Milk Composition during Lactation Suggests a Mechanism for Male Biased Allocation of Maternal Resources in the Tammar Wallaby (Macropus eugenii)

Recent research has found empirical evidence in support of the Trivers-Willard Hypothesis that offspring sex allocation is correlated with maternal investment. Tammar wallabies birthing sons have higher investment ability; however a mechanism for sex specific differential allocation of maternal resources in wallabies remains elusive. In metatherians the majority of maternal investment is during lactation. To examine if differential allocation occurs during lactation, we measured total milk protein, lipid and carbohydrates, from mothers with male and female pouch young, during phase 2B (100–215 days post partum) and phase 3 (215–360 days post partum) of lactation. Mothers of sons allocated significantly higher levels of protein than mothers of daughters during phase 2B of lactation, however no sex specific difference in maternal allocation was found for lipids, carbohydrates, or any milk component during phase 3 of lactation. We were unable to measure milk production to establish any differences in the amount of milk allocated. However, with the production of more milk comes a dilution effect on milk components. Given that we find no apparent dilution of milk components may suggest equality in milk production. Offspring body weight at 14 months of age was related to protein allocation during phase 2B of lactation, providing a maternal mechanism for differential allocation with fitness consequences. We believe collection of earlier phase 2A (0–100 days post partum) milk may yield important results given that differential investment in metatherians may be most apparent early in lactation, prior to any significant maternal investment, when a decision on termination of investment can be made with very little energetic loss to the mother. Interestingly, small mothers did not birth sons and better maternal condition was associated with raising sons. These data are in support of TWH and demonstrate a potential mechanism through which condition dependent and sex specific maternal investment may occur.

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title: Facultative adjustment of mammalian sex ratios in support of the Trivers–Willard hypothesis: evidence for a mechanism
abstract: Evolutionary theory predicts that mothers of different condition should adjust the birth sex ratio of their offspring in relation to future reproductive benefits. Published studies addressing variation in mammalian sex ratios have produced surprisingly contradictory results. Explaining the source of such variation has been a challenge for sex–ratio theory, not least because no mechanism for sex–ratio adjustment is known. I conducted a meta–analysis of previous mammalian sex–ratio studies to determine if there are any overall patterns in sex–ratio variation. The contradictory nature of previous results was confirmed. However, studies that investigated indices of condition around conception show almost unanimous support for the prediction that mothers in good condition bias their litters towards sons. Recent research on the role of glucose in reproductive functioning have shown that excess glucose favours the development of male blastocysts, providing a potential mechanism for sex–ratio variation in relation to maternal condition around conception. Furthermore, many of the conflicting results from studies on sex–ratio adjustment would be explained if glucose levels in utero during early cell division contributed to the determination of offspring sex ratios.

title: Life-history analysis of the Trivers and Willard sex-ratio problem
abstract: Phenotypic quality, such as condition or size, often varies between individuals. For species with extensive maternal care, the quality of offspring may partially be determined by the quality of their mother. Trivers and Willard (1973) predicted that high quality females should prefer offspring of the sex whose reproductive success is most strongly influenced by maternal care, which in many cases will be sons. Correspondingly, low quality females should prefer daughters. However, this prediction is not based on a proper analysis of variation in reproductive value. Using state-dependent life-history theory, I show here that high quality females should prefer offspring of the sex whose reproductive value is most strongly influenced by maternal care. I also show that when offspring quality is strongly determined by their mother's quality, but not influenced by their father's quality, high quality females can have higher reproductive value than high quality males, even though their reproductive success may be much lower. In such cases, high quality females should prefer daughters and, correspondingly, low quality females should prefer sons.

title: Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring
abstract: Theory and data suggest that a male in good condition at the end of the period of parental investment is expected to outreproduce a sister in similar condition, while she is expected to outreproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. Data from mammals support the model: As maternal condition declines, the adult female tends to produce a lower ratio of males to females.

title: Early development and fitness in birds and mammals.
abstract: Conditions experienced during early development affect survival and reproductive performance in many bird and mammal species. Factors affecting early development can therefore have an important influence both on the optimization of life histories and on population dynamics. The understanding of these evolutionary and dynamic consequences is just starting to emerge.

title: When Should Avian Parents Differentially Provision Sons and Daughters?
abstract: Given the scarcity of data on sex differences in the behavior, provisioning, growth, and development of young birds, this paper is necessarily speculative. Definitive treatments of the topic will have to wait until more empirical data are available. However, at this point, it is clear that factors besides relative body size can affect the food requirements and provisioning rates of young male and female birds. Relationships between food intake and growth rates can be affected by a number of factors, and in species with sexual size dimorphism, these functional relationships are probably different for young males and females. Several hypotheses predict relatively egalitarian feeding of both sexes in sexually size-dimorphic species or preferential feeding of the members of one sex in sexually size-monomorphic species. These include hypotheses related to competition among the siblings for parental provisioning, competition between young around the time of independence, and sex-biased dispersal in the period immediately following independence. In addition, there are suggestions that male and female young of the same age might allocate food to different components of growth and development, as a result of different developmental schedules or of selection for the early maturation of structures that enhance competitive ability. Hence, the topic of sex-biased provisioning in birds would seem to be a fertile field for further discussion and empirical studies.

title: Age-related body weight constraints on prenatal and milk provisioning in Iberian red deer (Cervus elaphus hispanicus) affect allocation of maternal resources.
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title: Calf growth in captive Iberian red deer (Cervus elaphus hispanicus): effects of birth date and hind milk production and composition.
abstract: This study examines effects of birth date, hind milk production and its composition, and weight of hind and calf at birth (HBW and CBW, respectively) on calf growth responses born to Iberian hinds (Cervus elaphus hispanicus) and lactating over 34 wk. Males showed daily gains greater than those of females (P = 0.04). Calf birth weight was strongly related to calf gain over a standard (15-wk) lactation (P < 0.01), but HBW did not influence growth or CBW (P > 0.10). After correcting for nutrient supply, birth date did not affect growth, but birth date x total protein yield (TPY), birth date x total fat yield (TFY), and birth date x total lactose yield (TLY) interactions influenced growth (P < 0.001), and early-born calves showed greater growth than those born late for wk 2 to 34 (P < 0.05). Calf birth weight showed the highest correlation with protein-to-fat ratio in milk (P < 0.001), a high correlation with milk protein content (P < 0.05), and a low negative correlation with fat (P < 0.10). Calf gains also showed the highest correlation with protein-to-fat ratio in milk (P < 0.05). Similarly, total milk yield (TMY), TPY, and TFY during lactation affected growth as single factors (P < 0.001). Calves showed not only an overall difference in daily gain between calves born early or late (P = 0.02), but also a greater speed of growth independently of CBW (percentage of weight gained per week, P < 0.001). Early-born calves were heavier at 12 and 18 mo (P < 0.05). Results suggest that selecting hinds of high milk production and nutrient supply and advancing calving date may increase growth of calves and their performance at adulthood.

title: Maternal quality and differences in milk production and composition for male and female Iberian red deer calves (Cervus elaphus hispanicus)
abstract: Several theories predict a sex-biased investment either through unbalanced sex ratios in offspring or through differences in provisioning. According to them, one would expect an optimisation in indirect fitness, or else a compensation for increased mortality of one sex. In addition, biases in provisioning may also arise as a consequence of weight-dependent non-adaptive nutrient demands by offspring. This study examines milk provisioning and sex biases in offspring sex ratio together with maternal quality variables. Mothers of higher quality (weight and age) showed greater milk provisioning ability (in terms of production) resulting in greater calf weight gain. Mothers of sons produced greater yields of milk, milk protein, fat and lactose than mothers of daughters, and increased percentage of protein after controlling for higher male birth weight. In contrast, mothers of males did not differ from mothers of females in age or any body weight variables related to maternal quality. These results suggest that differences in milk production and composition for sons and daughters are rather a mechanism to optimise indirect fitness than a mechanism to compensate for increased mortality in male calves, or a consequence of greater weight-dependent nutrient demands by heavier male calves. Results also suggest that biases in milk provisioning may occur without biases in offspring sex ratio, and furthermore, in contrast to the prediction that biases should be relative to the mean investment of the population, that milk provisioning biases might not be relative.

title: Effect of milk minerals on calf gains and sex differences in mineral composition of milk from Iberian red deer (Cervus elaphus hispanicus).
abstract: Milk mineral content has received little attention in studies focusing on milk nutrient effects on offspring growth. This study examines calf growth in Iberian deer and compares the influence of milk minerals, other nutrients, and lactation variables relevant for growth to discern the relative weight of each factor. In addition, because Iberian deer hinds are the first mammal found to produce different milk for sons and daughters, the present study examines whether there are also sex differences in milk mineral composition. Concentrations and yields of Ca, P, Mg, Na, K, Fe, and Zn in milk of 46 red deer hinds were monitored through 18 weeks of lactation. Calf growth was influenced by Ca and P percent, and total Fe production. Milk for males had a lower content in Ca and P, a greater content of K, and Mg, whereas no sex effects were found in Na, Fe, or Zn percentages. Higher percentages in Ca and P for daughters might constitute a compensatory response, as daily production was not biased towards females in Ca or P, whereas in the latter and all the other minerals daily production was greater for heavier calves, which are usually males. In conclusion, milk mineral content and production influence calf growth even after controlling for other important lactation variables and nutrients, and they show effects and interactions more complicated than expected.

title: First-time macaque mothers bias milk composition in favor of sons
abstract: Mammalian females invest heavily in each of their offspring, but little is known about the magnitude and sources of variation in the most energetically expensive form of maternal investment; milk production [1–5]. Investment strategies may change as females mature because females often begin to reproduce before they have completed their own growth . Milk production may also be an important mechanism for sex-biased investment [5,6]. Here, I present data from 106 rhesus macaque ( Macaca mulatta ) mothers which show that primiparous mothers produce richer milk for sons than daughters, above a general sex bias among all mothers. This difference seems to reflect the tradeoffs between the benefits derived from additional investment in sons and the costs of diverting energy from maternal growth and development.

title: Richer milk for sons but more milk for daughters: Sex‐biased investment during lactation varies with maternal life history in rhesus macaques
abstract: Lactation represents the greatest postnatal energetic expenditure for human and non‐human primate females, and the ability to sustain the costs of lactation is influenced by a mother's physical condition. This is especially true for young mothers that initiate reproduction shortly after adolescence. These mothers have fewer bodily reserves available for lactation and face tradeoffs between reproduction and their own growth. Milk synthesis among captive rhesus macaques (Macaca mulatta) was investigated at the California National Primate Research Center from 2005 to 2007 (N = 114). Rhesus macaques produced low energy density milk typical of the primate order, but there was substantial individual variation among mothers in both milk energy density and yield. As a consequence, the available milk energy (AME), the product of milk energy density and milk yield, to support infant growth, development, and activity, varied tenfold among mothers. Primiparous mothers (N = 40) had fewer bodily resources, as measured by mass and body mass index, available for lactation than did multiparous mothers (N = 74) and showed poorer lactational performance. Mothers of sons produced milk of higher energy density, especially primiparous mothers, but lower milk yield, such that AME was the same for sons and daughters. Although AME from the mother was the same for sons and daughters, there was significant sexual dimorphism in infant mass. These data indicate that selection has likely favored sex‐specific regulation of growth and development that is not necessarily contingent on greater maternal investment.

title: Sex-Ratio Variation in Marsupials
abstract: Many marsupials produce sex ratios biased towards male or female young. In several cases these changes are comfortably accommodated in the existing theory of sex allocation. Local resource competition and the Trivers-Willard hypothesis have been usefully applied to several data sets, and preliminary experimental work has supported the main tenets of theory. By contrast, several data sets lack explanation, and provide challenges to theoreticians. The high frequency of bias in marsupials does not result from data-dredging, as bias is usually reported in descriptive accounts of marsupial reproduction, without recourse to any theoretical or mechanistic explanations. It is not possible to distinguish whether the marsupial mode of reproduction is well suited to manipulate sex allocation, or whether it facilitates measurement of biased sex allocation. As for most eutherians and birds, the mechanism of prenatal sex allocation is unknown for any marsupial. However, the current interest in sex-determining mechanisms in marsupials suggests a profitable avenue for collaboration between geneticists, physiologists and evolutionary ecologists.

title: Emerging sex allocation research in mammals: marsupials and the pouch advantage
abstract: 1. Adaptive adjustments in offspring sex ratios in mammals have long been reported, but the conditions and mechanisms that prompt shifts in the proportion of sons and daughters born are still unclear. 
 
2. Empirical evidence indicates that offspring sex in mammals can be related to a diversity of environmental and maternal traits. However, the underlying assumptions regarding offspring and maternal fitness are rarely tested. 
 
3. Physiological mechanisms of maternal selection of offspring sex may occur at many stages during the prolonged maternal investment stage, and a pluralistic approach to studying mechanisms might prove fruitful. 
 
4. This review highlights the apparent frequency, in marsupial mammals, of sex ratio bias, which has largely been recorded as conforming to one of a few hypotheses. 
 
5. Marsupials are ideally suited to experiments involving cross-fostering of offspring, which can allow rigorous tests of the fitness consequences of rearing one sex vs. the other. The reproductive biology of marsupials lends the group to detailed studies of the timing and physiological correlates of offspring sex biases. 
 
6. Many components of metatherian biology may prove advantageous in experimental studies of sex allocation in mammals, and together may provide a prosperous avenue for examining adaptive and mechanistic hypotheses in mammalian sex allocation.

title: Reproduction, Growth and Age Determinatipon in the Yellow Footed Rock Wallaby Petrogale xanthopus Gray, in Captivity
abstract: Yellow-footed rock-wallabies were studied in captivity over 13 years. Individuals of both sexes attained sexual maturity from age 18 months and were capable of breeding throughout the year. The ranges recorded were: for length of oestrous cycle 32-37 days; gestation 31-33 days; pouch life 190-201 days. Parturition was usually followed by an oestrus and mating with a consequent lactation-controlled embryonic quiescence. The mean interval from removal of pouch young to birth was 31.5 days, and to oestrus without an intervening birth, 34 days. Weight of the neonate within the 1st day was <500 mg; the sex ratio of 62 young of known sex revealed a significant departure from parity with 41 boys and 21 girls (100:51). Growth curves were fitted for length of head, ear, arm, leg, foot, tail and weight. These measurements provided a useful means of determining age within the 1st year and to a lesser extent the 2nd year, length of head being the best criterion. Both sexes maintained similar growth rates when within the pouch, but males grew larger once they vacated it. Patterns of molar eruption and molar progression provided a useful means of determining age in older animals but, on the data available, accuracy was restricted to the year and possibly no more than the season of birth.

title: Offspring sex varies with maternal investment ability: empirical demonstration based on cross-fostering
abstract: Despite decades of interest, adaptive explanations for biased offspring sex ratios in mammals remain contentious, largely because direct tests of the underlying fitness assumptions of adaptive hypotheses are rarely conducted. These tests are complicated by the difficulty of manipulating offspring sex prior to significant maternal investment owing to the biological constraints of viviparity. We test the adaptive advantage of sex allocation through cross-fostering offspring by sex in tammar wallabies. We examine whether offspring sex is correlated with maternal investment ability (i.e. Trivers–Willard hypothesis, TWH). In addition, we test the assumption that maternal investment has a greater influence on the fitness of sons than of daughters. We failed to find statistical support for maternal investment ability influencing a son's weaning success or body size more than a daughter's, although this result was probably owing to small sample sizes. In support of the TWH, females that gave birth to a son had higher investment ability (likelihood of weaning an offspring) regardless of the sex of offspring fostered.

title: A trade-off between current and future sex allocation revealed by maternal energy budget in a small mammal
abstract: Sex-allocation theories generally assume differential fitness costs of raising sons and daughters. Yet, experimental confirmation of such costs is scarce and potential mechanisms are rarely addressed. While the most universal measure of physiological costs is energy expenditure, only one study has related the maternal energy budget to experimentally controlled offspring sex. Here, we experimentally test this in the bank vole (Myodes glareolus) by simultaneously manipulating the litter's size and sex ratio immediately after birth. Two weeks after manipulation, when mothers were at the peak of lactation and were pregnant with concurrent litters, we assessed their energy budget. We found that maternal food consumption and daily energy expenditure increased with the size of the litters being lactated. Importantly, the effects of offspring sex on energy budget depended on the characteristics of the simultaneously gestating litters. Specifically, the mothers nursing all-male litters and concurrently pregnant with male-biased litters had the highest energy expenditure. These had consequences for the next generation, as size of female offspring from the concurrent pregnancy of these mothers was compromised. Our study attests a higher cost of sons, consequently leading to a lower investment in them, and reveals the significance of offspring sex in moulding the trade-off between current and future maternal investment.

title: Reproductive physiology of marsupials
abstract: Preface 1. Historical introduction 2. Breeding biology of marsupials by family 3. Sexual differentiation and development 4. Male anatomy and spermatogenesis 5. The female urogenital tract and oogenesis 6. Ovarian function and control 7. Pregnancy and parturition 8. Lactation 9. Neuroendocrine control of seasonal breeding 10. Marsupials and the evolution of mammalian reproduction References Index.

title: Milk Consumption and Energetics of Growth in Pouch Young of the Tammar Wallaby, Macropus-Eugenii
abstract: Milk consumption rates of young tammar wallabies, Macropus eugenii, were measured during the first 32 weeks of lactation by means of 22*Na turnover. Milk consumption rates were low during the first 18 weeks or so of lactation, rising from 1.2 to 9.0 ml d-'. Milk consumption rose to 43 ml d-' at 30 weeks post-partum. Changes in milk consumption were paralleled by increases in the size of mammary glands and weight gain by the sucklings. The mass gain for each millilitre of milk consumed (crude growth efficiency) averaged 0.23 g ml-I during the first 26 weeks of lactation, but then increased to more than 0.35 g ml-'. The increased growth efficiency was associated with massive increases in the lipid and energy content of milk from 26 weeks onwards. The conversion efficiencies of milk protein and energy to body materials were intermediate (55-87%, 23-36%, respectively) to those of other mammals, which suggests that the slow growth of pouch young during the first 17 weeks of lactation is the result of restricted milk production by the mother. Milk production and the growth of young were closely correlated with maternal mass (r=0.96; r=0.80, respectively) at 16 weeks post-partum.

title: Maternal Regulation of Milk Composition, Milk Production, and Pouch Young Development During Lactation in the Tammar Wallaby (Macropus eugenii )1
abstract: Specific changes in milk composition during lactation in the tammar wallaby (Macropus eugenii) were correlated with the ages of the developing pouch young (PY). The present experiment was designed to test the hypothesis that the sucking pattern of the PY determines the course of mammary development in the tammar wallaby. To test this hypothesis, groups of 60-day-old PY were fostered repeatedly onto one group of host mothers so that a constant sucking stimulus on the mammary gland was maintained for 56 days to allow the lactational stage to progress 42 days ahead of the age of the young. Analysis of the milk in fostered and control groups showed the timing of changes in the concentration of protein and carbohydrate were essentially unaffected by altering the sucking regime. The only change in milk protein secretion was a small delay in the timing of down-regulation of the secretion of whey acidic protein and early lactation protein in the host tammars. In addition, the rates of growth and development of the foster PY were significantly increased relative to those of the control PY because of ingesting more milk with a higher energy content and different composition than normal for their age. The present study demonstrates that the lactating tammar wallaby regulates both milk composition and the rate of milk production and that these determine the rates of PY growth and development, irrespective of the age of the PY.

title: Survival of very small macropod pouch young followingshort‐term isolation from the pouch at various environmental temperatures
abstract: There is considerable interest in the use of assisted breeding techniques as a component of conservation programmes for a variety of macropods threatened with extinction. While cross-fostering is being conducted in some programmes in captivity, little is known about the best techniques for carrying this procedure out from wild populations. In this study we compare the success of various procedures for isolating small tammar wallaby (Macropus eugenii) and brush-tailed rock wallaby (Petrogale penicillata) pouch young (0.4 g–410 g) for short periods (6 hours) as a first step towards establishing a methodology for recruiting endangered macropod pouch young directly from the wild for foster-rearing in captivity. Pouch temperature and humidity were determined. Pouch young from females in experimental groups were weighed, measured and then isolated, at 30°C, 27°C or 23°C, and 100% humidity. After isolation the weight of pouch young maintained at 30°C and 27°C had declined significantly (2–17% of body weight), whereas those held at 23°C and 100% humidity lost less than 0.5% of body weight. All young were reattached to the active teat of their mother following pouch isolation and their survival and growth monitored. Pouch young from the control group and those isolated at 23°C and 100% humidity survived and grew at normal rates. Only the largest pouch young maintained in isolation at either 30°C or 27°C survived to day 7 following reattachment. Data indicated that the proportion of weight lost by pouch young as a result of isolation decreased with increasing size and age of the pouch young. These trials indicate that it would be possible to harvest very small macropod pouch young from a species in the wild with a very high probability that they would survive short-term isolation from the pouch and reattachment to the teat. The use of this procedure in combination with cross-fostering techniques will allow small pouch young from threatened macropod species to be recruited directly from the wild into captivity, for captive breeding or to improve genetic diversity in captive colonies. It should also act to reactivate diapause embryos in these animals and hence may accelerate breeding in wild-based mothers.

title: Collection of fore and hind milk from the sow and the changes in milk composition during suckling.
abstract: A new sampling method for the collection of fore and hind milk from the sow has been developed which resembles normal milk removal by the piglet, yet overcomes the difficulties of collecting milk that is available for only a short time (10-20 s) at each let-down. Samples of hind milk were collected immediately after the completion of a successful sucking, while the fore milk was collected at the beginning of the next natural let-down. Modification of existing assays for fat, protein and lactose was required to provide rapid analysis of the small volumes (less than 0.5 ml) of milk collected using this procedure, and these methods were validated by comparison with reference methods. Total solids and the concentration of fat in whole milk, and protein and lactose in skim milk, were measured in fore and hind milk collected from 4, 20, 12 and 12 sows respectively, 6-11 d post partum. For fore milk, the results (mean +/- SD (n)) were: total solids, 199.9 +/- 9.9 g/l (8); fat, 96.7 +/- 13.9 g/l (41), protein, 47.7 +/- 4.5 g/l (27) and lactose, 58.3 +/- 4.0 g/l (27). In hind milk, there was a significant increase in the concentration of fat (15.3 g/l, P less than 0.001, n = 41) which was reflected by a significant increase in total solids (14.7 g/l, P less than 0.001, n = 8) and calculated energy (511 kJ/l, P less than 0.001, n = 27), but there was no significant difference in the concentration of either protein or lactose. This increase in milk fat during milk let-down is in contrast to the results of most previous studies in the sow and is discussed in terms of the possible mechanisms that may cause the concentration of fat to increase as milk is removed from the mammary gland.

title: Studies on the carbohydrate content of milk of the crabeater seal (Lobodon carcinophagus).
abstract: 1. The mean carbohydrate content of six samples of milk of the crabeater seal (a phocid), measured as total hexose, was 1.5 +/- 0.3% (w/v). Ultrafiltrates of the skim milk of these samples had a mean carbohydrate content of 1.9 +/- 0.2%. 2. Thin-layer chromatography of the ultrafiltrates showed that this carbohydrate consists mainly of various oligosaccharides of low chromatographic mobility; lactose and traces of free glucose and galactose were also detected. 3. These oligosaccharides consisted mainly of D-galactose and N-acetylhexosamine; L-fucose, D-glucose and sialic acid were additional minor components. 4. The mean lactose content of the ultrafiltrates, determined by a specific enzymic method, was 0.021 +/- 0.007% (w/v); this is similar to the levels which have been reported for the milk of otariids.

title: Reproductive ecology of wild tammar wallabies in natural and developed habitats on Garden Island, Western Australia
abstract: Reproduction may be influenced by major environmental changes experienced by an entire population as well as variation within a population in maternal resource availability or quality. We examined relationships between body condition and reproductive traits in two wild populations of the seasonally breeding tammar wallaby (Macropus eugenii) on Garden Island, Western Australia, that differed in access to supplemental food resources. Body condition changed predictably over the year, with females losing condition over the dry summer and gaining condition over the winters, when lactation occurs and most annual precipitation falls. Body condition influenced reproduction, with females of greater body condition more likely to have a pouch young, and to have a larger pouch young, early in the reproductive season. This intrapopulation pattern was opposite to that seen across populations – females in a native bushland were in poorer condition yet were more likely to have pouch young, and had larger pouch young, in March than did females living in a water-supplemented habitat on a naval base. Body condition did not influence the probability of weaning a pouch young in a year, nor did reproductive success influence changes in body condition across seasons. Instead, annual variation in precipitation had a dramatic effect on population weaning success in the native bushland, but not on the naval base. In summary, individual variation in body condition as well as large climatic variation influenced the reproduction of tammar wallabies on Garden Island, but the nature of the effect depended on the different habitats experienced by the two study populations.

title: Infant sex predicts breast milk energy content
abstract: During human evolutionary history, and for many around the world, breast milk is the primary source of nutritional energy for infants. Variation in breast milk quality might logically have important effects on infant health, growth, and development, yet the sources of this variation remain largely unelucidated. We quantified nutrient and energy content of breast milk from 25 healthy, well‐nourished Massachusetts mothers with infants aged 2–5 months. We examined several potential sources of variation in milk quality, particularly feeding patterns, infant sex, and maternal breast growth during pregnancy. After controlling for time since last feeding, a known correlate of milk composition, we found that mothers of male infants produced milk that had 25% greater energy content than mothers of female infants (P < 0.001). Change in maternal bra cup size during pregnancy was associated with 16.17 kcal/100 ml greater energy content of milk (P = 0.009), but was not significant after taking infant sex into account. Greater nutritional investment in sons may account for the greater observed growth rates in male compared to female infants.

title: In poor families, mothers' milk is richer for daughters than sons: a test of Trivers-Willard hypothesis in agropastoral settlements in Northern Kenya.
abstract: The Trivers-Willard hypothesis predicts the unequal parental investment between daughters and sons, depending on maternal condition and offspring reproductive potential. Specifically, in polygynous populations where males have higher reproductive variance than females, it predicts that mothers in good condition will invest more in sons, whereas mothers in poor condition will invest more in daughters. Previous studies testing this hypothesis focused on behavioral investment, whereas few examined biological investment. This study investigates the Trivers-Willard hypothesis on both behavioral and biological parental investment by examining breastfeeding frequencies and breast milk fat concentrations. Data from exclusively breastfeeding mothers in Northern Kenya were used to test hypotheses: Economically sufficient mothers will breastfeed sons more frequently than daughters, whereas poor mothers will breastfeed daughters more frequently than sons, and economically sufficient mothers will produce breast milk with higher fat concentration for sons than daughters, whereas poor mothers will produce breast milk with higher fat concentration for daughters than sons. Linear regression models were applied, using breastfeeding frequency or log-transformed milk fat as the dependent variable, and offspring's sex (son = 1/daughter = 0), socioeconomic status (higher = 1/lower = 0), and the sex-wealth interaction as the predictors, controlling for covariates. Our results only supported the milk fat hypothesis: infant's sex and socioeconomic status interacted (P = 0.014, n = 72) in their relation with milk fat concentration. The model estimated that economically sufficient mothers produced richer milk for sons than daughters (2.8 vs. 1.74 gm/dl) [corrected] while poor mothers produced richer milk for daughters than sons (2.6 vs. 2.3 gm/dl). Further research on milk constituents in relation to offspring's sex is warranted.

title: Observations on the attatchment of marsupial pouch young to the teats and on the rearing of pouch young by foster-mothers of the same or different species
abstract: The buccal cavity is modified in young red kangaroos by hemispherical indentations into hard palate and tongue which receive the bulbous swelling at the end of the teat. Attachment to the teat is aided by the formation of ridges on the hard palate and the lateral fusing of the lips of the young. The epiglottis of the young red kangaroo is intra-nasopharyngeal rather than intra-narial as is stated to be the case in other marsupials. Red kangaroos less than 1 day old were removed from the teat to which they had attached and replaced on another teat in the same pouch. A grey kangaroo young aged 13 days was replaced on the teat after removal and was removed and replaced at 7-day intervals thereafter. No difficulty was experienced in replacing 15 young aged between 41 and 100 days on the teats from which they were removed. The following transfers of young less than 1 day old were made: two red kangaroos to foster-mothers of the same species, one red kangaroo to a grey kangaroo, two grey kangaroos to foster-mothers of the same species, one tammar to a red kangaroo, and two swamp wallabies to red kangaroos. All the transfers were initially successful; however, one red kangaroo and one grey kangaroo were lost soon after the transfer, apparently because the foster-parents were at the incorrect stage of their reproductive cycles. The followmg transfers of young 2-25 days old were made to foster-mothers suckling young 2-20 days old: two swamp wallabies to red kangaroos, one red kangaroo to a swamp wallaby, one red kangaroo to a red-necked wallaby, one grey kangaroo to a red kangaroo, one tammar to a red kangaroo, and one red-necked wallaby to a red kangaroo. All the transfers were initially successful except a 13-day-old tammar which failed to attach to the teat of its foster-mother. A swamp wallaby young transferred at the age of 25 days to a red kangaroo showed accelerated growth and early sexual maturity compared to control swamp wallabies raised by their own mothers. A total of 12 inter-species and intra-species transfers of young aged 41-255 days old were made. A 53-day-old young of the yellow-footed rock wallaby failed to attach to the teat of a red kangaroo but all other transfers were initially successful and, in most cases, growth of the foster-young was normal and they were reared to at least the latter stages of pouch life. Young placed in the pouches of foster-mothers were readily accepted and there were indications that the behaviour patterns of the foster-mother were altered so that they responded to calls made by the foster-young. Foster-young of species which have a longer pouch life than the red kangaroo remained in the pouches of red kangaroo foster-mothers for the time usual in their own species. Foster-young transferred to the pouches of other species were usually reared to the end of pouch life if adult sizes of transferred young and foster-mother were nearly equal. Young of small species transferred to the pouches of larger species were often lost before the end of pouch life.

title: Does dietary protein in early life affect the development of adiposity in mammals?
abstract: This article examines the proposition that dietary protein in pre- and early postnatal life influences the development of adiposity in later life. In rodents, low protein intake during gestation can result in low birth weight and subsequently leads to various metabolic disturbances in adulthood, such as high blood pressure, impaired glucose tolerance and insulin resistance. The few controlled studies conducted in animals suggest that high protein or energy intake during gestation leads to low birth weights. Observational studies in humans have been inconclusive in establishing a relationship between dietary protein intake in pregnancy and effects on birth weight and adiposity of the offspring later in life. There is only weak epidemiological evidence linking high protein intake during early childhood and the development of obesity. By contrast, studies in domestic animals have found that higher levels of protein intake are often associated with lower rates of fat accretion. Additional studies are proposed to explore claims linking protein nutrition in early life to the postnatal development of obesity and disease in humans.

title: Sexual behaviour of male and female tammar wallabies (Macropus eugenii) at post‐partum oestrus
abstract: This study describes the sexual behaviour of the adult male and female tammar wallaby from the time a female gives birth to the end of post-partum oestrus. Eleven females were continuously observed from around the time of birth until up to 3 h after the last observed mating attempt. Males began to associate with females from around the time of birth, thus females appear to be attractive to males at, but not prior to parturition. Females subsequently allowed males to mate with them from 1.3±0.8h (mean±S.D.) post-partum, although the first ejaculation was delayed until 1.8±0.8h after birth owing to intense intermale aggression directed towards any male which attempted to mate with an oestrous female. Mating chases, in which a post-partum female was pursued by several males, were observed from 1.3±0.8h post-partum. All of this mating activity usually occurred within the first 6h after birth.

title: Analysis of the expression of immunoglobulins throughout lactation suggests two periods of immune transfer in the tammar wallaby (Macropus eugenii).
abstract: Marsupial young are born in an under-developed state without mature immune responses. Prior to the maturation of an immune system, marsupial young are heavily reliant upon immune factors secreted in the milk to defend them against potential microbial pathogens in the environment. In this study, we identified and characterized the immunoglobulin heavy chain constant regions, light chains, polymeric Ig receptor (pIgR), J chain, neonatal Fc receptor (alpha chain) (FcRn) and the chemokine CCL28 from the model marsupial species, the tammar wallaby (Macropus eugenii). Low levels of conservation were seen in motifs in C alpha and C gamma associated with receptor binding and or transcytosis, and this may have potential implications for functionality. We evaluated the expression of immunoglobulin genes in the tammar mammary gland throughout lactation and found that two periods of increased expression of immunoglobulin genes occur. These two periods coincide with the birth of the young, and with its first emergence from the pouch. This increased expression may represent a strategy for maternal immunological protection of the pouch young.

title: Effects of Nutritional Stress During Lactation on Immunity Costs and Indices of Future Reproduction in Iberian Red Deer (Cervus elaphus hispanicus)1
abstract: Nutrition may affect the balance between immunity and traits such as reproduction or growth. This study examines the effect of low nutrient availability on immunity indices and lactation in captive Iberian red deer. Twelve hinds and their calves were allotted to a food-restricted (50–60% daily energy requirements) or a control group just after calving. Low calorie intake exerted a greater effect on the immunity of calves than on that of hinds. Whereas no difference was found for hinds, calves of the low intake group showed mean immunoglobulin (Ig) levels higher than those on a standard diet, which suggests that Ig level may indicate the level of fighting against pathogens. Serum indices of body condition in calves showed generally positive correlations with milk nutrient production. In contrast, Ig level within each group showed a pattern inverse to that of the other group for early lactation: in the standard diet group, the greater the milk nutrient produced and calf growth, the lower the Ig level; this relationship was inversed in the low-nutrition group. These results suggest that, on a standard diet, high Ig levels may indicate high levels of pathogen fighting paired to poorer body condition. Inversely, once the first barriers of innate immunity are surpassed, only those calves on the low-nutrition group with greater resources would be able to spend more resources to fight infection. Thus, low calorie intake might boost its slowing effect on growth by increasing the costs of infection fighting.

title: The evolution of parental care
abstract: Synthesizing studies of parental care in a wide variety of animals, this book is the first attempt to provide general answers to the following important questions: Why does the extent of parental care vary so widely between species? Why do only females care for eggs and young in some animals, only males in others, and both parents in a few? To what extent is parental care adjusted to variation in its benefits to offspring and its costs to parents? How do parents divide their resources between their sons and daughters? In this book separate chapters examine the evolution of variation in egg and neonate size, of viviparity and other forms of bearing, and of differences in the duration of incubation, gestation, and lactation. The book reviews theoretical and empirical predictions concerning the evolution of parental care and examines the extent to which these are supported by empirical evidence. The author examines the distribution of parental care among offspring, reviews the empirical evidence that parents invest to different extents in their sons and daughters, and discusses the degree to which parents manipulate the sex ratio of their progeny in relation to the availability of resources.

title: Rhesus macaque milk: magnitude, sources, and consequences of individual variation over lactation.
abstract: Lactation represents the greatest postnatal energetic expenditure for mammalian mothers, and a mother's ability to sustain the costs of lactation is influenced by her physical condition. Mothers in good condition may produce infants who weigh more, grow faster, and are more likely to survive than the infants of mothers in poor condition. These effects may be partially mediated through the quantity and quality of milk that mothers produce during lactation. However, we know relatively little about the relationships between maternal condition, milk composition, milk yield, and infant outcomes. Here, we present the first systematic investigation of the magnitude, sources, and consequences of individual variation in milk for an Old World monkey. Rhesus macaques produce dilute milk typical of the primate order, but there was substantial variation among mothers in the composition and amount of milk they produced and thus in the milk energy available to infants. Relative milk yield value (MYV), the grams of milk obtained by mammary evacuation after 3.5-4 h of maternal-infant separation, increased with maternal parity and was positively associated with infant weight. Both milk gross energy (GE) and MYV increased during lactation as infants aged. There was, however, a trade-off; those mothers with greater increases in GE had smaller increases in MYV, and their infants grew more slowly. These results from a well-fed captive population demonstrate that differences between mothers can have important implications for milk synthesis and infant outcome.

title: Milk composition and growth in wild and captive Tasmanian pademelons, Thylogale billardierii (Marsupialia)
abstract: Changes in milk composition (total solids, carbohydrate, protein, lipid and calculated gross energy content) during lactation in three groups of wild (recently culled) and one captive group (fed ad libitum) of Tasmanian pademelon (Thylogale billardierii) were related to growth rates and body condition. The habitats of the three wild groups differed. Total milk solids were generally greater in the captive group but this difference disappeared in late lactation. Milk carbohydrates showed a general increase to mid-lactation in all groups, decreasing subsequently, but were always greater in the captive group. The captive group’s milk protein was always greater than those of wild Groups 1 and 2 but differed from wild Group 3 only in mid-lactation. Milk lipid concentrations started low in all groups; thereafter, the captive group had higher concentrations of lipid in mid-lactation but there were considerable differences between the groups in late lactation with Group 2 having the highest concentrations. Other than in the captive group there was little difference in energy content between early and mid-lactation. Growth rates of young differed between all wild groups, with the captive population exhibiting more rapid growth than all others. Thus, differences in milk composition resulting from different planes of nutrition can lead to differences in growth rates of marsupial young.

title: Altering Milk Composition by Feeding
abstract: Nutrition offers a means of making rapid changes in milk composition, but the relationship between feed constituents and milk composition is complex. The greatest changes can be brought about in the concentration of milk fat. Particularly important dietary factors are the amount of roughage, forage:concentrate ratio, the carbohydrate composition of the con-centrates, lipids, intake, and meal frequency. Far smaller changes are possible in milk protein concentration. The best documented effects are for intake and lipid supplements. Dietary protein has only small effects on either milk fat or protein concentration. Very small changes in lactose concentration occur sometimes in response to diet but they are inconsistent and not of practical value. Exploitation of these possibilities requires repeatable responses and accurate prediction of overall animal performance. Empirical prediction equations have been developed for some factors but the complexity of the interrelationships of the several different responses to a single dietary change suggest that mechanistic models covering complete nutrient utilization by the dairy cow may be necessary. Whatever the technical developments, economic factors will be the final determinant of the uptake of such techniques by the dairy farmer.

title: Effect of nutrition on pregnancy and lactation.
abstract: Pregnancy and lactation constitute states of considerable physiological stress which impose increased nutritional demands. If these demands are not adequately met, it may be expected that not only the nutritional status of the subject will be affected, but also the course of pregnancy and lactation. While a great deal of work with experimental animals has been carried out to elucidate the role of nutrition in pregnancy and lactation, the question arises how far these experimental results are applicable to human subjects. The unfortunate nutritional situation prevalent in certain under-developed countries affords opportunities for the study of the effects of nutritional deficiencies on the course of pregnancy and lactation in the human subject. In this paper, the available literature on the effect of maternal nutrition on the course of pregnancy and the condition of the infant at birth is reviewed, as is the effect of the state of maternal nutrition on the output and chemical composition of milk in nursing mothers. The review reveals many important gaps in our knowledge and highlights the need for further work on this important problem.

title: Energy Allocation in Mammalian Reproduction
abstract: SYNOPSIS. On behavioral, hormonal, and physiological grounds, mammalian reproduction can be compartmentalized into the following continuous sequence of events: mating (courtship, estrous), gestation, parturition, lactation, post-lactational parental care, and maternal recovery. We point out that comparing the relative allocation of energy for these events across mammals is difficult because of life history variability ( e.g. , litter size, birth weight), allometry, phylogeny, and individual variation. We review the empirical and theoretical literature on each of these events with respect to: different methodologies in measuring energy use;broad patterns of energy consumption across diverse mammalian taxa; and, identification of particular reproductive characteristics ( e.g. , birthing, parental care) which may be costly but have yet to receive energetic measurements. Although most studies have consideredgestation and lactation the critical reproductive events for energy expenditure, variation in these events is substantial and almost certainly is a function of relative allocation of time togestation vs . lactation as well as the presumed energetic costs of mating, birthing and parental care. In addition, repeated observations show that behavioral compensation is an extremely important strategy for minimizing energy requirements during reproduction. From this review, we argue that more complete analyses will come from (1) incorporating energetic measurements in studies of mammalian behavior and (2) including mechanisms of behavioral compensation into physiological studies.

title: Ancient Antimicrobial Peptides Kill Antibiotic-Resistant Pathogens: Australian Mammals Provide New Options
abstract: To overcome the increasing resistance of pathogens to existing antibiotics the 10×'20 Initiative declared the urgent need for a global commitment to develop 10 new antimicrobial drugs by the year 2020. Naturally occurring animal antibiotics are an obvious place to start. The recently sequenced genomes of mammals that are divergent from human and mouse, including the tammar wallaby and the platypus, provide an opportunity to discover novel antimicrobials. Marsupials and monotremes are ideal potential sources of new antimicrobials because they give birth to underdeveloped immunologically naïve young that develop outside the sterile confines of a uterus in harsh pathogen-laden environments. While their adaptive immune system develops innate immune factors produced either by the mother or by the young must play a key role in protecting the immune-compromised young. In this study we focus on the cathelicidins, a key family of antimicrobial peptide genes. Principal Finding We identified 14 cathelicidin genes in the tammar wallaby genome and 8 in the platypus genome. The tammar genes were expressed in the mammary gland during early lactation before the adaptive immune system of the young develops, as well as in the skin of the pouch young. Both platypus and tammar peptides were effective in killing a broad range of bacterial pathogens. One potent peptide, expressed in the early stages of tammar lactation, effectively killed multidrug-resistant clinical isolates of Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii.  The genomes of our distant relatives may hold the key for the development of novel drugs to combat multidrug-resistant pathogens.

title: Changes in the milk proteins during lactation in the tammar wallaby, Macropus eugenii.
abstract: Samples of whey proteins from the milk of tammar wallabies, Macropus eugenii, were examined by acrylamide gel electrophoresis at all stages of lactation up to 280 days post partum. Whey albumin, beta-globulin and gamma-globulin fractions had similar electrophoretic mobility to that of the equivalent serum protein fractions, but the proteins in the alpha-globulin and pre-albumin regions differed markedly. The alpha-globulins are presumed polymorphic because individuals at the same stage of lactation showed great variability in these electrophoretic regions: up to five polymorphic bands were recognized. Milk proteins changed qualitatively throughout lactation, and in particular the concentration of the pre-albumin and alpha-globulin fractions increased from approximately day 180 to the end of lactation. Total protein concentration of both whole milk and whey approximately doubled in the second half of lactation compared to the first half, reaching maximum mean values of 114 +/- 47 and 96 +/- 50 gl-1, respectively. Whole milk contained consistently more protein than whey, presumably due to the casein it contains.

title: Lactation in the tammar wallaby (Macropus eugenii). I. Milk consumption and the algebraic description of the lactation curve
abstract: The milk intake of suckling tammar wallabies (Macropus eugenii) was estimated between 213 and 339 days of age using a double-isotope procedure in which tritiated water (TOH) was injected into the dams and deuterium oxide (D2O) injected into the offspring. Recycling of isotopes between mothers and offspring was shown not to be a significant source of error. Estimates of body water (isotope dilution space) in the mothers or offspring, as a proportion of their body weight, were similar to values obtained with other macropodids and with placental mammals (0.73–0.75). Total water inflow in the offspring increased throughout the period, but the proportion of this contributed by milk fell in sigmoid fashion from 95.6% at 213 d to 3.7% at 340 d. Milk intakes reached a peak of about 86 ml/d, which was low compared with placental species. Before the peak, intakes were more closely related to body weight than age. Peak milk intake corresponded with the period of emergence from the pouch. Milk intakes were also in excellent agreement with published data obtained earlier in lactation, in animals drawn from the same population. These data were therefore combined to provide estimates of intake for the whole of lactation in the tammar wallaby, and algebraic models fitted to describe the pattern of milk intake in relation to body weight or age. With body weight, the pattern of milk intake was well described by a rising linear phase to a peak intake of about 86 ml/d near 1110 g body weight, followed by a gradual exponential decline. When related to age, the pattern was well described by a rising logistic phase (peak at 251 d) followed by a sharp exponential decline. It is shown that this latter pattern is markedly similar to the shape of the functions describing the energy requirements for the sum of pregnancy and lactation in a placental species, the sheep.