Seasonality, division of labor, and dynamics of colony-level nutrient storage in the ant Pheidole morrisi

Nutritional provisioning is a critical component of life history strategies, and of particular interest in social insect colonies because of the role that division of labor plays in resource allocation. To explore the mechanisms that underlie colony nutritional strategies, I examined three populations of the ant Pheidole morrisi across a gradient of overwinter food scarcity over two seasons. P. morrisi colonies were found to employ amixed strategy of fat storage with regard to a longer overwinter period: members of both worker castes increase their percent-fat in a graded manner, while the proportion of a specialized subcaste of majors known as “repletes”, also increased within the colony. Geographic variation in other colony traits such as mean colony size, mean worker size, and minor/major caste ratio were also found, although not always in a manner clearly relating to fat storage. These results indicate that colony demography responds to seasonal fluctuations in food availability through behavioral alterations (increased fat stores and recruitment of replete workers) rather than physical alterations (changes in lean body sizes or caste ratio). The findings illustrate the dynamic role division of labor plays in the success of insect colonies confronting environmental variability. Received 9 May 2006; revised 19 July 2006; accepted 24 July 2006.     

Unbalanced biparental care during colony foundation in two subterranean termites

Parental care is a major component of reproduction in social organisms, particularly during the foundation steps. Because investment into parental care is often costly, each parent is predicted to maximize its fitness by providing less care than its partner. However, this sexual conflict is expected to be low in species with lifelong monogamy, because the fitness of each parent is typically tied to the other's input. Somewhat surprisingly, the outcomes of this tug‐of‐war between maternal and paternal investments have received important attention in vertebrate species, but remain less known in invertebrates. In this study, we investigated how queens and kings share their investment into parental care and other social interactions during colony foundation in two termites with lifelong monogamy: the invasive species Reticulitermes flavipes and the native species R. grassei. Behaviors of royal pairs were recorded during six months using a non‐invasive approach. Our results showed that queens and kings exhibit unbalanced investment in terms of grooming, antennation, trophallaxis, and vibration behavior. Moreover, both parents show behavioral differences toward their partner or their descendants. Our results also revealed differences among species, with R. flavipes exhibiting shorter periods of grooming and antennation toward eggs or partners. They also did more stomodeal trophallaxis and less vibration behavior. Overall, this study emphasizes that despite lifelong monogamy, the two parents are not equally involved in the measured forms of parental care and suggests that kings might be specialized in other tasks. It also indicates that males could play a central, yet poorly studied role in the evolution and maintenance of the eusocial organization.     

Age- and subcaste-related patterns of serotonergic immunoreactivity in the optic lobes of the ant Pheidole dentata

Serotonin, a biogenic amine known to be a neuromodulator of insect behavior, has recently been associated with age-related patterns of task performance in the ant Pheidole dentata. We identified worker age- and subcaste-related patterns of serotonergic activity within the optic lobes of the P. dentata brain to further examine its relationship to polyethism. We found strong immunoreactivity in the optic lobes of the brains of both minor and major workers. Serotonergic cell bodies in the optic lobes increased significantly in number as major and minor workers matured. Old major workers had greater numbers of serotonergic cell bodies than minors of a similar age. This age-related increase in serotonergic immunoreactivity, as well as the presence of diffuse serotonin networks in the mushroom bodies, antennal lobes, and central complex, occurs concomitantly with an increase in the size of worker task repertoires. Our results suggest that serotonin is associated with the development of the visual system, enabling the detection of task-related stimuli outside the nest, thus playing a significant role in worker behavioral development and colony-wide division of labor.     

How brood influences caste aggregation patterns in the dimorphic ant species Pheidole pallidula

Spatial distribution of ant workers and, notably their aggregation/segregation behaviour, is a key-element of the colony social organization contributing to the efficiency of task performance and division of labour. In polymorphic species, specialized worker castes notably differ in their intrinsic aggregation behaviour. In this context, knowing the preponderant role of minors in brood care, we investigate how a stimulus such as brood can influence the spatial patterns of Pheidole pallidula worker castes. In a homogeneous area without brood, it was shown that minors display only a low level of aggregation while majors form large clusters in the central area. Here we find out that these aggregation patterns of both minors and majors can be deeply influenced by the presence of brood. For minors, it nucleates or enhances the formation of a large stable cluster. Such high sensitivity of minors to brood stimuli fits well with their role as main brood tenders in the colony. For majors, interattraction between individuals still remains the prevailing aggregation factor while brood strongly influences the localisation of their cluster. We discuss how the balance between interattraction and sensitivity to environmental stimuli determines the mobility of each worker castes and, consequently, the availability of minors and majors to participate in everyday colony tasks. Moreover, we will evoke the functional value of majors’ cluster location close to the brood, namely with respect to social regulation of the colony caste ratio. Received 30 May 2005; revised 11 January 2006; accepted 13 January 2006.     

Regulation of Brood-Care Behavior in the Dimorphic Castes of the Ant Pheidole morrisi (Hymenoptera: Formicidae): Effects of Caste Ratio, Colony Size, and Colony Needs

This study examines the social stimuli that regulate brood-care behavior in the two physical castes of the ant Pheidole morrisi. By increasing the proportion of major workers in a colony, brood-care behavior could be induced in individuals of this caste, which do not normally care for brood. Minor and major worker brood-care rates increased with the proportion of majors in the colony or as the need for brood care increased. Changes in colony size did not significantly affect the rate of either minor or major brood care. Major workers began to care for brood when the caste ratio reached a critical threshold but did not appear to be as efficient at rearing larvae as minor workers, which normally perform this task. After a perturbation that skewed the caste ratio toward majors, minor workers increased their rate of brood care, apparently to compensate for the inefficiency of brood care provided by majors. These results suggest that caste plasticity involves a social mechanism of ldquo;coupled compensation that maintains the efficiency of labor by ensuring that tasks are completed.     

Differential gene expression between adult queens and workers in the ant Lasius niger

Ants and other social insects forming large societies are generally characterized by marked reproductive division of labour. Queens largely monopolize reproduction whereas workers have little reproductive potential. In addition, some social insect species show tremendous lifespan differences between the queen and worker caste. Remarkably, queens and workers are usually genotypically identical, meaning that any phenotypic differences between the two castes arise from caste-specific gene expression. Using a combination of differential display, microarrays and reverse Northern blots, we found 16 genes that were differentially expressed between adult queens and workers in the ant Lasius niger, a species with highly pronounced reproductive division of labour and a several-fold lifespan difference between queens and workers. RNA ligase mediated rapid amplification of cDNA ends (RLM-RACE) and gene walking were used to further characterize these genes. On the basis of the molecular function of their nearest homologues, three genes appear to be involved in reproductive division of labour. Another three genes, which were exclusively overexpressed in queens, are possibly involved in the maintenance and repair of the soma, a candidate mechanism for lifespan determination. In-depth functional analyses of these genes are now needed to reveal their exact role.     

Ovarian development and insulin-signaling pathways during reproductive differentiation in the queenless ponerine ant Diacamma sp.

In many social hymenopteran species, workers possess functional ovaries that are physiologically inactive in the presence of queens. We investigated the ovarian regulatory mechanism of workers and reproductives in a queenless ponerine ant, Diacamma sp., using histological and molecular techniques. In this ant, clear reproductive differentiation occurs via a highly sophisticated dominance behavioral interaction called “gemmae mutilation”. This clear and rapid bifurcation of reproductive physiology allows us to elucidate the detailed ovarian differentiation process. Histological characteristics of functional ovaries (fusomes and ring canals) were found in both workers and reproductives, suggesting that early oogenesis is not blocked in workers. Since insulin/insulin-like growth factor signaling (IIS) is known to control insect reproduction, orthologs of 2 positive IIS regulators, insulin receptor and serine-threonine kinase Akt (protein kinase B), were cloned in Diacamma (DiaInR, DiaAkt); their expression patterns during reproductive differentiation were examined by real-time quantitative polymerase chain reaction; DiaInR and DiaAkt were strongly expressed in the gasters of reproductives. Whole-mount in situ hybridization of ovaries indicated that DiaInR and DiaAkt were expressed in nurse cells, oocytes, and upper germarial regions of reproductives but not of workers. Our data suggest that the IIS pathway accounts for reproductive differentiation in late oogenesis.     

金毛弓背蚁行为谱与社会分工的研究

本研究在室内模拟自然蚁巢的结构和条件下,使用个体标记和直接观察法对一巢金毛弓背蚁Componotus tonkinus的行为类型和社会分工进行了研究。共34只来自同一巢穴的工蚁被标记。在持续一周的观察过程中对每只蚂蚁所执行的每种行为的频率进行了统计和聚类分析。结果表明：金毛弓背蚁可以区分出12种基本行为类型;该蚂蚁的成员大致可以分为5个功能组, 即繁殖（蚁后1个）、觅食（由10个工蚁组成,主要负责觅食）、巢穴内的维护及护育（由16个工蚁组成,主要负责巢穴的维修、清理及护育）、巢穴的防卫（包括3个工蚁,行巢穴防卫）及不活跃型（含5个工蚁）。     

Maternal and paternal care in the rock cavy,Kerodon rupestris,a South American hystricomorph rodent

The maternal and paternal behavior of Kerodon rupestris was examined. Quantitative differences between fathers and mothers and between mothers raising young with fathers present and with fathers absent were assessed. Growth rates of young raised by paired females and by lone females were compared. The male provides direct paternal care to the young by engaging in allogrooming, sniffing, and huddling. There is no significant difference between the sexes in the amount of contact promoting behavior given to the offspring, nor are the sexes significantly different in the amount of exploratory sniffing of the offspring. When the male is absent, the female spends a greater amount of time in contact with the young. Young raised by lone females gained significantly more weight than young raised by paired females. The suggestion that indirect paternal care acts to reduce female aggression to the young and relieve the energy expenditure burden of the female is discussed. The results indicate that social experience is gained at the expense of physical nurturing when the male is present.     

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.     

Specialization in policing behaviour among workers in the ant Pachycondyla inversa

Most animal societies are non-clonal and thus subject to conflicts. In social insects, conflict over male production can be resolved by worker policing, i.e. eating of worker-laid eggs (WLE) or aggression towards reproductive workers. All workers in a colony have an interest in policing behaviour being expressed, but there can be asymmetries among workers in performing the actual behaviour. Here, we show that workers of the ant Pachycondyla inversa specialize in policing behaviour. In two types of behavioural assays, workers developed their ovaries and laid eggs. In the first experiment, reproductive workers were introduced into queenright colonies. In the second experiment, WLE were introduced. By observing which individuals policed, we found that aggressive policing was highly skewed among workers that had opportunity to police, and that a similar tendency occurred in egg policing. None of the policing workers had active ovaries, so that policing did not incur a direct selfish benefit to the policer. This suggests that policing is subject to polyethism, just like other tasks in the colony. We discuss several hypotheses on the possible causes of this skew in policing tasks. This is the first non-primate example of specialization in policing tasks without direct selfish interests.     

Lunar influence on prey availability,diet shifts and niche overlap between Engraulidae larvae in tropical mangrove creeks

The influence of the lunar cycle on prey availability, diet shifts and overlap between larval Anchovia clupeoides and Cetengraulis edentulus was evaluated in mangrove creeks of the Goiana Estuary. Copepod eggs were highly abundant in the first and last quarter, at the full moon and zoea of Ucides cordatus (Ocypodidae) in the new moon. The Engraulidae larvae fed on microcrustaceans, algae and early planktonic stages of benthic organisms. The relative importance of prey varied according to prey availability in all moon phases. Larval diets were more even in the full and new moons, when the relative importance of calanoid copepods and zoeae of U. cordatus as food items increased (index of relative importance, >80% I_RI). Mangrove creeks were very important feeding grounds for engraulid larvae during spring tides. Larval diets were more diverse in the first and last‐quarter moon and included protozoeae of Caridean shrimp, larvae of Anomalocardia brasiliana (Veneridae), Isopoda, Gastropoda, ephippium of Daphnia sp. and nauplii of Cirripedia, Harpacticoidia and cyclopoid Copepoda. The last five items were not found in the creeks, suggesting feeding in the main channel. During neap tides, mangrove creeks were probably also used as refugia. These larvae are opportunistic and feed on highly available prey and both species feed on the same items, leading to high dietary overlap in all moon phases. The lunar cycle, which is related to the spring‐neap tidal cycle, was the major driver of quantitative and qualitative changes in feeding of engraulid larvae on a short time scale.     

Male and female contributions to provisioning rates of thin-billed prions, Pachyptila belcheri , in the South Atlantic

We recorded individual provisioning patterns of male and female thin-billed prions in the largest known colony on New Island (Falkland Islands, South Atlantic Ocean), to determine male and female contributions to provisioning rates and to compare them with data from their other main breeding site, on Kerguelen, in the Southern Indian Ocean. Both male and female birds from New Island undertook trips of 1–8 days’ duration (median 3 days), similar to those on Kerguelen, although we did not observe a clear distinction between long and short trips. Meal sizes increased with longer trips but did not differ between male birds and female birds. Thus, as on Kerguelen, male and female thin-billed prions on New Island contributed equally to chick provisioning. The proportion of short trips was comparable to those observed in a more favourable year, and was higher than those in a poor year, on Kerguelen. In order to avoid potential disturbance to the birds in the colony by frequent capture and handling, we used miniature radio-tags to record the presence of individuals in the colony and to evaluate the influence of transmitter load on the birds. Despite generally deteriorating conditions towards the end of the breeding season, chicks of tagged adults were fed normally, indicating that the method is adequate.     

Trophallaxis by temporal subcastes in the fire ant, Solenopsis invicta, in response to honey

ABSTRACT. Trophallactic behaviour of temporal subcastes in Solenopsis invicta Buren colonies was studied in two separate experiments. First, radiolabeled honey was presented to small colonies containing larvae, queens and marked workers; radioactivity in the head, thorax and abdomen of each ant was measured after 0.25, 1, 6, 12, 24, 48 and 72 h. The quantity of honey per subcaste was dependent on the total amount of honey collected. As more honey entered the colony, the quantity in foragers, queens and reserves increased more rapidly than that in nurses or larvae. The internal distribution of radioactivity in the head, thorax or abdomen indicated that differences between subcaste members in either the rate of food exchange or digestion existed. In a second experiment behavioural observations were made on marked workers in colonies before and after the presentation of honey. Reserves spent significantly more time engaged in trophallaxis than either foragers or nurses, both as active donors and active receivers. Based on number of encounters, nurses were more likely to receive honey while reserves and foragers were more likely to donate honey. The duration of encounters involving nurses tended to be shorter than those involving reserves or foragers.     

Extreme gender-based post-fledging brood division in the toc-toc

The possibility that parents of one sex may preferentially investin offspring of a certain sex raises profound evolutionary questionsabout the relative worth of sons and daughters to their mothersand fathers. Post-fledging brood division—in which eachparent feeds a different subset of offspring—has beenwell documented in birds. However, a lack of empirical evidencethat this may be based on offspring sex, combined with the theoreticaldifficulty of explaining such an interaction, has led researchersto consider a gender bias in post-fledging brood division highlyunlikely. Here we show that in the toc-toc, Foudia sechellarum,post-fledging brood division is extreme and determined by sex;where brood composition allows, male parents exclusively provisionmale fledglings, whereas female parents provision female fledglings.This is the first study to provide unambiguous evidence, basedon molecular sexing, that sex-biased post-fledging brood divisioncan occur in birds. Male and female parents provisioned at thesame rate and neither offspring nor parent survival appearedto be affected by the sex of the parent or offspring, respectively.The current hypotheses predicting advantages for brood divisionand preferential care for one specific type of offspring arediscussed in the light of our results.     

Lay eggs, live longer: division of labor and life span in a clonal ant species

Abstract Due to a trade-off between reproduction and life span, highly fertile individuals often live shorter lives than nonreproductive conspecifics. Perennial eusocial insects are exceptional in that reproductive queens live considerably longer than the nonreproductive workers. The two female castes may differ strongly in morphology, ontogeny, physiology, diet, behavior, and mating, and all these differences could be responsible for life span differences. In the ponerine ant Platythyrea punctata , morphological and ontogenetic caste differences do not exist. Instead, all workers are capable of producing diploid offspring through thelytokous parthenogenesis, and colonies are essentially clones. Here, we show that reproductives live significantly longer than nonreproductive workers. Reproductives stay in the nest during their whole life, whereas nonreproductives switch from intranidal tasks to foraging when they get older. Different work load and different hormone titers might proximately underlie the different life span of reproductives and nonreproductives in this ant.     

Behaviour of worker subcastes in the fire ant, Solenopsis invicta, in response to proteinaceous food

ABSTRACT. The effects of division of labour on response behaviour to food in the red imported fire ant, Solenopsis invicta Buren, were examined to determine if caste members differ in amount of food taken, in rate of food transfer, or in internal distribution of food; and to see if food availability, time, or temporal subcaste pairing affect feeding behaviour. To measure differences in behaviour we fed radioiodinated albumin mixed with egg yolk to colonies containing larvae, queens, and (a) foragers and nurses, or (b) foragers and reserves, or (c) nurses and reserves. Samples were taken over a 72-h period and radioactivity in the head, thorax and abdomen of each worker was determined. There were significant differences between nurses, foragers and reserves in quantity of food consumed, rate of transfer, and internal distribution of radioactivity. These differences were related to their respective roles of foraging, food storage and transfer, and brood tending. The quantity of food taken per subcaste was dependent on the total amount of food in the colony, with transfer rates differing between subcastes as the quantity of food in the colony increased. The rate at which protein was transferred between subcastes was slower in the reserves than that in either foragers or nurses. Therefore, reserves may serve as a temporary store of protein for the colony.     

Dietary self-selection for vitamins and lipid by larvae of the corn earworm, Heliothis zea

Last instar larvae of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), require lipid and certain vitamins in their diet in order to complete larval development. When experimental larvae were offered two nutritionally incomplete diets, each lacking a different one of the requirements, they invariably ate from both diets, self-selecting a mixture that was nutritionally superior to either diet alone.

---

Résumé Les chenilles de dernier stade d' H. zea (Boddie) (Lep.:Noctuidae) ont besoin de lipides et de certaines vitamines dans leur régime alimentaire, probablement parce qu'elles n'en contiennent pas assez provenant des stades précédents. Quand deux régimes incomplete ont été fournis aux chenilles (chacun privé différemment de l'un de ces consituants: lipide, chlorure de choline ou un ensemble de vitamines), elles ont consommé systématiquement des deux régimes et autosélectionné un aliment de qualité supèrieure à celle de chaque régime séparément. D'un autre côté, les chenilles témoins à qui on a offert deux régimes identiques et nutritionnellement complets, ont choisi apparemment leur aliment au hasard, et presque la moitié d'entre elles ont consommé exclusivement on presque exclusivement l'un des régimes, tandis que l'autre moitié a choise exclusivement or presque exclusivement l'autre.

     

Association between the African lycaenid,Anthene usamba,and an obligate acacia ant,Crematogaster mimosae

The African lycaenid butterfly, Anthene usamba, is an obligate myrmecophile of the acacia ant, Crematogaster mimosae. Female butterflies use the presence of C. mimosae as an oviposition cue. The eggs are laid on the foliage and young branches of the host plant, Acacia drepanolobium. Larvae shelter in the swollen thorns (domatia) of the host tree, where they live in close association with the acacia ants, and each larva occupies a domatium singly. Anthene usamba are tended by ants that feed from the dorsal nectary organ at regular intervals. Larvae also possess tentacle organs flanking the dorsal nectary organ and appear to signal to ants by everting these structures. Larvae were observed to spend most of their time within the domatia. Stable isotope analysis of matched host plant–ant–butterfly samples revealed that Anthene usamba are δ¹⁵N enriched relative to the ants with which they associate. These data, based on the increase in δ¹⁵N through trophic levels, indicate that the caterpillars of these butterflies are aphytophagous and either exploit the ant brood of C. mimosae within the domatia, or are fed mouth to mouth by adult workers via trophallaxis. This is the first documented case of aphytophagy in African Anthene. Pupation occurs inside the domatium and the imago emerges and departs via the hole chewed by the larva. The adult females remain closely associated with their natal patch of trees, whereas males disperse more widely across the acacia savannah. Females prefer to oviposit on trees with the specific host ant, C. mimosae, an aggressive obligate mutualist, and avoid neighbouring trees with other ant species. Adult butterflies are active during most months of the year, and there are at least two to three generations each year. Observations made over a 5‐year period indicate that a number of different lycaenid species utilize ant‐acacias in East Africa, and these observations are summarized, together with comparisons from the literature. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013 , 109 , 302–312.