Shifting foraging strategies in colonies of the social wasp Polybia occidentalis (Hymenoptera, Vespidae)

Social insect colonies can be expected to forage at rates that maximize colony fitness. Foraging at higher rates would increase the rate of worker production, but decrease adult survival. This trade-off has particular significance during the founding stage, when adults lost are not replaced. Prior work has shown that independent-founding wasps rear the first workers rapidly by foraging at high rates. Foraging rates decrease after those individuals pupate, presumably reducing the risk of foundress death. In the swarm-founding wasps, colony-founding units have many workers, making colony death by forager attrition less likely. Do swarm-founding wasps show similar shifts in foraging rates during the founding stage? We measured foraging rates of the swarm-founding wasp, Polybia occidentalis at four stages of colony development. At each stage, foraging rates correlated with the number of larvae present, which, in the founding stages, correlated with the number of cells in the new nest. Thus, foraging rates appear to be demand-driven, with the level of demand in the founding stage set by the size of nest that is constructed. During the founding stage, foraging rates per larva were high initially, suggesting that colonies minimize the development times of larvae early in the founding stage. Later in the stage, foraging rates decreased, which would reduce worker mortality until new workers eclose. This pattern is similar to that shown for independent-founding wasps and likely results from conflicting pressures to maximize colony growth and minimize the risk of colony death by forager attrition.     

Testing the limits of social resilience in ant colonies

Social resilience is the ability of Leptothorax ant colonies to re-assemble after dissociation, as caused, for example, by an emigration to a new nest site. Through social resilience individual workers re-adopt their spatial positions relative to one another and resume their tasks without any time being wasted in worker respecialisation. Social resilience can explain how an efficient division of labour can be maintained throughout the trials and tribulations of colony ontogeny including the, often substantial, period after the queen dies when the ability to conserve worker social relationships may be essential for efficiency to be maintained. The mechanism underlying social resilience is, therefore, expected to be robust even in the absence of many of the colony’s components, such as the queen, the brood and even a large proportion of the workers. Such losses are likely, given the ecology of this genus. Using sociotomy experiments, we found that social resilience can occur in the absence of the queen. Furthermore, the spatial component of social resilience can occur even when the queen, the brood, as well as a large proportion of the workers, are all absent simultaneously and hence many of the tasks are missing. We conclude, therefore, that social resilience is indeed robust. This does not, however, preclude worker flexibility in response to changes in task supply and demand. We propose a possible sorting mechanism based on worker mobility levels which might explain the robustness underlying this phenomenon. Received: 25 October 1999 / Accepted: 1 April 2000     

Optimal biomass allocation in heterogeneous environments in a clonal plant—Spatial division of labor

When interconnected ramets of clonal plants are growing in heterogeneous environments, ramets may specialize to uptake locally abundant resources rather than scarce resources. This biomass allocation pattern may result in more efficient sharing of resources through physiological integration and an overall benefit to the plants (spatial division of labor; DoL).     

Prior residency as a key determinant of social dominance in the willow tit (Parus montanus)

Summary We studied how age, body size and prior residency affected social dominance in the willow tit (Parus montanus) groups. The contribution of each variable was experimentally tested in unisexual two-bird trials, in which the birds were matched for all variables except the one studied. Large birds were dominant over smaller ones (Fig. 1). The effect of body size was more prominent in males than in females. Age had no influence on dominance. Residents became dominant more often than newcomers (Fig. 2). Adulthood or larger body size did not override the advantage of prior residency (Fig. 2). Therefore, the proximate reason for the age-dependent dominance seen in natural willow tit flocks is most likely the prior residency advantage of the adults. Factors connected with fighting ability (body size and age) seem to be less important than the time of establishment of rank, which may reflect the importance of resource value differences between residents and newcomers in this context. The advantage of residency might make it advantageous to be a member of a flock even as a subordinate, rather than being solitary.     

The functional organization of resin work in honeybee colonies

Resin is an important building material in the nests of honeybees, but little is known about how it is handled within the nest and how its collection is controlled. We studied the functional organization of resin work to better understand how a colony adaptively controls its intake of resin. Two hypotheses have been proposed for how resin collectors stay informed of the need for additional resin: (1) the unloading difficulty hypothesis (resin need is sensed indirectly by the unloading delay) and (2) the caulking activity hypothesis (resin need is sensed directly while engaged in using resin). A falsifiable prediction of the latter hypothesis, but not of the former, is that resin collectors not only gather resin outside the hive but also regularly handle resin inside the hive (taking it from other bees and using it to caulk crevices). Consistent with this prediction are our findings that in the resin sector of a colony’s economy, unlike in the pollen, nectar, and water sectors, there is no strict division of labor between the collectors and the users of a material. Over the course of a day, bees seen collecting resin were also commonly seen using resin. Moreover, we found that the unloading locations of resin collectors are unlike those of water and nectar collectors, being deep inside the hive (at the sites of resin use) rather than at the hive entrance. This arrangement facilitates the engagement in resin use by resin collectors. We conclude that the caulking activity hypothesis is well-supported, but that the unloading difficulty hypothesis also remains viable, for we found that resin collectors experience variable delays in getting rid of their loads, from less than 15 min to more than an hour, consistent with this hypothesis. The stage is now set for experimental tests of these two hypotheses. Both may be correct, which if true will imply that social insect workers, despite their small brains, can acquire and integrate information from multiple sources to improve their knowledge of conditions within the colony.     

The control of water collection in honey bee colonies

A honey bee (Apis mellifera) colony adaptively controls the collection of water by its foragers, increasing it when high temperatures necesssitate evaporative cooling inside the hive and decreasing it when the danger of overheating passes. This study analyzes the mechanisms controlling water collection once it has begun, that is, how a colony's water collectors know whether to continue or stop their activity. M. Lindauer suggested that water collectors acquire information about their colony's need for more water by noting how easily they can unload their water to bees inside the hive. In support of this hypothesis, we found that a water collector's ease of unloading does indeed change when her colony's need for water changes. How does a water collector sense the ease of unloading? Multiple variables of the unloading experience change in relation to a colony's water need. Three time-based variables – initial search time, total search time, and delivery time – all change quite strongly. But what changes most strongly is the number of unloading rejections (refusals by receiver bees to take the water), suggesting that this is the primary index of ease of unloading. Why does a water collector's ease of unloading change when her colony's need for water changes? Evidently, what links these two variables is change in the number of water receivers. These are middle-aged bees that receive water just inside the hive entrance, then transport it deeper inside the hive, and finally smear it on the walls of cells or give it to other bees, or both. A colony increases the number of water receivers when its water need increases by having bees engaged in nectar reception and other tasks (and possibly also bees that are not working) switch to the task of water reception. Evidently the activation of additional water receivers does not strongly reduce the number of nectar receivers in a colony, since a colony can increase greatly its water collection without simultaneously decreasing its collection of rich nectar. This study provides a clear example of the way that the members of a social insect colony can use indirect indicators of their colony's labor needs to adaptively control the work that they perform.     

Division of labour and worker size polymorphism in ant colonies: the impact of social and genetic factors

Division of labour among workers is central to the organisation and ecological success of insect societies. If there is a genetic component to worker size, morphology or task preference, an increase in colony genetic diversity arising from the presence of multiple breeders per colony might improve division of labour. We studied the genetic basis of worker size and task preference in Formica selysi, an ant species that shows natural variation in the number of mates per queen and the number of queens per colony. Worker size had a heritable component in colonies headed by a doubly mated queen (h ²=0.26) and differed significantly among matrilines in multiple-queen colonies. However, higher levels of genetic diversity did not result in more polymorphic workers across single- or multiple-queen colonies. In addition, workers from multiple-queen colonies were consistently smaller and less polymorphic than workers from single-queen colonies. The relationship between task, body size and genetic lineage appeared to be complex. Foragers were significantly larger than brood-tenders, which may provide energetic or ergonomic advantages to the colony. Task specialisation was also often associated with genetic lineage. However, genetic lineage and body size were often correlated with task independently of each other, suggesting that the allocation of workers to tasks is modulated by multiple factors. Overall, these results indicate that an increase in colony genetic diversity does not increase worker size polymorphism but might improve colony homeostasis.     

Control of reproduction in social insect colonies: individual and collective relatedness preferences in the paper wasp, Polistes annularis

Social insect colonies often have one or a few queens. How these queens maintain their reproductive monopoly, when other colony members could gain by sharing in the reproduction, is not generally known. DNA microsatellite genotyping is used to determine reproductive interests of various classes of colony members in the paper wasp, Polistes annularis. The relatedness estimates show that the best outcome for most individuals is to be the reproductive egg-layer. For workers, this depends on the sex of offspring: they should prefer to lay their own male eggs, but are indifferent if the queen lays the female eggs. The next-best choice is usually to support the current queen. As a rule, subordinates and workers should prefer the current queen to reproduce over other candidates (though subordinates have no strong preference for the queen over other subordinates, and workers may prefer other workers as a source of male eggs). This result supports the theory that reproductive monopoly stems from the collective preferences of non-reproductives, who suppress each other in favor of the queen. However, we reject the general hypothesis of collective worker control in this species because its predictions about who should succeed after the death of the present queen are not upheld. The first successor is a subordinate foundress even though workers should generally prefer a worker successor. If all foundresses have died, an older worker succeeds as queen, in spite of a collective worker preference for a young worker. The results support the previous suggestion that age serves as a conventional cue serving to reduce conflict over queen succession. Received: 3 May 1996 / Accepted after revision: 22 September 1996     

Cofoundress relatedness and group productivity in colonies of social <Emphasis Type="Italic">Dunatothrips</Emphasis> (Insecta: Thysanoptera) on Australian <Emphasis Type="Italic">Acacia</Emphasis>

Facultative joint colony founding by social insects provides opportunities to analyze the roles of genetic and ecological factors in the evolution of cooperation. Although cooperative nesting is observed in range of social insect taxa, the most detailed studies of this behavior have been conducted with Hymenoptera (ants, bees, and wasps). Here, we show that foundress associations in the haplodiploid social thrips Dunatothrips aneurae (Insecta: Thysanoptera) are most often comprised of close relatives (sisters), though groups with unrelated foundresses are also found. Associations among relatives appear to be facilitated by limited female dispersal, which results in viscous population structure. In addition, we found that per capita productivity declined with increasing group size, sex ratios were female-biased, and some female offspring apparently remained in their natal domicile for some time following eclosion. D. aneurae thus exhibits a suite of similarities with eusocial Hymenoptera, providing evidence for the convergent evolution of associated social and life-history traits in Hymenoptera and Thysanoptera.     

The effects of colony-level selection on the social organization of honey bee (Apis mellifera L.) colonies: colony-level components of pollen hoarding

Two-way selection for quantities of stored pollen resulted in the production of high and low pollen hoarding strains of honey bees (Apis mellifera L.). Strains differed in areas of stored pollen after a single generation of selection and, by the third generation, the high strain colonies stored an average 6 times more pollen than low strain colonies. Colony-level organizational components that potentially affect pollen stores were identified that varied genetically within and between these strains. Changes occurred in several of these components, in addition to changes in the selected trait. High strain colonies had a significantly higher proportion of foragers returning with loads of pollen, however, high and low strain colonies had equal total numbers of foragers Colony rates of intake of pollen and nectar were not independent. Selection resulted in an increase in the number of pollen collectors and a decrease in the number of nectar collectors in high strain colonies, while the reciprocal relationship occurred in the low strain. High and low strain colonies also demonstrated different diurnal foraging patterns as measured by the changing proportions of returning pollen foragers. High strain colonies of generation 3 contained significantly less brood than did low strain colonies, a consequence of a constraint on colony growth resulting from a fixed nest volume and large quantities of stored pollen. These components represent selectable colony-level traits on which natural selection can act and shape the social organization of honey bee coloniesCommunicated by R.F.A. Moritz     

Identification of optimal strategies for improving eco-resilience to floods in ecologically vulnerable regions of a wetland

In this study, a mixed integer fuzzy interval-stochastic programming model was developed for supporting the improvement of eco-resilience to floods in wetlands. This method allows uncertainties that are associated with eco-resilience improvement and can be presented as both probability distributions and interval values to be incorporated within a general modeling framework. Also, capacity-expansion plans of eco-resilience can be addressed through introducing binary variables. Moreover, penalties due to ecological damages which are associated with the violation of predefined targets can be effectively incorporated within the modeling and decision process. Thus, complexities associated with flood resistance and eco-resilience planning in wetlands can be systematically reflected, highly enhancing robustness of the modeling process. The developed method was then applied to a case of eco-resilience enhancement planning in three ecologically vulnerable regions of a wetland. Interval solutions under different river flow levels and different ecological damages were generated. They could be used for generating decision alternatives and thus help decision makers identify desired eco-resilience schemes to resist floods without causing too much damages. The application indicates that the model is helpful for supporting: (a) adjustment or justification of allocation patterns of ecological flood-resisting capacities, (b) formulation of local policies regarding eco-resilience enhancement options and policy interventions, and (c) analysis of interactions among multiple administrative targets within a wetland.     

Larval chemical defence and evolution of host shifts in Chrysomela leaf beetles

Summary. Larvae of Chrysomela leaf beetles release for defence volatile compounds belonging to various chemical families. This study focuses on the defensive strategy based on the esterification of isobutyric acid and 2-methylbutyric acid with a wide variety of alcohols taken up from the host plant. To date, only two species are known to produce these repellents C. interrupta, which is associated with Betulaceae and C. lapponica which occurs either on Betulaceae or Salicaceae.? In order to know if other species have developed this chemical defence and how the food plant influences the secretion of these toxins, we targeted by mass spectrometry the presence of iso- and 2-methylbutyric acids and esters of them in the defensive secretions of Chrysomela larvae exclusively associated with Betulaceae or Salicaceae. ?Screening analyses reveal that the synthesis of these compounds is a common character restricted to all the members belonging to the C. interrupta group sensu Brown (1956) regardless of the host-plant family. These results suggest that the biochemical mechanism leading to the synthesis of these compounds could be considered as a synapomorphy meaning that the group is probably monophyletic. ?Defensive secretions of the members of the interrupta group are quantitatively assayed for iso- and 2-methylbutyric acids and their (Z)-3-hexenyl esters. Results reveal a chemical plasticity developed by Chrysomela species associated with Salicaceae. The amounts of iso- and 2-methylbutyric acids derivatives and of salicylaldehyde in their larval secretions depend on the food plant and on its content in phenolglucosides. Received 5 October 1998; accepted 25 November 1998.     

The dissolution of cooperative groups: mechanisms of queen mortality in incipient fire ant colonies

In several species of ants, queens often form temporary cooperative associations during colony foundation. These associations end soon after the eclosion of the first workers with the death or expulsion of all but one of the queens. This study examined competition between foundress queens of the fire ant Solenopsis invicta. Although attacks by the workers contributed to queen mortality, queens gained no advantage by producing more workers than their co-foundresses. Restriction fragment length polymorphism analysis of mitochondrial DNA showed that the queen producing more workers during colony founding was no more likely to survive than the less productive queen. In experimentally manipulated colonies in which all the workers were daughters of only one of the queens, the mother of the workers was no more likely to survive than the unrelated queen. Queens producing diploid males reared fewer offspring but were as likely to survive as queens producing only workers. These results suggest that workers do not discriminate between related and unrelated queens within colonies. Aggressive encounters between queens were common. Queens were more likely to die or be expelled if paired with heavier queens or if they lost more weight than their co-foundress during the claustral period. Finally, when queens were separated by screens through which workers could pass, the workers usually attacked and killed the queen farther from the brood. These results suggest that queen survival is promoted by a high fighting ability relative to co-foundresses, rather than by increased worker production, and that workers respond to queen differences that are independent of kinship. Received: 8 September 1995/Accepted after revision: 5 March 1996     

Ontogenetic and spatio-temporal patterns of induced volatiles in <Emphasis Type="Italic">Glycine max</Emphasis> in the light of the optimal defence hypothesis

Summary. Plants attacked by herbivorous insects emit a blend of volatile compounds that serve as important host location cues for parasitoid wasps. Variability in the released blend may exist on the whole-plant and withinplant level and can affect the foraging efficiency of parasitoids. We comprehensively assessed the kinetics of herbivore-induced volatiles in soybean in the context of growth stage, plant organ, leaf age, and direction of signal transport. The observed patterns were used to test the predictions of the optimal defence hypothesis (OD). We found that plants in the vegetative stage emitted 10-fold more volatiles per biomass than reproductive plants and young leaves emitted >2.6 times more volatiles than old leaves. Systemic induction in single leaves was stronger and faster by one day in acropetal than in basipetal direction while no systemic induction was found in pods. Herbivore-damaged leaves had a 200-fold higher release rate than pods. To some extent these findings support the OD: i) indirect defence levels were increased in response to herbivory and ii) young leaves, which are more valuable, emitted more volatiles. However, the fact that reproductive structures emitted no constitutive or very few inducible volatiles is in seeming contrast to the OD predictions. We argue that in case of volatile emission the OD can only partially explain the patterns of defence allocation due to the peculiarity that volatiles act as signals not as toxins or repellents.     

The optimal harvest and management in the models of animal populations

We extended zero-cost optimization model for population of domestic animals. Also the model of hiring of labor in cattle-breeding farm is constructed and investigated.     

The evolution of female social relationships in nonhuman primates

Considerable interspecific variation in female social relationships occurs in gregarious primates, particularly with regard to agonism and cooperation between females and to the quality of female relationships with males. This variation exists alongside variation in female philopatry and dispersal. Socioecological theories have tried to explain variation in female-female social relationships from an evolutionary perspective focused on ecological factors, notably predation and food distribution. According to the current “ecological model”, predation risk forces females of most diurnal primate species to live in groups; the strength of the contest component of competition for resources within and between groups then largely determines social relationships between females. Social relationships among gregarious females are here characterized as Dispersal-Egalitarian, Resident-Nepotistic, Resident-Nepotistic-Tolerant, or Resident-Egalitarian. This ecological model has successfully explained differences in the occurrence of formal submission signals, decided dominance relationships, coalitions and female philopatry. Group size and female rank generally affect female reproduction success as the model predicts, and studies of closely related species in different ecological circumstances underscore the importance of the model. Some cases, however, can only be explained when we extend the model to incorporate the effects of infanticide risk and habitat saturation. We review evidence in support of the ecological model and test the power of alternative models that invoke between-group competition, forced female philopatry, demographic female recruitment, male interventions into female aggression, and male harassment. Not one of these models can replace the ecological model, which already encompasses the between-group competition. Currently the best model, which explains several phenomena that the ecological model does not, is a “socioecological model” based on the combined importance of ecological factors, habitat saturation and infanticide avoidance. We note some points of similarity and divergence with other mammalian taxa; these remain to be explored in detail. Received: 30 September 1996 / Accepted after revision: 20 July 1997     

The mating system of Hanuman langurs: a problem in optimal foraging

Using data from 23 populations of Indian langurs (Presbytis entellus), we show that the proportion of one-male groups is a function of the males’ ability to defend groups of females, as predicted by the monopolisation model of Emlen and Oring (1977). However, we show that in addition to the number of females in the group and their reproductive synchrony, home range size is also a factor, probably because it affects a male’s willingness to search for other groups. These variables in turn are shown to be functions of environmental parameters (rainfall volume and seasonality, and mean ambient temperature) which probably act via the density of resources and refuges in habitats. Received: 3 March 1994 / Accepted after revision: 24 June 1996     

Disease prevention and resistance in social insects: modeling the survival consequences of immunity,hygienic behavior,and colony organization

Understanding the origin of disease resistance in social insects is difficult due to the lack of well-established phylogenies of presocial and eusocial species and the absence of extant basal and intermediate forms. Moreover, comprehensive accounts of infection-control traits in social insect lineages are not available. Therefore, to explore the evolution of pathogen control in social insects we used cellular automata models to analyze the efficacy of immunity and nest hygiene, which we assumed were basal traits, and allogrooming, which likely followed the transition to eusociality, and their interactions with colony demography and patterns of worker spatial distribution. Models showed that nest hygiene provided an immediate survival benefit and that immunity lowered overall disease susceptibility under both constant and periodic exposure scenarios. Allogrooming increased survivorship in chronically challenged colonies but also increased pathogen transmission rates under conditions of periodic exposure. Colonies having demographies biased towards young or old individuals had slightly higher mortality than those with heterogeneous demographies. The distribution of older individuals relative to the nest center had no significant effect on susceptibility and provided only a minor survival advantage. Models indicated that nest hygiene and immunity function on different temporal scales and can interact with demography to lower disease risks. Our results suggest how infection control systems in social insects could have been built upon the inducible immune defenses and nest hygienic behaviors of solitary and presocial ancestors and served as important preadaptations to manage disease exposure and transmission in colonies of eusocial species.     

The role of social media for sustainable development in mountain region tourism in Pakistan

This research letter focuses on tourist behavior and tourism business operators’ contributions to rural mountain region economic growth and sustainable development when using social media. Data were collected from 43 interviews from different tourism business operators, and a questionnaire survey of 576 tourists from the Gilgit-Baltistan, Pakistan. Drawing on development communication theory, the study reveals that there is a positive relationship between the tourists’ intentions and rural mountain region sustainable development. The study also reveals that most tourists are willing to pay more taxes when touring mountain regions. The real business outcomes from tourism business operators show that rural mountain region tourism creates better employment opportunities for the rural population. All tourists demonstrated the motivation to take part in rural mountain region sustainable development while touring rural locations. The study also offers policy implications.