Aggression and worker control of caste fate in a multiple-queen wasp, Parachartergus colobopterus

Although famously cooperative, social insect colonies harbour considerable potential for genetic conflict among colonymates. This conflict may be expressed behaviourally as aggression by workers. We investigated aggression in 34 colonies of the wasp Parachartergus colobopterus, by evaluating the characteristics of both instigators and victims of aggressive interactions. We estimated genetic relatedness and queen number using DNA microsatellites and found that workers and emerging females should be most in conflict over the caste of the latter when there are many queens on the nest. We found that aggressive interactions are more likely to involve older workers attacking either males or younger workers, and that victim and aggressor females have more ovarian development than randomly sampled colonymates. Moreover, mated females with low levels of ovarian development relative to active queens were also more likely to be aggressors and victims than were randomly sampled females. Aggression among females supports the hypothesis that older workers use aggression towards younger females as a means of policing the development of emerging females into queens. Workers also may use aggression to suppress the reproduction of some mated females. Our findings thus support the hypothesis that genetic conflicts of interest motivate worker aggression in swarm-founding wasp colonies.     

Anorexia: A “losing” strategy?

Several theorists have tried to model anorexia on Wasser and Barash’s (1983) “reproductive suppression model” (RSM). According to the RSM, individual females adaptively suppress their reproductive functioning under conditions of social or physiological stress. From this perspective, mild anorexia is viewed as an adaptive response to modern conditions; more severe anorexia is viewed as an adaptation gone awry. Previous models have not, however, examined the full richness of the RSM. Specifically, Wasser and Barash documented not only self-imposed reproductive suppression, but also manipulative reproductive suppression of subordinate females by dominants. I propose that the modern “epidemic” of anorexia is explained neither by adaptive self-suppression nor by environmental mismatch (an adaptation gone awry); I propose that the “epidemic” levels of anorexia seen in modern western society are a direct consequence of intrasexual competition, the scope of which has been enhanced by the power and reach of modern communications media. According to this perspective, anorexia, even in its mild forms, is a manipulative strategy imposed on subordinates by dominants. Anorexia is, in both senses, a “losing” strategy. Linda Mealey developed the intrasexual manipulation model of anorexia while on a three-year stint in the psychology department of the University of Queensland; she is currently at the College of St. Benedict in central Minnesota, where she is associate professor of psychology. She is President of the International Society for Human Ethology, a councilor of the Human Behavior and Evolution Society, on the editorial board of Politics and the Life Sciences, and chair of the 1999 and 2000 Aaron Beck New Investigator Award Committee (sponsored by ASCAP: Across Species Comparisons and Psychiatry).     

Female reproductive competition within families in rural Gambia

Many studies show that the extended human family can be helpful in raising offspring, with maternal grandmothers, in particular, improving offspring survival. However, less attention has been given to competition between female kin and co-residents. It has been argued that reproductive conflict between generations explains the evolution of menopause in cooperatively breeding species where females disperse, and that older females are related to the offspring of younger females through their sons, whereas younger, incoming females are unrelated to older females. This means the pattern of help will be asymmetric, so older females lose in reproductive conflict and become 'sterile helpers'. Here, we seek evidence for female reproductive competition using longitudinal demographic data from a rural Gambian population, and examine when women are helping or harming each other's reproductive success. We find that older women benefit and younger women suffer costs of reproductive competition with women in their compound. But the opposite is found for mothers and daughters; if mother and daughter's reproductive spans overlap, the older woman reduces her reproduction if the younger woman (daughter) reproduces, whereas daughters' fertility is unaffected by their mothers' reproduction. Married daughters are not generally co-resident with their mothers, so we find not only competition effects with co-resident females, but also with daughters who have dispersed. Dispersal varies across human societies, but our results suggest reproductive conflict could be influencing reproductive scheduling whatever the dispersal pattern. A cultural norm of late male marriage reduces paternal grandmother/daughter-in-law reproductive overlap almost to zero in this population. We argue that cultural norms surrounding residence and marriage are themselves cultural adaptations to reduce reproductive conflict between generations in human families.     

Dominance hierarchy among workers changes with colony development in Polistes japonicus (Hymenoptera, Vespidae) paper wasp colonies with a small number of workers

Dominance hierarchy in the primitively eusocial wasp Polistes japonicus was analysed in four colonies for two periods: (1) the first-brood period, when only early emerging workers are present on the nest, and (2) the mixed-brood period, when the first and second (last) broods are present on the nest. The rank in the dominance hierarchy was determined based on a sociogram showing a dominance–subordinance relationship for all pairs of workers. During the first-brood period, older workers were likely to be more dominant (older dominance hierarchy), while the rank of workers was reversed during the mixed-brood period, with younger workers being likely to be more dominant (younger dominance hierarchy). However, the oldest and youngest workers were not always the top-ranked workers in the dominance hierarchy during the first- and mixed-brood periods, respectively, and during the mixed-brood period no younger dominance hierarchy was evident when the first or second brood was analysed separately. Higher ranked workers displayed dominance behaviour more frequently, and the lowest ranked worker hardly displayed dominance behaviour. Most workers displayed dominance behaviours primarily towards the worker ranked immediately below in the dominance hierarchy during the mixed-brood period but not during the first-brood period. The bodies of younger workers were larger for the mixed brood, but not for the first brood in some colonies or the second brood in all colonies. The association between body size and rank in the dominance hierarchy was negative during the first-brood period and positive during the mixed-brood period, with a nearly significant trend also seen even when the analysis was limited to the second brood. To explain the above temporal change from an older dominance hierarchy to a younger dominance hierarchy, we propose the hypothesis that the probability of a worker inheriting the colony increases rapidly with colony development, and consequently younger larger workers attempt to move up the dominance hierarchy in order to produce their own offspring by becoming the superseder late in colony development, rather than working harmoniously so as to boost the overall production of reproductive progeny for a colony, which is the strategy adopted early in colony development.     

Mate Choice and the Origin of Menopause

Human menopause is an unsolved evolutionary puzzle, and relationships among the factors that produced it remain understood poorly. Classic theory, involving a one-sex (female) model of human demography, suggests that genes imparting deleterious effects on post-reproductive survival will accumulate. Thus, a ‘death barrier’ should emerge beyond the maximum age for female reproduction. Under this scenario, few women would experience menopause (decreased fertility with continued survival) because few would survive much longer than they reproduced. However, no death barrier is observed in human populations. Subsequent theoretical research has shown that two-sex models, including male fertility at older ages, avoid the death barrier. Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility and thus produce a menopausal period. Our model requires neither the initial assumption of a decline in older female fertility nor the effects of inclusive fitness through which older, non-reproducing women assist in the reproductive efforts of younger women. Our model helps to explain why such effects, observed in many societies, may be insufficient factors in elucidating the origin of menopause.     

Aging and Repeated Thought Suppression Success

Intrusive thoughts and attempts to suppress them are common, but while suppression may be effective in the short-term, it can increase thought recurrence in the long-term. Because intentional suppression involves controlled processing, and many aspects of controlled processing decline with age, age differences in thought suppression outcomes may emerge, especially over repeated thought suppression attempts as cognitive resources are expended. Using multilevel modeling, we examined age differences in reactions to thought suppression attempts across four thought suppression sequences in 40 older and 42 younger adults. As expected, age differences were more prevalent during suppression than during free monitoring periods, with younger adults indicating longer, more frequent thought recurrences and greater suppression difficulty. Further, younger adults’ thought suppression outcomes changed over time, while trajectories for older adults’ were relatively stable. Results are discussed in terms of older adults’ reduced thought recurrence, which was potentially afforded by age-related changes in reactive control and distractibility.     

Sex Differences in Mobility and Spatial Cognition

The fertility and parental care hypothesis interprets sex differences in some spatial-cognitive tasks as an adaptive mechanism to suppress women’s travel. In particular, the hypothesis argues that estrogens constrain travel during key reproductive periods by depressing women’s spatial-cognitive ability. Limiting travel reduces exposure to the dangers and caloric costs of navigating long distances into unfamiliar environments. Our study evaluates a collection of predictions drawn from the fertility and parental care hypothesis among the Twe and Himba people living in a remote region of Namibia. We find that nursing mothers travel more than women at any other stage of their reproductive career. This challenges the assumption that women limit travel during vulnerable and energetically demanding reproductive periods. In addition, we join previous studies in identifying a relationship between spatial ability and traveling among men, but not women. If spatial ability does not influence travel, hormonally induced changes in spatial ability cannot be used as a mechanism to reduce travel. Instead, it appears the fitness consequences of men’s travel is a more likely target for adaptive explanations of the sex differences in spatial ability, navigation, and range size.     

Differential fertility in the United States, 1980: continuity or change?

This paper considers how changes in women's sociocultural characteristics have influenced recent patterns of differential fertility in the US and whether the convergence of fertility differentials observed up to 1970 has continued. The data are drawn from the June 1980 US Current Population Survey, which is a probability sample survey selected to represent the civilian non-institutionalized population living in households. The study population consists of 20,621 ever-married White and Black women aged 25-44, a group for various reasons considered to have a high impact from the point of view of fertility behavior. Fertility to date and ever expected fertility are the dependent variables. The respondents were separated into age cohorts, and differentiated by race. The data suggest that there has been no change in differential fertility in recent years: the 2 youngest cohorts (25-29 and 30-34 years) have similar expected fertilities that are lower than those of the older cohorts. Age at 1st birth, length of 1st birth interval, income, and education were negatively associated with fertility, among both older and younger women, of both races. Differentials by race have narrowed slightly. When fertility expectations were examined, the association of the independent variables with expected completed fertility was weaker among younger women, indicating that there has been some convergence in expected fertility. Further narrowing of differentials in actual fertility depends on how successful the younger women are in preventing future unplanned births. If the present tendency towards surgical sterilization (among both races and groups above and below the poverty level) persists, it will make it possible for more women to stay within their expected total fertility levels.     

Scientific molecular basis for treatment of reproductive failure in the human: An insight into the future

Purpose. The purpose of this review is to summarize science-based new treatments for human reproductive failure and future developments. Results. First will be discussed popular but erroneous myths of current non-science based treatments. Then will be discussed new treatments and their scientific base, including ovary and egg freezing, and transplantation to preserve fertility in young women undergoing gonadotoxic chemotherapy and radiation for cancer; new perspectives on human epididymal sperm maturation based on a comparison between ICSI (intracytoplasmic sperm injection) with testis sperm versus epididymal sperm; simplifying IVF and reducing cost by more intelligent and milder ovarian stimulation; improving pregnancy rate in older women; searching the genome to find genes which control spermatogenesis and whose deletion or mutation causes spermatogenic failure; and human spermatogenic stem cell culture to treat azoospermia, and to preserve fertility in pre-pubertal boys undergoing cancer treatment. Conclusion. With stem cell biology and molecular understanding of reproductive failure, new therapies for previously untreatable infertility are currently on the near horizon. Conversely our clinical results with new therapeutic approaches are adding to our understanding of the basic science of reproduction. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.     

The social biology of human populations: Spontaneous group formation conforms to evolutionary predictions of adaptive aggregation patterns

Two experiments tested whether city commuter and pedestrian groups conformed with ecological predictions of adaptive group size, age, and sex composition. It was predicted that individuals with the greatest reproductive potential would optimize mating contacts and minimize competitive interference by segregating into small, mixed-sex groups, whereas more vulnerable individuals, too young or old for optimum fertility, would tend to aggregate independently of gender in larger groups, which may offer advantages for foraging and predator avoidance. To maximize reproductive potential, mature males should prefer grouping with young women of high fertility, whereas older women should prefer younger men. In Experiment 1, 2,432 persons in three cities were observed on buses, automobiles, and sidewalks, in yoked observations. As predicted, reproductively immature preschool and grade-school children formed larger groups than mature adults (p < 0.0001) and showed no sex differences in grouping. Elderly adults (with decreased reproductive potential) were also found in larger groups than younger adults (p < 0.01) and also showed no sex differences. Sexually mature men and women grouped more with the opposite sex than in all-male or all-female groups (p < 0.00001). Mature adult men were the least aggregative category (p < 0.01): they tended to be alone or in pairs with women, and all-male groups were conspicuously absent (p < 0.005). These findings were consistent across different socioeconomic levels, ethnicities, and subcultures in our samples (p = NS). In Experiment 2, 475 bus passengers in three cities were observed selecting seatmates in a naturalistic choice paradigm. Only sexually mature adults exhibited a significant preference for the sex of their seatmates (p < 0.0005): Young women chose most often to sit with other women, whereas young adult men more frequently chose seatmates of the opposite sex. Young women were chosen more often as seat partners than all age/sex categories combined (p < 0.0005). Young women chose older partners (p < 0.05), while middle-aged women preferred younger women and men (p < 0.0005) as companions. Results are explained in the context of canalized behaviors arising early in human evolution.     

Sociosexual development,pair bond formation,and mechanisms of fertility suppression in female cotton-top tamarins (Saguinus oedipus oedipus)

The effect of various social environments on sociosexual behavior was examined in six young female cotton-top tamarins (Saguinus oedipus oedipus) and in three established breeding females. Behavioral observations and hormonal samples were collected on young females while they were living with their families, when they were isolated from conspecifics, and after they were paired with an unrelated male. While living with the family, all females showed a suppression of fertility and low frequencies of sociosexual behavior. Following removal from the family, isolated females displayed an increase in rate of scent marking and an increase in hormonal levels. When young females were paired with males, they were exposed to scent secretions from their natal families, from an unfamilar family, and from a control for a total of 24 weeks. After pairing, hormonal levels increased dramatically, and ovarian cyclicity began. An increase in sociosexual behavior and elevated levels of scent marking accompanied this physiological change. Newly paired females had higher rates of affiliative behavior and scent marking than did established breeding females. However, both newly paired and established breeding males were more likely to initiate contact, grooming bouts, and social sniffing than were females. Time to first ovulation was later in females who were exposed to scent secretions from their natal families than it was in those females given a control for the first 8 weeks following pairing. No female conceived during exposure to scent secretions. However, once normal ovarian cycling had begun or a pregnancy was established, exposure to scent secretions had no effect. Thus, the social environment influences the fertility, sociosexual behavior, and pair bond formation of cotton-top tamarins. In addition, chemical stimuli found in the scent secretions produced by the natal family are most likely involved in reproductive suppression.     

Age differences between distributions of genotypes among pregnant women: evidence of fertility selection

The number of children produced by a modern woman is usually below her total reproductive capacity and is determined by circumstances other than natural selection. It is, therefore, practically impossible to detect differences in natural fertilities associated with different types (e.g. phenotypes, genotypes) of women. This does not mean, however, that natural selection at the reproductive level cannot at all be detected today. If women of a particular type have high natural fertility, this usually means that they reproduce (become pregnant) at a higher rate than women of a type with lower natural fertility. Hence, when there is a limit on the number of children, women of the first type will reach the limit at an earlier age than women of the second type. As a result, types that have a higher natural fertility should be overrepresented among pregnant women of younger ages and, consequently, underrepresented among older ones, as compared to types with a lower natural fertility. Based on this notion, a model of age-related differences between distributions of types among pregnant women is suggested. The model is applied to data on MNSs-blood group and PGM1 (phosphoglucomutase) types in a sample of pregnant women and an evidence of natural selection at the reproduction level associated with these genetic markers is obtained.     

Continuing fertility transitions in a plural society: ethnic trends and differentials in Peninsular Malaysia

Fertility in Peninsular Malaysia has declined continuously from the late 1950s, reaching a total fertility rate of 3735 in 1983. All ethnic groups in Malaysia have contributed to this modern demographic transition but the rate of change has been most rapid for Chinese and Indians, Malay fertility having reached a plateau in the early 1980s. The effect of age structure, marital patterns and marital fertility (by parity) on the fertility declines for each ethnic community are analyzed. There has been a tendency, in each ethnic group, for the age distribution within the group of reproductive-age women to grow younger, reflecting the entry into the younger reproductive ages of the large birth cohorts of the 1950s and early 1960s. The effect of this on crude birth rates is hard to determine, because rising age at marriage and increasing use of contraception meant that fertility was increasingly concentrated in the more central reproductive ages. By the 1990s, the earlier declines in fertility will bring about a decline in the proportion of the total population made up of females in the main reproductive ages. After that point, further declines in fertility will be reflected in a sharper decline in the crude birth rate and hence the rate of population increase. Between 1947 and 1980, the age at marriage changed dramatically for females of all ethnic groups. The transition to higher age at marriage for Chinese was completed earlier, and since 1970 has risen by only a year. For Malays and Indians, the rise began later, proceeded faster and continued right up to 1980 when the medium ages at 1st marriage were Malays 22, Indians 23, Chinese 24 years. In 1980, Malay women on average were marrying 5 years later, and Indian women 6 years later than had their mothers' generation in 1947. The proportion never-married among Malay and Indian women aged 20-24 rose from 1/10 to 1/2 over this period; relatively greater changes are evident at ages 25-29. Other factors are the almost complete shift from parent-arranged to self-arranged marriages. Family size desired has decreased for all groups and the decline in breastfeeding has been offset by the sharp increase in the practice of contraception. Continuation of these trends would lead to replacement-level fertility for Malaysian Chinese and Indians by the year 2000. Malay fertility is likely to continue to decline but at a more moderate pace.     

Estimating differential reproductive success from nests of related individuals, with application to a study of the mottled sculpin, Cottus bairdi

Understanding how variation in reproductive success is related to demography is a critical component in understanding the life history of an organism. Parentage analysis using molecular markers can be used to estimate the reproductive success of different groups of individuals in natural populations. Previous models have been developed for cases where offspring are random samples from the population but these models do not account for the presence of full- and half-sibs commonly found in large clutches of many organisms. Here we develop a model for comparing reproductive success among different groups of individuals that explicitly incorporates within-nest relatedness. Inference for the parameters of the model is done in a Bayesian framework, where we sample from the joint posterior of parental assignments and fertility parameters. We use computer simulations to determine how well our model recovers known parameters and investigate how various data collection scenarios (varying the number of nests or the number of offspring) affect the estimates. We then apply our model to compare reproductive success among different age groups of mottled sculpin, Cottus bairdi, from a natural population. We demonstrate that older adults are more likely to contribute to a nest and that females in the older age groups contribute more eggs to a nest than younger individuals.     

Age and Behavior of Honey Bee Workers,Apis mellifera,that Interact with Drones

Colony reproduction in honey bees involves complex interactions between sterile workers and reproductive castes. Although worker–queen interactions have been studied in detail, worker–drone interactions are less well understood. We investigated caste interactions in honey bees by determining the age and behavior of workers that perform vibration signals, trophallaxis, and grooming with drones. Workers of all ages could engage in the different interactions monitored, although workers that performed vibration signals on drones were significantly older than those engaging in trophallaxis and grooming. Only 3–8% of workers engaged in the different behaviors were monitored. Compared with workers that performed vibration signals only on workers (‘worker vibrators’), those that performed signals on both workers and drones (‘drone vibrators’) had greater movement rates inside the nest, higher vibration signaling rates, and were more likely to have an immediate association with foraging. Both worker vibrators and drone vibrators contacted drones of all ages as they moved through the nest. However, drone vibrators contacted drones at higher rates, contacted slightly, but significantly younger drones, and were more likely to engage in trophallaxis and grooming with drones, in addition to vibrating them. Taken together, our results suggest that tiny proportions of workers belonging to separate, but overlapping age groups provide most of the care received by adult drones, and that drone vibrators comprise a subset of signalers within a colony that have an increased tendency to contact and interact with drones. Vibratory, tactile signals are involved in colony reproductive and movement decisions in a number of species of bees, wasps and ants, and may provide valuable tools for investigating caste interactions in many insect societies.     

Women's work and fertility in a sub-Saharan urban setting: a social environment approach

Data from three separate studies conducted in Maputo, Mozambique, in 1993 are used to analyse the relationship between the type of social environment in which women work and their fertility and contraceptive use. The analysis finds that women who work in more collectivized environments have fewer children and are more likely to use modern contraception than women who work in more individualized milieus and those who do not work outside the home. Most of these differences persist in multivariate tests. It is argued that collectivized work environments are most conducive to diffusion and legitimation of reproductive innovations. In contrast, individualized environments tend to isolate women and therefore may retard their acceptance of innovative fertility-related behaviour.     

Reproductive plasticity in Polistes paper wasp workers and the evolutionary origins of sociality

Regulatory pathways in solitary species provide the raw materials for the evolution of sociality. Therefore, comparing the mechanisms that mediate reproductive plasticity in social species and their solitary ancestors can provide insight into the evolutionary origin of sociality. In many solitary insects, the effect of juvenile hormone (JH) on fertility is mediated through the fat body; individuals in good physical condition show a stronger fertility response to JH than individuals in poor physical condition. Here, we test whether a similar, condition-dependent JH response mediates fertility in workers of the primitively eusocial Polistes dominulus wasps. We test how body weight, JH, and adult nutrition influence worker ovarian development. Both JH-treatment and adult nutrition dramatically increased ovarian development. Body weight also influenced ovarian development, as large workers developed more eggs than smaller workers. Body weight and fat are strongly linked in P. dominulus workers, so these results suggest that the fat-dependent JH responsiveness common in solitary insects is conserved in social wasps. The simple, ancestral relationship between reproductive investment and physical condition may facilitate cooperation by allowing workers to adaptively allocate energy into reproduction based on their probability of successfully becoming a queen.