N. A. Buck

Expression of insulin pathway genes during the period of caste determination in the honey bee, Apis mellifera.

Female honeybees have two castes, queens and workers. Developmental fate is determined by larval diet. Coding sequences made available through the Honey Bee Genome Sequencing Consortium allow for a pathway‐based approach to understanding caste determination. We examined the expression of several genes of the insulin signalling pathway, which is central to regulation of growth based on nutrition. We found one insulin‐like peptide expressed at very high levels in queen but not worker larvae. Also, the gene for an insulin receptor was expressed at higher levels in queen larvae during the 2nd larval instar. These results demonstrate that the insulin pathway is a compelling candidate for pursing the relationship between diet and downstream signals involved in caste determination and differentiation.

Highly similar microbial communities are shared among related and trophically similar ant species.

Ants dominate many terrestrial ecosystems, yet we know little about their nutritional physiology and ecology. While traditionally viewed as predators and scavengers, recent isotopic studies revealed that many dominant ant species are functional herbivores. As with other insects with nitrogen‐poor diets, it is hypothesized that these ants rely on symbiotic bacteria for nutritional supplementation. In this study, we used cloning and 16S sequencing to further characterize the bacterial flora of several herbivorous ants, while also examining the beta diversity of bacterial communities within and between ant species from different trophic levels. Through estimating phylogenetic overlap between these communities, we tested the hypothesis that ecologically or phylogenetically similar groups of ants harbor similar microbial flora. Our findings reveal: (i) clear differences in bacterial communities harbored by predatory and herbivorous ants; (ii) notable similarities among communities from distantly related herbivorous ants and (iii) similar communities shared by different predatory army ant species. Focusing on one herbivorous ant tribe, the Cephalotini, we detected five major bacterial taxa that likely represent the core microbiota. Metabolic functions of bacterial relatives suggest that these microbes may play roles in fixing, recycling, or upgrading nitrogen. Overall, our findings reveal that similar microbial communities are harbored by ants from similar trophic niches and, to a greater extent, by related ants from the same colonies, species, genera, and tribes. These trends hint at coevolved histories between ants and microbes, suggesting new possibilities for roles of bacteria in the evolution of both herbivores and carnivores from the ant family Formicidae.

Hexameric storage proteins during metamorphosis and egg production in the diamondback moth, Plutella xylostella (Lepidoptera)

As in many Lepidoptera, Plutella xylostella adults do not feed on protein and females must use accumulated reserves to supply vitellogenin synthesis. Storage proteins were quantified in females and males from the late larval stage through day 4 of adult life. The level of storage protein peaked in the early pupal stage, with females having about twice as much as males. In males, the level fell through pupal development and dropped to a trace by one day after eclosion. In females, level of storage proteins fell until eclosion, and then rose dramatically within four hours after the molt to about 2/3 of the original peak level. This post-eclosion increase, which has not been reported previously in insects, suggests that adult females synthesize hexamerins to resequester amino acids. Subsequently, the level of storage proteins fell as vitellogenin appeared and eggs were laid. The ability to synthesize and sequester amino acids as storage proteins during the adult stage has wide-ranging implication for protein management in insects, particularly those that are long-lived and have flexible schedules of reproduction.

Storage proteins in ants during development and colony founding

Three classes of storage proteins from larvae of four species of ants (Crematogaster opuntiae, Pheidole spadonia, Solenopsis xyloni and Conomyrma sp.) were identified and characterized for native and subunit sizes, density and amino acid composition. First, hexamerins contained moderately high proportions of aromatic amino acids (x = 12.9 mol%). A second type of storage protein contained extremely high proportions of glutamine/glutamic acid (x = 21.1 mol%). Third, dimeric proteins had densities suggesting they were very high density lipoproteins (VHDL). These VHDLs may be homologous with similar proteins that carry chromophores in Lepidoptera. The same types of storage proteins found in larvae were also present in the fat bodies of adult queens at the time of their mating flights. The class of the dominant protein varied with species. In Cr. opuntiae queens, storage proteins were almost completely depleted during colony founding. In ants, the ability of adult females to express storage protein genes may have been an important step in the evolution of the claustral mode of colony initiation, in which females can produce the first set of workers without leaving the nest to search of food.

Storage proteins in vespid wasps: characterization, developmental pattern, and occurrence in adults

Wasps of family Vespidae contain three types of major proteins that have the size, amino acid composition, subunit composition, immunological reactivity, and pattern of occurrence characteristic of storage proteins. The three types of storage protein, which have been identified in other Hymenoptera, are very high density lipoprotein, high glutamine/glutamic acid protein, and hexamerin. The predominant pattern of occurrence for these proteins is as known from most or all Holometabola: synthesis during the last larval instar and utilization as an amino acid source during metamorphosis. Hexamerin also occurred in a large young adult female Monobia quadridens but not a small one, which suggests that carry-over into adult females is a reaction norm response to quantity of larval provisions, because these wasps could not have fed as adults. In two paper wasp species of the genus Polistes, hexamerin was present in large adult females which emerged during the colony cycle phase when reproductive females are typically produced, but not in adult female offspring that emerged earlier in the colony cycle or in adult females that were workers. It cannot be confirmed by these data that the hexamerin in the adult paper wasps represented carry-over from metamorphosis rather than post-emergence feeding, but the pattern of occurrence suggests that presence of storage protein may play a role in caste differentiation in paper wasps. No storage protein was found in any adult Vespula maculifrons, a yellowjacket wasp, suggesting that caste differentiation in vespine wasps does not incorporate storage protein as a component.

Response of storage protein levels to variation in dietary protein levels.

Storage proteins have been found to play a major role in insect metamorphosis and egg production and are accumulated during the actively feeding larval stage. Yet few studies have focused on how nutrition affects storage protein levels. Three storage proteins were identified in male and female Heliothis virescens pupae, one arylphorin and two putative high-methionine hexamers. Storage proteins were quantified in early pupae and in pharate adults. Storage protein levels peaked in 48-h pupae and were more abundant in females across all stages. Both male and female pharate adults retained a portion of total storage protein levels and females retained greater levels overall. In females, post-eclosion protein reserves will likely be used toward egg manufacturing, while the role of protein reserves in males remains speculative. In our previous study of H. virescens larvae, we found that protein-derived growth in females progressively increased as dietary protein levels increased. Our present data show that levels of storage protein also increased progressively along with dietary protein levels. This suggests that females allocated protein, in excess of adult tissue formation needs, toward storage protein. Our study is the first to demonstrate how responsive storage protein levels can be in face of varying levels of dietary protein.

Depletion of reserves in ant queens during claustral colony founding

SummaryGynes in the claustrally-founding speciesCrematogaster opuntiae andCamponotus festinatus accumulate large amounts of protein and lipid between the time of eclosion and mating. During colony founding, protein is depleted from both the thorax and abdomen and lipid from the abdomen. The abdomen, and specifically its accumulated storage protein, provides an amino acid store equivalent to or larger than that of flight muscle. The importance of this second major protein reserve in the evolution of claustral colony founding should be considered.

A role for storage proteins in autogenous reproduction in Aedes atropalpus

Abstract In the autogenous mosquito, Aedes atropalpus , storage proteins accumulated during the larval stage may serve as an amino acid reserve for oogenesis, in addition to metamorphosis. Hexameric storage proteins accumulate during larval development and include subunits of three different masses: 62.5, 66, 72.5 kDa. All three types of subunits are found in the female but only the larger two are in males. In females, storage proteins are only partially depleted by the time of eclosion. The remaining protein amounts to about 40% of the original store. Males, in contrast, exhaust their supply of stored protein during metamorphosis. In the female, the storage proteins disappear over the first days after eclosion, and are depleted before vitellogenin/vitellin levels reach their maximum. This suggests that the amino acids held in storage proteins are transferred to vitellogenesis, enabling autogenous egg development. The fact that these amino acids are not available for egg development until after eclosion, later than in many other insects, probably reflects a relatively recent evolution from blood-feeding ancestors.

Protein, lipid and carbohydrate use during metamophosis in the fire ant, Solenopsis xyloni

Abstract. Concentrations of total sugars, lipids and soluble proteins were measured in prepupae and pupae of a native fire ant, Solenopsis xyloni W. M. wheeler (Hymenoptera: Formicidae). Changes in the concentratons of these reserves were examined over the course of metamorphosis, in response to starvation, and in relation to body size. During metamorphosis, only lipid concentrations changed during the prepuapal period, dropping slightly. During the pupal state, however, approximately 75% of total sugars, 45% of lipids and 40% of soluble proteins were used. Starvation immediately prior to metamorphosis greatly decreased the quantity of carbohydrate detected at the beginning of the prepupal stage. Soluble protein levels were also slightly reduced. In contrast, lipid concentrations in prepupae increased in individuals that had been starved for 2–4 days immediately before metamorphosis. The relationship between body size and amount depended on the type of reserve. Lipid concetrations decreased with increasing size, while carbohydrate levels tended to increase slightly. Overall, soluble protein concentration did not change with size. Gel electrophoresis showed that two major polypeptides account for most of the soluble protein and one on these decreased sharply over the pupal period.

Storage Protein Content as a Functional Marker for Colony‐Founding Strategies: A Comparative Study within the Harvester Ant Genus Pogonomyrmex

Claustral colony founding, in which new queens rear their first clutch of workers solely from internal reserves, is common in the higher ant subfamilies and is believed to represent a major innovation in ant life histories. The ability to store large amounts of amino acids contained in storage proteins is an essential physiological trait for claustral colony founding by ant queens. To determine whether there is an association between storage protein content and colony‐founding strategy, we identified and quantified two major storage proteins in queens of five harvester ant species in the genus Pogonomyrmex that differ in colony‐founding strategy. Queens of the fully claustral nonforaging species Pogonomyrmex rugosus and Pogonomyrmex maricopa contained the greatest amount of these proteins. Facultatively foraging semiclaustral Pogonomyrmex occidentalis queens contained an intermediate amount. Obligately foraging semiclaustral Pogonomyrmex californicus queens from two different populations contained significantly less storage protein than the other independent‐founding species. Queens of the dependent‐founding social parasite Pogonomyrmex anergismus also contained little storage protein. Our results suggest that storage protein content has evolved in concert with colony‐founding strategies in the genus Pogonomyrme and provides a good functional marker for colony‐founding strategy.