Hox Gene Expression Leads to Differential Hind Leg Development between Honeybee Castes

Beyond the physiological and behavioural, differences in appendage morphology between the workers and queens of Apis mellifera are pre-eminent. The hind legs of workers, which are highly specialized pollinators, deserve special attention. The hind tibia of worker has an expanded bristle-free region used for carrying pollen and propolis, the corbicula. In queens this structure is absent. Although the morphological differences are well characterized, the genetic inputs driving the development of this alternative morphology remain unknown. Leg phenotype determination takes place between the fourth and fifth larval instar and herein we show that the morphogenesis is completed at brown-eyed pupa. Using results from the hybridization of whole genome-based oligonucleotide arrays with RNA samples from hind leg imaginal discs of pre-pupal honeybees of both castes we present a list of 200 differentially expressed genes. Notably, there are castes preferentially expressed cuticular protein genes and members of the P450 family. We also provide results of qPCR analyses determining the developmental transcription profiles of eight selected genes, including abdominal-A, distal-less and ultrabithorax (Ubx), whose roles in leg development have been previously demonstrated in other insect models. Ubx expression in workers hind leg is approximately 25 times higher than in queens. Finally, immunohistochemistry assays show that Ubx localization during hind leg development resembles the bristles localization in the tibia/basitarsus of the adult legs in both castes. Our data strongly indicate that the development of the hind legs diphenism characteristic of this corbiculate species is driven by a set of caste-preferentially expressed genes, such as those encoding cuticular protein genes, P450 and Hox proteins, in response to the naturally different diets offered to honeybees during the larval period.

Cuticular Hydrocarbon Variation of Castes and Sex in the Weaver Ant Camponotus textor (Hymenoptera: Formicidae)

Cuticular hydrocarbons play important roles as chemical signatures of individuals, castes, sex and brood. They also can mediate the regulation of egg laying in ants, by informing directly or indirectly the reproductive status of queens. In this study we asked whether cuticular hydrocarbon profiles are correlated with castes and sex of Camponotus textor. Cuticular hydrocarbons were extracted from part of a mature colony (80 workers, 27 major workers, 27 queens, 27 virgin queens and 27 males). Results showed that cuticular hydrocarbons varied quantitatively and qualitatively among the groups and this variation was sufficiently strong to allow separation of castes and genders. We discuss the specificity of some compounds as possible regulatory compounds of worker tasks and reproduction in C. textor.

Shape differences rather than size differences between castes in the Neotropical swarm-founding wasp Metapolybia docilis (Hymenoptera: Vespidae, Epiponini)

Abstract Background Swarm-founding epiponine wasps are an intriguing group of social insects in which colonies are polygynic (several queens share reproduction) and differentiation between castes is often not obvious. However, caste differences in some may be more pronounced in later phases of the colony cycle. Results Using morphometric analyses and multivariate statistics, it was found that caste differences in Metapolybia docilis are slight but more distinct in latter stages of the colony cycle. Conclusions Because differences in body parts are so slight, it is proposed that such variation may be due to differential growth rates of body parts rather than to queens being larger in size, similar to other previously observed epiponines.

Key to the soldiers of Angularitermes Emerson with a new species from Brazilian Amazonia (Isoptera: Termitidae: Nasutitermitinae)

An identification key based on characters of the soldier caste is provided for species of Angularitermes. Soldiers of previously described species in the genus, A. clypeatus, A. nasutissimus, A. orestes, A. pinocchio and A. tiguassu, are illustrated along with a new species, Angularitermes coninasus, n. sp., that is described and illustrated from soldier and worker castes. Samples of the new species were collected from epigeal nests at the Brazilian Amazon rainforest. The soldier of A. coninasus, n. sp. is distinguished from its congeners by having a short conical frontal tube, much wider at its base.

Revision of the Neotropical termite genus Orthognathotermes Holmgren (Isoptera: Termitidae: Termitinae)

This is a taxonomic revision of the Neotropical genus Orthognathotermes Holmgren, 1910 (Termitidae, Termitinae), previously with nine species: O. aduncus, O. brevipilosus, O. gibberorum, O. heberi, O. humilis, O. insignis, O. macrocephalus, O. orthognathus and O. wheeleri. We redescribe these species and describe six new species: O. longilamina sp. nov., O. mirim sp. nov., O. okeyma sp. nov., O. pilosus sp. nov., O. tubesauassu sp. nov., and O. uncimandibularis sp. nov., based on soldiers and, when possible, imago castes along with the first description of imagos of O. wheeleri and O. heberi. We present a key for soldier identification and distribution maps for all species.

Molecular characterization of a mariner-like element in the Atta sexdens rubropilosa genome

Mobile elements are widely present in eukaryotic genomes. They are repeated DNA segments that are able to move from one locus to another within the genome. They are divided into two main categories, depending on their mechanism of transposition, involving RNA (class I) or DNA (class II) molecules. The mariner-like elements are class II transposons. They encode their own transposase, which is necessary and sufficient for transposition in the absence of host factors. They are flanked by a short inverted terminal repeat and a TA dinucleotide target site, which is duplicated upon insertion. The transposase consists of two domains, an N-terminal inverted terminal repeat binding domain and a C-terminal catalytic domain. We identified a transposable element with molecular characteristics of a mariner-like element in Atta sexdens rubropilosa genome. Identification started from a PCR with degenerate primers and queen genomic DNA templates, with which it was possible to amplify a fragment with mariner transposable-element homology. Phylogenetic analysis demonstrated that this element belongs to the mauritiana subfamily of mariner-like elements and it was named Asmar1. We found that Asmar1 is homologous to a transposon described from another ant, Messor bouvieri. The predicted transposase sequence demonstrated that Asmar1 has a truncated transposase ORF. This study is part of a molecular characterization of mobile elements in the Atta spp genome. Our finding of mariner-like elements in all castes of this ant could be useful to help understand the dynamics of mariner-like element distribution in the Hymenoptera.

Cell-sealing efficiency and reproductive workers in the species Melipona bicolor (Hymenoptera, Meliponini): double standard and possible rogue conduct

In many hymenopteran insect societies, selfish workers are policed, as selfishness can negatively affect the average inclusive fitness of one or both castes by reducing either the degree of average relatedness to the colony's male offspring or colony efficiency. In stingless bees, the rapid capping of brood cells could aid in controlling selfishness; to this end, we studied cell-sealing efficacy in Melipona bicolor. Execution of cell sealing was found to be both rapid and almost continuous. Comparing the performance of reproductive and non-reproductive workers, the former sealed the cells more efficiently when they contained their own eggs, but less so when the queens' eggs were involved. We argue that the occurrence of disruptions in cell sealing through self-serving reproductive workers is capable of undermining sealing efficacy as a policing instrument, thus making reproductive workers potential rogue individuals.

An illustrated key to the soldiers of Cyranotermes Araujo with a new species from Amazonia (Isoptera: Termitidae: Nasutitermitinae)

Until now, the Neotropical termite genus Cyranotermes was known from three species: C. timuassu Araujo, C. glaber Constantino, and C. caete Cancello. In this paper a new species, Cyranotermes karipuna, n. sp., is described and illustrated from imago, worker, and soldier castes, along with its nest. It is also provided an illustrated identification key to species of Cyranotermes, a map with the occurrence of all species, and the first description of the imago caste of Cyranotermes, based on the first description of the imago of C. timuassu, and the imago of the new species.

A morphologically specialized soldier caste improves colony defense in a neotropical eusocial bee

Division of labor among workers is common in insect societies and is thought to be important in their ecological success. In most species, division of labor is based on age (temporal castes), but workers in some ants and termites show morphological specialization for particular tasks (physical castes). Large-headed soldier ants and termites are well-known examples of this specialization. However, until now there has been no equivalent example of physical worker subcastes in social bees or wasps. Here we provide evidence for a physical soldier subcaste in a bee. In the neotropical stingless bee Tetragonisca angustula, nest defense is performed by two groups of guards, one hovering near the nest entrance and the other standing on the wax entrance tube. We show that both types of guards are 30% heavier than foragers and of different shape; foragers have relatively larger heads, whereas guards have larger legs. Low variation within each subcaste results in negligible size overlap between guards and foragers, further indicating that they are distinct physical castes. In addition, workers that remove garbage from the nest are of intermediate size, suggesting that they might represent another unrecognized caste. Guards or soldiers are reared in low but sufficient numbers (1-2% of emerging workers), considering that <1% usually perform this task. When challenged by the obligate robber bee Lestrimelitta limao, an important natural enemy, larger workers were able to fight for longer before being defeated by the much larger robber. This discovery opens up opportunities for the comparative study of physical castes in social insects, including the question of why soldiers appear to be so much rarer in bees than in ants or termites.