Evolutionary transition to a semelparous life history in the socially parasitic ant Acromyrmex insinuator

The recently discovered social parasite Acromyrmex insinuator ( 25 ) exploits colonies of the leafcutter ant A. echinatior. We document that A. insinuator represents a rare early stage in the evolution of social parasitism, because a worker caste is still partially present and mating phenology has remained at least partially similar to that of the host. A. insinuator is tolerant of host queens, and sexual offspring produced in parasitized colonies can be either exclusively A. insinuator or a mix of A. insinuator and A. echinatior. The remarkably high abundance of A. insinuator in nests of the investigated Panamanian host population and the fact that A. insinuator colonies readily reproduce under laboratory conditions allowed us to test evolutionary predictions on reproductive life history evolution that are not possible in most other socially parasitic ants. We show that (1) A. insinuator has a semelparous ‘big bang’ reproductive life history which exploits host colonies without leaving reserves for survival; (2) social parasite sexuals are significantly smaller than A. echinatior host sexuals, but still large compared to host workers, confirming an evolutionary scenario of gradual size reduction and loss of the worker caste after transition towards a socially parasitic life history; (3) major changes in the life history of ants can evolve relatively quickly compared to adaptations in morphology, caste differentiation and mating phenology.     

Heterogeneity of Soluble Neural Cell Adhesion Molecule

Soluble neural cell adhesion molecule (NCAM) from rat brain neuronal cell culture media consists predominantly of a polypeptide of Mr approximately 115,000. Minor amounts of a polypeptide of Mr approximately 180,000 and two inconsistently appearing components of Mr 160,000 and 145,000 are also observed. The Mr 115,000 component is derived from the neuronal membrane NCAM components NCAM-A of Mr 190,000, NCAM-B of Mr 140,000, or both. Thus, as a part of the catabolism of membrane NCAM-A plus -B, a minor fraction is posttranslationally cleaved and recovered in the media as discernible soluble NCAM polypeptides. The half-life of membrane NCAM-A plus -B is less than 24 h. Astrocyte culture media contains a predominant soluble NCAM component of Mr 120,000 derived from membrane-associated NCAM-C. A close comparison of deglycosylated soluble NCAM from astrocyte and neuronal cultures showed a small but consistent difference in Mr, a result suggesting that different NCAM polypeptides are released from the membrane of neurons and astrocytes. In contrast to the Mr 115,000-120,000 NCAM polypeptides, the Mr 180,000 polypeptide from neuronal culture media does not seem to be derived from membrane-attached NCAM and may therefore represent a secreted NCAM isoform.     

No evidence for recognition errors in Acrocephalus warblers

Failure to recognise own eggs (recognition errors) may be an important selective force behind acceptance of parasitic eggs, leading to a balance between rejecters and acceptors in a host population (the equilibrium hypothesis). We predicted that recognition errors should occur frequently among host species with intermediate rejection rates, whose rejection behaviour shows many conditional responses. The reed warbler Acrocephalus scirpaceus and great reed warbler A. arundinaceus fulfil these requirements. These two species were therefore used in an experiment where host birds were exposed to a common cuckoo Cuculus canorus dummy, either <2 m or 5–10 m from the nest, at fishponds in southern Moravia (Czech Republic). The hosts responded to the cuckoo dummy, great reed warblers being much more aggressive than reed warblers, and both species being more aggressive towards the dummy when it was close to the nest than when it was farther away. We furthermore predicted that there should be more eggs rejected (ejected or nest abandoned) due to recognition errors among hosts exposed to a dummy close to the nest than among both those exposed to a dummy farther away from the nest and towards controls not exposed to cuckoo dummies. When comparing egg loss between groups of birds that were exposed to a cuckoo dummy with those that were not, we found no significant difference. However, partial egg loss was frequent among hosts in the studied population, most probably due to cuckoo depredation. We discuss why there were no detectable recognition errors in the studied population, when other researchers have claimed to have found such errors in host populations elsewhere.     

Tissue organization ofFarrea occa (Porifera,Hexactinellida)

Summary The tissue organization ofFarrea occa has been examind by light microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). It was found to agree closely with the hexactinellid model established forRhabdocalyptus dawsoni by Mackie and Singla (1983) in consisting of a thin general syncytium incorporating few discrete cellular components, several of which share membrane continuity with the general syncytium by distinctive plug junctions. The general syncytium, supported by a thin collagenous mesolamella, is specialized regionally as dermal membrane, gastral membrane, peripheral trabecular strands, and primary reticulum (R1) of flagellated chambers. Extensions of the syncytium, which lack mesolamella support, form the distinctive secondary reticulum (R2) inside chambers and a newly discovered structure, the inner membrane, which occupies the central region of flagellated chambers. The choanosyncytia are enucleate networks of collar bodies and stolons embedded in R1 and plugged to R1 and choanoblasts. The discrete cell population consists of choanoblasts and archeocytes located in the thin mesohyle space and plugged to syncytial elements, cystencytes and vacuolar cells also located in the mesohyle but lacking plug connections, and granular cells emergent on R1 and apparently not bearing plug connections. The status of scleroblast syncytia has not been resolved. Large populations of rod-shaped bacteria occupy the mesohyle space; intracellular ovoid bodies, possible symbiotic prokaryotes, are common in R1 and R2. The previously unknown inner membrane probably functions to control flagellar activity on a very localized scale and to accumulate and release egesta in packages.Abbreviations ac archeocyte congeries - ap apopyle - ar archeocyte - b bacterium - c collagen fibrils - cb collar body - cbl choanoblast - cbs collar body socket - ch choanosome - cm collar microvilli - co choanocyte collar - cr crystalloid - cs connecting strand - dm dermal membrane - dv debris vacuole - e exhalant opening - ex exhalant space - f flagellum - fn filamentous network - Gb Golgi body - gf glycocalyx filaments - gm gastral membrane - im inner membrane - is inhalant space - ml mesolamella - ms mesohyle space - mt mitochondrion - n1 nucleus of R1 - o ostium - ob ovoid body - os osmiophilic body - pm plasma membrane - pr prosopyle - pt peripheral trabeculae - R1 primary reticulum - R2 secondary reticulum - s spicule space - ser smooth endoplasmic reticulum - ts trabecular strand     

Patterns of Obesity Development before the Diagnosis of Type 2 Diabetes: The Whitehall II Cohort Study

Background

Patients with type 2 diabetes vary greatly with respect to degree of obesity at time of diagnosis. To address the heterogeneity of type 2 diabetes, we characterised patterns of change in body mass index (BMI) and other cardiometabolic risk factors before type 2 diabetes diagnosis.

Methods and Findings

We studied 6,705 participants from the Whitehall II study, an observational prospective cohort study of civil servants based in London. White men and women, initially free of diabetes, were followed with 5-yearly clinical examinations from 1991–2009 for a median of 14.1 years (interquartile range [IQR]: 8.7–16.2 years). Type 2 diabetes developed in 645 (1,209 person-examinations) and 6,060 remained free of diabetes during follow-up (14,060 person-examinations). Latent class trajectory analysis of incident diabetes cases was used to identify patterns of pre-disease BMI. Associated trajectories of cardiometabolic risk factors were studied using adjusted mixed-effects models. Three patterns of BMI changes were identified. Most participants belonged to the “stable overweight” group (n = 604, 94%) with a relatively constant BMI level within the overweight category throughout follow-up. They experienced slightly worsening of beta cell function and insulin sensitivity from 5 years prior to diagnosis. A small group of “progressive weight gainers” (n = 15) exhibited a pattern of consistent weight gain before diagnosis. Linear increases in blood pressure and an exponential increase in insulin resistance a few years before diagnosis accompanied the weight gain. The “persistently obese” (n = 26) were severely obese throughout the whole 18 years before diabetes diagnosis. They experienced an initial beta cell compensation followed by loss of beta cell function, whereas insulin sensitivity was relatively stable. Since the generalizability of these findings is limited, the results need confirmation in other study populations.

Conclusions

Three patterns of obesity changes prior to diabetes diagnosis were accompanied by distinct trajectories of insulin resistance and other cardiometabolic risk factors in a white, British population. While these results should be verified independently, the great majority of patients had modest weight gain prior to diagnosis. These results suggest that strategies focusing on small weight reductions for the entire population may be more beneficial than predominantly focusing on weight loss for high-risk individuals. Please see later in the article for the Editors'' Summary     

Testing relationships between macroalgal cover and Secchi depth in the Baltic Sea

The present study tests whether relationships between macroalgal cover and water quality, recently developed for Danish coastal waters, are more universal and also applies at the other extreme of the Baltic Sea in Finnish coastal waters. We found that algal cover increases as a function of Secchi depth according to the same logarithmic function in Danish and Finnish coastal waters. Algal cover at a given depth (here modelled for 4 m) increases with increasing Secchi depth and approaches a maximum at the high Secchi depths found in the clearest areas of the Danish coastal waters. For a given Secchi depth the combined Danish/Finnish algal model thus predicts a similar cover of the algal community at a given water depth at both extremes of the Baltic Sea which represent quite different algal habitats. These results suggest that light limitation, and thus shading effects of eutrophication may cause similar reductions of macroalgal cover across ecosystems.     

DISENTANGLING THE EFFECTS OF EVOLUTIONARY, DEMOGRAPHIC, AND ENVIRONMENTAL FACTORS INFLUENCING GENETIC STRUCTURE OF NATURAL POPULATIONS: ATLANTIC HERRING AS A CASE STUDY

The spatial structuring of intraspecific genetic diversity is the result of random genetic drift, natural selection, migration, mutation, and their interaction with historical processes. The contribution of each has been typically difficult to estimate, but recent advances in statistical genetics have provided valuable new investigative tools to tackle such complexity. Using a combination of such methods, we examined the roles of environment (i.e., natural selection), random genetic processes (i.e., drift), and demography and life histories (e.g., feeding migrations) on population structure of a widely distributed and abundant marine pelagic fish of economic importance, Atlantic herring ( Clupea harengus ). Individuals were collected during peak spawning time from 19 spawning locations spanning the region from the western North Sea to the eastern Baltic Sea ( N = 1859, eight microsatellite loci). We carried out separate analyses of neutral and selected genetic variation, which allowed us to establish that the two most important factors affecting population structure were selection due to salinity at spawning sites and feeding migrations. The genetic signal left by the demographic history of herring, on the other hand, seems to have been largely eroded, which is not surprising given the large reproductive potential and presumed enormous local effective population sizes of pelagic fish that constrain the effect of stochastic processes. The approach we used can in principle be applied to any abundant and widely distributed aquatic or terrestrial species.     

The highly leukotoxic JP2 clone of Aggregatibacter actinomycetemcomitans: evolutionary aspects, epidemiology and etiological role in aggressive periodontitis

For many years, attention has been given to the oral bacterium Aggregatibacter actinomycetemcomitans, as a species possibly implicated in the etiology of aggressive periodontitis in adolescents. One of the major virulence factors of A. actinomycetemcomitans is the leukotoxin which is able to kill important cells of the immune system. As demonstrated in population genetic analyses, the population structure of A. actinomycetemcomitans is mainly clonal with evolutionary lineages corresponding to the serotypes. A particular highly leukotoxic clone (JP2) of serotype b has been discovered. The JP2 clone, with an estimated origin some 2400 years ago, is found to be highly conserved, based on analyses of a collection of JP2 clone strains collected through more than 20 years from individuals of diverse origin and living geographically widespread. Despite demonstration of minor evolutionary changes within the genome of JP2 clone strains of A. actinomycetemcomitans, the JP2 clone strains constitute a unique clonal type, the characteristics of which include a 530 basepair deletion in the leukotoxin operon implicated in the enhanced leukotoxic activity of the clone. Mapping of the geographic occurrence of the JP2 clone of A. actinomycetemcomitans has revealed that its colonization is largely restricted to individuals of African descent. Characteristic mutations, which allow JP2 clone isolates from the Mediterranean region to be distinguished from isolates from West Africa, including the Cape Verde islands, suggest that the JP2 clone initially emerged as a distinct genotype in the Mediterranean region of Africa and subsequently spread to West Africa, from where it might have been transferred to the American continent during the transatlantic slave trade. The finding of a sustained selective colonization of individuals of African descent, despite geographical separation from the African continent for centuries, suggests that the JP2 clone might have a distinct host tropism. Further studies are needed to elucidate the reasons for the apparent selective colonization of the Mediterranean and Western African populations. The JP2 clone of A. actinomycetemcomitans appears to play a prominent role in the etiology of aggressive periodontitis compared to other clonal types of the species. While A. actinomycetemcomitans, in general, is considered an opportunistic pathogen of the resident oral microbiota, the JP2 clone has features similar to those of an exogenous pathogen. Clonal types other than JP2 can be isolated from healthy as well as periodontally diseased individuals, whereas the JP2 clone has been isolated primarily from periodontally diseased individuals. As demonstrated in a prospective cohort study in Morocco, where the JP2 clone is endemically present, the presence of this clone in dental plaque confers a remarkably increased risk for development of aggressive periodontitis, suggesting that the JP2 clone is an important etiological agent of aggressive periodontitis in adolescents. Support for association of clonal types other than JP2 of A. actinomycetemcomitans with aggressive periodontitis has also been provided, but the association is much weaker. Nearly half of the JP2 clone carriers were found to be persistently infected during a two-year follow-up period, which indicates a level of stability of colonization with the JP2 clone similar to that previously reported for non-JP2 clonal types of A. actinomycetemcomitans. The relative risk of aggressive periodontitis is highest for individuals with stable JP2 clone colonization. Although the method used is not quantitative, this finding adds to the evidence for a causal role of the JP2 clone in aggressive periodontitis. Longitudinal data shows that few individuals are colonized with the JP2 clone de novo after puberty. Patterns of parent-child carriage and shared colonization of JP2 clone strains among siblings have been demonstrated in other studies, altogether indicating that transmission of the JP2 clone, like other clonal types of A. actinomycetemcomitans, occurs vertically, and through close person to person contacts. In conclusion, a conserved and highly leukotoxic clone of A. actinomycetemcomitans with unique characteristics and with an apparent linkage to individuals of African descent has been identified. Being aware that the genetic constitution of the hosts has not been considered and that focus in our studies has been on A. actinomycetemcomitans only, and not on other members of the oral microbiota, we conclude that the JP2 clone of A. actinomycetemcomitans is a likely etiological agent of aggressive periodontitis in adolescents.