams, together with their litters and feeders, were weighed daily during lactation. Activity budgets were taken of 10 dams in each group. Pregnant dams increased their food intake and withdrew milk earlier than non-pregnant ones. In addition, postpartum-conceived litters contained significantly heavier and fewer pups at birth than first litters and the sex ratio shifted in favour of males. Since male house mouse embryos are known to suffer more severely than females from nutritional stress, it is concluded that the sex ratio variation is not due to energy shortage during concurrent pregnancy and lactation. Rather, it may attributed to adaptive maternal manipulation, because postpartum-conceived pups will be heavier at weaning than other ones and males might benefit more strongly from being heavy at weaning than females. Finally, pregnant dams devoted more time to maternal care than did non-pregnant ones during the last 6 days of lactation. This contradicts the results on milk yield, if a direct proportionality of nursing time and amount of ejected milk is assumed, but is in agreement with the expected differences in maternal motivation of the dams.

Two experiments were designed to test whether wild house mice discriminate between olfactory cues from different kin and, if so, whether given preferences would relate to actual reproductive decisions. Experimental animals were mice born to the offspring of wild-caught house mice. Litter-mates stayed together until 60 d of age and were then housed individually. In a choice test, animals were placed in the middle of an arena with 4 openings which led to small cages containing bedding material from opposite-sex animals of known kinship (full-sib, cousin, unrelated) or clean material. Test animals (11 oestrous females, 11 males tested with oestrous females' bedding, 8 males tested with material from non-oestrous females) preferred conspecific to control bedding. Males tested with oestrous females' bedding significantly preferred unrelated to full-sib odours. In a second experiment, 34 males were each mated simultaneously to 3 females (sister, cousin, unrelated) and these groups were then housed together for 5, 10, and 15 d. Females were checked for litters during the next 20 d. Reproductive rate increased significantly in the 15 d cohabitation group, and significantly more cousin and unrelated females than sisters gave birth to a litter.