Specific antigen-binding and antibody-secreting lymphocytes associated with the erythrocyte autoantibody responses of NZB and genetically unrelated mice.

The receptor characteristics as well as incidence of antigen-binding lymphocytes (ABL) or B and T cell classes with membrane receptors specific for the exposed (X) and cryptic (HB) murine erythrocyte autoantigens were examined in NZB and nine control strains of mice. Whereas only NZB and NZB hybrid mice synthesize anti-X autoantibody pathogenetically implicated in the genetically determined autoimmune hemolytic anemia, the NZB as well as control strains synthesize the ubiquitous anti-HB anti-erythrocyte autoantibody. By utilizing immunocytoadherence assays, maximum numbers of specific ABL of both B and T lymphocyte classes were optimally demonstrated at erythrocyte:lymphocyte ratios of 20:1 and after lymphocyte fixation at 56 degrees C for 20 min. Surface membrane receptor specificity was established by inhibition with semi-purified soluble X or HB autoantigen. Inhibition of immunocyto-adherence with class specific antisera to mouse immuno-globulins demonstrated that the receptors on both B and T cells were of IgM class. Specific receptors regenerated in vitro after trypsinization which excluded the role of cytophilic antibody in the immunocytoadherence reactions. B lymphocyte ABL reactive with the X autoantigen were demonstrable in NZB, NZB hybrid, and control mice. Only in NZB and NZB hybrid mice, strains that uniformly synthesize anti-X autoantibody, were X ABL of T lymphocyte class demonstrated. The presence and incidence of T lymphocyte X ABL is compatible with the expression of a single dominant gene carried by the NAB strain. The incidence of B lymphocyte X ABL increased with age, suggesting proliferation of this cell population. HB ABL of both B and T lymphocyte classes were observed in all strains, concordant with the ubiquitous presence of humoral anti-HB autoantibodies. Differentiation of precursor B cells are evaluated by PFC assay of cells secreting specific autoantibodies. Anti-X PFC were observed only in NZB and NZB hybrid mice; and the observed frequency suggested that less than 3.5% of the specific ABL were differentiated for the secretion of anti-X autoantibody. Anti-HB PFC were observed in all strains and represented as high as 11.8% of specific ABL. Genetic determination of the anti-X anti-erythrocyte autoantibody response does not prescribe the presence of precursors of the antibody-forming cell, but rather appears to influence regulation of the differentiation of these cells. These data suggest that circumvention of immunologic tolerance to this specific erythrocyte autoantigen may occur at the level of the T lymphocyte; or alternatively, that T lymphocytes as well as B lymphocytes, are induced to proliferate and differentiate in the NZB strain.     

Change in movement and subdivision of Myrmica punctiventris (Hymenoptera, Formicidae) colonies in north temperate forests is related to a long-term shift in social organization

We assessed temporal and spatial patterns of nest site use in the cavity dwelling ant, Myrmica punctiventris in a well-studied temperate forest site in central New York State. We evaluated changes in nest site use by repeatedly censusing the ants inhabiting artificial nests (hollow dowels) for three consecutive growing seasons. We confirm a shift towards more polydomy in this population of M. punctiventris, first reported by DeHeer et al. (2001), but extend these findings by demonstrating that this shift has occurred gradually over several years. We are unable to determine if this polydomy is seasonal or year round. We explore various explanations for the occurrence of polydomy and suggest that long-term changes in sex allocation are indirectly driving the shift in nesting strategies. Received 15 July 2004; revised 11 April and 19 October 2005; accepted 25 October.     

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.     

A comparison of the colony-founding potential of queens from single- and multiple-queen colonies of the fire antSolenopsis invicta

Newly mated queens from the polygyne (multiple-queen) form of S. invicta show a weight polymorphism that correlates with their genotype at the protein locus Gp-9. Although this variation in weight might be expected to translate into variation in the ability of queens to initiate new colonies using stored energy reserves, a systematic examination of the colony-founding ability of newly mated polygyne-derived queens of different weights has never been reported. Here I compare the ability of monogyne-derived queens (Gp-9^BB M), heavy polygyne-derived queens (Gp-9^BB P), and light polygyne-derived queens (Gp-9^Bb P) to initiate their own colonies using only stored energy reserves. Most measurements of the ants' abilities yielded the following scale of competency:Gp-9^BB M>Gp-9^BB P>Gp-9^Bb P. Surprisingly, most mated polygyne-derived queens of even the lighter genotype were capable of rearing considerable numbers of workers in isolation. This ability may be enhanced substantially in the field if such queens cooperate in initiating new nests (pleometrosis). These results are concordant with the growing body of work that implicates a simply inherited genetic polymorphism for the control of a complex social trait in this ant, and they indicate that the modes of reproduction in polygyne fire ants may show considerable diversity.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Evidence for a B lymphocyte defect underlying the anti-X anti-erythrocyte autoantibody response of NZB mice.

The autoimmune hemolytic anemia of NZB mice is pathogenetically mediated by a genetically prescribed anti-erythrocyte autoantibody response directed to the X erythrocyte autoantigen. The cellular locus of the immunoregulatory defect underlying the anti-X response was explored by adoptively transferring bone marrow cells (BMC) from NZB mice to lethally irradiated histocompatible recipients. Before adoptive transfer, BMC from donor mice were assayed for antigen-binding lymphocytes with receptors for the X autoantigen (X-ABL) by immunocytoadherence assays and for anti-X autoantibody-secreting cells (X-PFC) by plaque-forming cell assays. Twelve weeks after adoptive transfer, splenic lymphocytes from recipient mice were assayed for X-PFC and humoral anti-X autoantibody by Coombs' tests. Transfer of 15 to 30 x 10(6) BMC containing 6 to 12 x 10(3) X-ABL but no X-PFC from 6- to 8-week-old NZB mice to lethally irradiated BALB/c, B10.D2, C57BL/Ks, and DBA/2 mice produced X-PFC in 70% of the recipients. Development of X-PFC was not simply dependent upon available X-ABL since transfer of 15-30 x 10(6) BMC, containing comparable numbers of X-ABL, from BALB/c, B10.D2, C57BL/Ks, or DBA/2 mice to NZB or syngeneic recipients did not produce X-PFC. Transfer of BMC from NZB mice to BALB/c, B10.D2, and DBA/2 mice with weekly administrations of AKR anti-theta antiserum had no effect on the development of X-PFC; Tlymphocyte ablation was evidenced by the absence of theta+ spleen cells. These results suggest that the pathogenetic anti-X response is not genetically prescribed at the level of macrophages, humoral factors, or T cells, but rather appears to be a phenotypic expression of a primary B lymphocyte defect permitting or promoting differentiation of NZB X-ABL.     

Delineation of spontaneous erythrocyte autoantibody responses of NZB and other strains of mice.

Four anti-erythrocyte autoantibody responses (anti-X, anti-HB, anti-HOL, and anti-I) that occur spontaneously in mice have been characterized with regard to antigenic specificities, predominant immunoglobulin class, and pathogenetic importance. Each autoantibody response exhibits specificity for an independent erythrocyte membrane autoantigen (X, HB, HOL, or I) or a soluble analogue (SEA-X or SEA-HB) present in the plasma. The anti-X response, unique to NZB mice, is directed to a normally exposed murine erythrocyte autoantigen, whereas the anti-HB response is directed to a cryptic erythrocyte autoantigen exposed by limited enzymatic cleavage of the membrane. The anti-I response also is directed to a cryptic but distinct autoantigen, and anti-HOL autoantibodies react with an erythrocyte autoantigen located at the cytoplasmic surface of the membrane. Analysis of the predominant immunoglobulin class of each of the autoantibodies has demonstrated that anti-HB and anti-I antibodies are predominantly of IgM class, whereas anti-X and anti-HOL antibodies are IgG immunoblobulins. Only anti-X and anti-HB autoantibodies are recovered from Coombs' positive erythrocytes from NZB mice and erythrocytes with surface C3 are detected only in NZB mice greater than 9 months of age. These data suggest that only the anti-X and anti-HB responses are pathogenetically implicated in the autoimmune hemolytic anemia of NZB mice.     

Putative native source of the invasive fire ant <Emphasis Type="Italic">Solenopsis invicta</Emphasis> in the USA

The ecological and evolutionary dynamics of newly introduced invasive species can best be understood by identifying the source population(s) from which they originated, as many species vary behaviorally, morphologically, and genetically across their native landscapes. We attempt to identify the source(s) of the red imported fire ant (Solenopsis invicta) in the southern USA utilizing data from three classes of genetic markers (allozymes, microsatellites, and mitochondrial DNA sequences) and employing Bayesian clustering simulations, assignment and exclusion tests, and phylogenetic and population genetic analyses. We conclude that the Mesopotamia flood plain near Formosa, Argentina represents the most probable source region for introduced S. invicta among the 10 localities sampled across the native South American range. This result confirms previous suspicions that the source population resides in northern Argentina, while adding further doubts to earlier claims that the Pantanal region of Brazil is the source area. Several lines of evidence suggest that S. invicta in the southern USA is derived from a single location rather than being the product of multiple invasions from widely separated source localities. Although finer-scale sampling of northern Argentina and Paraguay combined with the use of additional genetic markers will be necessary to provide a highly precise source population assignment, our current results are of immediate use in directing future sampling and focusing ongoing biological control efforts.     

Coevolution in host-parasite systems: behavioural strategies of slave-making ants and their hosts

Recently, avian brood parasites and their hosts have emerged as model systems for the study of host-parasite coevolution. However, empirical studies of the highly analogous social parasites, which use the workers of another eusocial species to raise their own young, have never explicitly examined the dynamics of these systems from a coevolutionary perspective. Here, we demonstrate interpopulational variation in behavioural interactions between a socially parasitic slave-maker ant and its host that is consistent with the expectations of host-parasite coevolution. Parasite pressure, as inferred by the size, abundance and raiding frequency of Protomognathus americanus colonies, was highest in a New York population of the host Leptothorax longispinosus and lowest in a West Virginia population. As host-parasite coevolutionary theory would predict, we found that the slave-makers and the hosts from New York were more effective at raiding and defending against raiders, respectively, than were conspecifics from the West Virginia population. Some of these variations in efficacy were brought about by apparently simple shifts in behaviour. These results demonstrate that defence mechanisms against social parasites can evolve, and they give the first indications of the existence of a coevolutionary arms race between a social parasite and its host.