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Biomedical subjects

L Keller

Publications and source records attributed to L Keller.

At least 37 records · Page 2Linked to original sources
PubMed2000

Alternative reproductive strategies: a queen perspective in ants.

Ant colonies are commonly thought to have a stable and simple family structure, with one or a few egg-laying queens and their worker daughters. However, recent genetic studies reveal that the identity of breeding queens can vary over time within colonies. In several species, some queens are apparently specialized to enter established colonies instead of initiating a new colony on their own. The previously overlooked occurrence of queen turnover within colonies has important consequences not only on the genetic structure and nature of kin conflict within colonies, but also on the evolution of social parasitism.

Journal Article↗
PubMed2000

Colony sex ratios vary with queen number but not relatedness asymmetry in the ant Formica exsecta.

Split-sex-ratio theory assumes that conflict over whether to produce predominately males or female reproductives (gynes) is won by the workers in haplodiploid insect societies and the outcome is determined by colony kin structure. Tests of the theory have the potential to provide support for kin-selection theory and evidence of social conflict. We use natural variation in kinship among polygynous (multiple-queen) colonies of the ant Formica exsecta to study the associations between sex ratios and the relatedness of workers to female versus male brood (relatedness asymmetry). The population showed split sex ratios with about 89% of the colonies producing only males, resulting in an extremely male-biased investment ratio in the population. We make two important points with our data. First, we show that queen number may affect sex ratio independently of relatedness asymmetry. Colonies producing only males had greater genetic effective queen number but did not have greater relatedness asymmetry from the perspective of the adult workers that rear the brood. This lack of a difference in relatedness asymmetry between colonies producing females and those producing only males was associated with a generally low relatedness between workers and brood. Second, studies that suggest support for the relatedness-asymmetry hypothesis based on indirect measures of relatedness asymmetry (e.g. queen number estimated from relatedness data taken from the brood only) should be considered with caution. We propose a new hypothesis that explains split sex ratios in polygynous social insects based on the value of producing replacement queens.

Animals↗
PubMed2000

Ant-like task allocation and recruitment in cooperative robots.

One of the greatest challenges in robotics is to create machines that are able to interact with unpredictable environments in real time. A possible solution may be to use swarms of robots behaving in a self-organized manner, similar to workers in an ant colony. Efficient mechanisms of division of labour, in particular series-parallel operation and transfer of information among group members, are key components of the tremendous ecological success of ants. Here we show that the general principles regulating division of labour in ant colonies indeed allow the design of flexible, robust and effective robotic systems. Groups of robots using ant-inspired algorithms of decentralized control techniques foraged more efficiently and maintained higher levels of group energy than single robots. But the benefits of group living decreased in larger groups, most probably because of interference during foraging. Intriguingly, a similar relationship between group size and efficiency has been documented in social insects. Moreover, when food items were clustered, groups where robots could recruit other robots in an ant-like manner were more efficient than groups without information transfer, suggesting that group dynamics of swarms of robots may follow rules similar to those governing social insects.

Algorithms↗
PubMed2000

X-ray determination of crystalline hydroxyapatite to amorphous calcium-phosphate ratio in plasma sprayed coatings.

A method to measure the amorphous calcium phosphate (ACP) content of plasma sprayed hydroxyapatite (HA) coatings is presented. The areas of the crystalline peaks and the broad amorphous "hump" in an X-ray diffraction scan of a mixture of crystalline and amorphous HA can be fitted using conventional nonlinear least-squares methods. The weight fraction of the amorphous component in a mixture of unknown proportions is obtained from the measured hump fraction using a linear expression requiring a single calibration constant. This calibration constant may be determined by applying the same sample preparation, X-ray measurement, and least-squares fitting methods to a single standard of known (weighed) proportions as used to measure the unknown(s). Application of this method to a set of 12 samples yields an "index of crystallinity" for plasma sprayed HA coatings with an estimated standard deviation of 1 wt % ACP across the entire compositional range.

Biocompatible Materials↗
PubMed2000

Wolbachia infections in native and introduced populations of fire ants (Solenopsis spp.).

Wolbachia are cytoplasmically inherited bacteria that induce a variety of effects with fitness consequences on host arthropods, including cytoplasmic incompatibility, parthenogenesis, male-killing and feminization. We report here the presence of Wolbachia in native South American populations of the fire ant Solenopsis invicta, but the apparent absence of the bacteria in introduced populations of this pest species in the USA. The Wolbachia strains in native S. invicta are of two divergent types (A and B), and the frequency of infection varies dramatically between geographical regions and social forms of this host. Survey data reveal that Wolbachia also are found in other native fire ant species within the Solenopsis saevissima species complex from South America, including S. richteri. This latter species also has been introduced in the USA, where it lacks Wolbachia. Sequence data reveal complete phylogenetic concordance between mtDNA haplotype in S. invicta and Wolbachia infection type (A or B). In addition, the mtDNA and associated group A Wolbachia strain in S. invicta are more closely related to the mtDNA and Wolbachia strain found in S. richteri than they are to the mtDNA and associated group B Wolbachia in S. invicta. These data are consistent with historical introgression of S. richteri cytoplasmic elements into S. invicta populations, resulting in enhanced infection and mtDNA polymorphisms in S. invicta. Wolbachia may have significant fitness effects on these hosts (either directly or by cytoplasmic incompatibility) and therefore these microbes potentially could be used in biological control programmes to suppress introduced fire ant populations.

Animals↗
PubMed2000

Mating frequency and genetic structure of the Argentine ant Linepithema humile.

The nest and population genetic structures of the Argentine ant, Linepithema humile were investigated using eight microsatellite loci. Genotypes of the sperm from spermathecae of 87 queens were consistent with all queens being singly inseminated. The probability of a double mating remaining undetected was low (0.012) suggesting that no queens or only a very low proportion mate multiply. The relatedness between the queens and their mates was negative (R = -0.164 +/- 0.044) and significantly different to zero (P = 0.020). However, the high negative relatedness value was caused by a significant allele frequency difference between the sexes at a single locus (Lhum-28). When this locus was removed from the analyses, the relatedness was not significantly different from zero (R = 0.013 +/- 0.050, P = 0.812). Analysis of 10 nests revealed that the genetic differentiation among nests was weak (FST = 0.003) and not distinguishable from zero (P = 0.468). Similarly, the overall relatedness among nestmate females was not significantly different from zero (R = 0.007 +/- 0.018, P = 0.706). These results are consistent with the lack of distinct nest boundaries and the large number of queens per nest in the population studied. Although mating takes place inside the nest, the inbreeding coefficient was close to zero (F = 0.007 +/- 0.025, P = 0.786). Overall, these data indicate substantial local gene flow mediated by movement of reproductives among colonies.

Animals↗
PubMed2000

RPLND or primary chemotherapy in clinical stage IIA/B nonseminomatous germ cell tumors? Results of a prospective multicenter trial including quality of life assessment.

BACKGROUND: In order to reduce therapy-related morbidity in patients with nonseminomatous testicular germ cell tumors in clinical stage IIA/B, we performed a prospective multicenter trial comparing the standard retroperitoneal lymph node dissection (RPLND) +2 cycles of chemotherapy (arm A) with 3-4 cycles of primary chemotherapy (arm B). METHODS: From February 1991 to July 1995, 57 participating centers from Germany and Austria recruited 187 evaluable patients. 109 received primary RPLND and 78 primary chemotherapy. Two different chemotherapies were applied (PEB and CEB as adjuvant or inductive treatment). The quality of life (QoL), therapy-related morbidity, suspected predictive factors (histology and size of metastases), and outcome were assessed. RESULTS: In arm A, 12% had pathological stage (PS) I, 70% PS II A/B, and 18% PS II C/III. In arm B, 67% achieved complete remission with chemotherapy alone, 33% required a secondary RPLND. After a median follow-up of 36 months, 7% of the patients in arm A and 11% in arm B had relapsed. Two patients died due to complications of chemotherapy. Surgical complications amounted to 12% in arm A and 27% of 26 postchemotherapy RPLNDs (9% in arm B). Loss of ejaculation occurred in 32% in arm A, and 16% in arm B. Acute toxicity of chemotherapy was higher in the group receiving primary chemotherapy. CONCLUSION: We recommend primary RPLND because adjuvant chemotherapy can be spared in PS I, two cycles of chemotherapy are less toxic than 3 or 4 cycles, the primary operation is associated with less complications than that following chemotherapy and, with modern surgical procedures, ejaculation can be preserved in most of the patients, provided that the operation is carried out by an experienced surgeon. No statistically significant differences in the QoL outcome occurred between the treatment groups, suggesting that chemotherapy alone is not superior to primary or secondary RPLND in this respect.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1999

[Quality control of medical documentation of in-patients at the St. Stephen Municipal Hospital in Budapest].

Within the frame of hospital quality control programme, the authors have investigated since 1997 the medical documentation concerning in-patients of St. Stephen Hospital Budapest. An assessment form of 26 items related to main elements of medical documentation has been created for the study. Choosing of both order of departments' succession and cases to be investigated took place at random. Evaluation was performed at a scala of 0-3 points, by a five-membered work-group; all members first carried out the qualifications independently of each other, and then they formed the final opinion together at common sessions. Investigation of 204 "first round" cases proved the feasibility of the applied method. As it turned out from the results, the quality of documentation showed statistically significant differences between departments of the hospital and the average standard of documentation could not be declared as satisfying at the period of basic survey. Deficiencies of documentation especially in respect of case history, disease course, personal data and informed consent have been found. On the other hand, registration of status on admission and final report got a relatively high average score-number. The authors call attention to the importance of ordinary control of medical documentation.

Analysis of Variance↗
PubMed1999

Effect of queen phenotype and social environment on early queen mortality in incipient colonies of the fire ant, Solenopsis invicta.

In many ant species, including the fire ant Solenopsis invicta, queens can found their colonies alone or in associations of two or more. Colonies founded by associations produce a larger worker brood, have higher survival and mature earlier than colonies founded by solitary queens. However, cofoundresses almost invariably fight after the eclosion of the first workers. As a result, only one queen survives and monopolizes the colony's future reproductive output. Queen mortality also occurs before worker eclosion, but neither the causes (e.g. starvation, conflict), nor the factors (e.g. social environment) potentially affecting its occurrence, have been investigated. We analysed the effect of social environment and queen body mass on early mortality by keeping queens (1) solitarily, (2) within associations of four queens of the same initial mass, and (3) within associations of four queens of random initial mass. Mortality was higher for queens within associations than for solitary queens. Within associations of equally heavy queens, mortality significantly increased with the queens' body mass. In contrast, mortality of solitary queens did not significantly depend on body mass. Early mortality was significantly more frequent in associations of queens of random initial mass than in associations of equally heavy queens. Altogether these results demonstrate that queen phenotype differentially affects early queen mortality depending on the social environment, and suggest that reproductive competition rather than starvation is the main cause of mortality in multiple-queen associations. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Testing kin selection with sex allocation data in eusocial hymenoptera

Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the effectiveness of kin selection, because queens and workers differ in their relatedness to females and males. The first studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne (= with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also affect sex allocation. Secondly, the relative cost of females and males is difficult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspecific studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always effective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes affecting sex allocation in eusocial Hymenoptera.

Journal Article↗
PubMed1999

Assessing genetic structure with multiple classes of molecular markers: a case study involving the introduced fire ant Solenopsis invicta.

We used 30 genetic markers of 6 different classes to describe hierarchical genetic structure in introduced populations of the fire ant Solenopsis invicta. These included four classes of presumably neutral nuclear loci (allozymes, codominant random amplified polymorphic DNAs (RAPDs), microsatellites, and dominant RAPDs), a class comprising two linked protein-coding nuclear loci under selection, and a marker of the mitochondrial DNA (mtDNA). Patterns of structure revealed by F statistics and exact tests of differentiation were highly concordant among the four classes of neutral nuclear markers, although the microsatellites were the most effective markers for detecting structure. The results from the mtDNA complemented those from the neutral nuclear markers by revealing that strong limitations to female-mediated gene flow were the cause of the local structure registered by the nuclear markers. The pattern of structure inferred from the selected nuclear loci was markedly different from the patterns derived from the other sets of markers but was predictable on the basis of the presumed mode of selection acting on these loci. In general, the results for all six classes of markers can be explained by known features of the social and reproductive biology of fire ants. Thus, the results from these diverse sets of markers, combined with detailed natural history data, provide an unusually complete picture of how the fundamental evolutionary forces of gene flow, drift, and selection govern the distribution of genetic variation within and between fire ant populations.

Animals↗
PubMed1999

So you want to be a Director of Nursing ... now what!

The authors believe that even an experienced DON might need at least two months to adequately adjust and/or professionally realign problematic areas of concern in a new position. This opinion is in direct contrast with Maun (1998). Maun states "If a DON is moving to this job from another similar position, the overall program may take a week, not including any other corporate or facility specific orientations. If a person is taking a DON job for the first time, the process could take two weeks to allow for identifying areas of deficiency." The position of Director of Nursing is dynamic and fluid; it is challenging and exciting. The key to success is communication, forward planning, flexibility and the willingness to grow with the demanding changes in the arena of long term care.

Career Choice↗
PubMed1998

Genetic control of social organization in an ant.

A central issue in evolutionary biology is the extent to which complex social organization is under genetic control. We have found that a single genomic element marked by the protein-encoding gene Gp-9 is responsible for the existence of two distinct forms of social organization in the fire ant Solenopsis invicta. This genetic factor influences the reproductive phenotypes and behavioral strategies of queens and determines whether workers tolerate a single fertile queen or multiple queens per colony. Furthermore, this factor affects worker tolerance of queens with alternate genotypes, thus explaining the dramatic differences in Gp-9 allele frequencies observed between the two social forms in the wild. These findings reveal how a single genetic factor can have major effects on complex social behavior and influence the nature of social organization.

Alleles↗
PubMed1997

Nasal immunotherapy in weed-induced allergic rhinitis.

BACKGROUND: Nasal immunotherapy with single allergen extracts, following premedication with cromolyn, has been reported to be effective in treating seasonal and perennial allergic rhinitis. METHODS: We conducted a double-blind, placebo-controlled study to assess the efficacy, tolerability, and mechanism of action of nasal immunotherapy for allergic rhinitis caused by weed pollens from three unrelated families. Twenty-seven weed-allergic patients underwent baseline nasal provocation and titrated skin test with a mixed weed extract containing ragweed, sage, and Chenopod extracts. Patients were randomized to receive either mixed weed extract or placebo. Nasal immunotherapy was self-administered daily to alternate nostrils preceded by 5.2 mg intranasal cromolyn. Beginning with 1:2500 wt/vol the concentration was increased to 1:10 wt/vol over an average period of 36 days. The maintenance dose (1:10 wt/vol) was administered daily for 12 to 16 weeks through the weed pollen season. Patients recorded nasal and eye symptoms and the use of rescue medications throughout the study. A nasal lavage for cytokine levels and nasal scraping with Rhinoprobe for nasal cytology were performed at the peak of the weed season. Nasal provocation and titrated skin tests with mixed weed extract were repeated after the weed season. Nasal lavage and scraping were also performed before and 24 hours after the final nasal provocation. RESULTS: During the peak weeks of the weed season the group receiving mixed weed extract by nasal instillation, compared with those treated with placebo, had significantly lower total nasal symptom scores, total eye symptom scores, and symptom medication scores. There were no significant differences in the nasal cytology or cytokines levels between the two groups, except for elevated IL-10 in the nasal lavage in the treated group at the peak of the season. Nasal symptoms and medication use were higher preseasonally in the active treatment group. CONCLUSION: Nasal immunotherapy with aqueous mixed weed extract administered with cromolyn sodium pretreatment for 17 to 21 weeks was effective in reducing both nasal and ocular symptoms of weed pollen-induced allergic rhinitis. There were increased nasal symptoms in the treated group preseasonally.

Administration, Intranasal↗
PubMed1997

Hierarchical analysis of genetic structure in native fire ant populations: results from three classes of molecular markers.

We describe genetic structure at various scales in native populations of the fire ant Solenopsis invicta using two classes of nuclear markers, allozymes and microsatellites, and markers of the mitochondrial genome. Strong structure was found at the nest level in both the monogyne (single queen) and polygyne (multiple queen) social forms using allozymes. Weak but significant microgeographic structure was detected above the nest level in polygyne populations but not in monogyne populations using both classes of nuclear markers. Pronounced mitochondrial DNA (mtDNA) differentiation was evident also at this level in the polygyne form only. These microgeographic patterns are expected because polygyny in ants is associated with restricted local gene flow due mainly to limited vagility of queens. Weak but significant nuclear differentiation was detected between sympatric social forms, and strong mtDNA differentiation also was found at this level. Thus, queens of each form seem unable to establish themselves in nests of the alternate type, and some degree of assortative mating by form may exist as well. Strong differentiation was found between the two study regions using all three sets of markers. Phylogeographic analyses of the mtDNA suggest that recent limitations on gene flow rather than longstanding barriers to dispersal are responsible for this large-scale structure.

Animals↗
PubMed1996

Conditional Manipulation of Sex Ratios by Ant Workers: A Test of Kin Selection Theory

Variable queen mating frequencies provide a unique opportunity to study the resolution of worker-queen conflict over sex ratio in social Hymenoptera, because the conflict is maximal in colonies headed by a singly mated queen and is weak or nonexistent in colonies headed by a multiply mated queen. In the wood ant Formica exsecta, workers in colonies with a singly mated queen, but not those in colonies with a multiply mated queen, altered the sex ratio of queen-laid eggs by eliminating males to preferentially raise queens. By this conditional response to queen mating frequency, workers enhance their inclusive fitness.

Journal Article↗
PubMed1996

Social evolution in a new environment: the case of introduced fire ants.

The inadvertent introduction of the fire ant Solenopsis invicta to the United States from South America provides the opportunity to study recent social evolution by comparing social organization in native and introduced populations. We report that several important elements of social organization in multiple-queen nests differ consistently and dramatically between ants in Argentina and the United States. Colonies in Argentina contain relatively few queens and they are close relatives, whereas colonies in the United States contain high numbers of unrelated queens. A corollary of these differences is that workers in the native populations are significantly related to the new queens that they rear in contrast to the zero relatedness between workers and new queens in the introduced populations. The observed differences in queen number and relatedness signal a shift in the breeding biology of the introduced ants that is predicted on the basis of the high population densities in the new range. An additional difference in social organization that we observed, greater proportions of permanently unmated queens in introduced than in native populations, is predicted from the loss of alleles at the sex-determining locus and consequent skewing of operational sex ratios in the colonizing ants. Thus, significant recent social evolution in fire ants is consistent with theoretical expectations based on the altered ecology and population genetics of the introduced populations.

Journal Article↗