The Physiology and Ecology of Puberty Modulation by Primer Pheromones

Olfaction scaffolds the developing human from neonate to adolescent and beyond

The impact of the olfactory sense is regularly apparent across development. The fetus is bathed in amniotic fluid (AF) that conveys the mother's chemical ecology. Transnatal olfactory continuity between the odours of AF and milk assists in the transition to nursing. At the same time, odours emanating from the mammary areas provoke appetitive responses in newborns. Odours experienced from the mother's diet during breastfeeding, and from practices such as pre-mastication, may assist in the dietary transition at weaning. In parallel, infants are attracted to and recognize their mother's odours; later, children are able to recognize other kin and peers based on their odours. Familiar odours, such as those of the mother, regulate the child's emotions, and scaffold perception and learning through non-olfactory senses. During juvenility and adolescence, individuals become more sensitive to some bodily odours, while the timing of adolescence itself has been speculated to draw from the chemical ecology of the family unit. Odours learnt early in life and within the family niche continue to influence preferences as mate choice becomes relevant. Olfaction thus appears significant in turning on, sustaining and, in cases when mother odour is altered, disturbing adaptive reciprocity between offspring and carer during the multiple transitions of development between birth and adolescence. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

THE ROLE OF DEME SIZE, REPRODUCTIVE PATTERNS, AND DISPERSAL IN THE DYNAMICS OF t-LETHAL HAPLOTYPES

The t-lethal haplotypes (t) found in house mouse (Mus musculus) populations are recessive lethals favored by gametic selection whereby male heterozygotes exhibit a non-Mendelian transmission ratio of about 95% t. The expected equilibrium frequency is 0.385; however, empirical values are lower, averaging close to 0.13. We examined the hypothesis that interdemic selection is the cause of the low empirical values by using a deme-structured simulation model that included overlapping generations, a realistic breeding system, differential deme productivity, and a large total population. We found that under some conditions interdemic selection could lower t frequency below 0.13 in the face of immigration rates up to 5%. Low frequencies were correlated with effective deme size (n_e ), regardless of whether n_e was changed through changing deme size (n) or through changing the proportion of breeding adults. Earlier workers showed how the first two phases of interdemic selection (random genetic differentiation and mass selection) interacted to reduce the haplotype frequency, but here we show the importance of the third phase (differential productivity of demes) once demes are linked by dispersal. The effect of this phase is not due to the (negative) covariation between deme productivity and haplotype frequency, but occurs when differential deme productivity generates a difference in t frequency between the population of juveniles recruited into their natal deme and the population of juvenile dispersers. This difference was maximized when the average productivity of demes was low, either because few adult females bred at any one time and/or because fecundity was low. Contrary to an earlier prediction, male-biased dispersal also reduced haplotype frequency, and this probably stems from the relative excess of wild-type genotypes among dispersers compared to the deme residents. Another unexpected finding was that the randomly generated excess of heterozygotes (F_IS < 0) found in small demes favored t haplotypes; however, the effect was only seen when the more powerful influence of the third phase of interdemic selection was removed. Simulations of neutral polymorphisms showed that a deme structure giving F_ST ≤ 0.6 is inconsistent with a haplotype frequency below 0.13. Based on current empirical estimates of F_ST (about 0.2), we concluded that immigration rates in the field are too high for interdemic selection alone to cause the observed deficit of lethal haplotypes. One factor that could combine with population structure effects is the observation that the transmission ratio is lowered to around 0.6 in litters produced from postpartum estrus (PPE). Incorporating this factor, we showed that interdemic selection could be effective in lowering the frequency of t below 0.13 when F_ST was above 0.43 even when migration rates were up to 10%. These results suggest that if empirical haplotype and F_ST estimates are accurate, then additional factors such as a lowered fitness of heterozygotes may be involved.

Characterization of the estrous cycle and reproductive traits of the aoudad (Ammotragus lervia) in captivity

In this study the estrous cycle of the aoudad has been analyzed and characterized for the first time, using non-invasive methods for tracking reproductive cyclicity. The duration of the estrous cycle is 23 days (range 16-32 days), with a luteal phase of 17 days (range 12-27 days) and an interluteal phase of 6 days (range 3-14 days). The estrous cycle did not differ between females, but it was affected by the time of the year. Intraindividual variation of the cycle was observed in one out of the nine individuals. The average hormone concentration values, the estrogen:progestogen ratio, as well as their minimum and maximum values for each interluteal and luteal phases of the estrous cycle, are shown. Interindividual differences found in these values were basically associated with age. Females tended to start their cycle when in the presence of an adult male. Anestrus was observed in study females except for the oldest (14 years old). Age and anestrus onset were correlated, with younger females starting earlier than the older ones. This study reveals that Ammotragus reproductive biology is more similar to that of Capra than Ovis, except for some endocrinological features.

Urine marking and social dominance in male house mice (Mus musculus domesticus)

House mice use urine marking for a variety of forms of social communication. Urine marking varies with dominance status; socially dominant male house mice urine mark more than those that are socially subordinate. Experiment I was designed to confirm this previous finding. Experiment II was designed to test whether urine marking, measured prior to testing males for aggression, could be used to predict social dominance. Mice were tested for urine marking in 20 cmx40 cm rectangular cages with filter paper below the wire mesh bottom of the cage. In Experiment I, groups of four males were tested in a round robin design to assess social dominance and were then placed individually in urine marking cages. Social dominance was a significant predictor of the number of 1 cm squares that contained urine marks, both with regard to interior squares and for perimeter squares in the test cage. In Experiment II, groups of four males were first tested individually in urine marking cages and then used for round robin aggressive encounters to assess social dominance. The number of interior squares with urine marks, and, to a lesser extent, the number of perimeter squares with urine marks, were both significant predictors of aggression scores and social dominance status. Being able to judge social dominance without having the mice encounter each other could be a valuable tool for future work; confounding effects on such parameters as hormone levels could be avoided while obtaining an estimate of male social dominance status.

Immunity costs and behavioural modulation in male laboratory mice (Mus musculus) exposed to the odours of females

In a previous study, male laboratory mice experimentally immunodepressed with anti-thymocyte serum (ATS) showed changes in behaviour (aggression, general locomotory activity, and sleeping) and testosterone that are consistent with decision-making being modulated adaptively with respect to immunocompetence. We tested this idea further by repeating the experiment with the addition of female odours (soiled sawdust) to the home cages of males following ATS/control treatment. We predicted that, in the presence of cues suggesting reproductive opportunity, immunodepressed males would trade off potential immunity costs by failing to modulate behaviour. This expectation was borne out in that ATS-treated mice showed no change in aggression, locomotory activity, mounting, or sleeping relative to control animals, and mice overall showed differences in behaviour in the expected direction compared with a previous study in which female odours were not presented. However, despite the lack of difference in behaviour between ATS and control treatments, there was still evidence of a degree of behavioural modulation in relation to measures of immunocompetence.

Behavioral selection of odor cues by young female mice affects age of puberty

Female house mice were reared from weaning at 21 days of age until first vaginal estrus in 40 1 aquaria in which they were given a choice of exposing themselves to bedding placed on opposite halves of the aquarium floor and sprayed with water or urine containing puberty-influencing chemosignals. In Experimental 1, mice housed with only male urine cues sprayed on the bedding matured significantly earlier and mice housed with only grouped female urine sprayed on the bedding matured significantly later than control mice where water was sprayed on the bedding for both halves of the aquarium. In Experiment 2, there were no significant differences in mean ages at vaginal introitus or first estrus for females reared with choices between (a) bedding sprayed with male urine versus bedding sprayed with water, (b) bedding sprayed with urine from grouped females versus bedding sprayed with water, (c) bedding sprayed with male urine versus bedding sprayed with urine from grouped females, or (d) the control condition where both sides of the aquarium contained bedding sprayed with water. Analysis of continuous video tapes of the locations of the females for Experiment 2 revealed that females chose initially to spend more time on the half of the floor with bedding that delayed puberty relative to the other side, but shifted their preference toward a more puberty-enhancing signal at about the time of first estrus. Female house mice appear to be able to exert some behavioral control over their own sexual maturation.

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli)

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.

Pre- and postweaning excretion of puberty-influencing chemosignals in house mice

Pre- and postweaning excretion of urinary chemosignals that influence puberty in female house mice were tested. The dependent variable used to assess the effectiveness of urine samples collected from donor mice was the age of first vaginal estrus in young female mice. Preweaning excretion of the puberty-delaying chemosignal by females was affected by litter sex composition; this effect interacted with the age of the young donor females. In litters of all females, the substance occurred from about the age of 9 days and in litters with 6 females and 2 males the delay substance was released from about the age of 17 days. Grouping dams during gestation but not prior to conception resulted in excretion of the puberty-delaying substance in the female progeny from the age of 17 days or possibly earlier. Young male mice do not excrete the puberty-accelerating chemosignal prior to the age of puberty. However, giving young males injections of testosterone resulted in an earlier first excretion of the acceleratory signal, suggesting that the machinery for chemosignal production is operative prior to the time of sexual maturity. Caging young males with an adult female prior to puberty resulted in earlier excretion of the puberty-accelerating substance, while caging young males with adult males retarded excretion of the substance. The findings are discussed in terms of early hormone effects on behavior and with regard to consequences for the chemosignal systems in house mice.

Of mice and kin: the functional significance of kin bias in social behaviour

1. Sharing recent ancestry (kinship) increases the degree of genetic similarity between individuals, where genetic similarity could mean anything from sharing a particular allele to sharing an entire genome. 2. Genetic similarity can influence behavioural and other responses between individuals in a number of ways, discriminatory and non-discriminatory. All are likely to result in kin bias, because of the correlation between genetic similarity and kinship, but only some should be regarded as involving kin discrimination. 3. Non-discriminatory kin bias could arise through close relatives sharing, for instance, physical characteristics (such as those influencing competitive ability), thresholds of behavioural response or requirements for particular resources. 4. Discriminatory kin bias could arise through the direct perception of genetic similarity between individuals (direct similarity discrimination) or the use of cues likely to correlate with genetic similarity (indirect similarity discrimination--of which kin discrimination is one form). Alternatively, it could arise incidentally through mistaken identity or discrimination at some other level, such as species identification. 5. Experiments with laboratory and wild house mice have revealed kin bias in a number of contexts, including (a) parental and infanticidal behaviour, (b) sexual development and behaviour and (c) investigatory behaviour and passive body contact among juveniles and adults. 6. While kin bias in mice has been interpreted as evidence for kin discrimination, there are several problems with such an interpretation. These include (a) pronounced and complex effects of familiarity on discrimination, (b) a high risk of error-proneness in the indirect cues used in apparent kin discrimination and (c) weak and easily disrupted kin bias effects in certain contexts. 7. Consideration of social structure and discriminatory responses within populations of wild house mice leads to an alternative explanation for some kin bias in terms of incidental discrimination based on social group membership. 8. Several results from laboratory experiments suggest incidental discrimination is a more parsimonious explanation than kin discrimination for some intrasexual kin bias in behaviour. However, kin or direct similarity discrimination appears to be the most likely explanation for other aspects of intrasexual kin bias and for intersexual kin bias.