Why make daughters larger? Maternal sex-allocation and sex-dependent selection for body size in a mass-provisioning wasp, Trypoxylon politum

Mass-provisioning wasps package maternal investment into broodcells, sealed structures that contain all the provisions necessaryfor an offspring's growth and development. Optimal sex-allocationtheory predicts that if maternal provisions determine the sizeof each offspring, and the amount of provisions available toeach offspring varies, females should allocate well-stockedbrood cells to the sex that benefits most from being large.I tested this hypothesis using observations of organ-pipe wasps,Trypoxylon politum, and dissections of their nests. A Mississippipopulation of T. politum was intensively studied from 1993 to1995. This population fit the assumptions of optimal sex-allocationmodels by Green and Brockmann and Grafen. Female weight at emergencewas 1.29 times that of males, and wing length was 1.15 timesthat of males. This discrepancy in size occurred because thevolume of parental provisions strongly influenced adult bodysize, and better-stocked brood cells were preferentially allocatedto daughters. Brood-cell volume correlated with both wing lengthand weight at emergence in both sexes, and the chance that agiven brood cell contained a female offspring increased withincreasing brood-cell volume. Fitness was positively relatedto body size for females, but I found no evidence of an advantageto large males. Although there was evidence of stabilizing selectionfor male wing length in one year, there was no evidence of anincreasing relationship between body size and fitness (directionalselection) for males in either 1993 or 1994. Female fecunditywas positively related to body size in both years, indicatingthat larger females have increased reproductive success. Therate at which females provisioned brood cells was also correlatedwith body size. Observed patterns of investment in brood cellsare quantitatively consistent with the predictions of optimalsex-allocation theory, but certain aspects of female provisioningbehavior suggest females are not following a single "optimal"strategy. Patterns of provisioning were variable among differentfemales at the study site during the same year. Large femalestended to produce larger offspring. Although Brockmann and Grafen'smodel predicts a single, population wide "switchpoint" fromthe production of male to female offspring, there was no evidencefor such a switchpoint     

Control and Consequences of Alternative Developmental Modes in a Poecilogonous Polychaete

SYNOPSIS. The poecilogonous polychaete Streblospio benedicti(Webster) exhibits both planktotrophic and lecithotrophic modesof larval development. The alternative trophic modes are associatedwith differences in age and size at maturation, offspring number,size and energetic investment, larval planktonic period, morphologyand survivorship. This paper reviews a decade of research intothe control and consequences of the traits associated with planktotrophyand lecithotrophy in S. benedicti. The dominant control on reproductiveand developmental characters is genetic. Significant additivegenetic variance has been detected for egg diameter, fecundity,larval planktonic period and aspects of larval morphology. However,environmental factors such as temperature, food quality andphotoperiod, and intrinsic factors such as maternal age, exertconsiderable influence on non-trophic developmental traits (e.g.,offspring number, size and energy content). Demographic consequencesof development mode are reviewed for field and laboratory demesof S. benedicti dominated by individuals exhibiting either planktotrophyor lecithotrophy. Similar population size structure, fluctuationsin abundance, P: B ratios, and estimated population growth ratesare achieved through trade-offs between survivorship and fecundity. Development mode may best be viewed as a complex set of traitsthat are intimately linked developmentally and evolutionarilyto other aspects of an organism's life history. Greater insightinto the control and consequences of development mode shouldresult from further investigation of these linkages     

Females allocate differentially to offspring size and number in response to male effects on female and offspring fitness

Female investment in offspring size and number has been observed to vary with the phenotype of their mate across diverse taxa. Recent theory motivated by these intriguing empirical patterns predicted both positive (differential allocation) and negative (reproductive compensation) effects of mating with a preferred male on female investment. These predictions, however, focused on total reproductive effort and did not distinguish between a response in offspring size and clutch size. Here, we model how specific paternal effects on fitness affect maternal allocation to offspring size and number. The specific mechanism by which males affect the fitness of females or their offspring determines whether and how females allocated differentially. Offspring size is predicted to increase when males benefit offspring survival, but decrease when males increase offspring growth rate. Clutch size is predicted to increase when males contribute to female resources (e.g. with a nuptial gift) and when males increase offspring growth rate. The predicted direction and magnitude of female responses vary with female age, but only when per-offspring paternal benefits decline with clutch size. We conclude that considering specific paternal effects on fitness in the context of maternal life-history trade-offs can help explain mixed empirical patterns of differential allocation and reproductive compensation.     

Energy expenditure, nestling age, and brood size: an experimental study of parental behavior in the great tit Parus major

A brood manipulation experiment on great tits Parus major was performedto study the effects of nestling age and brood size on parentalcare and offspring survival. Daily energy expenditure (DEE)of females feeding nestlings of 6 and 12 days of age was measuredusing the doubly-labeled water technique. Females adjusted theirbrooding behavior to the age of the young. The data are consistentwith the idea that brooding behavior was determined primarilyby the thermoregulatory requirements of the brood. Female DEEdid not differ with nestling age; when differences in body masswere controlled for, it was lower during the brooding periodthan later. In enlarged broods, both parents showed significantlyhigher rates of food provisioning to the brood. Female DEE wasaffected by brood size manipulation, and it did not level offwith brood size. There was no significant effect of nestlingage on the relation between DEE and manipulation. Birds wereable to raise a larger brood than the natural brood size, althoughlarger broods suffered from increased nestling mortality ratesduring the peak demand period of the nestlings. Offspring conditionat fledging was negatively affected by brood size manipulation,but recruitment rate per brood was positively related to broodsize, suggesting that the optimal brood size exceeds the naturalbrood size in this population.     

Differential allocation in a lekking bird: females lay larger eggs and are more likely to have male chicks when they mate with less related males

The differential allocation hypothesis predicts increased investment in offspring when females mate with high-quality males. Few studies have tested whether investment varies with mate relatedness, despite evidence that non-additive gene action influences mate and offspring genetic quality. We tested whether female lekking lance-tailed manakins (Chiroxiphia lanceolata) adjust offspring sex and egg volume in response to mate attractiveness (annual reproductive success, ARS), heterozygosity and relatedness. Across 968 offspring, the probability of being male decreased with increasing parental relatedness but not father ARS or heterozygosity. This correlation tended to diminish with increasing lay-date. Across 162 offspring, egg volume correlated negatively with parental relatedness and varied with lay-date, but was unrelated to father ARS or heterozygosity. Offspring sex and egg size were unrelated to maternal age. Comparisons of maternal half-siblings in broods with no mortality produced similar results, indicating differential allocation rather than covariation between female quality and relatedness or sex-specific inbreeding depression in survival. As males suffer greater inbreeding depression, overproducing females after mating with related males may reduce fitness costs of inbreeding in a system with no inbreeding avoidance, while biasing the sex of outbred offspring towards males may maximize fitness via increased mating success of outbred sons.     

Determinants of reproductive success in female adders,Vipera berus

Summary Female lifetime reproductive success in a small population of individually-marked adders in southern Sweden was studied over a period of seven years. Reproductive characteristics varied little from year to year and were consistent through time in individual females. Most females mature at four years of age and reproduce every two years. The total number of offspring produced by a female depends on her adult body size (and thus, litter size) and longevity (and thus, number of litters per lifetime). Adult body size in females is influenced mainly by subadult growth rates. Offspring size depends on maternal body size and a tradeoff between offspring size and offspring number. Maternal age does not affect litter sizes and offspring sizes except through ontogenetic changes in maternal body size.Survival of females after parturition is low because of the high energy costs of reproduction, compounded by low feeding rates of gravid females because of their sedentary behaviour at this time. About one-half of females produce only a single litter during their lifetimes, although some females live to produce four or five litters. On a proximate basis, rates of energy accumulation for growth (in subadults) and reproduction (in adults) may be the most important determinants of fitness in female adders.     

An integrated approach to life-cycle evolution using selective landscapes

A model which defines fitness in terms of the intrinsic rate of increase of phenotypes is used to analyse which life cycles are appropriate to which ecological circumstances. The following predictions are made for asexual animals and those sexual animals producing on average more than one daughter per brood. If there are no behavioural or physiological interactions between variables, then number of offspring per breeding should be maximized, survival until first/next breeding should be maximized, and time to first/next breeding should be minimized. If interactions occur such that altering one life-cycle variable affects another, then there are trade-offs between variables and the optimum trade-off will maximize fitness.Number of offspring per breeding will generally affect adult survivorship until next breeding. Given certain reasonable assumptions about this trade-off, high juvenile survivorship selects towards semelparity (many offspring per brood), low juvenile survivorship selects towards iteroparity (few offspring per brood). If juvenile survival depends on adult feeding, as in altricial birds, then juvenile survivorship declines as clutch size is increased. Optimal clutch size maximizes the number of surviving offspring per brood.Two trade-offs involve parental care. If parents guard their offspring they should take more risks if brood size is larger. The amount that parents feed their offspring should depend on how effective feeding is in enhancing growth. Growth may also be enhanced by taking risks, in juveniles or adults. The extent of risk-taking should depend on how effective risk-taking is in enhancing growth.If the number of offspring per brood is related to growing conditions for offspring, the prediction is that more offspring per brood should be produced if growing conditions for offspring are better. If the adult can protect the offspring, for example by encapsulating them, the amount of protection provided should depend on how effective the protection is in increasing offspring survivorship.     

Experimental manipulation of maternal effort produces differential effects in sons and daughters: implications for adaptive sex ratios in the blue-footed booby

Sex allocation theory predicts that mothers in good conditionshould bias their brood sex ratio in response to the differentialbenefits obtained from increased maternal expenditure in sonsand daughters. Although there is well-documented variationof offspring sex ratios in several bird species according tomaternal condition, the assumption that maternal condition has different fitness consequences for male and for female offspringremains unclear. The blue-footed booby (Sula nebouxii) is asexually size-dimorphic seabird, with females approximately31% heavier than males. It has been reported that the sex ratiois male biased in years with poor feeding conditions, whichsuggests that either females adjust their sex ratio in accordancewith their condition or that they suffer differential brood mortality before their sex can be determined. In this studyI tested whether the condition of mothers affected their daughters'fitness more than their sons' fitness. I manipulated maternalinvestment by trimming the flight feathers and thereby handicappingfemales during the chick-rearing period. Adult females in thehandicapped group had a poorer physical condition at end ofchick growth, as measured by mass and by the residuals of masson wing length compared to control birds. Female chicks wereaffected by the handicapping experiment, showing a lower massand shorter wing length (reduced approximately 8% in both measures)than controls. However, this effect was not found in male chicks.Hatching sex ratios were also related to female body conditionat hatching. The brood sex ratio of females in poor conditionwas male biased but was female biased for females in good condition.Overall, these results suggest that the variation in the sexratio in blue-footed boobies is an adaptive response to thedisadvantage daughters face from being reared under poor conditions.     

Resource quality effects on Daphnia longispina offspring fitness

The present study addressed the question: is the fitness ofDaphnia longispina neonates related to the quality (species)of the resource their mothers consumed? A 2 2 factorial designwith two maternal and neonate resource types was employed, withRhodomonas and Microcystis used as high- and low-quality resources,respectively. Neonate fitness was assessed using demographicparameters obtained from a life-table study. The resource typeneonates consumed always had a stronger effect on the neonatesthan did the maternal type. Neonate consumption of Rhodomonas.relative to Microcystis. increased fitness, as estimated bythe instantaneous population growth rate, by 25–28%. whilematernal consumption of Rhodomonas increased fitness by 6-8%.Neonate Rhodomonas consumption also reduced the age at reachingthe primiparous instar; increased brood size at the primiparousinstar and body length immediately after the primiparous instar;increases average dutch size, number of clutches produced, totalegg production. and mean body length up to and on age 30 days.Regardless of resource type, maternal Rhodomonas consumptionresulted in neonates which reached maturity at an earlier ageand had a larger individual size immediately after reachingmaturity. The mean clutch size, total egg production, and lengthup to and at age 30 days were all significantly affected bymaternal diet when neonates consumed Microcystis; however, thesevariables were not influenced by maternal type when neonatesconsumed Rhodomonas. This is the first study to document maternallymediated effects of resource quality on the fitness of crustaceanzooplankton neonates.     

Evidence for inbreeding depression in a species with limited opportunity for maternal effects

It is often assumed that mating with close relatives reduces offspring fitness. In such cases, reduced offspring fitness may arise from inbreeding depression (i.e., genetic effects of elevated homozygosity) or from post‐mating maternal investment. This can be due to a reduction in female investment after mating with genetically incompatible males (“differential allocation”) or compensation for incompatibility (“reproductive compensation”). Here, we looked at the effects of mating with relatives on offspring fitness in mosquitofish, Gambusia holbrooki. In this species, females are assumed to be nonplacental and to allocate resources to eggs before fertilization, limiting differential allocation. We looked at the effects of mating with a brother or with an unrelated male on brood size, offspring size, gestation period, and early offspring growth. Mating with a relative reduced the number of offspring at birth, but there was no difference in the likelihood of breeding, gestation time, nor in the size or growth of these offspring. We suggest that due to limited potential for maternal effects to influence these traits that any reduction in offspring fitness, or lack thereof, can be explained by inbreeding depression rather than by maternal effects. We highlight the importance of considering the potential role of maternal effects when studying inbreeding depression and encourage further studies in other Poeciliid species with different degrees of placentation to test whether maternal effects mask or amplify any genetic effects of mating with relatives.     

Bioenergetics of age-related versus size-related reproductive tactics in female Viviparus georgianus

Individual Viviparus georgianus from a New York population are iteroparous, maturing in their second year. Ovoviviparous females have a maximum lifespan 1 year longer than that of males (4 + versus 3+ years), though individuals of both sexes can be reproductively active for three consecutive years. Embryophores are carried over winter and released each spring. Female survivorship is positively size related, as is incremental growth within any year. Reproductive effort is age related, increasing from 5.3% for modal 2-year females to 79.7% for modal 4-year females. Reproduction is size limited in 2-year females, no females below 16 mm shell length were found containing broods. The lack of observable survivorship penalties related to reproduction may result from reproductive females have greater biomass and hence greater survivorship. Spat size is positively correlated with female age irrespective of female size, though brood numbers increase with maternal size and growth rates. Caged experiments have shown spat born early to older females grow fastest. Data presented indicate that the young of older females have greater expected lifetime fecundity and fitness. In this population, 3-year females produce approximately 50.0% of each new cohort, with 2-year and 4-year females producing 21.0% and 26.0% respectively. Matrix models of the natural population and modified hypothetical populations emphasize the importance of survivorship and early reproduction in such stable, age-structured populations.     

Brood ball size but not egg size correlates with maternal size in a dung beetle,Onthophagus atripennis

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THE GENETIC BASIS OF LIFE-HISTORY CHARACTERS IN A POLYCHAETE EXHIBITING PLANKTOTROPHY AND LECITHOTROPHY

The polychaete Streblospio benedicti is unusual in that several field populations consist of individuals that exhibit either planktotrophic or lecithotrophic larval development. Planktotrophy in this species involves production of many small ova that develop into feeding larvae with a two- to three-week planktonic period. Lecithotrophy involves production of fewer, larger ova that develop into nonfeeding larvae that are brooded longer and have a brief planktonic stage. Reciprocal matings were performed to investigate genetic variance components and the correlation structure of life-history traits associated with planktotrophy and lecithotrophy. Our objective was to better understand persistence of this developmental dichotomy in Streblospio benedicti, and among marine invertebrates in general. Substantial additive genetic variation (75–98% of total) was detected for the following characters at first reproduction: female length; position of the first gametogenic setiger and first brood pouch; ovum diameter; three traits related to fecundity (numbers of ova per ovary, larvae per brood pouch, and larvae per brood); median larval planktonic period and the presence of larval swimming setae; but not for total number of brood pouches; larval length; larval feeding; and larval survivorship. Based on the unusual geographic distribution of development modes in this species, we hypothesize that the developmental traits have evolved in allopatry and have only recently come into contact in North Carolina. The high additive contribution to variance observed for many traits may be inflated due to (a) nonrandom breeding in nature, and (b) examination of only one component of an age-structured population at one time. Nuclear interaction variance and maternal variance accounted for 84% of the total variation in larval survivorship. This observation supports other empirical studies and theoretical predictions that nonadditive components of variance will increase in importance in individual traits that are most closely tied to fitness. A network of life-history trait correlations was observed that defines distinct planktotrophic and lecithotrophic trait complexes. Negative genetic correlations were present between fecundity and egg size, between fecundity and position of the first gametes, and between larval survivorship and median planktonic period. Positive genetic correlations were detected between fecundity and female size at first reproduction and between planktonic period and the presence of swimming setae. Intergenerational product-moment correlations were negative for larval length and fecundity, planktonic period and egg size, female size and larval survivorship, and fecundity and larval survivorship. If the genetic correlation structure observed in the laboratory persists in the field, it may constrain responses of individual characters to directional selection, and indirectly perpetuate the dichotomies associated with planktotrophy and lecithotrophy.     

Optimal allocation of reproductive effort: manipulation of offspring number and size in the bank vole

The number of offspring attaining reproductive age is an important measure of an individual's fitness. However, reproductive success is generally constrained by a trade-off between offspring number and quality. We conducted a factorial experiment in order to study the effects of an artificial enlargement of offspring number and size on the reproductive success of female bank voles (Clethrionomys glareolus). We also studied the effects of the manipulations on growth, survival and reproductive success of the offspring. Potentially confounding effects of varying maternal quality were avoided by cross-fostering. Our results showed that the number of offspring alive in the next breeding season was higher in offspring number manipulation groups, despite their smaller body size at weaning. Offspring size manipulation had no effect on offspring growth or survival. Further, the first litter size of female offspring did not differ between treatments. In conclusion, females may be able to increase the number of offspring reaching reproductive age by producing larger litters, whereas increasing offspring size benefits neither the mother nor the offspring.     

Allocation of parental investment among individual offspring in the European beewolf Philanthus triangulum F. (Hymenoptera: Sphecidae)

Optimal allocation of parental resources is an important life history trait. However, it has been rarely investigated empirically. We tested aspects of optimal allocation theory in a digger wasp, the European beewolf. Investment allocation theory assumes (1) a trade‐off between investment per offspring and offspring number and (2) a convex relationship between investment per offspring and fitness returns. From mis relationship an optimum amount of investment per offspring can be derived and parents are predicted to provide each offspring with this optimum amount of investment. We used the number of bees in a brood cell as a measure of parental investment. Offspring fitness was quantified as both survival until emergence and success as adults. There is evidence for a trade‐off between current and future reproduction, suggesting that the first assumption is met. In contradiction to the second assumption, one mortality factor, parasitism, increased proportionally with the number of bees in a brood cell. However, overall mortality until emergence significantly decreased with the number of bees in a brood cell as assumed by the theory. The determination of the optimum amount of investment per offspring is complicated because the sexes possibly differ in their relationship between amount of investment and fitness. Individual males received considerably fewer bees (2.2 ± 0.8) than females (3.8 ± 0.5). Two independent estimates of the investment specific survival suggested that sons with two bees had the highest fitness returns per single bee and, consistent with the prediction, most sons were provisioned with two bees. For daughters, four bees is probably the optimum amount and most daughters were provisioned with this number. In both sexes the variation of investment per offspring was less than expected by a Poisson distribution with the same mean. These findings support the view that parental investment is allocated in a way that optimizes the trade‐off between offspring number and investment per offspring. However, variation contradicting the hypothesis still occurred. This might be explained either by adaptive variation in the amount of investment per offspring, constraints in the adjustment of the optimum amount of investment, or problems in measuring parental investment.     

The influence of maternal age and mating frequency on egg size and offspring performance in Callosobruchus maculatus (Coleoptera: Bruchidae)

Maternal age influences offspring quality of many species of insects. This observed maternal age influence on offspring performance may be mediated through maternal age effects on egg size, which in turn may be directly influenced by the female's nutritional state. Thus, behaviors that influence a female's nutritional status will indirectly influence egg size, and possibly offspring life histories. Because males provide nutrients to females in their ejaculate, female mating frequency is one behavior which may influence her nutritional status, and thus the size of her eggs and the performance of her offspring. In this paper, I first quantify the influences of maternal age on egg size and offspring performance of the bruchid beetle, Callosobruchus maculatus. I then examine whether nutrients transferred during copulation reduce the magnitude of maternal age effects on egg size and larval performance when mothers are nutrient-stressed. Egg size and egg hatchability decreased, and development time increased, with increasing maternal age. Multiple mating and adult feeding by females both resulted in increased egg size. This increase in egg size of females mated multiply did not translate into reduced development time or increased body size and egg hatchability, but did correlate with improved survivorship of offspring produced by old mothers. Thus, it appears that because the influence of mating frequency on egg size is small relative to the influence of maternal age, the influence of nutrients derived from multiple mating on offspring life history is almost undetectable (detected only as a small influence on survivorship). For C. maculatus, female multiple mating has been demonstrated to increase adult female survivorship (Fox 1993a), egg production (Credland and Wright 1989; Fox 1993a), egg size, and larval survivorship, but, contrary to the suggestion of Wasserman and Asami (1985), multiple mating had no detectable influence on offspring development time or body size.     

Open-cell parasitism shapes maternal investment patterns in the Red Mason bee Osmia rufa

Brood cell parasitism inflicts high fitness costs on solitary,nest-constructing bees. Many of these parasites enter open cellsduring its provisioning, when the mother bee is absent. Therefore,females can reduce the risk of open-cell parasitism by limitingthe time they are away from the nest. However, provisioningefficiency (provisioning time per unit of progeny body mass)decreases due to aging. To limit the increasing risk of open-cellparasitism as the nesting season progresses, female bees couldoptimize their maternal investment strategy by shifting thesex ratio and the body size of offspring during the nestingseason. This prediction was tested in the Red Mason bee Osmiarufa (O. bicornis), a stem- or hole-nesting, polylectic, univoltinemegachilid bee. In O. rufa, the risk of open-cell parasitismwas found to be correlated with cell provisioning time. Additionally,the provisioning efficiency of females declined during the nestingseason to one-fourth of the initial value. However, cell-provisioningtime did not increase correspondingly. Bees dealt with theirdecreasing provisioning efficiency by reducing the amount ofstored larval food, leading to a reduction of offspring sizeand a seasonal shift toward males in the offspring sex ratio.The influence of provisioning efficiency and risk of open-cellparasitism on optimal offspring size was analyzed by means ofa statistical model. The observed maternal investment patternof Red Mason bees is an adaptive strategy to reduce open-cellparasitism.     

The effect of partial brood loss on male desertion in a cichlid fish: an experimental test

There is little experimental evidence testing whether currentbrood size and past brood mortality influence mate desertion.In the cichlid Aequidens coeruleopunctatus both parents initiallydefend offspring. In a field study, all experimental broods,irrespective of initial brood size (222.9 ± 60.4, mean± SD), were manipulated to a size of 100 fry. Neitherthe duration nor investment of females in parental care differed between control and brood reduced pairs, even though care seemedcostly. On average, females lost 5.1 ± 4.8% of initialweight while guarding a brood until independence. In contrast,males with experimentally reduced broods guarded fry for significantlyfewer days before deserting their mate than did males fromcontrol pairs with natural-sized broods (20.5 ± 7.5 vs. 14.2 ± 6.2 days). In at least 20% of cases (n = 9/45),the deserting male immediately mated with another female. Maleswith experimentally reduced broods also spent less time guardingfry before deserting and attacked fewer brood predators thandid males with control broods. For broods manipulated to have100 fry, there was a significant negative relationship betweenthe days until male desertion and the proportion of the initialbrood removed. This indicates that male assessment of the futuresuccess of the current brood (hence its reproductive value)is based on past mortality and/or that there is variation amongmales in the expected size of future broods. Both current broodsize and brood size relative to initial brood size are thereforepredictors of male, but not female, parental behavior and matedesertion. Female care may be unaffected by brood reductiondue to limited breeding opportunities and partial compensationfor reduced male care.     

Is There Adaptive Value to Reproductive Termination in Japanese Macaques? A Test of Maternal Investment Hypotheses

Evolutionary biologists often argue that menopause evolved in the human female as the result of selection for a postreproductive phase of life, during which increased maternal investment in existing progeny could lead to enhanced survivorship of descendents. Adaptive theories relating menopause to enhanced maternal investment are known as the mother (first-generation) and grandmother (second-generation-offspring) hypotheses. Although menopause—universal midlife termination of reproduction—has not been documented in primates other than humans, some researchers have argued that postreproductive alloprimates also have a positive impact on the survivorship of first and second generation progeny. We tested the maternal investment hypotheses in Japanese macaques by comparing the survivorship of offspring, final infants, and great-offspring of females that terminated reproduction before death with females that continued to reproduce until death. SURVIVAL analyses revealed no significant difference in the survivorship of descendents of postreproductive and reproductive females, though final infants of postreproductive females were 13% more likely to survive than final infants of females that reproduced until death were. We also explored possible differences between these two groups of females, other than survivorship of progeny. We found no difference in dominance rank, matrilineal affiliation, body weight, infant sex ratio, age at first birth, fecundity rate or lifetime reproductive success. However, postreproductive females are significantly longer-lived than reproductive females and as a result experienced more years of reproduction and produced more infants in total. Apart from final infants, offspring survival is marginally lower in postreproductive females. Since offspring survival is not significantly enhanced in postreproductive females, the greater number of infants produced did not translate into greater lifetime reproductive success. Our findings fail to support the maternal investment hypotheses and instead suggest that reproductive termination in this population of Japanese macaques is most closely associated with enhanced longevity and its repercussions.     

The effect of maternal and fetal corticosteroids on the development of function of the pituitary-adrenocortical system.

The pituitary-adrenocortical system of rat fetuses was stimulated (larger adrenals at birth) by maternal adrenalectomy, or suppressed (smaller adrenals at birth) by implantation of an ACTH secreting pituitary tumor (MtTF4). Offspring were delivered by caesarean section and fostered to untreated females. Offspring of intact females delivered by caesarean section and normally delivered offspring of intact mothers both fostered to untreated lactating females served as controls. Body growth in the first three weeks of life was delayed in offspring of tumor bearing mothers in Control-fostered subjects as compared to the 2 other groups. At 70 days of age female offspring of the tumor implanted and adrenalectomized mothers, as well as the Control-caesarean females, had smaller adrenals than Control-fostered animals of the same sex. The adrenal size of males was not significantly affected. No significant differences were found in resting concentrations of corticosterone in plasma, although offspring of adrenalectomized mothers had high values. Suppressed adrenal response to ether stress was found in offspring of tumor bearing mothers. The supposition is that interference with maternal pituitary-adrenocortical activity during pregnancy has a long lasting effect on fetal hypothalamo-pituitary-adrenocortical system.