Caste and division of labor in leaf-cutter ants (Hymenoptera: Formicidae: Atta)

Summary Leaf cutting was selected for an evaluation of ergonomic efficiency in the fungus-growing ant Atta sexdens because it is performed largely by medias (head width 1.8–2.8 mm), which attend to relatively few other functions and hence are less likely to be evolutionarily compromised by the demands of competing tasks (Fig. 1).Three alternative a priori criteria of evolutionary optimization were envisioned that are consistent with natura selection theory: the reduction of predation by means of defense and evasion during foraging, the minimization of foraging time through skill and running velocity during foraging, and energetic efficiency, which must be evaluated with reference to both the energetic construction costs of new workers and the energetic cost of maintenance of the existing worker force.In order to measure the performance of various size groups within the A. sexdens worker caste in isolation, I devised the pseudomutant technique: in each experiment, groups of foraging workers were thinned out until only individuals of one size class were left outside the nest. Measurements were then made of the rate of attraction, initiative in cutting, and performance of each size group at head-width intervals of 0.4 mm (Figs. 2, 3, and 7). Other needed measurements were made in body weight, oxygen consumption, and running velocity (Figs. 5, 6, and 8).The size-frequency distribution ff leaf cutters in the A. sexdens conforms closely to the optimum predicted by the energetic efficiency criterion for harder forms of vegetation, such as rhododendron leaves. The distribution is optimum with reference to both construction and maintenance costs. The difference between the predicted and actual modal size groups specializing on leaf cutting is 10% or less of the total size range of the sexdens worker caste.A model was next constructed in which attraction and initiative were allowed to evolve genetically to uniform maximum levels. The theoretical maximum efficiency levels obtained by this means were found to reside in the head-width 2.6–2.8 mm size class, or 8% from the actual maximally efficiency class (head width 2.2–2.4 mm). In the activity of leaf cutting, A. sexdens can therefore be said to be not only at an adaptive optimum but also, within at most a relatively narrow margin of error, to have been optimized in the course of evolution.     

Between-caste aversion as a basis for division of labor in the ant Pheidole pubiventris (Hymenoptera: Formicidae)

Summary When deprived of minor workers under expermental conditions, major workers of the ant Pheidble pubiventris dramatically increase their repertory and rate of activity, and the change is due in good part to the greater attention they pay the brood. When minor workers are reinstated in appropriate numbers, the majors reduce their attention to the immature stages to the ordinary, low levels. Their response consists of the active avoidance of minors while in the vicinity of the immature stages. However, majors do not turn from other majors near the brood as much as they do from the minors, and they do not avoid minors at all while in other parts of the nest. In addition, minors do not avoid either minors or majors anywhere in the nest. The result is a striking division of labor with reference to brood care.     

The relation between caste ratios and division of labor in the ant genus Pheidole (Hymenoptera: Formicidae)

Summary Ten species of Pheidole, representing as many species groups from various localities in North and South America, Asia, and Africa, were analyzed to probe for possible relationships between caste ratios and division of labor.Minor workers are behaviorally almost uniform among the species, but major workers vary in repertory from 4 to 19 behavioral acts (Table 1, Fig. 2). The major repertory size increases significantly across the species with the percentage of majors in the worker force (Fig. 3). This trend is consistent with the basic prediction of ergonomic optimization models under an assumption of colony-level selection. There is also a trend toward reduction of behavioral repertory with increase of size in the major relative to the minor, a second relation expected from theory, but the data are not sufficient to reach statistical significance.When the minor:major ratio was lowered to below 1:1 (from the usual 3:1 to 20:1, according to species), in three widely different species (guilelmimuelleri, megacephala, pubiventris), the repertory size increased by 1.4–4.5X and the rate of activity by 15–30X (Table 1, Figs. 4–6). The change occurred within 1 h of the ratio change and was reversed in comparably short time when the original ratio was restored.This abrupt and important shift in behavior permitted the major workers to serve as an emergency stand-by caste, available to be summoned to a nearly full repertory when the minor worker caste was depleted. The majors also restored 75% or more of the missing minor workers' activity rate under laboratory conditions. Their transformation allowed continued oviposition by the queen and the rearing of larvae to the adult stage.In line with these findings, a distinction is made between programmed elasticity in the repertory of individual workers and castes and the resiliency of the colony as a whole, which depends upon the pattern of caste-specific elasticity.     

Dominance and polyethism in the eusocial wasp Mischocyttarus mastigophorus (Hymenoptera: Vespidae)

Dominance interactions affected patterns of non-reproductive division of labor (polyethism) in the eusocial wasp Mischocyttarus mastigophorus. Socially dominant individuals foraged for food (nectar and insect prey) at lower rates than subordinate individuals. In contrast, dominant wasps performed most of the foraging for the wood pulp used in nest construction. Social dominance also affected partitioning of materials collected by foragers when they returned to the nest. Wood pulp loads were never shared with nest mates, while food loads, especially insect prey, were often partitioned with other wasps. Dominant individuals on the nest were more likely to take food from arriving foragers than subordinate individuals. The role of dominance interactions in regulating polyethism has evolved in the eusocial paper wasps (Polistinae). Both specialization by foragers and task partitioning have increased from basal genera (independent-founding wasps, including Mischo-cyttarus spp.) to more derived genera (swarm-founding Epiponini). Dominance interactions do not regulate forager specialization or task partitioning in epiponines. I hypothesize that these changes in polyethism were enabled by the evolution of increased colony size in the Epiponini. Received: 8 December 1997 / Accepted after revision: 28 March 1998     

Effects of intracolony variability in behavioral development on plasticity of division of labor in honey bee colonies

There is a genetic component to plasticity in age polyethism in honey bee colonies, such that workers of some genotypes become precocious foragers more readily than do workers of other genotypes, in colonies lacking older bees. Using colonies composed of workers from two identifiable genotype groups, we determined that intracolony differences in the likelihood of becoming a precocious forager are a consequence of differences in rates of behavioral development that are also evident under conditions leading to normal development. An alternative hypothesis, that differences in the likelihood of becoming a precocious forager are due to differences in general sensitivity to altered colony conditions, was not supported. In three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single cohort colonies also foraged at relatively younger ages in colonies in which workers exhibited normal behavioral development. In contrast, in three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single-cohort colonies did not show disproportionately more overaged nursing in colonies in which workers exhibited delayed development. These results indicate that genotypic differences in plasticity in age-related division of labor are based on genotypic differences in rates of behavioral development.     

Effects of parasites on foraging and defense behavior of a termitophagous ant,Pheidole titanis Wheeler (Hymenoptera: Formicidae)

Summary Pheidole titanis Wheeler, an ant that occurs in desert and deciduous thorn forest in the southwestern United States and western Mexico, is a predator on termites. In the dry season well-coordinated raids against termite foraging parties occur early in the morning or late in the afternoon, whereas in the wet season most raids occur at night. This seasonal shift in the timing of raids is due to the increased activity of a fly (Diptera: Phoridae) that is a specialist parasitoid on P. titanis workers and soldiers. When parasitic flies discover P. titanis nest entrances or raiding columns, workers stop foraging and defend themselves against oviposition attacks. Flies are only active during the day and never interfere with foraging at night. However, P. titanis does not increase the frequency of raids at night and, as a result, colonies collect less food in the wet season compared to the dry season. Presence of parasitic flies also interferes with normal defense behavior of P. titanis against conspecific and heterospecific enemy ants. Dissections of P. titanis workers and soldiers suggest that the parasitism rate by flies is less than 2% and observations indicate that parasitic flies are much rarer than their host workers and soldiers. Nonetheless, these parasites exert a strong ecological impact on their host.     

Patterns of brood division and an absence of behavioral plasticity in a neotropical passerine

Studies of parental behavior in various habitats provide an opportunity to gain insight into how different environments may mold strategies of parental care. Brood division by parents has been hypothesized to occur facultatively within and among species. Brood division occurs when each parent cares for specific offspring within a brood. We studied brood division in a neotropical passerine, the western slaty antshrike (Thamnophilus atrinucha). Our results present a unique picture of a highly specialized example of avian brood division. Division was a fixed behavioral pattern in the population studied: all broods divided by fledging and remained divided during the entire post-fledging period. Brood division before fledging, a previously unreported phenomenon, occurred in 40% of nests observed. Parents that preferentially fed a certain offspring (defined as their focal offspring) in the nest fed the same individual after fledging. Each parent fed only its focal offspring in broods of one and two. The male parent cared for the heavier offspring and the first offspring to leave the nest. Siblings were segregated spatially during the time of highest predation risk. These observations suggest that a consistently high risk of predation on offspring has favored initial spatial segregation and inflexibility of brood division behavior in this species. Factors other than predation risk alone may explain the observed patterns of long-term, perfect brood division. Because high predation is common and relatively predictable in the tropics, selection for fixed brood division may be stronger in tropical birds than in the temperate zone.     

Parasitic flies (Diptera: Phoridae) influence foraging rhythms and caste division of labor in the leaf-cutter ant,Atta cephalotes (Hymenoptera: Formicidae)

Summary Three lines of evidence, including interspecific comparisons, temporal division of foraging between size castes, and experimental manipulations, suggest that the diurnal parasitoid Neodohrniphora curvinervis (Diptera: Phoridae) influences both the caste sizes and numbers of leaf-cutter ants (Atta cephalotes) that leave their underground nests to collect leaves. At Parque Nacional Corcovado in Costa Rica, A. cephalotes was attacked by Neodohrniphora during the daytime, and foraged less during the day than at night; a closely related ant at the same site, A. colombica, had no phorid parasites and foraged exclusively during the day. Most daytime foragers of A. cephalotes were smaller than the lower size threshold for attack by Neodohrniphora, while nocturnal foragers, active when parasitoids were absent, were both larger than this threshold and within the energetically optimal size range for foraging. When I supplied artificial lighting to allow phorids to hunt at A. cephalotes colonies past dusk, ants foraged less than when light was provided but flies were removed. The influence of Neodohrniphora on the foraging activity of A. cephalotes may explain why investigations focusing on abiotic factors have largely failed to discover what drives this ant's daily foraging cycles, and suggests that forager sizes are influenced not only by energetic efficiency, but also by the threat of parasitism.     

The effect of colony size and starvation on food flow in the fire ant,Solenopsis invicta (Hymenoptera: Formicidae)

Summary Food-sharing experiments were performed with laboratory colonies of Solenopsis invicta containing 1000, 10,000, or 20,000 workers and starved for 0, 3, 7, or 14 days. The effect of these variables was measured on the uptake of radioactive sugar water (1 M) by 1% of the colony's workers and on the trophallactic flow of food from these foragers to the remainder of the colony.Patterns of food distribution in small colonies differed significantly from those in larger nests. In 1000-ant nests, small workers more frequently received food than large workers, but in bigger colonies the opposite occurred.Fire ants were adept at distributing sugar water, with food from a few workers rapidly reaching the majority of the colony as foragers donate their crop contents to groups of recipients and these recipients may themselves act as donors.Foragers respond to colony starvation by individually taking up more food and sharing this fluid with a greater proportion of nestmates. Even foragers from satiated colonies can retrieve at least small amounts of liquid.The forager's state of hunger plays an important role in regulating food distribution. In sugar-satiated nests, previously starved foragers are highly successful at passing on labelled sugar whereas prviously fed foragers are not.     

Experimental analysis of worker division of labor in bumblebee nest thermoregulation (<Emphasis Type="Italic">Bombus huntii</Emphasis>, Hymenoptera: Apidae)

Bumblebee colonies experience daily and seasonal fluctuations in ambient temperature, but proper brood development requires a stable nest temperature. This study examined how adaptive colony responses to changing ambient temperature are achieved through the in-nest workers’ behavioral plasticity. We studied three Bombus huntii colonies in the laboratory. In the first experiment, we manipulated ambient temperature and recorded brood cell incubation and wing fanning by individually marked, known-age bees. The colonies maintained their nests closer to appropriate brood development temperatures (28 to 32°C) when exposed to a range of ambient temperatures from 10.3 to 38.6°C. Incubation activity was greater in cooler treatment conditions, whereas in the highest temperature treatment, some bees fanned and others moved off the brood. As the ambient temperature dropped, workers increased the duration of their incubating bouts, but, except at the highest temperature, the number of workers that incubated did not differ significantly among treatments. A subset of the bees incubated significantly more than their nest mates, some of which never incubated. Worker body size, but not age, was a good predictor of incubation rates, and smaller bees incubated at higher rates. In the second experiment, we removed the most actively incubating workers. Immediately after removals, the total colony incubation effort was lower than pre-removal levels, but incubation effort rebounded toward pre-removal levels after 24 h. The increased thermoregulatory demand after removals was met primarily by bees increasing their rates of incubation rather than by bees switching from a different task to incubation. We conclude that some B. huntii workers specialize on nest thermoregulation, and that changes in work rates are more important than task switching in meeting thermal challenges.     

Analysis of behavioral changes of zebrafish (Danio rerio) in response to formaldehyde using Self-organizing map and a hidden Markov model

Two computational methods were applied to classification of movement patterns of zebrafish (Danio rerio) to elucidate Markov processes in behavioral changes before and after treatment of formaldehyde (0.1 mg/L) in semi-natural conditions. The complex data of the movement tracks were initially classified by the Self-organizing map (SOM) to present different behavioral states of test individuals. Transition probabilities between behavioral states were further evaluated to fit Markov processes by using the hidden Markov model (HMM). Emission transition probability was also obtained from the observed variables (i.e., speed) for training with the HMM. Experimental transition and emission probability matrices were successfully estimated with the HMM for recognizing sequences of behavioral states with accuracy rates in acceptable ranges at central and boundary zones before (77.3-81.2%) and after (70.1-76.5%) treatment. A heuristic algorithm and a Markov model were efficiently combined to analyze movement patterns and could be a means of in situ behavioral monitoring tool.     

转Bt-cry1Ac棉花花粉对意大利蜜蜂生长发育的影响

研究了取食转Bt-cry1Ac棉花花粉对意大利蜜蜂的影响,主要包括意大利蜜蜂的生长发育、体内酶活性的变化.结果发现,取食转Bt-cry1Ac基因棉花花粉的意大利蜜蜂与取食非转基因亲本棉花花粉的蜜蜂(CK)相比,4、5、6日龄幼虫体重差异不显著,幼虫及蛹的历期也没有明显差异.取食转Bt-cry1Ac基因棉花花粉的意大利蜜蜂6日龄幼虫体内的谷胱甘肽-S-转移酶、总蛋白酶活力与CK相比,没有显著差异.取食转Bt-cry1Ac基因棉花花粉的意大利蜜蜂幼虫体内的α-乙酸萘酯酶、乙酰胆碱酯酶活力极显著高于CK,强碱性、弱碱性类胰蛋白酶活力极显著低于CK,类胰凝乳蛋白酶活力显著低于CK.另外,采用酶联免疫(ELISA)方法在取食转Bt-cry1Ac基因棉花花粉的蜜蜂6日龄幼虫体内能够检测到Bt杀虫蛋白.表4参12     

Degree-day accumulation controlling allopatric and sympatric variations in the sociality of sweat bees, <Emphasis Type="Italic">Lasioglossum</Emphasis> (<Emphasis Type="Italic">Evylaeus</Emphasis>) <Emphasis Type="Italic">baleicum</Emphasis> (Hymenoptera: Halictidae)

Halictine bees exhibit a wide range of social behaviour that varies both inter- and intraspecifically. Although previous studies suggested that the intraspecific variation might be attributed to temperature differences, there was no direct evidence to detect the relationships between temperature and socialities. Lasioglossum (Evylaeus) baleicum exhibited solitary behaviour in a cooler locality (Kawakita) because of the shorter breeding season; in a warmer locality (Nishioka Park), however, this bee species exhibited eusociality at sunny site and solitary behaviour at shady site, whereas a molecular phylogeny confirms that all of these colonies are evidently conspecific. Therefore, we examined the effect of degree-day accumulation on the sympatric social variation of L. baleicum by rearing the bees to calculate the threshold temperature. Whereas they showed high mortality, the threshold temperature was estimated to be 10.33°C and the expected degree-day accumulation was 340 degree days. When we use this value of a degree-day accumulation to estimate the expected eclosion date, the estimated dates were always consistent with observed eclosion dates. In any sites where the bees were solitary, the degree-day accumulation was not enough for the second eclosion by the end of the bee-active season. In Nishioka Park, sex ratio of the first brood was female biased, and daughters were smaller than mothers; in Kawakita, however, there was no sex bias, and daughters were as large as their mothers indicating that the foundresses seem to produce gyne-sized females in Kawakita but worker-sized females in Nishioka though these females do not become workers at shady site.     

Mapping the economic costs and benefits of Coral Triangle Initiative (CTI) and Mangrove Rehabilitation Projects (MRP) in Solomon Islands: a study of two MPAs and one MRP

This paper reports a study of costs and benefits of Coral Triangle Initiatives (CTI) and Mangrove Rehabilitation Projects (MRP) in the Solomon Islands. It was observed that the communities have different attitudes and perceptions toward climate change challenges. The different scales and magnitudes of climate change impacts that are perceived at these sites, and the different subsistence realities make them have varied responses and points of view regarding such impacts. For instance, respondents from Oibola experienced the most adverse impacts from climatic change events compared to those living in the Naro and Sairaghi sites. Introduction of CTI and MRP has driven the villagers to travel out far from their traditional fishing grounds to catch enough fish to sell and support their families. This implies higher fishing costs and time for commute. From a social perspective, this weakens the communal bond in the community. In spite of these trade-offs, the respondents expressed satisfaction with the level of benefits received from the projects, which included the rehabilitation of the ecosystems and breeding grounds for fish and habitats around the area. We mapped the costs and benefits of these projects to the villagers, and although no amounts or figures were disclosed, the benefits are compared against corresponding costs. One key factor for the success of the initiatives was the cooperation and involvement of recipient villagers, and even including the management MPAs.     

The reproductive biology of a new species of sea cucumber, Holothuria (Mertensiothuria) arenacava in a Kenyan marine protected area: the possible role of light and temperature on gametogenesis and spawning

The sea cucumber Holothuria arenacava was discovered in the Mombasa marine reserve in 1997 and described by Samyn et al. (2001). The reproductive biology of this holothurian was investigated in order to (1) characterize the reproductive pattern, (2) examine the relationship among environmental parameters including temperature, light and lunar period, and (3) examine the relationship between the reproductive pattern and feeding of this new species. The gonad index method and microscopic examination of gonads was used to analyze samples collected for a period of 13 months. H. arenacava displayed an annual reproductive cycle with gametogenesis commencing in July during the south-east monsoons, when temperature and light intensity are lowest along the Kenyan coast. Gonad growth peaked in February–March at the end of the north-east monsoons when temperatures and light reach their annual maxima along the Kenyan coast. The higher correlation between light intensity and gonad growth (r=93) than temperature (r=0.71), coupled with the fact that temperatures continued to drop for a month after gametogenesis had already commenced, suggests that light intensity and not temperature is the cue for the onset of gametogenesis in this species. Spawning was synchronized between females and males and occurred during a short period between March and May (inter-monsoonal period) when both temperature and light intensity decrease along the Kenyan coast. Male and female gonad indices showed significant variation with lunar day and no lunar periodicity was observed in this sea cucumber. The sex ratio of the population of H. arenacava was skewed towards significantly more females than males, and females were significantly larger and had larger gonads and gonad indices than males. These life history strategies including spawning during a short discrete period, more and larger females that have larger gonads (i.e., typically more fecund), and spawning just prior to the peak in phytoplankton concentrations, a time that is probably more favorable for larval development, may serve to increase the reproductive success of this sea cucumber.     

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.