Brood Care Research Articles

Social regulation of insulin signaling and the evolution of eusociality in ants.

Queens and workers of eusocial Hymenoptera are considered homologous to the reproductive and brood care phases of an ancestral subsocial life cycle. However, the molecular mechanisms underlying the evolution of reproductive division of labor remain obscure. Using a brain transcriptomics screen, we identified a single gene, insulin-like peptide 2 (ilp2), which is always up-regulated in ant reproductives, likely because they are better nourished than their nonreproductive nestmates. In clonal raider ants (Ooceraea biroi), larval signals inhibit adult reproduction by suppressing ilp2, thus producing a colony reproductive cycle reminiscent of ancestral subsociality. However, increasing ILP2 peptide levels overrides larval suppression, thereby breaking the colony cycle and inducing a stable division of labor. These findings suggest a simple model for the origin of ant eusociality via nutritionally determined reproductive asymmetries potentially amplified by larval signals.

The evolution of sociality in termites from cockroaches: A taxonomic and phylogenetic perspective.

Despite multiple studies and advances, sociality still puzzles evolutionary biologists in numerous ways, which might be partly addressed with the advent of sociogenomics. In insects, the majority of sociogenomic studies deal with Hymenoptera, one of the two groups that evolved eusociality with termites. But, to fully grasp the evolution of sociality, studies must obviously not restrict to eusocial lineages. Multiple kinds of social system transitions have been recorded and they all bring complementary insights. For instance, cockroaches, the closest relatives to termites, display a wide range of social interactions and evolved convergently subsocial behaviors (i.e., brood care). In this context, we emphasize the need for natural history, taxonomic, and phylogenetic studies. Natural history studies provide the foundations on which building hypotheses, whereas taxonomy provides the taxa to sample to test these hypotheses, and phylogenetics brings the historical framework necessary to test evolutionary scenarios of sociality evolution.

Phylogenomic Evidence Overturns Current Conceptions of Social Evolution in Wasps (Vespidae).

The hypothesis that eusociality originated once in Vespidae has shaped interpretation of social evolution for decades and has driven the supposition that preimaginal morphophysiological differences between castes were absent at the outset of eusociality. Many researchers also consider casteless nest-sharing an antecedent to eusociality. Together, these ideas endorse a stepwise progression of social evolution in wasps (solitary → casteless nest-sharing → eusociality with rudimentary behavioral castes → eusociality with preimaginal caste-biasing (PCB) → morphologically differentiated castes). Here, we infer the phylogeny of Vespidae using sequence data generated via anchored hybrid enrichment from 378 loci across 136 vespid species and perform ancestral state reconstructions to test whether rudimentary and monomorphic castes characterized the initial stages of eusocial evolution. Our results reject the single origin of eusociality hypothesis, contest the supposition that eusociality emerged from a casteless nest-sharing ancestor, and suggest that eusociality in Polistinae + Vespinae began with castes having morphological differences. An abrupt appearance of castes with ontogenetically established morphophysiological differences conflicts with the current conception of stepwise social evolution and suggests that the climb up the ladder of sociality does not occur through sequential mutation. Phenotypic plasticity and standing genetic variation could explain how cooperative brood care evolved in concert with nest-sharing and how morphologically dissimilar castes arose without a rudimentary intermediate. Furthermore, PCB at the outset of eusociality implicates a subsocial route to eusociality in Polistinae + Vespinae, emphasizing the role of mother–daughter interactions and subfertility (i.e. the cost component of kin selection) in the origin of workers.

Vitellogenin-like A-associated shifts in social cue responsiveness regulate behavioral task specialization in an ant.

Division of labor and task specialization explain the success of human and insect societies. Social insect colonies are characterized by division of labor, with workers specializing in brood care early and foraging later in life. Theory posits that this task switching requires shifts in responsiveness to task-related cues, yet experimental evidence is weak. Here, we show that a Vitellogenin (Vg) ortholog identified in an RNAseq study on the ant T. longispinosus is involved in this process: using phylogenetic analyses of Vg and Vg-like genes, we firstly show that this candidate gene does not cluster with the intensively studied honey bee Vg but falls into a separate Vg-like A cluster. Secondly, an experimental knockdown of Vg-like A in the fat body caused a reduction in brood care and an increase in nestmate care in young ant workers. Nestmate care is normally exhibited by older workers. We demonstrate experimentally that this task switch is at least partly based on Vg-like A–associated shifts in responsiveness from brood to worker cues. We thus reveal a novel mechanism leading to early behavioral maturation via changes in social cue responsiveness mediated by Vg-like A and associated pathways, which proximately play a role in regulating division of labor.

Efektifitas Perawatan Metode Kangguru (PMK) dan Terapi Murottal terhadap Peningkatan Berat Badan dan Suhu pada Bayi BBLR

Infants with low birth weight (LBW) are at high risk of health problems. LBW infants require special care to minimize the risk of infant mortality. LBW treatments apart from the treatment in the incubator and kangaroo mother care (KMC). This study was to determine the increase in body weight and body temperature through murottal therapy as one of the stimulations of nursing LBW infants. The research design was quasi-experimental with pretest control group design. The study was conducted at Dr. H Abdul Moeloek Hospital (RSUAM) Bandar Lampung. The population of the study was all babies of LBW treated in the RSUAM Perinatology Room. Sampling technique was using probability sampling. The sample size was determined using different hypothesis test formula. The results showed there were differences in weight and body temperature increase on days II, III and IV in the intervention group. This study recommends the use of morottal therapy in the treatment of LBW with KMC. Because therapy morottal system works similar to therapy music that causes a sense of comfort and improves sleep patterns baby.

Plover parents care more for young of the opposite sex

Within some socially monogamous species, the relative contribution of care provided by each parent varies substantially, from uniparental to equitable biparental care. The provision of care is influenced by its costs and benefits, which may differ between parents (leading to inter-parental “conflict”) and are expected to change in relation to the needs of young (which vary with age) and potentially to traits such as their sex. If the fitness benefits to parents differ with the sex of offspring, parents may adjust their investment in young of different sexes to optimize their own fitness. We radio-tracked 42 Red-capped Plover Charadrius ruficapillus broods and found that, at least diurnally, females cared for the brood for the first half of brood-rearing, while gradually reducing care. Males contributed little diurnal care early in brood-rearing, then increased care, taking over from females as young approached independence. The sex-ratio of the brood influenced the division of care between parents; male parents attended the brood more when there were greater proportions of female chicks, whereas female parents attended the brood more when there were a greater proportion of male chicks. This is apparently the first recorded case in a precocial bird where each parents’ investment in brood care is influenced by the brood sex-ratio. Our results defy unambiguous explanation.

Changes in maternal investment with climate moderate social behaviour in a facultatively social bee

Facultatively social species allow for empirical examination of the factors underlying evolutionary transitions between primitive and complex forms of sociality. Variation in climate along altitudinal and latitudinal gradients often influences social behaviour in these species. This facultative sociality has been well-documented in the ground-nesting bees, which have consistently greater social complexity in warmer, lower latitudes and altitudes. However, the potential combined effects of nesting biology and local climatic condition on social behaviour remain largely overlooked. To address this, we performed a long-term study on the facultatively social stem-nesting bee, Ceratina australensis, by assessing populations in three distinct climate zones over the course of three consecutive years. We compared nesting strategies across populations and found that the frequency of social nesting was stable with latitudinal changes in climate. Further, offspring survival was high for both solitary and social colonies, despite large fluctuations in the rate of parasitism across years, indicating that both nesting strategies are successful. However, maternal brood investment, which can strongly affect the social environment of a colony, was observed to fluctuate with climatic variation. Most notably, mothers produced small offspring of both sexes in the hottest driest years. Across all populations, social females were slightly larger than solitary females on average. As such, changes in maternal investment in response to annual and latitudinal climatic variation may be one of the many factors that ultimately determine that rate of social nesting. Variation in nest composition and climatic condition thus suggest that reproductive strategies in facultatively social stem-nesting bees may be influenced by climate constraints on maternal investment. Climate alters the expression of social behaviour in many arthropod species but the relationship between climate and behaviour can vary broadly with taxa. For facultatively social species, theory generally predicts that sociality will increase in warmer climates, as longer brood rearing seasons provide opportunities for overlapping generations and cooperative brood care. However, little is known of the effect of compounding life-history factors, such as nesting biology. Here, we present a 3-year study on an incipiently social stem-nesting bee, Ceratina australensis. We find that the rate of sociality is stable across a broad latitudinal and climatic gradient, and we discuss the idea that nesting biology could potentially temper behavioural responses to climate. However, foundresses may alter their offspring investment in response to both annual weather and regional climatic variation, and this responsiveness could influence colony social behaviour.

The Circadian Clock of the Ant Camponotus floridanus Is Localized in Dorsal and Lateral Neurons of the Brain.

The circadian clock of social insects has become a focal point of interest for research, as social insects show complex forms of timed behavior and organization within their colonies. These behaviors include brood care, nest maintenance, foraging, swarming, defense, and many other tasks, of which several require social synchronization and accurate timing. Ants of the genus Camponotus have been shown to display a variety of daily timed behaviors such as the emergence of males from the nest, foraging, and relocation of brood. Nevertheless, circadian rhythms of isolated individuals have been studied in few ant species, and the circadian clock network in the brain that governs such behaviors remains completely uncharacterized. Here we show that isolated minor workers of Camponotus floridanus exhibit temperature overcompensated free-running locomotor activity rhythms under constant darkness. Under light-dark cycles, most animals are active during day and night, with a slight preference for the night. On the neurobiological level, we show that distinct cell groups in the lateral and dorsal brain of minor workers of C. floridanus are immunostained with an antibody against the clock protein Period (PER) and a lateral group additionally with an antibody against the neuropeptide pigment-dispersing factor (PDF). PER abundance oscillates in a daily manner, and PDF-positive neurites invade most parts of the brain, suggesting that the PER/PDF-positive neurons are bona fide clock neurons that transfer rhythmic signals into the relevant brain areas controlling rhythmic behavior.

Helpers increase food abundance in the territory of a cooperatively breeding fish

In cooperatively breeding or eusocial animals, increasing resources such as food is a major task of brood care helpers or workers. While such food acquisition has been shown in several animal taxa, evidence is absent in fishes. Here, we provide the first evidence of increased food abundance caused by helpers in a cooperatively breeding fish. Helpers of the cichlid Neolamprologus obscurus excavate cavities by digging sand from under stones, which serve as shelter for the group members. We test whether these cavities additionally increase the abundance of benthic invertebrates in the territory. Stomach content analyses of wild-caught fish revealed that benthic invertebrates pose the main food resource of N. obscurus. Experimental assessments of daily benthic invertebrate immigration into artificial cavities demonstrate a significant increase in invertebrate prey abundance according to the size of the excavated stone area. Finally, by applying correlational and experimental approaches in the field, we show that helpers play a crucial role in the maintenance of the excavated cavities. In combination, these results demonstrate that helpers increase the abundance of benthic invertebrates inside the territory of breeders in N. obscurus. Our results provide the first evidence of increased food abundance through helpers in fishes. Such foraging system may resemble those described in other species living in highly social groups, and appears to be a ubiquitous mechanism underpinning the maintenance of complex societies in animals. Evidence of elaborate food acquisition such as farming or trap building is only known from a limited number of animal taxa. The cichlid Neolamprologus obscurus is a highly social fish, where all group members create and maintain cavities under stones, which serve as shelters. These fish feed on benthic invertebrates, which hide inside such cavities during daytime. We show that the cavities of N. obscurus additionally increase the food abundance in their territory. Behavioral observation and experiment in the field revealed that group members increase the excavated cavities in their territory, and food abundance increases according to the size of excavated cavities. Our results provide the first evidence of food acquisition by group members in fishes.

Mouthpart dimorphism in male and female wasps of Vespula vulgaris and Vespula germanica (Vespidae, Hymenoptera)

Social wasps perform a variety of tasks with their mouthparts. Female workers use them to feed on carbohydrate-rich fluids, to build nests by collecting wood fibers and forming paper, to hunt and manipulate insect prey for feeding larvae as well as for brood care. Since male wasps neither feed on insects nor participate in nest building, sex-specific differences in mouthpart morphology are expected. Despite these different applications, general mouthpart morphology of male and female wasps from the genus Vespula was similar. However, males possessed significantly shorter mandibles with fewer teeth than females. Furthermore, the adductor muscles of the mandibles were distinctly smaller in males than in females. Male wasps showed a higher number of sensilla on the mandibles and the labial palpi. Mouthpart dimorphism and functional morphology of fluid uptake are discussed.

Why are males more attractive after brood care? Proximate causes of enhanced sex pheromone emission in a burying beetle

AbstractRecent studies demonstrate that pheromones can be costly to produce and emit and, therefore, the types and quantities that they express are likely to covary with individual condition. Previous experiments reveal that, when given the opportunity to breed and care for young, male burying beetles Nicrophorus vespilloides go on to produce a higher amount of their sex pheromone and attract more females than control males that do not exhibit parental care. This finding is surprising because parental care is usually assumed to be energetically costly, reducing the future capacity to invest in sexual signalling. However, burying beetles reproduce on dead vertebrates and the carrion meal might enable males to acquire resources that can subsequently be allocated to pheromone signalling. Alternatively, males might accumulate pheromone precursors because they do not emit their sex pheromone during brood care. To shed light on the mechanisms of enhanced pheromone emission after brood care, in the present study, we test the effect of diet quality, social condition during care (biparental versus uniparental care) and an experimentally enforced calling pause on subsequent male pheromone emission, body weight and energy storage components. The experimentally enforced calling pause and social condition during brood care demonstrate no impact on pheromone quantity. However, the results of the present study suggest that the vertebrate carrion meal during brood care partly explains enhanced pheromone release after care. Unravelling the biosynthetic pathways of the pheromone components and analyzing the impact of potential microbial symbionts on pheromone production represents a fruitful avenue for future research.

Interventions to prevent hypothermia at birth in preterm and/or low birth weight infants.

Interventions to prevent hypothermia at birth in preterm and/or low birth weight infants.

Maternal care by Early Cretaceous cockroaches

Most cockroaches produce a special capsular structure, the ootheca, to enclose eggs for protection and maternal brood care. However, the origin and early evolution of the cockroach ootheca is poorly known, attributable to a lack of fossil evidence from the Mesozoic. Here, we report the earliest known cockroach fossil possessing an internally partitioned ootheca: Piniblattella yixianensis Gao, Shih & Ren sp. nov. is described from the mid Early Cretaceous Yixian Formation of China. The ootheca of this species measures 46–62% of its body length, contains 60–70 eggs, and exhibits the oviparity B reproduction mode, similar to that of the extant ectobiid and blattid cockroaches. In conjunction with several isolated ootheca specimens preserved in the mid-Cretaceous Myanmar amber (Burmite), we infer that the cockroach reproductive mode using the complete oothecate structure occurred during or before the mid Early Cretaceous. Maternal care associated with the oothecate condition in these Cretaceous cockroaches added a unique and major life-history trait, later resulting in true viviparity. This new life-history trait providing maternal protection and care may have been a key factor in the subsequent evolutionary diversification and ecological expansion of modern cockroach lineages.http://zoobank.org/urn:lsid:zoobank.org:pub:588C91F4-FB8D-43E5-8C2D-86D50393B851

Kangaroo mother care and its physiological effects in low birth weight and preterm neonates

Objectives: The present study was undertaken to study and compare anthropometry and physiological parameters in preterm and low birth weight infants during conventional care and Kangaroo Mother Care (KMC). Methods: This prospective case–control study was conducted in the department of pediatrics of a tertiary care hospital in central India from June 2016 to September 2017. Study on KMC was conducted on 200 newborns weighing <2.0 kg meeting study criteria with similar baseline characteristics. With minimum duration of 6 hrs/day where as controls given incubator and cot care. Parameters were studied until discharge criteriawere meet. The primary outcome variable was “weight gain and anthropometry” and secondary measures included breastfeeding and duration of hospitalization and physiological parameters. Results: KMC group showed a significant decrease in the duration of hospital stay (11.69±5.14 vs. 18.5±1.8 days) (p=0.0001) and better rate of breastfeeding (66% vs. 21%) as compared to control group. KMC group also shows higher weight gain (19.7±6.3 g/day) in comparison to control (11.4±3.3 g/day), (p=0.001). There was a mean increase of 0.7 cm/week in head circumference in KMC group and 0.4 cm/week in the control group (p=0.000). The mean increase in length was 0.89 cm/week in KMC group and 0.45 cm/week in control group (p=0.0001). The mean heart rate and respiratory rate were similar in both the groups (p=0.498 and p=0.555, respectively). The mean temperature difference was significant and shows that KMC group has a higher temperature of 0.4°F (p=0.001). In other physiological parameters, no episodes of apnea and hypoglycemia were present in KMC group as compared to 4 episode of hypoglycemia and 3 episodes of apnea in the control group. Conclusion: Newborns receiving KMC showed better growth parameters as compared to the routine care along with a better breastfeeding rate. Better thermal control and decreased episodes of hypoglycaemia & apnea in KMC group.

Oxidative physiology of reproduction in a passerine bird: a field experiment

Organisms face resource trade-offs to support their parental effort and survival. The life-history oxidative stress hypothesis predicts that an individual’s redox state modulates the trade-off between current and residual fitness, but this has seldom been tested experimentally in non-captive organisms. In this study, we manipulated the brood size in breeding pairs of barn swallows (Hirundo rustica) and found that females tending enlarged broods had increased levels of plasma oxidative damage (malondialdehyde concentration). This effect, however, was not accompanied by either a depletion, or defensive upregulation in antioxidants (glutathione, total antioxidant capacity, and uric acid) that may explain the increase in oxidative damage. Brood size manipulation and the level of plasma oxidative damage during brood rearing are not translated into decreased annual return rate, which does not support the oxidative stress hypothesis of life-history trade-offs. On the contrary, we found that female’s oxidative damage and total glutathione levels, an important intracellular non-enzymatic antioxidant measured at hatching decreased and correlated positively, respectively with annual return rate, suggesting that oxidative condition at hatching might be a more important contributor to fitness than the oxidative physiology measured during chick rearing. We also show that individual traits and ecological factors, such as the timing of breeding and the abundance of blood-sucking nest mites, correlated with the redox state of males and females during brood care. Oxidative stress is one of the most important physiological costs of reproduction and thus a key modulator of life-history trade-offs. In this study, we manipulated reproductive effort in breeding pairs of barn swallows and found that females tending enlarged broods had increased levels of plasma oxidative damage. This effect, however, was not accompanied by either a depletion or upregulation in antioxidants that may explain the increase in oxidative damage. We found that female’s oxidative damage and total glutathione levels measured at hatching decreased and correlated positively, respectively with annual return rate, suggesting that oxidative condition at hatching might be an important contributor to fitness. Brood size manipulation and the increased levels of plasma oxidative damage are not translated into decreased annual return rate; thus, our results support the hypothesis that reproductive effort has a transient effect on oxidative physiology.

Lowering prolactin reduces post-hatch parental care in male and female zebra finches (Taeniopygia guttata)

Parental care is a widespread phenomenon observed in many diverse taxa. Neuroendocrine systems have long been thought to play an important role in stimulating the onset of parental behavior. In most birds with altricial young, circulating prolactin (PRL) levels are low during non-breeding times and significantly increase during late incubation and early post-hatch chick care. Because of this pattern, PRL has been suggested to be involved in the initiation of parental care in birds, but rarely has this hypothesis been causally tested. To begin testing the hypothesis, we inhibited the release of endogenous PRL with bromocriptine (BR) on the 3days prior to hatching in incubating parents and the first 2days of post-hatch care, when PRL was found to be highest in zebra finches. Nest temperatures were recorded during all 5days and parental behavior was recorded on days 1–2 post-hatch. In addition to hormonal systems, reproductive experience may also influence parental care; therefore, we tested age-matched inexperienced and experienced pairs in each group. BR either eliminated or drastically reduced chick brooding and feeding behavior, resulting in decreased nest temperatures on days 1 and 2 post-hatch. Experienced control birds fed chicks more than inexperienced birds and control females fed more than males. Chick feeding behavior was positively correlated in control male-female pairs, but not in BR pairs. This is one of the few causal studies to demonstrate that PRL is necessary for post-hatch care in a biparental songbird, and is the first to show this effect in zebra finches.

Interactions between leaf-cutter ants and fungus garden: Effects of division of labor, age polyethism, and egg cannibalism

Division of labor (DOL), age polyethism, and egg cannibalism all play roles in shaping colony-level population dynamics in social insect colonies. The ways in which these mechanisms interact with one another to shape population dynamics is not currently understood. In this study, we examine how these mechanisms influence population dynamics in colonies of fungus-gardening leaf-cutter ants by developing and studying two sets of models: (1) We study age polyethism contribution to the dynamics of this multi-species interaction model which incorporates mechanisms of DOL; (2) We explore effects of egg cannibalism in colony dynamics and understand how to model such social conflict behavior realistically using different functional responses. Our results suggest that: (a) Age polyethism is important to keep stable population dynamics. (b) Large maturation rate and mortality rate of inside workers induce colony death. (c) Small enough egg cannibalism rate benefits adult worker ant’s growth and (or) development, large proportion of ants performing a given task can promote colony survival, and too large egg cannibalism rate can lead to colony’s death. (d) Increasing energy invested on brood care and (or) the conversion rate between fungus and ants could induce oscillatory dynamics in models with cannibalism.

The effect of skin‐to‐skin care on cerebral oxygenation during nasogastric feeding of preterm infants

To describe cerebral oxygenation during gavage feeding of preterm infants during incubator and skin-to-skin care. Further analysis of data from two crossover studies comparing cerebral oxygenation, heart rate and oxygen saturation during skin-to-skin care with incubator care. Data were analysed in three epochs; 10 minutes prefeed, during-feed and 10 minutes postfeed. Measurements from infants fed during incubator care were compared with those obtained during skin-to-skin care. In 39 infants [median (IQR) 27.8 (26.1-30.0) weeks' gestation], there was no difference in cerebral oxygenation between pre-, during- and postfeed. Heart rate increased by three beats per minute postfeed compared with during-feed. Twenty infants received two gavage feeds, one feed in the incubator and another during skin-to-skin care. There was no difference in cerebral oxygenation and heart rate; peripheral oxygen saturation decreased by 3% during feeding whilst skin-to-skin care compared with feeding in the incubator. Cerebral oxygenation remained stable before, during and after gavage feeding in an incubator and during skin-to-skin care. The small decrease in oxygen saturation whilst receiving gavage feeding during skin-to-skin care is unlikely to be clinically important, providing reassurance that preterm infants maintain physiological stability during skin-to-skin care.

Effects of neonicotinoid imidacloprid exposure on bumble bee (Hymenoptera: Apidae) queen survival and nest initiation.

Neonicotinoids are highly toxic to insects and may systemically translocate to nectar and pollen of plants where foraging bees may become exposed. Exposure to neonicotinoids can induce detrimental sublethal effects on individual and colonies of bees and may have long-term impacts, such as impaired foraging, reduced longevity, and reduced brood care or production. Less well-studied are the potential effects on queen bumble bees that may become exposed while foraging in the spring during colony initiation. This study assessed queen survival and nest founding in caged bumble bees [Bombus impatiens (Cresson) (Hymenoptera: Apidae)] after chronic (18-d) dietary exposure of imidacloprid in syrup (1, 5, 10, and 25 ppb) and pollen (0.3, 1.7, 3.3, and 8.3 ppb), paired respectively. Here we show some mortality in queens exposed at all doses even as low as 1 ppb, and, compared with untreated queens, significantly reduced survival of treated queens at the two highest doses. Queens that survived initial imidacloprid exposure commenced nest initiation; however, they exhibited dose-dependent delay in egg-laying and emergence of worker brood. Furthermore, imidacloprid treatment affected other parameters such as nest and queen weight. This study is the first to show direct impacts of imidacloprid at field-relevant levels on individual B. impatiens queen survival and nest founding, indicating that bumble bee queens are particularly sensitive to neonicotinoids when directly exposed. This study also helps focus pesticide risk mitigation efforts and highlights the importance of reducing exposure rates in the early spring when bumble bee queens, and other wild bees are foraging and initiating nests.

Vertical organization of the division of labor within nests of the Florida harvester ant, Pogonomyrmex badius.

In the Florida harvester ant, Pogonomyrmex badius, foragers occur only in the top 15 cm of the nest, whereas brood and brood-care workers reside mostly in the deepest regions, yet the food and seeds foragers collect must be transported downward 30 to 80 cm to seed chambers and up to 2 m to brood chambers. Using mark-recapture techniques with fluorescent printer's ink, we identified a class of workers that ranges widely within the vertical structure of the nest, rapidly moving materials dropped by foragers in the upper regions downward, and excavated soil from deeper upward. Within the nest, only 5% of foragers were recovered below 20 cm depth, but about 30% of transfer workers and 82% of unmarked workers were found there. Below 70 cm depth, 90% of workers were unmarked, and were probably involved mostly in brood care. During the summer, the transfer workers comprise about a quarter of the nest population, while foragers make up about 40%. Workers marked as transfer workers later appear as foragers, while those marked as foragers die and disappear from the foraging population, suggesting that transfer workers are younger, and age into foraging. The importance of these findings for laboratory studies of division of labor are discussed. The efficient allocation of labor is a key component of superorganismal fitness.