Prevalence and Genetic Diversity of a Microsporidian Parasite in the Black Imported Fire Ant and Its Social Parasitic Ant (Formicidae: Myrmicinae: Solenopsis) in Buenos Aires Province, Argentina

Microsporidia are natural pathogens of arthropods and have been used as biological control against insect pests. In the United States, efforts to control the invasive Red Imported Fire Ant, Solenopsis invicta, and Black Imported Fire Ant, Solenopsis richteri, have included the use of the microsporidium, Kneallhazia solenopsae. However, there is limited information about the genetic differences among the microsporidian variants found in S. invicta and in S. richteri. In this study, we assessed the prevalence and genetic diversity of K. solenopsae in native populations of S. richteri in Argentina (South America). Additionally, we examined the social parasitic ant, Solenopsis daguerrei, which is found in some S. richteri nests, for the presence of this microsporidium. The survey of 219 S. richteri nests revealed K. solenopsae infections in all five sites analyzed, with 28 colonies (12.8%) positive for the microsporidium. Among the 180 S. daguerrei individuals collected, seven ants (3.9%) from three sites tested positive for K. solenopsae. Phylogenetic analyses of the microsporidian variants present in S. richteri and S. daguerrei based on partial small subunit ribosomal gene sequences (SSU rRNA) showed that both ant species shared the same variant, which is different from the ones found in S. invicta. Further studies are needed to determine the pathogenicity of genetically different K. solenopsae variants among Solenopsis species.

Direct and indirect genetic effects of a social supergene

Indirect genetic effects describe phenotypic variation that results from differences in the genotypic composition of social partners. Such effects represent heritable sources of environmental variation in eusocial organisms because individuals are typically reared by their siblings. In the fire ant Solenopsis invicta, a social supergene exhibits striking indirect genetic effects on worker regulation of colony queen number, such that the genotypic composition of workers at the supergene determines whether colonies contain a single or multiple queens. We assessed the direct and indirect genetic effects of this supergene on gene expression in brains and abdominal tissues from laboratory-reared workers and compared these with previously published data from field-collected prereproductive queens. We found that direct genetic effects caused larger gene expression changes and were more consistent across tissue types and castes than indirect genetic effects. Indirect genetic effects influenced the expression of many loci but were generally restricted to the abdominal tissues. Further, indirect genetic effects were only detected when the genotypic composition of social partners differed throughout the development and adult life of focal workers, and were often only significant with relatively lenient statistical cutoffs. Our study provides insight into direct and indirect genetic effects of a social supergene on gene regulatory dynamics across tissues and castes in a complex society.

Development and Characterization of 20 Genomic SSR Markers for Ornamental Cultivars of Weigela

Weigela (Caprifoliaceae) is a genus of ornamental plants popular for its phenotypic variation and hardiness, that includes species hybridized to produce the commercially available cultivars. Despite its popularity, limited genetic resources exist for the genus. Twenty genomic simple sequence repeat (gSSR) markers distributed across the genome were developed using low coverage whole-genome sequencing data of Weigela Spilled Wine^®. A cross-amplification evaluation with these 20 gSSR markers on a collection of 18 Weigela cultivars revealed a total of 111 unique alleles, including 36 private alleles. A diagrammatic key was constructed to identify cultivars using only six of the gSSR markers, demonstrating the newly developed gSSR markers are immediately useful for cultivar identification. Future uses could include breeding with marker-assisted selection, determining the history of hybridization of the current cultivated lines, aiding in the construction of genetic maps, and assessing the patterns of population genetic structure of Weigela spp.

Evolution of a supergene that regulates a trans-species social polymorphism

Supergenes are clusters of linked genetic loci that jointly affect the expression of complex phenotypes, such as social organization. Little is known about the origin and evolution of these intriguing genomic elements. Here we analyse whole-genome sequences of males from native populations of six fire ant species and show that variation in social organization is under the control of a novel supergene haplotype (termed Sb), which evolved by sequential incorporation of three inversions spanning half of a 'social chromosome'. Two of the inversions interrupt protein-coding genes, resulting in the increased expression of one gene and modest truncation in the primary protein structure of another. All six socially polymorphic species studied harbour the same three inversions, with the single origin of the supergene in their common ancestor inferred by phylogenomic analyses to have occurred half a million years ago. The persistence of Sb along with the ancestral SB haplotype through multiple speciation events provides a striking example of a functionally important trans-species social polymorphism presumably maintained by balancing selection. We found that while recombination between the Sb and SB haplotypes is severely restricted in all species, a low level of gene flux between the haplotypes has occurred following the appearance of the inversions, potentially mitigating the evolutionary degeneration expected at genomic regions that cannot freely recombine. These results provide a detailed picture of the structural genomic innovations involved in the formation of a supergene controlling a complex social phenotype.

Genetic Diversity and Wolbachia Infection Patterns in a Globally Distributed Invasive Ant

Understanding the phylogeographic history of an invasive species may facilitate reconstructing the history and routes of its invasion. The longhorn crazy ant, Paratrechina longicornis, is a ubiquitous agricultural and household pest throughout much of the tropics and subtropics, but little is known about the history of its spread. Here, we examine worldwide genetic variation in P. longicornis and its associated Wolbachia bacterial symbionts. Analyses of mtDNA sequences of 248 P. longicornis workers (one per colony) from 13 geographic regions reveal two highly diverged mtDNA clades that co-occur in most of the geographic regions. These two mtDNA clades are associated with different Wolbachia infection patterns, but are not congruent with patterns of nDNA (microsatellite) variation. Multilocus sequence typing reveals two distinct Wolbachia strains in P. longicornis, namely, wLonA and wLonF. The evolutionary histories of these two strains differ; wLonA appears to be primarily transmitted maternally, and patterns of mtDNA and nDNA variation and wLonA infection status are consistent with a relatively recent Wolbachia-induced selective sweep. In contrast, the observed patterns of mtDNA variation and wLonF infections suggest frequent horizontal transfer and losses of wLonF infections. The lack of nDNA structure among sampled geographic regions coupled with the finding that numerous mtDNA haplotypes are shared among regions implies that inadvertent long-distance movement through human commerce is common in P. longicornis and has shaped the genetic structure of this invasive ant worldwide.

Joint Evolution of Asexuality and Queen Number in an Ant

Ants exhibit a striking diversity of reproductive systems, varying in traits such as the number of reproductives per colony [1], the mode of daughter production (sexual or asexual) [2], and the mode of caste determination (genetic or environmental) [3]. Species employing mixed reproductive systems present a unique opportunity to explore the causes and consequences of alternative breeding strategies. Mixed reproductive systems in ants include social polymorphism in colony queen number, whereby single-queen (monogyne) and multiple-queen (polygyne) colonies co-occur within species [4-7], and facultative asexuality, in which female offspring may be produced sexually or asexually within colonies [8-13]. Here, we document a remarkable confluence of multiple mixed reproductive systems in the tropical fire ant, Solenopsis geminata, in a population with three important features: (1) polygyne colonies produce workers sexually but queens asexually, whereas monogyne colonies produce both castes sexually; (2) polygyne queens mate with monogyne males to produce workers, but monogyne queens do not mate with polygyne males; and (3) different asexual/polygyne lineages evidently were founded separately by genetically distinct founder queens, which appear to have originated from the same neighboring monogyne population. Multiple asexual/polygyne genomes are transmitted undiluted in this system, but sterile workers produced with sperm from a sexually-reproducing/monogyne population are necessary for the persistence of these lineages. The intersection of social polymorphism, facultative asexuality, and genetic caste determination marks this population of S. geminata as an embodiment of the diversity of ant reproductive systems and suggests previously unknown connections between these phenomena.

Supercolonial structure of invasive populations of the tawny crazy ant Nylanderia fulva in the US

BACKGROUND

Social insects are among the most serious invasive pests in the world, particularly successful at monopolizing environmental resources to outcompete native species and achieve ecological dominance. The invasive success of some social insects is enhanced by their unicolonial structure, under which the presence of numerous queens and the lack of aggression against non-nestmates allow high worker densities, colony growth, and survival while eliminating intra-specific competition. In this study, we investigated the population genetics, colony structure and levels of aggression in the tawny crazy ant, Nylanderia fulva, which was recently introduced into the United States from South America.

RESULTS

We found that this species experienced a genetic bottleneck during its invasion lowering its genetic diversity by 60%. Our results show that the introduction of N. fulva is associated with a shift in colony structure. This species exhibits a multicolonial organization in its native range, with colonies clearly separated from one another, whereas it displays a unicolonial system with no clear boundaries among nests in its invasive range. We uncovered an absence of genetic differentiation among populations across the entire invasive range, and a lack of aggressive behaviors towards conspecifics from different nests, even ones separated by several hundreds of kilometers.

CONCLUSIONS

Overall, these results suggest that across its entire invasive range in the U.S.A., this species forms a single supercolony spreading more than 2000 km. In each invasive nest, we found several, up to hundreds, of reproductive queens, each being mated with a single male. The many reproductive queens per nests, together with the free movement of individuals between nests, leads to a relatedness coefficient among nestmate workers close to zero in introduced populations, calling into question the stability of this unicolonial system in which indirect fitness benefits to workers is apparently absent.

Unexpected patterns of segregation distortion at a selfish supergene in the fire ant Solenopsis invicta

BACKGROUND

The Sb supergene in the fire ant Solenopsis invicta determines the form of colony social organization, with colonies whose inhabitants bear the element containing multiple reproductive queens and colonies lacking it containing only a single queen. Several features of this supergene - including suppressed recombination, presence of deleterious mutations, association with a large centromere, and "green-beard" behavior - suggest that it may be a selfish genetic element that engages in transmission ratio distortion (TRD), defined as significant departures in progeny allele frequencies from Mendelian inheritance ratios. We tested this possibility by surveying segregation ratios in embryo progenies of 101 queens of the "polygyne" social form (3512 embryos) using three supergene-linked markers and twelve markers outside the supergene.

RESULTS

Significant departures from Mendelian ratios were observed at the supergene loci in 3-5 times more progenies than expected in the absence of TRD and than found, on average, among non-supergene loci. Also, supergene loci displayed the greatest mean deviations from Mendelian ratios among all study loci, although these typically were modest. A surprising feature of the observed inter-progeny variation in TRD was that significant deviations involved not only excesses of supergene alleles but also similarly frequent excesses of the alternate alleles on the homologous chromosome. As expected given the common occurrence of such "drive reversal" in this system, alleles associated with the supergene gain no consistent transmission advantage over their alternate alleles at the population level. Finally, we observed low levels of recombination and incomplete gametic disequilibrium across the supergene, including between adjacent markers within a single inversion.

CONCLUSIONS

Our data confirm the prediction that the Sb supergene is a selfish genetic element capable of biasing its own transmission during reproduction, yet counterselection for suppressor loci evidently has produced an evolutionary stalemate in TRD between the variant homologous haplotypes on the "social chromosome". Evidence implicates prezygotic segregation distortion as responsible for the TRD we document, with "true" meiotic drive the most likely mechanism. Low levels of recombination and incomplete gametic disequilibrium across the supergene suggest that selection does not preserve a single uniform supergene haplotype responsible for inducing polygyny.

Evolution of Olfactory Functions on the Fire Ant Social Chromosome

Understanding the molecular evolutionary basis of social behavior is a major challenge in evolutionary biology. Social insects evolved a complex language of chemical signals to coordinate thousands of individuals. In the fire ant Solenopsis invicta, chemical signals are involved in the determination of a polymorphic social organization. Single-queen (monogyne) or multiqueen (polygyne) social structure is determined by the "social chromosome," a nonrecombining region containing ∼504 genes with two distinct haplotypes, SB and Sb. Monogyne queens are always SBB, while polygyne queens are always SBb. Workers discriminate monogyne from polygyne queens based on olfactory cues. Here, we took an evolutionary genomics approach to search for candidate genes in the social chromosome that could be responsible for this discrimination. We compared the SB and Sb haplotypes and analyzed the evolutionary rates since their divergence. Notably, we identified a cluster of 23 odorant receptors in the nonrecombining region of the social chromosome that stands out in terms of nonsynonymous changes in both haplotypes. The cluster includes twelve genes formed by recent Solenopsis-specific duplications. We found evidence for positive selection on several tree branches and significant differences between the SB and Sb haplotypes of these genes. The most dramatic difference is the complete deletion of two of these genes in Sb. These results suggest that the evolution of polygyne social organization involved adaptations in olfactory genes and opens the way for functional studies of the molecular mechanisms underlying social behavior.

Viral infections in fire ants lead to reduced foraging activity and dietary changes

Despite the presence of conserved innate immune function, many insects have evolved a variety of mechanical, chemical, and behavioral defensive responses to pathogens. Illness-induced anorexia and dietary changes are two behavioral defensive strategies found in some solitary insects, but little is known regarding the role of such behaviors in social insects, especially in ants. In the present study we examined if such reduced foraging activity exists for a social insect, the invasive fire ant Solenopsis invicta, and its viral pathogen, Solenopsis invicta virus 1 (SINV-1). Virus-free fire ant colonies were split into two colony fragments, one of which subsequently was inoculated with SINV-1. Four food resources with different macronutrient ratios were presented to both colony fragments. SINV-1-inoculated colony fragments consistently displayed reduced foraging performance (e.g., foraging intensity and recruitment efficiency), a decline in lipid intake, and a shift in dietary preference to carbohydrate-rich foods compared with virus-free fragments. These findings provide the first evidence for virus-induced behavioral responses and dietary shifts in shaping the host-pathogen interactions in fire ants. The findings also suggest a possible mechanism for how fire ant colonies respond to viral epidemics. Potential implications of these behavioral differences for current management strategies are discussed.

Positive selection on sociobiological traits in invasive fire ants

The fire ant Solenopsis invicta and its close relatives are highly invasive. Enhanced social cooperation may facilitate invasiveness in these and other invasive ant species. We investigated whether invasiveness in Solenopsis fire ants was accompanied by positive selection on sociobiological traits by applying a phylogenomics approach to infer ancient selection, and a population genomics approach to infer recent and ongoing selection in both native and introduced S. invicta populations. A combination of whole-genome sequencing of 40 haploid males and reduced-representation genomic sequencing of 112 diploid workers identified 1,758,116 and 169,682 polymorphic markers, respectively. The resulting high-resolution maps of genomic polymorphism provide high inference power to test for positive selection. Our analyses provide evidence of positive selection on putative ion channel genes, which are implicated in neurological functions, and on vitellogenin, which is a key regulator of development and caste determination. Furthermore, molecular functions implicated in pheromonal signalling have experienced recent positive selection. Genes with signatures of positive selection were significantly more often those overexpressed in workers compared with queens and males, suggesting that worker traits are under stronger selection than queen and male traits. These results provide insights into selection pressures and ongoing adaptation in an invasive social insect and support the hypothesis that sociobiological traits are under more positive selection than nonsocial traits in such invasive species.

Evolution of long centromeres in fire ants

BACKGROUND

Centromeres are essential for accurate chromosome segregation, yet sequence conservation is low even among closely related species. Centromere drive predicts rapid turnover because some centromeric sequences may compete better than others during female meiosis. In addition to sequence composition, longer centromeres may have a transmission advantage.

RESULTS

We report the first observations of extremely long centromeres, covering on average 34 % of the chromosomes, in the red imported fire ant Solenopsis invicta. By comparison, cytological examination of Solenopsis geminata revealed typical small centromeric constrictions. Bioinformatics and molecular analyses identified CenSol, the major centromeric satellite DNA repeat. We found that CenSol sequences are very similar between the two species but the CenSol copy number in S. invicta is much greater than that in S. geminata. In addition, centromere expansion in S. invicta is not correlated with the duplication of CenH3. Comparative analyses revealed that several closely related fire ant species also possess long centromeres.

CONCLUSIONS

Our results are consistent with a model of simple runaway centromere expansion due to centromere drive. We suggest expanded centromeres may be more prevalent in hymenopteran insects, which use haplodiploid sex determination, than previously considered.

Agricultural applications of insect ecological genomics

Agricultural entomology is poised to benefit from the application of ecological genomics, particularly the fields of biofuels generation and pest control. Metagenomic methods can characterize microbial communities of termites, wood-boring beetles and livestock pests, and transcriptomic approaches reveal molecular bases behind wood-digesting capabilities of these insects, leading to potential mechanisms for biofuel generation. Genome sequences are being exploited to develop new pest control methods, identify candidate antigens to vaccinate livestock, and discover RNAi target sequences and potential non-target effects in other insects. Gene content analyses of pest genome sequences and their endosymbionts suggest metabolic interdependencies between organisms, exposing potential gene targets for insect control. Finally, genome-wide association studies and genotyping by high-throughput sequencing promise to improve management of pesticide resistance.

Dynamic changes in host-virus interactions associated with colony founding and social environment in fire ant queens (Solenopsis invicta)

The dynamics of host-parasite interactions can change dramatically over the course of a chronic infection as the internal (physiological) and external (environmental) conditions of the host change. When queens of social insects found a colony, they experience changes in both their physiological state (they develop their ovaries and begin laying eggs) and the social environment (they suddenly stop interacting with the other members of the mother colony), making this an excellent model system for examining how these factors interact with chronic infections. We investigated the dynamics of host-viral interactions in queens of Solenopsis invicta (fire ant) as they transition from mating to colony founding/brood rearing to the emergence of the first workers. We examined these dynamics in naturally infected queens in two different social environments, where queens either founded colonies as individuals or as pairs. We hypothesized that stress associated with colony founding plays an important role in the dynamics of host-parasite interactions. We also hypothesized that different viruses have different modalities of interaction with the host that can be quantified by physiological measures and genomic analysis of gene expression in the host. We found that the two most prevalent viruses, SINV-1 and SINV-2, are associated with different fitness costs that are mirrored by different patterns of gene expression in the host. In fact SINV-2, the virus that imposes the significant reduction of a queen's reproductive output is also associated with larger changes of global gene expression in the host. These results show the complexity of interactions between S. invicta and two viral parasites. Our findings also show that chronic infections by viral parasites in insects are dynamic processes that may pose different challenges in the host, laying the groundwork for interesting ecological and evolutionary considerations.

Sociogenomics of cooperation and conflict during colony founding in the fire ant Solenopsis invicta

One of the fundamental questions in biology is how cooperative and altruistic behaviors evolved. The majority of studies seeking to identify the genes regulating these behaviors have been performed in systems where behavioral and physiological differences are relatively fixed, such as in the honey bee. During colony founding in the monogyne (one queen per colony) social form of the fire ant Solenopsis invicta, newly-mated queens may start new colonies either individually (haplometrosis) or in groups (pleometrosis). However, only one queen (the “winner”) in pleometrotic associations survives and takes the lead of the young colony while the others (the “losers”) are executed. Thus, colony founding in fire ants provides an excellent system in which to examine the genes underpinning cooperative behavior and how the social environment shapes the expression of these genes. We developed a new whole genome microarray platform for S. invicta to characterize the gene expression patterns associated with colony founding behavior. First, we compared haplometrotic queens, pleometrotic winners and pleometrotic losers. Second, we manipulated pleometrotic couples in order to switch or maintain the social ranks of the two cofoundresses. Haplometrotic and pleometrotic queens differed in the expression of genes involved in stress response, aging, immunity, reproduction and lipid biosynthesis. Smaller sets of genes were differentially expressed between winners and losers. In the second experiment, switching social rank had a much greater impact on gene expression patterns than the initial/final rank. Expression differences for several candidate genes involved in key biological processes were confirmed using qRT-PCR. Our findings indicate that, in S. invicta, social environment plays a major role in the determination of the patterns of gene expression, while the queen's physiological state is secondary. These results highlight the powerful influence of social environment on regulation of the genomic state, physiology and ultimately, social behavior of animals.

The characterization of the genomic basis for complex behaviors is one of the major goals of biological research. The genomic state of an individual results from the interplay between its internal condition (the “nature”) and the external environment (the “nurture”), which may include the social environment. Colony founding in the fire ant Solenopsis invicta is a complex process that serves as a useful model for investigating how the interplay between genes and social environment shapes social behavior. Unrelated, newly mated S. invicta queens may start a new colony as a group, but ultimately only one queen will survive and gain full reproductive dominance. By uncovering the genetic basis for founding behavior in fire ants we therefore provide useful insights into how cooperative behavior evolved in a context that might be considered primitively eusocial, because newly mated queens in a founding association are morphologically, physiologically and genetically very similar and display no evident division of labor. Our results suggest that social environment (founding singly or in pairs, switching dominance rank vs. maintaining rank) is a much greater driver of gene expression changes than social rank itself, suggesting that social environment, and not reproductive state, is a key regulator of gene expression, physiology and ultimately, behavior.

A Y-like social chromosome causes alternative colony organization in fire ants

Intraspecific variability in social organization is common, yet the underlying causes are rarely known. In the fire ant Solenopsis invicta, the existence of two divergent forms of social organization is under the control of a single Mendelian genomic element marked by two variants of an odorant-binding protein gene. Here we characterize the genomic region responsible for this important social polymorphism, and show that it is part of a pair of heteromorphic chromosomes that have many of the key properties of sex chromosomes. The two variants, hereafter referred to as the social B and social b (SB and Sb) chromosomes, are characterized by a large region of approximately 13 megabases (55% of the chromosome) in which recombination is completely suppressed between SB and Sb. Recombination seems to occur normally between the SB chromosomes but not between Sb chromosomes because Sb/Sb individuals are non-viable. Genomic comparisons revealed limited differentiation between SB and Sb, and the vast majority of the 616 genes identified in the non-recombining region are present in the two variants. The lack of recombination over more than half of the two heteromorphic social chromosomes can be explained by at least one large inversion of around 9 megabases, and this absence of recombination has led to the accumulation of deleterious mutations, including repetitive elements in the non-recombining region of Sb compared with the homologous region of SB. Importantly, most of the genes with demonstrated expression differences between individuals of the two social forms reside in the non-recombining region. These findings highlight how genomic rearrangements can maintain divergent adaptive social phenotypes involving many genes acting together by locally limiting recombination.

Propagule pressure and colony social organization are associated with the successful invasion and rapid range expansion of fire ants in China

We characterized patterns of genetic variation in populations of the fire ant Solenopsis invicta in China using mitochondrial DNA sequences and nuclear microsatellite loci to test predictions as to how propagule pressure and subsequent dispersal following establishment jointly shape the invasion success of this ant in this recently invaded area. Fire ants in Wuchuan (Guangdong Province) are genetically differentiated from those found in other large infested areas of China. The immediate source of ants in Wuchuan appears to be somewhere near Texas, which ranks first among the southern USA infested states in the exportation of goods to China. Most colonies from spatially distant, outlying areas in China are genetically similar to one another and appear to share a common source (Wuchuan, Guangdong Province), suggesting that long-distance jump dispersal has been a prevalent means of recent spread of fire ants in China. Furthermore, most colonies at outlier sites are of the polygyne social form (featuring multiple egg-laying queens per nest), reinforcing the important role of this social form in the successful invasion of new areas and subsequent range expansion following invasion. Several analyses consistently revealed characteristic signatures of genetic bottlenecks for S. invicta populations in China. The results of this study highlight the invasive potential of this pest ant, suggest that the magnitude of international trade may serve as a predictor of propagule pressure and indicate that rates and patterns of subsequent range expansion are partly determined by the interplay between species traits and the trade and transportation networks.

Odorant binding proteins of the red imported fire ant, Solenopsis invicta: an example of the problems facing the analysis of widely divergent proteins

We describe the odorant binding proteins (OBPs) of the red imported fire ant, Solenopsis invicta, obtained from analyses of an EST library and separate 454 sequencing runs of two normalized cDNA libraries. We identified a total of 18 putative functional OBPs in this ant. A third of the fire ant OBPs are orthologs to honey bee OBPs. Another third of the OBPs belong to a lineage-specific expansion, which is a common feature of insect OBP evolution. Like other OBPs, the different fire ant OBPs share little sequence similarity (∼ 20%), rendering evolutionary analyses difficult. We discuss the resulting problems with sequence alignment, phylogenetic analysis, and tests of selection. As previously suggested, our results underscore the importance for careful exploration of the sensitivity to the effects of alignment methods for data comprising widely divergent sequences.

Wolbachia wSinvictaA infections in natural populations of the fire ant Solenopsis invicta: testing for phenotypic effects

Wolbachia are intracellular bacteria that commonly infect many arthropods and some nematodes. In arthropods, these maternally transmitted bacteria often induce a variety of phenotypic effects to enhance their own spread within host populations. Wolbachia phenotypic effects generally either provide benefits to infected host females (cytoplasmic incompatibility, positive fitness effects) or bias host sex ratio in favor of females (male-killing, parthenogenesis, feminization), all of which increase the relative production of infected females in host populations. Wolbachia surveys have found infections to be exceedingly common in ants, but little is known at this juncture as to what phenotypic effects, if any, they induce in this group. Previous studies have demonstrated that individuals from native populations of the invasive fire ant Solenopsis invicta commonly harbor one or more of three Wolbachia variants. One of the variants, wSinvictaA, typically occurs at low prevalence in S. invicta populations, appears to have been transmitted horizontally into S. invicta three or more times, and has been lost repeatedly from host lineages over time. In order to determine the phenotypic effects and likely population dynamics of wSinvictaA infections in these ants, brood production patterns of newly mated fire ant queens were studied during simulated claustral founding and measured wSinvictaA transmission fidelity within mature single-queen families. No clear evidence was found for Wolbachia-induced cytoplasmic incompatibility, significant fitness effects, or male-killing. Maternal transmission was perfect to both virgin queens and males. Possible mechanisms for how this variant could be maintained in host populations are discussed.

Mitochondrial genome evolution in fire ants (Hymenoptera: Formicidae)

Background

Complete mitochondrial genome sequences have become important tools for the study of genome architecture, phylogeny, and molecular evolution. Despite the rapid increase in available mitogenomes, the taxonomic sampling often poorly reflects phylogenetic diversity and is often also biased to represent deeper (family-level) evolutionary relationships.

Results

We present the first fully sequenced ant (Hymenoptera: Formicidae) mitochondrial genomes. We sampled four mitogenomes from three species of fire ants, genus Solenopsis, which represent various evolutionary depths. Overall, ant mitogenomes appear to be typical of hymenopteran mitogenomes, displaying a general A+T-bias. The Solenopsis mitogenomes are slightly more compact than other hymentoperan mitogenomes (~15.5 kb), retaining all protein coding genes, ribosomal, and transfer RNAs. We also present evidence of recombination between the mitogenomes of the two conspecific Solenopsis mitogenomes. Finally, we discuss potential ways to improve the estimation of phylogenies using complete mitochondrial genome sequences.

Conclusions

The ant mitogenome presents an important addition to the continued efforts in studying hymenopteran mitogenome architecture, evolution, and phylogenetics. We provide further evidence that the sampling across many taxonomic levels (including conspecifics and congeners) is useful and important to gain detailed insights into mitogenome evolution. We also discuss ways that may help improve the use of mitogenomes in phylogenetic analyses by accounting for non-stationary and non-homogeneous evolution among branches.

LIGO: The Laser Interferometer Gravitational-Wave Observatory

The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics of gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.

A new method for distinguishing colony social forms of the fire ant, Solenopsis invicta

Two distinct forms of colony social organization occur in the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae): colonies of the monogyne social form are headed by a single egg-laying queen, whereas those of the polygyne social form contain multiple egg-laying queens. This major difference in social organization is associated with genetic variation at a single gene (Gp-9) whereby all polygyne queens possess at least one b-like allele, while monogyne queens lack such b-like alleles and instead harbor B-like alleles only. Further, a recent study of native populations revealed that all b-like alleles in polygyne queens consistently contain three diagnostic amino acid residues: possession of only one or two of these critical residues is not sufficient for polygyny. TaqMan allelic discrimination assays were developed to survey the variable nucleotide sites associated with these three critical amino acid residues. The assays were validated by surveying nests of known social form from the species' introduced in the USA and from native South American ranges, as well as by comparing the results to Gp-9 sequence data from a subset of samples. The results demonstrate these new molecular assays consistently and accurately identify the variable nucleotides at all three sites characteristic of the B-like and b-like Gp-9 allele classes, allowing for accurate determination of colony social form.

Creating a career ladder for nursing assistants in long-term care

This article describes the development, implementation, and evaluation of a career ladder for certified nursing assistants in long-term care. A career ladder is an effective way to maximize the use of unlicensed workers without changing the skill mix (eg, no loss of licensed nursing positions) and allow the licensed nurse more time to perform higher-level clinical tasks, such as assessments, patient education, and documentation. Implementation of an unlicensed worker career ladder also can improve nursing assistant retention.

The utility of rifampin in diagnosing Gilbert's syndrome

OBJECTIVE

The aim of this study was to evaluate the effect of rifampin (the "rifampin test") on serum bilirubin in patients with and without Gilbert's syndrome.

METHODS

We conducted a clinical trial in which the effect of rifampin on serum bilirubin level in 15 patients with Gilbert's syndrome was compared with 10 patients without Gilbert's syndrome (controls) in a General Internal Medicine/Primary Care clinic of a Veterans Affairs medical center. Each participant underwent a "rifampin test," i.e., bilirubin measurement at baseline and 2, 4, and 6 h after the administration of 900 mg of rifampin. Measurements included complete blood count, blood chemistry including liver panel tests (ALP, AST, LDH, and albumin) along with total serum bilirubin levels. Ten patients with Gilbert's and nine control patients had haptoglobin level measured at baseline and 6 h after the administration of rifampin.

RESULTS

While fasting, the mean rise in total serum bilirubin at 2, 4, and 6 h after the administration of rifampin, respectively, was 0.5, 0.7, and 0.7 mg/dl (analysis of variance, p < 0.001) in control patients and 0.6, 1.0, and 1.1 mg/dl (p < 0.001) in the study patients. In 15 fed subjects (six control and nine study), the mean rise in total serum bilirubin at 2, 4, and 6 h, respectively, was 0.3, 0.5, and 0.6 mg/dl (p < 0.001) in controls and 0.5, 1.0, and 1.2 mg/dl (p < 0.001) in study subjects. In the fasting state, rise in total serum bilirubin to >1.9 mg/dl distinguished patients with Gilbert's syndrome from those without at 2, 4, and 6 h (sensitivity 100%, 93%, and 93%; specificity 100%, 100%, and 100% at 2, 4, and 6 h, respectively). In the nonfasting state, rise in total serum bilirubin to > 1.5 mg/dl at 4 and 6 h after rifampin administration distinguished the two groups (sensitivity 90% and 100%; specificity 100% and 100%, respectively).

CONCLUSIONS

Rifampin increases total serum bilirubin levels in patients with and without Gilbert's syndrome. On fasting for 12 to 24 h, an absolute increase of bilirubin to >1.9 mg/dl 2 to 6 h after the administration of 900 mg of rifampin distinguishes patients with Gilbert's syndrome from those without it. In the nonfasting state, an increase in total serum bilirubin to > 1.5 mg/dl 4 to 6 h after the administration of rifampin distinguishes persons with Gilbert's syndrome from those without it.

Quantitative CMV antigenemia correlated with ophthalmoscopic screening for CMV retinitis in AIDS patients

To assess the efficacy of the cytomegalovirus (CMV) antigen test in detecting the clinical presence of CMV retinitis. A retrospective chart review was conducted on 86 HIV positive patients who underwent dilated fundus exams for CMV retinitis. All patients had a CMV antigen assay performed within three months of their retinal exam. At a level of 45, the antigen test has a sensitivity of 96% in correctly detecting CMV retinitis and a specificity of 90.2%. The negative and positive predictive values of the antigen test were 98.2% and 80%, respectively. CMV antigen blood test provides a useful screening tool in detecting the presence or absence of CMV retinitis. An antigen level less than 45 strongly suggests the absence of retinitis.

Grazing collisions of black holes via the excision of singularities

We present the first simulations of non-head-on (grazing) collisions of binary black holes in which the singularities are excised from the simulation. Initially equal mass m black holes (spinning or not) are separated by approximately 10m and with impact parameter approximately 2m. Evolutions to t approximately 35m are obtained where two separate horizons are present for t approximately 3.8m; then a single enveloping horizon forms indicating that the holes merged. Apparent horizon area estimates suggest gravitational radiation of about 2%-3% of the total mass. The evolutions end after a moderate amount of time because of instabilities.

Randomized, dose-escalation study of SD/01 compared with daily filgrastim in patients receiving chemotherapy

PURPOSE

To explore the use of SD/01 (a polyethylene glycol-conjugated filgrastim shown in preclinical studies to have a prolonged half-life) in patients with chemotherapy-induced neutropenia.

PATIENTS AND METHODS

Thirteen patients with non-small-cell lung cancer were randomized to receive daily filgrastim (5 microg/kg/d) or a single injection of SD/01 (30, 100, or 300 microg/kg) 2 weeks before chemotherapy and again 24 hours after administration of carboplatin and paclitaxel. Pharmacodynamic, pharmacokinetic, and safety analyses were performed.

RESULTS

Peak serum concentrations of SD/01 and the duration of increased serum concentrations were dependent on the SD/01 dose. SD/01 concentrations remained increased longer in patients with chemotherapy-induced neutropenia. Prechemotherapy median absolute neutrophil counts (ANCs) in patients receiving SD/01 were increased in a dose-dependent fashion, with the duration of this effect also being dose dependent. After chemotherapy, median ANC nadirs were similar in the filgrastim cohort and the cohort receiving SD/01 30 microg/kg, with higher nadirs seen in the cohorts receiving SD/01 100 or 300 microg/kg. Dose-limiting toxicities were not noted. CD34(+) cells were mobilized in all cohorts.

CONCLUSION

A single dose of SD/01 increases the serum concentration of SD/01 for several days in a dose-dependent fashion and is not associated with significant toxicity. The effects of SD/01 on ANC and CD34(+) cell mobilization are comparable or greater than those achieved with daily filgrastim. The self-regulation of this molecule provides a potential therapeutic advantage in a variety of clinical settings associated with neutropenia.

The next $120,000: a case study to illustrate analysis of alternative farm investments in fixed assets

Dairy scientists specializing in the area of farm management are increasingly involved in analysis of farm investments in fixed assets. There have been instances where the wrong procedures were used to assess investments in fixed assets, leading to erroneous and possibly disastrous conclusions. A detailed case study of a dairy farm facing the decision of where best to invest an unexpected $120,000 windfall is used to illustrate the various facets of financial analysis. Indicators of profitability, liquidity, solvency, repayment capacity, and financial efficiency are explained and applied to the farm case to produce a detailed analysis of the current financial position of the firm. Long-range budgets of four alternate investment options and their impact on all financial indicators are presented. The four options are: 1) to pay down debt, 2) to purchase an additional 100 cows, 3) to install automatic milk yield recording in the parlor, and 4) to build new heifer facilities. All four investments are profitable. Therefore, an analysis limited to profitability indicators would conclude that any of the four options is a good investment. However, liquidity and financial efficiency issues showed that the option of purchasing 100 cows is far superior to the three others. We conclude that a complete and thorough financial analysis is required to evaluate the impact of long-run investments in fixed assets.

Experimental test of an alignment-sensing scheme for a gravitational-wave interferometer

An alignment-sensing scheme for all significant angular degrees of freedom of a power-recycled Michelson interferometer with Fabry-Perot cavities in the arms was tested on a tabletop interferometer. The response to misalignment of all degrees of freedom was measured at each sensor, and good agreement was found between measured and theoretical values.

Alignment of an interferometric gravitational wave detector

Interferometric gravitational wave detectors are designed to detect small perturbations in the relative lengths of their kilometer-scale arms that are induced by passing gravitational radiation. An analysis of the effects of imperfect optical alignment on the strain sensitivity of such an interferometer shows that to achieve maximum strain sensitivity at the Laser Interferometer Gravitational Wave Observatory requires that the angular orientations of the optics be within 10(-8) rad rms of the optical axis, and the beam must be kept centered on the mirrors within 1 mm. In addition, fluctuations in the input laser beam direction must be less than 1.5 x 10(-14) rad/ radicalHz in angle and less than 2.8 x 10(-10) m/ radicalHz in transverse displacement for frequencies f > 150 Hz in order that they not produce spurious noise in the gravitational wave readout channel. We show that seismic disturbances limit the use of local reference frames for angular alignment at a level approximately an order of magnitude worse than required. A wave-front sensing scheme that uses the input laser beam as the reference axis is presented that successfully discriminates among all angular degrees of freedom and permits the implementation of a closed-loop servo control to suppress the environmentally driven angular fluctuations sufficiently.

Signal extraction in a power-recycled michelson interferometer with fabry-perot arm cavities by use of a multiple-carrier frontal modulation scheme

We present a signal extraction scheme for longitudinal sensing and control of an interferometric gravitational-wave detector based on a multiple-frequency heterodyne detection technique. Gravitational-wave detectors use multiple-mirror resonant optical systems where resonance conditions must be satisfied for multiple degrees of freedom that are optically coupled. The multiple-carrier longitudinal-sensing technique provides sensitive signals for all interferometric lengths to be controlled and successfully decouples them. The feasibility of the technique is demonstrated on a tabletop-scale power-recycled Michelson interferometer with Fabry-Perot arm cavities, and the experimentally measured values of the length-sensing signals are in good agreement with theoretical calculations.