Biparental care in incipient colonies of the dampwood termiteZootermopsis angusticollis Hagen (Isoptera: Termopsidae)

Parental care and division of labor in male and female primary reproductives in incipient colonies of the dampwood termite Zootermopsis angusticolliswere studied by recording repertory sizes, behavior frequencies, time budgets, and transition probabilities of acts. Repertory sizes for males and females were identical, and behaviors were performed at similar frequencies. Time budget data also suggested equal participation in parental care by both sexes. Transition probability analysis suggested that males and females did not organize their behavior in roles. We therefore found no indication of sex-based division of labor during colony foundation and the incipient stages of colony growth. The lack of behavioral specialization may be due to the fact that acts might be related and/or have more than one function, and different tasks are not spatially associated. Our observations are consistent with the hypothesis that monogamous mating systems in termites involve mate assistance.     

Influence of caste polyethism on longevity of workers in social insect colonies

Different patterns of division of labor can affect the expected longevity of social insects workers. It has been earlier suggested that when tasks performed inside and outside colony are equally risky then the expected longevity of workers in colonies with caste polyethism is greater than that in colonies without polyethism. To verify these predictions I used a model assuming two sets of tasks, associated with different mortality rates. In the colony without polyethism the workers preformed safe and risky tasks in turn, while in the colony with caste polyethism the workers specialized in only one set of tasks. The outcomes suggest that the expected longevity of workers in colonies with caste polyethism cannot be greater than that in colonies without polyethism. Only if there is no aging and under some special and rare conditions are there no differences in expected longevity between colonies with and without caste polyethism. If aging is independent of activity, caste polyethism does not shorten longevity when all tasks in the colony are equally risky. The results can explain why caste polyethism is not as widespread among social insects as age polyethism.     

On the origin of termite workers: weighing up the phylogenetic evidence

Resolving the phylogenetic history of a 'true' worker caste in termites is essential to our understanding of termite eusocial evolution. Whether this caste is ancient and monophyletic or derived and polyphyletic will have a tremendous impact on our interpretation of termite eusocial history and remains an outstanding question in termite biology. Recent work has begun to re-examine this question in light of new phylogenetic information, but new questions have now arisen about how best to model character state changes in termite caste systems. In the present paper, we compare the models of Grandcolas and D'Haese [J. Evol. Biol. 15 (2002) 885] and Thompson et al. [J. Evol Biol. 13 (2000) 8691 and attempt to make explicit how these proposals differ with respect to the number of, and homology between, character states. We highlight the support each model has for the two principal, but competing, evolutionary hypotheses outlined above.     

Colour variation and polyethism of the soldier caste in the termite Macrotermes bellicosus

Based on abdominal colour three categories of major soldiers were found in Macrotermes bellicosus (Smeathman) (Isoptera: Termitidae). The three main colour types, yellow, red and brown are due to the colour of the defence-secretion stored in the labial gland's reservoirs. The order of these categories correlates with the uric acid titres of the whole individuals. It is concluded that colour could be used as a label for the relative age of a soldier. Age dependent polyethism was observed in soldiers: the individuals of the highest age class were the only ones leaving the nest to accompany the foraging workers, whereas all age categories were found inside the nest. After a significant loss of old individuals younger individuals show flexibility by replacing the missing outgoing nestmates. Caste regulation takes place by an increased rate of soldier development.     

Open-Air Litter Foraging in the Nasute Termite Longipeditermes longipes (Isoptera: Termitidae)

The Southeast Asian nasute termite Longipeditermes longipes forages on the open ground on leaf litter. Its monomorphic workers carry back food balls in their mandibles while dimorphic soldiers defensively surround the marching columns and the foraging patches. When mechanically disturbed, workers hide under the litter, whereas antennating soldiers face as closely as possible the source of disturbance. Foragers prefer the lower, nitrogen-rich layer of the litter. Soldier behavior and column organization (returning workers in the center lanes, outgoing workers in the two flanking lanes) are similar to those in the related genera Hospitalitermes and Lacessititermes, which, however, tend to forage above ground.     

Male soldier caste larvae are non-aggressive in the polyembryonic wasp Copidosoma floridanum

Polyembryonic wasps are the only parasitoids in which sociality has evolved. Theory implicates both competition and sex ratio manipulation in the evolution of a sterile soldier caste. However, investment in soldiers by males and females is predicted to differ depending upon how offspring are allocated to hosts and the mating system. Here, we compared male and female soldiers in the polyembryonic wasp Copidosoma floridanum. We found that male and female soldiers are morphologically identical. Unlike females, however, male soldiers were non-aggressive towards all competitors. We discuss these results in relation to theory and polyembryonic wasp biology.     

Panic escape polyethism in worker and soldier Coptotermes formosanus (Isoptera: Rhinotermitidae)

Termites were the first animal to form societies. Two hundred million years of evolution provide for a multitude of innate social behaviors that can be experimentally dissected. These fine‐tuned patterns of behavior are especially interesting when observing group decision making in the panic mode. In this study, we examined behavioral patterns of termites under panic conditions to gain insight into how an escape flow self‐organizes. One hundred worker and 10 soldier Coptotermes formosanus were released into agar plates. After a disturbance was created most workers followed each other and ran along the wall of dishes, thus forming a unidirectional escape flow, whereas soldiers showed a significantly higher frequency of moving to the center of the arena or on periphery of the escape flow as compared to workers. Agonistic behavior was usually observed as soldiers moved to center or periphery. This is the first report on the behavioral repertoire of termites when panicked, with details on the behavioral polymorphism of workers and soldiers during an escape.     

Age polyethism and defense in a tropical social wasp (Hymenoptera: Vespidae)

Although tapping the nest in simulated vertebrate attack caused all but 1-day-old workers of Polybia occidentalis to rush from inside and cover the envelope, defense itself—attack of a target—was shown to be carried out only by workers older than about 10 days. While foraging was also performed by older workers, the frequency-age distribution of defensive behavior was skewed to a significantly younger age than was that of foraging. The plot of mean individual probability of defending as a function of age was logistic, leveling off at 0.11 by the age of about 13 days. The distribution of the probability of defending among workers 13 days of age was random, indicating that there is no specialized defender class among older workers. Workers that defended were recruited from among both nest workers and foragers. Although foragers were more likely to defend than were nonforagers, nonforagers contributed more individuals to the pool of defenders because they were more numerous.     

Proximate mechanisms and evolution of caste polyphenism in social insects: From sociality to genes

Evidence has accumulated over several decades to prove the kin selection theory of evolution of social insects, however, proximate mechanisms of social behavior, and/or caste differentiation remain obscure. Genes that regulate these mechanisms are apparently selected through kin selection, and organisms have consequently acquired sociality. Here, I will discuss several studies that were performed recently by Matsumoto Laboratory, University of Tokyo, Tokyo, Japan, in various social insects, such as termites and ants, in order to reveal the regulatory mechanisms of social behavior and the evolutionary processes of sociality. First, I will review the foraging behavior of the black marching termite Hospitalitermes medioflavus, where well-organized task allocation among castes is apparent. This suggests that regulation of postembryonic development is important in social behavior. Next, I will summarize recent progress in identifying caste-specific gene expression in the damp-wood termite Hodotermopsis sjostedti. This constitutes the basis for molecular mechanisms of caste differentiation, and moreover, the genes identified might be good markers for social evolution. Finally, the mechanism underlying winglessness in ant workers is reviewed. Apoptotic cell death was detected at the stage of pupation in wingless worker castes. Furthermore, the areas of study recently designated as sociogenomics and ecological developmental biology are discussed.     

Phylogenetic evidence for a single,ancestral origin of a ‘true’ worker caste in termites

Phylogenetic analysis based on sequence variation in mitochondrial large‐subunit rRNA and cytochrome oxidase II genes was used to investigate the evolutionary relationships among termite families. Maximum likelihood and parsimony analyses of a combined nucleotide data set yield a single well‐supported topology, which is: (((((Termitidae, Rhinotermitidae), Serritermitidae), Kalotermitidae), (Hodotermitidae, Termopsidae)), Mastotermitidae). Although some aspects of this topology are consistent with previous schemes, overall it differs from any published. Optimization of ‘true’ workers onto the tree suggests that this caste originated once, early in the history of the lineage and has been lost secondarily twice. This scenario differs from the more widely accepted notion that workers are derived and of polyphyletic origin and that extant pseudergates, or ‘false’ workers, are their developmentally unspecialized ancestor caste. Worker gains and losses covary directly in number and direction with shifts in ‘ecological life type’. A test for correlated evolution which takes phylogenetic structure into account indicates that this pattern is of biological significance and suggests that the variable occurrence of a worker caste in termites has ecological determinants, apparently linked to differences in feeding and nesting habits.     

The evolution of caste polymorphism in social insects:0 Genetic release followed by diversifying evolution

Caste polymorphism, defined as the presence within a colony of two or more morphologically differentiated individuals of the same sex, is an important character of highly eusocial insects both in the Hymenoptera (ants, bees and wasps) and in the Isoptera (termites), the only two groups in the animal kingdom where highly eusocial species occur. Frequently, caste polymorphism extends beyond mere variations in size (although the extent of variations in size can be in the extreme) and is accompanied by allometric variations in certain body parts. How such polymorphism has evolved and why, in its extreme form, it is essentially restricted to the social insects are questions of obvious interest but without satisfactory answers at the present time. I present a hypothesis entitled ‘genetic release followed by diversifying evolution’, that provides potential answers to these questions. I argue that genetic release followed by diversifying evolution is made possible under a number of circumstances. One of them I propose is when some individuals in a species begin to rely on the indirect component of inclusive fitness while others continue to rely largely on the direct component, as workers and queens in social insects are expected to do. Thus when queens begin to rely on workers for most of the foraging, nest building and brood care, and workers begin to rely increasingly on queens to lay eggs—when queen traits and worker traits do not have to be expressed in the same individual—I postulate the relaxation of stabilizing selection and new spurts of directional selection on both queen-trait genes and worker-trait genes (in contrasting directions) leading to caste polymorphism.     

Behavioral flexibility in age castes of the antPheidole dentata

Division of labor among size and age classes in social insect colonies is a fundamental aspect of sociality, with such classes typically showing behavioral specialization and being associated with particular tasks for prolonged periods of time (i.e., forming castes). Theoretically, such specialization and division of labor enhance efficiency and, ultimately, reproductive success, and the ratios among members of those castes are hypothesized to be under selection and adaptive. However, our recent field study of the ant Pheidole dentatashowed no correlation between ecological factors which should affect colony growth and those caste ratios but implied flexibility in the association between minor worker age castes and their tasks. In laboratory experiments on behavioral flexibility in minor age castes of P. dentataold workers in colonies without young workers competently perform both old worker (castetypical) and young worker (atypical) tasks, and vice versa. The implications of these results for ergonomie theory are considered.     

Soldier caste with morphological and reproductive division in the aphid tribe Nipponaphidini

Summary. We investigated demographic, morphological and histological aspects of Distylaphis foliorum, a gall-forming nipponaphidine aphid from Java, Indonesia, whose first instar nymphs had been reported to have enlarged forelegs and attack other insects. The gall inhabitants of D. foliorum consisted of two discrete populations; one developing normally and the other remaining at the first instar. Morphometric analysis identified two types of first instar nymphs; nymphs with relatively long forelegs and slender abdomen, and nymphs with relatively short forelegs and fat abdomen. The former nymphs were found from both young galls and mature galls, while the latter nymphs were from young galls only. Histological analysis strongly suggested a reproductive division in the first instar. In the former nymphs from mature galls, ovaries and mycetomes were degenerate and replaced by well-developed fat body cells. These results indicated that D. foliorum has a morphologically differentiated sterile soldier caste in the first instar. This study is the first report of a soldier caste with morphological and reproductive division in the aphid tribe Nipponaphidini, and suggests that highly specialized soldier castes have evolved at least four times in aphids.Received 25 June 2004; revised 24 September 2004; accepted 11 October 2004.     

Of cast net and caste identity: Memetic differentiation between two fishing communities of Karnataka

Two fishing castes, Ambiga and Harikantra, of Karnataka employ different techniques for throwing cast nets in the same habitat. Ambigas throw the net from above the head, as opposed to the far easier Harikantra method of throwing at the waist level. These different techniques are described here as memes, transmitted through learning. A logico- deductive hypothesis is developed here to explain the origin and maintenance of the memetic difference between the castes, with the help of circumstantial semiotic and anthropological evidence.     

Caste differences in behavioral thresholds as a basis for polyethism during food recruitment in the ant,Pheidole pallidula (Nyl.) (Hymenoptera: Myrmicinae)

During foraging, societies of the polymorphic ant, Pheidole pallidula,display several collective patterns which differ in the ratio of recruited majors. The intensity of behavioral stimuli required to induce this majors' recruitment is determined by studying trail-laying and tactile invitations for the following two food recruitments: (I) the slow and weak recruitment of minors, without majors, to a pile of small, individually retrievable fruit flies and (2) the massive recruitment of both minors and majors to large, unretrievable cockroaches. The selective mobilization of majors only to large prey such as cockroaches is due both to their preferential invitation and to their higher behavioral threshold of response to recruiting stimuli. The experimental evidence of caste behavioral thresholds allow us to reconsider behavioral elasticity in the major caste as well as principles of division of labor in ant societies.     

Adaptation of a radiochemical assay for juvenile hormone biosynthesis to study caste differentiation in a primitive termite

A radiochemical assay measuring juvenile hormone synthesis by corpora allata incubated in vitro was adapted for use with the termite Zootermopsis angusticollis. Corpora allata from 3–4-day old virgin female neotenic reproductives were used in these studies because this caste showed the highest rates of juvenile hormone synthesis (0.6 pmol h^?1 per pair corpora allata). Juvenile hormone-III synthesis was linear for up to 6 h over the range of concentrations of labelled l-methionine from 27–280 μM. Rates of juvenile hormone synthesis were stimulated up to 10-fold in a dose-dependent manner by the addition of farnesoic acid to the incubation medium. However, the relatively high concentration of 120 μM farnesoic acid reduced the rates of juvenile hormone synthesis. The radiochemical assay was used to determine rates of juvenile hormone synthesis in vitro by corpora allata from larvae with a queen and king vs orphaned larvae. The presence of reproductives resulted in a suppression of larval corpus allatum activity relative to orphaned controls.     

Evolution of eusociality and the soldier caste in termites: a validation of the intrinsic benefit hypothesis

In termites the evolution of reproductive altruism is not based on a particularly high relatedness between nestmates. For the evolution and maintenance of the ancestral sterile soldier caste, the benefits generated by the soldiers' presence must compensate the loss of the soldiers' reproductive potential. To study the impact of soldiers on colony's fitness, we manipulated the proportion of soldiers to nonsoldiers in colonies of the dry-wood termite Cryptotermes secundus.'Soldier-less' colonies were obtained by removing soldiers and inhibiting their development with an extract of soldier heads. The colonies were set up for 1 year in experimental nests in the field. 'Soldier-less' colonies produced fewer soldiers. The reduction of soldiers neither affected colony survival nor helper growth, but fewer dispersing sexuals were produced in 'soldier-less' than in control colonies. This confirms what was only supposed so far, that in termites soldiers are maintained for their intrinsic benefit to cost ratio.