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The fate of a social insect colony is partially determined by its ability to allocate individuals to the caste most appropriate for the requirements for growth, maintenance, and reproduction. In pairs of dependent lineages of Pogonomyrmex barbatus, the allocation of individuals to the queen or worker caste is constrained by genotype, a system known as genetic caste determination (GCD). In mature GCD colonies, interlineage female eggs develop into sterile workers, while intralineage eggs become reproductively capable queens. Although the population-level consequences of this system have been intensively studied, the proximate mechanisms for GCD remain unknown. To elucidate these mechanisms, we brought newly mated queens into the laboratory and allowed them to establish colonies, nearly half of which unexpectedly produced virgin queens only seven months after colony founding. We genotyped eggs, workers, and the virgin queens from these colonies. Our results showed that queens in young colonies produce both interlineage and intralineage eggs, demonstrating that queens of GCD colonies indiscriminately use sperm of at least two lineages to fertilize their eggs. Intralineage eggs were more frequent in colonies producing virgin queens. These findings suggest that intralineage eggs are predetermined to become queens and that workers may cull these eggs when colonies are not producing queens. Virgin queens produced by young GCD colonies were smaller than field-caught virgin queens, and often had developmental problems. Hence, they are probably nonfunctional and represent an intense resource drain for developing colonies, not a contribution to colony fitness. Key words: genetic caste determination; Pogonomyrmex barbatus; reproduction; social insects.

Research has been conducted on the social insect queen multiple mating. The hypothesis that the queens mate multiply in manipulating sex ratios to their advantage in spite of mortality risk has been investigated and the results indicate that sex-ratio manipulation theory is unable to explain the multiple mating evolution in these insects.

Research has been conducted on the sexual selection by scramble competition. The effect of gravity on the sexual size dimorphism evolution in spiders has been investigated and the results indicate that the gravity imposed constraint on climbing males is a selective factor in male dwarfism determination.

Research has been conducted on the sociality evolution in insects. The study of the solitary and social behavior phylogenetic patterns and their relationship with ecological changes carried out via the analysis of the biogeographical and historical sociality patterns in the socially polymorphic sweat bee species is presented.

Causes of queen size dimorphism of the Leptothorax fugatuus ant have been studied in the first work on ant to find the heritability of quantitative traits in a quantitative genetic framework in a formal way. A positive scenario for evolutionary maintenance in the species is suggested.

Worker reproduction was not found, although expected, in three out of four ant species studied. Sex ratio biasing does occur among the three species and may be a mutually exclusive strategy for worker ants. The species Formica truncorum, F. exsecta and Myrmica ruginodis did not show evidence of worker reproduction, although worker reproduction could have occurred in F. rupa.

A microsatellite DNA study of multiple paternity in the leafcutter ant Atta colombica is discussed. Results confirm earlier nongentic sudies which found high levels of multiple mating by queens in higher leafcutter ants. These results are related to known patterns of paternity and polyandry in other eusocial Hymenoptera.

Workers of certain insect populations can strategically manipulate reproductive outcomes according to data they receive on their colonies. Studies of bees, ants and wasps show that genetic heterogeneity data are used by workers to maintain genetic integrity through the queens and regulate mating flights to determine spatially differentiated speciation.

The high level of relatedness among members of epiponine wasp colony is best explained by the cyclical oligogny hypothesis. This hypothesis postulates that recently built colonies are likely to be populated by many young queens with few eggs each. Nests of these wasps that are about to swarm have fewer older queens with mature ovaries and developing queens. Therefore, the population of queens in a colony is inversely proportional to the age of the colony.

Research has been conducted on breeding and dispersal patterns in monogyne ant population. The authors have demonstrated the existance of both inbreeding and sex-biased gene flow in Formica exsecta monogyne population.

Although 'polymorphic castes' in social insects are well known as one of the most important phenomena of polyphenism, few studies of caste-specific gene expressions have been performed in social insects. To identify genes specifically expressed in the soldier caste of the Japanese damp-wood termite Hodotermopsis japonica, we employed the differential-display method using oligo(dT) and arbitrary primers, compared mRNA from the heads of mature soldiers and pseudergates (worker caste), and identified a clone (PCR product) 329 bp in length termed SOL1. Northern blot analysis showed that the SOL1 mRNA is about 1.0 kb in length and is expressed specifically in mature soldiers, but not in pseudergates, even in the presoldier induction by juvenile hormone analogue, suggesting that the product is specific for terminally differentiated soldiers. By using the method of 5'- and 3'-rapid amplification of cDNA ends, we isolated the full length of SOL1 cDNA, which contained an ORF with a putative signal peptide at the N terminus. The sequence showed no significant homology with any other known protein sequences. In situ hybridization analysis showed that SOL1 is expressed specifically in the mandibular glands. These results strongly suggest that the SOL1 gene encodes a secretory protein specifically synthesized in the mandibular glands of the soldiers. Histological observations revealed that the gland actually develops during the differentiation into the soldier caste.

Castes in social insects are a dramatic example of polyphenism. Polyphenic insects can develop into alternative forms, usually in response to environmental cues. We recently were successful in using suppressive subtractive hybridization (Clontech) to find >100 unique ESTs differentially expressed during development of queen and worker honey bees. We have extended the study to include soldier determination in Pheidole ants. As in queen determination in honey bees, the switch to soldier development in Pheidole is mediated by juvenile hormone. In contrast, the switch in Pheidole ants is inhibited by the presence of adult soldiers. Our approach includes construction of subtracted libraries for bipotential larvae and soldier larvae. Differentially expressed ESTs are used to probe time series of mRNA from developing larvae under various conditions, including those treated with juvenile hormone and exposed to adult soldiers. The results indicate gene expression patterns that can be attributed to nutritional and hormonal signals that constitute the developmental switching mechanism.