Female Investment Research Articles

Increased population density reduces body growth and female investment in a simultaneous hermaphrodite.

Sex allocation theory applied to hermaphrodites assumes that there is a trade off between the allocation of resources to male and female functions, within a fixed reproductive resource budget. Charnov's classic resource allocation model predicts a more female-biased sex allocation when competition among different sperm donors is low due to diminishing fitness returns for male investment. By manipulating the social group size, one automatically changes the population density at which individuals live. Increasing population density may affect reproductive allocation, leading to resource competition and/or to increased concentration of harmful metabolites. This could lead to an over- or underestimation of the individual adjustment of sex allocation responses to mating opportunities. In this article, we tested the effects of density and social group size separately on female investment and body growth (considered as proxy of the overall energy budget) in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema. We manipulated social group size (i.e., monogamous and promiscuous regimes) and density (i.e., 4 levels) using a full-factorial design, to identify the underlying factor affecting female allocation (in terms of egg production) and body growth. In contrast to findings of previous experiments, we found that an increase in population density reduced body growth and egg production of hermaphrodites irrespective of social group size. We advance the hypothesis that the increase of catabolites and oxygen consumption in high-density conditions reduces the overall resource budget and this could obscure group size effects on female fecundity.

Potential syndromes linking dispersal and reproduction in the hermaphrodite land snail Cornu aspersum

AbstractDispersal plays a key role in many ecological and evolutionary processes, in particular through correlations, or syndromes, with other life‐history traits. Here, we investigated the potential syndromes linking movement behaviour, body mass and male and female sexual organs development, to explain a previously described subadult dispersal pattern in the hermaphrodite land snail Cornu aspersum. We found elements indicating that this snail may not strictly be a simultaneous hermaphrodite, but presents a male‐biased phase before reaching adulthood and hermaphroditism. Body mass was positively correlated with both patch‐leaving propensity and movement speed. However, because the dry mass of the female albumen gland, which represents on average in adults masses equivalent to 42.6% of somatic soft tissues dry mass, was negatively correlated with patch‐leaving propensity, snails of intermediate age are expected to be more likely to leave than older ones. No relationship between male organ size and movement characteristics was found. We discuss briefly the interesting consequences the existence of a syndrome linking movement propensity with female investment in a protandric hermaphrodite species might have in terms of life‐history evolution and on the maintenance of hermaphroditism in dispersal‐favouring environments.

Women's Investment in Career and Household Division of Labor

The effects of women’s strong investments in career on the intra-household division of labor, particularly the share of partners in domestic work, constitute important but unaddressed issues. We use the 2010 French Time Use survey, focusing on two-income couples. We first build indicators of female investment in career, measured in comparison to other similar women or to the woman’s partner. We then investigate how the partners allocate time according to the intensity of women’s investment. To achieve this objective, we estimate a five-equation model of domestic and labor market work by partners and the use of domestic help. We show that couples where women are invested in career tend to share tasks more equally. These women do less domestic work during weekdays. This diminution is partly compensated on weekends by their partners, but also slightly by women themselves on weekends when they invest more in their careers than their partners do. Also, when they are heavily invested in their careers compared to other women, they tend to use more often domestic help. However, even when women dedicate themselves more than their partners to their careers, women still spend more time on domestic tasks than their partners on average, implying no role reversal in the division of labor.

Effects of diapause on post‐diapause reproductive investment in the moth Ostrinia scapulalis

AbstractDiapause is a strategy used by many insect species to survive adverse environmental conditions. However, diapause incurs costs that may have adverse effects on post‐diapause development and reproduction. We herein investigated the effects of diapause on the post‐diapause reproductive investment of males and females in a multivoltine moth, the adzuki bean borer, Ostrinia scapulalis (Walker) (Lepidoptera: Crambidae). We found that (1) post‐diapause males and females were smaller and had lower mating success than non‐diapause individuals, (2) post‐diapause females had lower fecundity and shorter longevity than non‐diapause females, (3) post‐diapause males transferred similar numbers of eupyrene and apyrene sperm as non‐diapause males, (4) the fecundity and longevity of non‐diapause females mated with post‐diapause males and those mated with non‐diapause males were not significantly different, and (5) no significant relationship was found between diapause duration (short and long) and post‐diapause reproductive investments in both males and females. These results suggest that post‐diapause males did not reduce reproductive investment in spite of the cost of diapause, and the significant decline in reproductive output in post‐diapause females was due to their reduced body weight and longevity, which appeared to be direct consequences of the cost of diapause.

The risk of exploitation during communal nursing in house mice, Mus musculus domesticus

Parental care is associated with costs. Communal offspring care in species with altricial young may reduce the costs for a parent, but it comes with a risk of exploitation, jeopardizing the evolution of stable cooperation. Female house mice can either rear their young alone or communally with one or several other females. In the latter case, females pool litters and do not discriminate in their maternal behaviour between their own and alien offspring. Differences in litter size between females, or differences in the amount of investment they provide, might therefore result in one female exploiting another. To analyse the potential for conflict during cooperation, we compared under laboratory conditions the maternal investment (milk quantity and quality at peak lactation, when a female's own offspring were 15 days old) of wild-bred females nursing communally with one partner with that of females nursing solitarily. To increase the probability of asymmetry in litter sizes between communally nursing females, we used a genetic tool to reduce in utero litter size for one of the two partners. Communally nursing females invested according to the total number of pups in the joint nest and not according to their own litter size, making them vulnerable to exploitation. Females that gave birth to the smaller litter consequently overinvested; they had a higher investment per weaned offspring than females that gave birth to larger litters in communal nests or solitarily nursing females. Communal nursing in house mice thus represents a public good situation. Both partners invest according to the combined litter size, but they differ in the benefit they gain, which is the number of weaned offspring.

Investment in Beauty, Exercise, and Self-esteem: Are They Related to Self-perception as a Romantic Partner?

Men and women prefer certain characteristics that are interpreted as clues to the reproductive quality of potential partners. Physical appearance, for example, is an important characteristic for both sexes because it can signal youth and fertility in females and capacity for protection, dominance, competitive ability, and high social status in males. Therefore, we predicted that people would put significant effort into improving their physical attractiveness in order to compete in the mating market, and this relationship would be influenced by self-perception and socioeconomic status. In order to investigate whether investment in beauty and exercise are related to self-perception as romantic partners and self-esteem, this study was conducted with 205 men and women of lower socioeconomic status from Brazil. They were asked about their self-esteem (Rosenberg self-esteem scale), socioeconomic status, investment in beauty, time exercising, and self-perception as a romantic partner. Although no significant relationship between self-perception as a romantic partner and exercise was found, our results suggest that female investment in beauty is related to their financial condition, whereas male investment in beauty is related to greater evaluation in handsome face, beautiful body, sociability, and agreeableness, being correlation stronger when controlled by participants’ self-esteem. The results support Leary and Baumeister’s sociometer theory (2000 cited in Bale and Archer Evolutionary Psychology, 11, 68–84, 2013) and Penke and Denissen’s (Journal of Research in Personality, 42, 1123–1129, 2008) findings, in which men would associate more characteristics of their self-perception in a mate market with their self-esteem.

Phenotypic plasticity in sex allocation and body size leads to trade-offs between male function and growth in a simultaneously hermaphroditic fish

Phenotypic plasticity in sex allocation enables organisms to maximize reproductive success in variable environments, and thus may generate different sex allocation patterns among populations that experience different mating opportunities. In this experiment, I test whether sex allocation is phenotypically plastic in Serranus tortugarum, a simultaneously hermaphroditic fish, by using reciprocal transplants among four reef study sites with populations at high and low densities and significant differences in sex allocation. Fish transplanted across different densities were predicted to alter sex allocation and body size through trade-offs in investments to somatic growth and male and/or female reproduction. As a control for effects of transplanting, I also transplanted fish across study sites with the same densities and marked and returned fish to their original study sites. As predicted, sex allocation and body size shifted significantly for fish transplanted across different densities but not for those transplanted across the same densities. Separate analyses revealed that the treatment effect on sex allocation was driven strongly by a reduction in male investment by fish transplanted from high to low density, and this reduction in male investment was accompanied by an increase in body size. Fish transplanted from low to high density did not appear to change either male or female investments, but they were smaller than transplants from low to low density. A trade-off between male and female function was not evident, but phenotypic plasticity in body size suggested a trade-off between growth and male function when sex allocation is adjusted. Large-scale empirical tests of sex allocation in the field are relatively rare, and the results of this experiment give novel insights into how animals respond to a change in mating opportunities under natural conditions. The effects of logistical problems associated with fieldwork, such as mortality of experimental animals, are considered in the discussion.

Female Faculty Memberss Investment Decision Making for Retirement Planning in the Shadow of Holistic Decision Making Model

Retirement planning is an integral part of financial planning for any individual. Every individual looks forward to spending the post retirement years in the lap of luxury. A person needs to take challenging investment decisions in order to optimally plan for retirement. These decisions as per finance theories have been motivated by reasoning while unfortunately the intuition aspect has been portrayed in a negative manner by behavioural finance advocates. Taking a clue from ‘MBA model’ proposed by eminent expert in Indian Management, Prof. Subhash Sharma, the Supervisor of the proposed doctoral work has extended the model by proposing a new model namely ‘Holistic Decision Making Model (HDMM)’ in a working research paper. Increasing the curiosity of the researcher, some past researches have hinted at efficacy of this model and the proposed research work seeks to explore the extent to which decision making is actually influenced by HDMM compared to behavioural finance. Furthermore the researcher seeks to evaluate attitude of female faculty members towards investment for retirement planning taking a sample of about 600 female teachers working in prominent institutions of Rajasthan. The outcome shall not only test efficacy of HDMM but also provide required guidelines to women to plan for retirement in better manner.In case the researcher can find some relevance of HDMM, it shall be a novel contribution in the field of Investment Management.

Egg Production Constrains Chemical Defenses in a Neotropical Arachnid.

Female investment in large eggs increases the demand for fatty acids, which are allocated for yolk production. Since the biosynthetic pathway leading to fatty acids uses the same precursors used in the formation of polyketides, allocation trade-offs are expected to emerge. Therefore, egg production should constrain the investment in chemical defenses based on polyketides, such as benzoquinones. We tested this hypothesis using the harvestman Acutiosoma longipes, which produces large eggs and releases benzoquinones as chemical defense. We predicted that the amount of secretion released by ovigerous females (OFs) would be smaller than that of non-ovigerous females (NOF). We also conducted a series of bioassays in the field and in the laboratory to test whether egg production renders OFs more vulnerable to predation. OFs produce less secretion than NOFs, which is congruent with the hypothesis that egg production constrains the investment in chemical defenses. Results of the bioassays show that the secretion released by OFs is less effective in deterring potential predators (ants and spiders) than the secretion released by NOFs. In conclusion, females allocate resources to chemical defenses in a way that preserves a primary biological function related to reproduction. However, the trade-off between egg and secretion production makes OFs vulnerable to predators. We suggest that egg production is a critical moment in the life of harvestman females, representing perhaps the highest cost of reproduction in the group.

Prudent female allocation by modular hermaphrodites: female investment is promoted by the opportunity to outcross in cyclostome bryozoans

Many sessile, suspension-feeding marine invertebrates mate by spermcasting: aquatic sperm are spawned and gathered by conspecific individuals to fertilize eggs that are generally retained during development. In two phylogenetically distant examples, a cheilostome bryozoan and an aplousobranch ascidian, the receipt of allosperm has previously been shown to alter sex allocation by triggering female investment in eggs and brooding. Here we report experiments demonstrating that two species of cyclostome bryozoan also show restrained female investment in the absence of mating opportunity. In Tubulipora plumosa, the production of female zooids and progeny is much reduced in reproductive isolation. In Filicrisia geniculata, development of distinctive female zooids (gonozooids) begins but halts in the absence of mating opportunity, and no completed gonozooids or progeny result. Reduced female investment in the absence of a mate thus occurs in at least two orders of Bryozoa, but significant differences in detail exist and the evolutionary history within the phylum of the mechanism(s) by which female investment is initiated might be complex. The broadening taxonomic spectrum of examples where female investment appears restrained until allosperm becomes available may signify a general adaptive strategy among outcrossing modular animals, analogous to similarly adaptive sex allocation typical of many flowering plants.

Two eggs, two different constraints: a potential explanation for the puzzling intraclutch egg size dimorphism in Eudyptes penguins.

Phenotypic plasticity and phenotypic stability are major components of the adaptive evolution of organisms to environmental variation. The invariant two-egg clutch size of Eudyptes penguins has recently been proposed to be a unique example of a maladaptive phenotypic stability, while their egg mass is a plastic trait. We tested whether this phenotypic plasticity during reproduction might result from constraints imposed by migration (migratory carry-over effect) and breeding (due to the depletion of female body reserves). For the first time, we examined whether these constraints differ between eggs within clutches and between egg components (yolk and albumen). The interval between colony return and clutch initiation positively influenced the yolk mass, the albumen mass, and the subsequent total egg mass of first-laid eggs. This time interval had only a slight negative influence on the yolk mass of second-laid eggs and no influence on their albumen and subsequent total masses. For both eggs, female body mass at laying positively influenced albumen and total egg masses. Female investment into the entire clutch was not related to the time in the colony before laying but increased with female body mass. These novel results suggest that the unique intraclutch egg size dimorphism exhibited in Eudyptes penguins, with first-laid eggs being consistently smaller than second-laid eggs, might be due to a combination of constraints: a migratory carry-over effect on the first-laid egg and a body reserve depletion effect on the second-laid egg. Both these constraints might explain why the timing of reproduction, especially egg formation, is narrow in migratory capital breeders.

Negative association between parental care and sibling cooperation in earwigs: a new perspective on the early evolution of family life?

The evolution of family life requires net fitness benefits for offspring, which are commonly assumed to mainly derive from parental care. However, an additional source of benefits for offspring is often overlooked: cooperative interactions among juvenile siblings. In this study, we examined how sibling cooperation and parental care could jointly contribute to the early evolution of family life. Specifically, we tested whether the level of food transferred among siblings (sibling cooperation) in the European earwig Forficula auricularia (1) depends on the level of maternal food provisioning (parental care) and (2) is translated into offspring survival, as well as female investment into future reproduction. We show that higher levels of sibling food transfer were associated with lower levels of maternal food provisioning, possibly reflecting a compensatory relationship between sibling cooperation and maternal care. Furthermore, the level of sibling food transfer did not influence offspring survival, but was associated with negative effects on the production of the second and terminal clutch by the tending mothers. These findings indicate that sibling cooperation could mitigate the detrimental effects on offspring survival that result from being tended by low-quality mothers. More generally, they are in line with the hypothesis that sibling cooperation is an ancestral behaviour that can be retained to compensate for insufficient levels of parental investment.

Female major histocompatibility complex type affects male testosterone levels and sperm number in the horse (Equus caballus).

Odours of vertebrates often contain information about the major histocompatibility complex (MHC), and are used in kin recognition, mate choice or female investment in pregnancy. It is, however, still unclear whether MHC-linked signals can also affect male reproductive strategies. We used horses (Equus caballus) to study this question under experimental conditions. Twelve stallions were individually exposed either to an unfamiliar MHC-similar mare and then to an unfamiliar MHC-dissimilar mare, or vice versa. Each exposure lasted over a period of four weeks. Peripheral blood testosterone levels were determined weekly. Three ejaculates each were collected in the week after exposure to both mares (i.e. in the ninth week) to determine mean sperm number and sperm velocity. We found high testosterone levels when stallions were kept close to MHC-dissimilar mares and significantly lower ones when kept close to MHC-similar mares. Mean sperm number per ejaculate (but not sperm velocity) was positively correlated to mean testosterone levels and also affected by the order of presentation of mares: sperm numbers were higher if MHC-dissimilar mares were presented last than if MHC-similar mares were presented last. We conclude that MHC-linked signals influence testosterone secretion and semen characteristics, two indicators of male reproductive strategies.

Reproductive biology and energy allocation of the sea star Cosmasterias lurida (Echinodermata: Asteroidea) from the Beagle Channel, Tierra del Fuego, Argentina

Seasonal fluctuations in environmental factors at high-latitude marine regions have a strong influence on the reproductive cycles of echinoderms. The purposes of this study on a population of Cosmasterias lurida in the Beagle Channel are to describe the reproductive cycle through histological analyses, to characterize the pattern of gonad and somatic indices, to determine the energy content of different organs and their temporal variation and to establish the pattern of energy allocation. During the study period, from August 2010 to June 2011, four seasonal samplings were performed in the subtidal zone of Ushuaia Bay. Indices (gonad, pyloric caeca and stomach), gonadal histology, organic matter and calorimetric measurements were determined. Gametogenesis begins in February and continues until June when oocyte size increases. The gonadal maximum development and gamete releasing take place between August and December. Temporal variation of energetic reserves in gonads occurs through the variation in gonad mass, with a GI major peak and energy content during August. Stomach and pyloric caeca show their maximum energy accumulation during June, while decrease of organic matter of the body wall takes place from August to December. The population of C. lurida from Beagle Channel suggests an annual reproductive cycle with two maturation events and the influence of water temperature on maturation and releasing of gametes. Different patterns of energy allocation to gonads between sexes were observed, with a greater energy investment in females than in males. Pyloric caeca, stomach and body wall were proposed as energy reservoirs for gonadal maturation and spawning.

The stress of growing old: sex- and season-specific effects of age on allostatic load in wild grey mouse lemurs.

Chronic stress [i.e. long-term elevation of glucocorticoid (GC) levels] and aging have similar, negative effects on the functioning of an organism. Aged individuals' declining ability to regulate GC levels may therefore impair their ability to cope with stress, as found in humans. The coping of aged animals with long-term natural stressors is virtually unstudied, even though the ability to respond appropriately to stressors is likely integral to the reproduction and survival of wild animals. To assess the effect of age on coping with naturally fluctuating energetic demands, we measured stress hormone output via GC metabolites in faecal samples (fGCM) of wild grey mouse lemurs (Microcebus murinus) in different ecological seasons. Aged individuals were expected to exhibit elevated fGCM levels under energetically demanding conditions. In line with this prediction, we found a positive age effect in the dry season, when food and water availability are low and mating takes place, suggesting impaired coping of aged wild animals. The age effect was significantly stronger in females, the longer-lived sex. Body mass of males but not females correlated positively with fGCM in the dry season. Age or body mass did not influence fGCM significantly in the rainy season. The sex- and season-specific predictors of fGCM may reflect the differential investment of males and females into reproduction and longevity. A review of prior research indicates contradictory aging patterns in GC regulation across and even within species. The context of sampling may influence the likelihood of detecting senescent declines in GC functioning.

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.

Within-plant variation in reproductive investment: consequences for selection on flowering time.

Variation among the leaves, flowers or fruit produced by a plant is often regarded as a nuisance to the experimenter and an impediment to selection. Here, we suggest that within-plant variation can drive selection on other plant-level traits. We examine within-plant variation in floral sex allocation and in fruit set and predict that such variation generates variation in male success among plants, thereby driving selection on flowering time. We tested this prediction in a simulation model estimating selection on flowering time through male fitness when floral sex allocation and/or fruit set vary directionally among flowers on plants. We parameterized the model through a quantitative literature survey of within-plant change in sex allocation. As predicted, within-plant variation in floral sex allocation and in fruit set probability can generate selection on flowering time through male fitness. Declining fruit set from first to last flowers on plants, as occurs in many species, selected for early flowering onset through male fitness. This result was robust to self-incompatibility and to varying returns on male versus female investment. Selection caused by declining fruit set was strong enough to reverse the selection for late flowering that can be caused by intrafloral protandry. Our model provides testable predictions regarding selection on flowering time through male fitness. The model also establishes the intriguing possibility that within-plant variation may influence selection on other traits, regardless of whether that variation is under selection itself.

Behavioural responses of great tits to experimental manipulation of nest temperature during incubation

In several bird species only one member of the pair incubates the eggs. This individual should trade-off the time between caring for the eggs and leaving the nest to forage or perform other self-maintenance activities. Thus, daytime incubation is intermittent, and the number of " sessions " and " recesses " , and their length, impact egg temperatures and therefore embryo development. We evaluated female investment decisions, and their reproductive consequences, by experimentally heating or cooling great tit Parus major nests during the incubation period in a Mediterranean population. Heated females were less often encountered within the nest incubating, and their recesses tended to be longer. Even though mean nest temperatures were higher in heated than in control nests, heating did not affect breeding success, size or condition of the nestlings, or parental condition or behaviour when feeding the nestlings. On the other hand, temperatures in cooled nests were lower than those in control nests during the daytime (but not during the night). However , females seemed able to compensate for the treatment, since breeding success was similar in cooled and control nests, and neither nestlings nor parents showed negative effects of the cooling treatment.

Reproductive state affects hiding behaviour under risk of predation but not exploratory activity of female Spanish terrapins

Female investment during reproduction may reduce survivorship due to increased predation risk. During pregnancy, the locomotor performance of gravid females might be diminished due to the additional weight acquired. In addition, egg production may also increase thermoregulatory, metabolic and physiological costs. Also, pregnant females have greater potential fitness and should take fewer risks. Thus, females should ponder their reproductive state when considering their behavioural responses under risky situations. Here, we examine how reproductive state influence risk-taking behaviour in different contexts in female Spanish terrapins (Mauremys leprosa). We simulated predator attacks of different risk levels and measured the time that the turtles spent hiding entirely inside their own shells (i.e. appearance times). We also assessed the subsequent time after emergence from the shell that the turtles spent immobile monitoring for predators before starting to escape actively (i.e. waiting times). Likewise, we performed a novel-environment test and measured the exploratory activity of turtles. We found no correlations between appearance time, waiting time or exploratory activity, but appearance times were correlated across different risk levels. Only appearance time was affected by the reproductive state, where gravid females reappeared relatively later from their shells after a predator attack than non-gravid ones. Moreover, among gravid females, those carrying greater clutches tended to have longer appearance times. This suggests that only larger clutches could affect hiding behaviour in risky contexts. In contrast, waiting time spent scanning for predators and exploratory activity were not affected by the reproductive state. These differences between gravid and non-gravid females might be explained by the metabolic-physiological costs associated with egg production and embryo maintenance, as well as by the relatively higher potential fitness of gravid females.

Larval deposition behaviour and maternal investment of females reflect differential habitat adaptation in a genetically diverging salamander population

Illuminating the ability of individuals to react to different selective forces caused by environmental differences is crucial to understand population divergence and speciation in the context of habitat adaptation. In a common environment experiment performed under standardised laboratory conditions, we examined whether female fire salamanders (Salamandra salamandra) originating from a recently adaptively diverged population displayed behavioural phenotype differences related to larval deposition behaviour. Females of this species typically deposit their larvae in small first-order streams; however, in our study population, females also use temporary ponds. These two habitat types display major ecological differences that strongly influence larval growth and survival. We observed that females differed in larval deposition behaviour and maternal investment. Pond-type females extended larval deposition over an increased time period and tended to exhibit more deposition events compared with stream-type females. Over successive deposition events, the body condition of larvae deposited by stream-type females decreased faster than that of larvae deposited by pond-type females. These differences in larval deposition behaviour may represent a bet-hedging strategy, given that ponds are more constrained in terms of desiccation and food availability than streams. The lengthened deposition period enabled pond-type females to deposit larger larvae towards the end of the deposition period, compared with stream-type females. Although the studied population only diverged recently, we observed significant behavioural differences between differentially adapted females, demonstrating the importance of behavioural differences in habitat adaptation in the context of speciation processes.