Female subsistence strategies among Ache hunter-gatherers of Eastern Paraguay

Anthropologists have frequently proposed that sexual division of labor is produced by childcare constraints on women's subsistence work. We present data on the forest activities of Ache women that show that differences in parental investment partially account for variation in food acquisition among individual women. Data also suggest that childcare constraints are important in understanding the sexual division of labor.     

Men's time allocation to subsistence work among the Ache of Eastern Paraguay

Quantitative data on men's time allocation among the Ache of Paraguay are presented. The data indicate that Ache men work almost 7 hours daily in direct food acquisition, which is the major daily activity. The amount of time Ache men work is compared with the amount reported for other modern hunter-gatherers and tribal horticulturalists. The characterization of hunter-gatherers as the original affluent society does not agree with currently available data. The results show high variance across societies, both hunting and horticultural, and suggest that time spent in subsistence work is not simply a function of food needs. We propose that the value of time spent in potential alternative activities must be considered in order to predict time spent in subsistence tasks.     

Labor specialization and the formation of markets for food in a Shipibo subsistence economy

Traditionally, the Shipibo economy was subsistence-based with shifting cultivation supplying calories, principally in the form of plantains and root crops, while fishing and hunting provided animal proteins to the diet. Some men, who recently began producing rice for sale in regional markets, now allocate less time to wild food procurement. Moreover, this trend has been accompanied by the nucleation of households, a growing cash market for agricultural labor, and the intravillage sale of faunal foods. This paper shows that with cash cropping, some Shipibo now freely distribute less food to others in relation to the amount they produce. To account for this change, a theory is developed based on time allocation and patterns of economic behavior reported throughout the Amazon. This theory is then applied to explain specialization and the formation of cash markets for food labor among the Shipibo.     

Cooperation and conflict: The behavioral ecology of the sexual division of labor

When it comes to subsistence, men and women in almost all societies do it differently. One long-standing explanation for this sexual division of labor is that men and women pair up to provision offspring and specialize in subsistence activities in order to maximize household productivity. This model of cooperative parental provisioning has generally been supported by the proposal that both male and female reproductive success is maximized by provisioning current offspring rather than deserting them in order to seek new mating opportunities. But recent analyses of bird behavior have often failed to support this premise. We now know that among many species conflicting reproductive strategies between males and females often result in less than optimal compromises with regard to mating and parenting. This new focus on the role of sexual selection in creating compromise and conflict between the sexes has the potential to illuminate many puzzling aspects of human partnerships between men and women. To demonstrate its potential, I compare the explanatory power of a cooperative provisioning model of sex difference in human foraging and food sharing with a model incorporating conflicting reproductive goals.     

Sexual dimorphism and cultural evolution in the Late Pleistocene and Holocene of Europe

Dental, cranial and body size data are reviewed for European Upper Paleolithic, Mesolithic and Neolithic males and females. Over these three periods there is a substantial decrease in the level of sexual dimorphism. From separate analysis of trends occurring between males and females, it is shown that the major cause for this decrease in sexual dimorphism is gracilization of the males between the Upper Paleolithic and Mesolithic. Reduction in males is related to shifting technological patterns associated with hunting and changes in the types of animals hunted. Further reduction in sexual dimorphism between the Mesolithic and Neolithic and from the Neolithic to modern European populations is shown to be more closely tied to changes occurring among females. Analysis of changing patterns of sexual dimorphism in Late Pleistocene and Holocene populations of Europe suggests an interrelationship between cultural and biological evolution.     

Sucrose response thresholds of honey bee (Apis mellifera) foragers are not modulated by brood ester pheromone

Division of labor is a hallmark of eusocial insects and their ecological success can be attributed to it. Honey bee division of labor proceeds along a stereotypical ontogenetic path based on age, modulated by various internal and external stimuli. Brood pheromone is a major social pheromone of the honey bee that has been shown to affect honey bee division of labor. It elicits several physiological and behavioral responses; notably, regulating the timing of the switch from performing in-hive tasks to the initiation of foraging. Additionally, brood pheromone affects future foraging choice. In honey bees, sucrose response threshold is a physiological correlate of age of first foraging and foraging choice. Brood pheromone has been shown to modulate sucrose response threshold in young bees, but its effects on sucrose response thresholds of bees in advanced behavioral states (foragers) are not known. In this study we examined the sucrose response thresholds of two different task groups, foragers (pollen and non-pollen) and non-foraging bees, in response to honey bee brood pheromone. Sucrose response thresholds were not significantly different between brood pheromone treatment and controls among both non-pollen and pollen foragers. However, the sucrose response threshold of non-foraging bees was significantly higher in the brood pheromone treatment group than in the control group. The switch to foraging task is considered a terminal one, with honey bee lifespan being determined at least partially by risks and stress accompanying foraging. Our results indicate that foragers are physiologically resistant to brood pheromone priming of sucrose response thresholds.     

Division of labor inPonera pennsylvannica (Formicidae: Ponerinae)

Summary We examined division of labor and colony demography in the antPonera pennsylvannica. Observation of three colonies with individually marked workers revealed a high degree of interindividual behavioral variation and a rough but consistent division of labor between brood tenders and foragers. This division was present both in colonies consisting entirely of workers produced in the previous summer and in colonies containing freshly eclosed ants. Two colonies showed typical age-based polyethism, with young ants focusing on brood care and overwintered ants on foraging. No such age basis was detected in the third colony. This difference may relate to variability in brood production schedules. Colonies showing temporal polyethism had two peaks of brood production and thus had relatively large brood populations when the first young workers eclosed, while the third colony had only one peak and little brood for the young workers to tend. Even if young ants have a lower threshold for brood care, it may have been concealed in the latter situation. Demographic data indicate that natural colonies produce one brood per year and that workers typically eclose into colonies with relatively low brood care demands. This suggests that overwintered workers do most of a colony's work and that the division of labor among overwintered ants is the more important one under natural conditions. The basis of this division is as yet unknown. These results also suggest that small colony size, univoltine brood schedule and a close association between foraging and brood care do not preclude division of labor among specialized castes, as has been suggested for another ponerine species (Traniello 1978).     

Reproductive ecology of Naididae (Oligochaeta)

Asexual reproduction is employed by species of Naididae during favorable environmental conditions. In species characteristic of aquatic habitats subject to rapid fluctuations in water levels and temperatures most individuals in a population become sexually mature, and there is degeneration of the alimentary tract, a shortened breeding season, and aclitellar formation of cocoons. Cocoon deposition allows a population to survive periods of environmental stress. Sexual reproduction predominates near the edges of ranges where stress conditions are more prevalent. Species that reproduce sexually in spring are intolerant of summer conditions, while those that breed in autumn are intolerant of winter. Species typical of environmentally stable bodies of water usually have a minority of the population mature at any time, an extended breeding season, and the ability to continue feeding while mature; thus, adaptations for survival in unstable habitats are lacking.     

Behavioral ecology and natural history of Blepharidatta brasiliensis (Formicidae, Blepharidattini)

Fungus-growing ants (Attini, Formicidae) originated about 45–65 million years ago when forging a mutualistic association with basidiomycete fungi (Lepiotaceae). Here we use information on the biology of the non-leafcutting fungus-growing ants and their close relatives in the genus Blepharidatta to evaluate hypotheses for the evolutionary origin of fungus-growing behavior in attine ants. Observations on the natural history, ecology, and behavior of the Amazonian species Blepharidatta brasiliensis are reported here for the first time. Like most attine species, B. brasiliensis and the great majority of species in the tribe Blepharidattini are inhabitants of moist tropical rainforest, suggesting a rainforest habitat also for the ancestral attine ant. The ancestral attine was probably a leaf litter dweller, building small to medium sized nests (e.g., 20–200 workers) either between leaves in the litter or in decaying wood on the rainforest floor. Received 20 December 2005; revised 1 March 2006; accepted 7 March 2006.     

Skeletal indicators of subsistence patterns and activity régime in the Mesolithic sample from Grotta dell’Uzzo (Trapani,Sicily): a case study

The skeletal sample from Grotta dell’Uzzo, Sicily (2 adult females and 5 adult males) was compared to a number of more representative population samples from Western Europe and the Mediterranean Basin. The majority of these were from Italian pre- and protohistoric sites. The research protocol analyzed skeletal indicators of labour activity and sexual division of labour (body size and proportions, sexual dimorphism, limb lateralization, bone robustness, the development of muscular attachments, accessory articular facets, signs of muscular hyperfunction). Sexual dimorphism and limb lateralization showed some regular patterns of possible general significance in all the samples examined here. A general pattern of gracilization and de-specialization of physical activity is observed in the Mesolithic as compared to the Upper Palaeolithic samples. The main features of the Mesolithic samples are: a reduction of body size and bone robustness, a lower degree of sexual dimorphism and limb bone asymmetry, a reduction of the mechanical stress on the lower limbs indicated by less pronounced muscular attachments and reduced talar flattening. This trend is reversed towards the Neolithic period. The main features of these variations are discussed in relation to economic and environmental changes. The Uzzo sample fits well into the general picture of the Western European Mesolithic, although showing some intermediate features between the Mesolithic and the Neolithic samples. This paper is dedicated to the memory of the late Roland Menk, who made significant contribution to our understanding of the Mesolithic transition.     

Worker Age, Ovary Development, and Temporal Polyethism in the Swarm-Founding Wasp Polybia occidentalis (Hymenoptera: Vespidae)

I measured oocyte sizes of Polybia occidentalis workers to assess whether ovary development corresponded with adult age or with individual variation in behavior. Workers exhibited temporal polyethism by first working inside the nest, then performing on-nest tasks, and later foraging and defending the nest. Individuals varied in their ages at first performance of each of these sets of behavioral acts. Ovary development corresponded strongly with adult age. Workers' ovaries declined quickly after an initial phase of partial development. The period of ovary decline overlapped with the age range at which most workers began performing tasks on the exterior nest surface. However, after accounting for age effects, individual behavioral differences (rate of temporal polyethism and performance of foraging and defense tasks) did not correspond with ovary development. These data suggest that ovary development had little or no effect on variation in task performance by P. occidentalis workers on the nest surface.     

Caste specialization in food storage in the dimorphic antColobopsis nipponicus (Wheeler)

Summary Food-storage abilities of both minor and major workers of the dimorphic antColobopsis nipponicus were examined to prove the hypothesis that major workers of this species have a trophic role in addition to a defensive one. Both worker subcastes accumulated water, that was supplied with water-soluble food, as well as fat, that probably originated from food given. However, the major workers accumulated much larger amounts of water and fat than did the minor workers. Difference in water accumulation increased as food supply increased. In spite of their difference in body weight, the residual amount of fat after starvation did not differ between the two subcastes. Although the amount of stored fat increased with colony size in both subcastes, the stored fat per dry weight of the major worker was significantly larger than that of the minor worker regardless of the colony size. When workers of a colony were starved, minor workers with a single major worker survived significantly longer than those without a major worker. In addition, about half the behavioral acts of major workers were regurgitation for minor workers. These results demonstrate that major workers ofC. nipponicus functioned as a trophic caste. On the basis of the results, quantitative relationships of storage abilities between the two worker subcastes are discussed.     

Expression of methyl farnesoate epoxidase (mfe) and juvenile hormone esterase (jhe) genes and their relation to social organization in the stingless bee Melipona interrupta (Hymenoptera: Apidae)

Social organization in highly eusocial bees relies upon two important processes: caste differentiation in female larvae, and age polyethism in adult workers. Juvenile Hormone (JH) is a key regulator of both processes. Here we investigated the expression of two genes involved in JH metabolism - mfe (biosynthesis) and jhe (degradation) - in the context of social organization in the stingless bee Melipona interrupta. We found evidence that the expression of mfe and jhe genes is related to changes in JH levels during late larval development, where caste determination occurs. Also, both mfe and jhe were upregulated when workers engage in intranidal tasks, but only jhe expression was downregulated at the transition from nursing to foraging activities. This relation is different than expected, considering recent reports of lower JH levels in foragers than nurses in the closely related species Melipona scutellaris. Our findings suggest that highly eusocial bees have different mechanisms to regulate JH and, thus, to maintain their level of social organization.     

Birth season glucocorticoids are related to the presence of infants in sifaka (Propithecus verreauxi)

The responses of plural breeding mammals to environmental stressors are little understood in free-ranging populations, but recent studies of singular breeders suggest that ecological factors and social milieu influence the variable physiological stress responses observed among individuals. Our previous studies examining faecal glucocorticoid (fGC)–behaviour interactions in plural breeding male sifaka (Propithecus verreauxi) show that fGC elevations coincide with specific dispersal events, particularly the eviction of subordinates by resident alpha males. This study examined the utility of fGC assays for assessing the stress responses of male sifaka to demographic changes in the population during the birth season. Analyses were based on 889 faecal samples collected over five birth seasons from 124 adult males residing in 55 different groups at Beza Mahafaly, Madagascar. Results show that fGC levels in males are unrelated to age, residence, group stability or rank, but are significantly and positively correlated with the presence of infants, annual elevations in weekly mean fGC concentrations in males paralleling increasing numbers of infants born annually in the population. These data are the first to show that in seasonal plural breeding species such as sifaka, elevated fGC in males reflects specific events related to reproduction rather than states or social context during the birth season.     

Worker connectivity: a review of the design of worker communication systems and their effects on task performance in insect societies

Within-group communication is a fundamental feature of animal societies. In order for animal groups to function as adaptive units, the members must share information such that group mates respond appropriately to each others’ behavior. One important function of social communication is to affect the allocation of tasks among group members. Theoretical and empirical findings on a diverse array of social insect taxa show that interactions among workers often play important roles in structuring division of labor. We review worker interactions that regulate division of labor in insect societies, which we refer to as worker connectivity. We present a framework for synthesizing and analyzing the study of worker connectivity. The widespread reliance on worker connectivity among eusocial insect taxa and the diversity of communicative mechanisms used to recruit workers suggest that the nature of worker interactions has evolved by natural selection. We suggest that colony-level selection acting on variation in task allocation has been an important force in the evolution of mechanisms for worker connectivity. We also propose that there are important links between individual worker cognition and task allocation at the colony level. Evolutionary changes in the cognitive aspects of worker responses may affect task allocation as much as changes in the communicative signals themselves. Received 9 December 2006; revised 18 May 2007; accepted 30 May 2007.     

Worker connectivity: a simulation model of variation in worker communication and its effects on task performance

We develop a simulation model of worker connectivity to analyze how variation in worker communication can influence task performance. The model generates predictions about how colony demography, worker communicative behavior, and worker cognition will affect the rate of recruitment of workers to a new task. The model explores some mechanisms for modulating the recruitment of workers. Under the conditions of our model– probabilistic interactions that lower worker’s response thresholds to tasks– worker recruitment follows a logistic growth pattern. The rate of recruiting workers increases exponentially toward an inflection point when 50% of the available force has been activated, then decreases toward the upper asymptote (all workers recruited). Many relevant features of colony design and worker behavior, including group size, probability of interacting, and strength of interaction effects on receivers, show a positive but decelerating effect on the rate of worker recruitment. We also identify features of worker cognition that can influence task recruitment, focusing on the time course of worker’s memories about previous interactions. Both learning (e.g., sensitization) and forgetting about previous interactions can influence the rate of worker recruitment to a task. The model suggests that worker cognition may be shaped by natural selection on task performance at the colony level. Forgetting about interactions may be especially costly, because it leads to unpredictable patterns of worker recruitment. We also show that social inhibition, when coupled with excitatory interactions, can effectively modulate worker recruitment at the colony level. Received 9 December 2006; revised 23 May 2007; accepted 30 May 2007.