Evolution of antigenic diversity in the tick-transmitted bacterium Borrelia afzelii: a role for host specialization?

Antigenic diversity in pathogenic microbes can be a result of at least three different processes: diversifying selection by acquired immunity, host-pathogen coevolution and/or host specialization. Here, we investigate whether host specialization drives diversity at ospC (which encodes an immunodominant surface protein) in the tick-transmitted bacterium Borrelia afzelii. We determined prevalence and infection intensity of ospC strains in naturally infected wild mammals (rodents and shrews) by 454 amplicon sequencing in combination with qPCR. Neither prevalence nor infection intensity of specific ospC strains varied in a species-specific manner (i.e. there were no significant ospC × host species interactions). Rankings of ospC prevalences were strongly positively correlated across host species. Rankings of ospC infection intensities were correlated more weakly, but only in one case significantly < 1. ospC prevalences in the studied mammals were similar to those in ticks sampled at the study site, indicating that we did not miss any mammal species that are important hosts for specific ospC strains. Based on this, we conclude that there is at best limited host specialization in B. afzelii and that other processes are likely the main drivers of ospC diversity.

In search of genetic constraints limiting the evolution of egg size: direct and correlated responses to artificial selection on a prenatal maternal effector.

Maternal effects are an important force in nature, but the evolutionary dynamics of the traits that cause them are not well understood. Egg size is known to be a key mediator of prenatal maternal effects with an established genetic basis. In contrast to theoretical expectations for fitness-related traits, there is a large amount of additive genetic variation in egg size observed in natural populations. One possible mechanism for the maintenance of this variation is through genetic constraints caused by a shared genetic basis among traits. Here we created replicated, divergent selection lines for maternal egg investment in Japanese quail (Coturnix japonica) to quantify the role of genetic constraints in the evolution of egg size. We found that egg size responds rapidly to selection, accompanied by a strong response in all egg components. Initially, we observed a correlated response in body size, but this response declined over time, showing that egg size and body size can evolve independently. Furthermore, no correlated response in fecundity (measured as the proportion of days on which a female laid an egg) was observed. However, the response to selection was asymmetrical, with egg size plateauing after one generation of selection in the high but not the low investment lines. We attribute this pattern to the presence of genetic asymmetries, caused by directional dominance or unequal allele frequencies. Such asymmetries may contribute to the evolutionary stasis in egg size observed in natural populations, despite a positive association between egg size and fitness.

Sex-specific effects of prenatal and postnatal nutritional conditions on the oxidative status of great tit nestlings.

The early life period is characterized by fast growth and development, which can lead to high reactive oxygen species (ROS) production. Young animals thus have to balance their investment in growth versus ROS defence, and this balance is likely mediated by resource availability. Consequently resources transferred prenatally by the mother and nutritional conditions experienced shortly after birth may crucially determine the oxidative status of young animals. Here, we experimentally investigated the relative importance of pre- and early postnatal nutritional conditions on the oxidative status of great tit nestlings (Parus major). We show that resources transferred by the mother through the egg and nutritional conditions encountered after hatching affect the oxidative status of nestling in a sex-specific way. Daughters of non-supplemented mothers and daughters which did not receive extra food during the early postnatal period had higher oxidative damage than sons, while no differences between sons and daughters were found when extra food was provided pre- or postnatally. No effect of the food supplementations on growth, fledging mass or tarsus length was observed, indicating that female nestlings maintained their investment in growth at the expense of ROS defence mechanisms when resources were limited. The lower priority of the antioxidant defence system for female nestlings was also evidenced by lower levels of specific antioxidant components. These results highlight the important role of early parental effects in shaping oxidative stress in the offspring, and show that the sensitivity to these parental effects is sex-specific.

Independent sources of condition dependency and multiple pathways determine a composite trait: lessons from carotenoid-based plumage colouration.

Many colour ornaments are composite traits consisting of at least four components, which themselves may be more complex, determined by independent evolutionary pathways, and potentially being under different environmental control. To date, little evidence exists that several different components of colour elaboration are condition dependent and no direct evidence exists that different ornamental components are affected by different sources of variation. For example, in carotenoid-based plumage colouration, one of the best-known condition-dependent ornaments, colour elaboration stems from both condition-dependent pigment concentration and structural components. Some environmental flexibility of these components has been suggested, but specifically which and how they are affected remains unknown. Here, we tested whether multiple colour components may be condition dependent, by using a comprehensive 3 × 2 experimental design, in which we carotenoid supplemented and immune challenged great tit nestlings (Parus major) and quantified effects on different components of colouration. Plumage colouration was affected by an interaction between carotenoid availability and immune challenge. Path analyses showed that carotenoid supplementation increased plumage saturation via feather carotenoid concentration and via mechanisms unrelated to carotenoid deposition, while immune challenge affected feather length, but not carotenoid concentration. Thus, independent condition-dependent pathways, affected by different sources of variation, determine colour elaboration. This provides opportunities for the evolution of multiple signals within components of ornamental traits. This finding indicates that the selective forces shaping the evolution of different components of a composite trait and the trait's signal content may be more complex than believed so far, and that holistic approaches are required for drawing comprehensive evolutionary conclusions.

Signatures of selection acting on the innate immunity gene Toll-like receptor 2 (TLR2) during the evolutionary history of rodents.

Patterns of selection acting on immune defence genes have recently been the focus of considerable interest. Yet, when it comes to vertebrates, studies have mainly focused on the acquired branch of the immune system. Consequently, the direction and strength of selection acting on genes of the vertebrate innate immune defence remain poorly understood. Here, we present a molecular analysis of selection on an important receptor of the innate immune system of vertebrates, the Toll-like receptor 2 (TLR2), across 17 rodent species. Although purifying selection was the prevalent evolutionary force acting on most parts of the rodent TLR2, we found that codons in close proximity to pathogen-binding and TLR2-TLR1 heterodimerization sites have been subject to positive selection. This indicates that parasite-mediated selection is not restricted to acquired immune system genes like the major histocompatibility complex, but also affects innate defence genes. To obtain a comprehensive understanding of evolutionary processes in host-parasite systems, both innate and acquired immunity thus need to be considered.

Short- and long-term consequences of early developmental conditions: a case study on wild and domesticated zebra finches.

Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life-history manipulation, compared to birds taken directly from the wild. In a 'common aviary' experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short- and long-term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short- and long-term morphological and life-history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life-history strategies and investment trade-offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life-history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.

No evidence for survival selection on carotenoid-based nestling coloration in great tits (Parus major).

In several vertebrate species evidence supports the hypothesis that carotenoid-based coloration of adults has evolved due to sexual selection. However, in some birds already the nestlings display carotenoid-based coloration. Because the nestling's body plumage is typically moulted before the first reproductive event, sexual selection cannot explain the evolution of these carotenoid-based traits. This suggests that natural selection might be the reason for its evolution. Here we test whether the carotenoid-based nestling coloration of great tits (Parus major) predicts survival after fledging. Contrary to our expectation, the carotenoid-based plumage coloration was not related to short- nor to long-term survival in the studied population. Additionally, no prefledging selection was detectable in an earlier study. This indicates that the carotenoid-based coloration of nestling great tits is currently not under natural selection and it suggests that past selection pressures or selection acting on correlated traits may have led to its evolution.

Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.).

Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality.

Antithrombin III and related parameters in surgical patients receiving blood components.

We examined the intra- and postoperative behavior of antithrombin III (AT), factor V, VIII, and fibrinogen in 27 elective surgical patients without evidence of disseminated intravascular coagulation (DIC) and treated according to the concept of blood component therapy inaugurated at our hospital in 1975. The intraoperative depletions of AT and fibrinogen were proportional to the transfusion volumes and correlated significantly. AT, fibrinogen, and especially factor V and VIII were significantly mobilized during surgery. A greater intraoperative depletion of AT was significantly associated with a faster recovery during the first 24 postoperative h. The AT activity was virtually stable over a period of 4 weeks in CPD-adenine red cell concentrates; fresh frozen plasma and whole blood are thus not essential as a source of AT. The application of our concept did not increase the frequency of thromboembolic complications, despite the fact that the intraoperative AT values fell below the presumed 'critical' level of 60-70% in some patients. The probable reasons are the brief duration of such levels, the simultaneous depletion of coagulation-promoting plasma constituents (e.g. fibrinogen), and the use of antithrombotic prophylaxis. Our results suggest no reasons for a routine use of fresh frozen plasma in patients with a loss and replacement of less than about 75% of their blood volume.

Influence of a blood component program on postoperative complication rates: a retrospective study in 372 patients.

We did a retrospective study of 372 thoracic and cardiovascular surgery patients, except open heart cases, which were treated by the same senior staff during the last year before (N = 197) and the first year after (N = 175) the introduction of a blood component program. There were no other basic changes of therapeutic policies. The two populations were comparable with respect to various basic characteristics. During the period 'before' the large majority of red cell units was 'deplasmatized' blood with a plasma deficit of 100 ml and a hematocrit of 40%. During the period 'after' it was red cell concentrates with a plasma deficit of 200 ml and a hematocrit of 70%. The usage pattern of red cell units did not change. The only statistically significant (and deliberate) quantitative difference between the transfusion regimens 'before' and 'after' was a more extensive intraoperative use of a gelatin plasma substitute to balance the plasma deficit of the red cell concentrates. As judged by various criteria, the postoperative courses of the patients 'before' and 'after' were virtually indistinguishable. We conclude that the blood component program practised at our hospital has no adverse effects on the postoperative course.

Clinical experience with 120,000 units of modified fluid gelatin.

We briefly review 20 years of clinical experience with 120.531 units of a 4% modified fluid gelatin as a plasma substitute. Its Mn is 22.500. The initial intravascular volume effect equals that of 4% albumin; the t0,5 of this effect is about 4 hours. It has no dosage-related side effects and specifically does not impair surgical hemostasis in volumes up to 10-15 litres within 24 hours. During the last 5 years, it has become an essential element of a blood component program, which has proven to be therapeutically satisfactory and logistically advantageous. More than 1000 patients have received more than 2000 ml within 24 hours as a part of massive transfusions. The incidence of serious anaphylactoid reactions has been 1 per 13,400 units, but only one fatality has occurred. At least one out of 7 "gelatin" reactions cannot have been caused by the colloid itself. These incidents were presumably due to trace contaminants. When compared to dextran, it appears that this gelatin is more prone to cause harmless cutaneous reactions, but less likely to induce severe cardiovascular incidents.

Red cells and gelatin as the core of a unified program for the national procurement of blood components and derivatives. Prediction, performance, and impact on supply of albumin and factor VIII.

The use of a gelatin plasma substitute as an integral part of a unified national program for the procurement of blood components and derivatives paves the way for the extensive use of red cell concentrates in the treatment of hemorrhage, the plasma from the original donations being partly diverted to the fractionation program of a national transfusion service. We estimated the potential of such a system paced by the demand for red cells and predicted that the use of 20% of fresh whole blood and 80% concentrates would not increase the demand for albumin, the yield of which would suffice to cover three-quarters of current needs in our country. The actual performance of a program using 85% of red cell concentrates in a university hospital with an exceptionally high incidence of major hemorrhage was analyzed in detail. The use of albumin per unit of transfused red cells rose by 9%. With a nationwide increase of this magnitude, 67% of the demand in our country could still be met and the estimated true need for albumin of 200 kg per million inhabitants and year would be fully covered. The yield of factor VIII is 200--300% of the demand. The determinants of the effects of such a system vary from country to country, but its fundamental potential is obviously considerable.

[Indications for plasma substitutes]. / Indikationsbereich von Plasmaersatzmitteln

During severe hemorrhage the O-2-transport capacity of blood is reduced due to the loss of hemoglobin. This reduction is, however, fully compensated down to 25% hematocrit by augmentation of the minute volume consequent on the decrease of blood viscosity due to hemodilution, though this holds only on condition that myocardial contractibility and total blood volume are not impaired. The compensation of lost intravasal fluid is therefore prevailing importance, but the substitute need not be blood and may consist of a suitable colloid solution. Physiogel, a modified fluid gelatin, has proved to be excellent for this primary substitution of blood losses. The plasma derivatives should be reserved for special indications, particularly for treatment of oncotic deficit, and here highly concentrated (10-20% albumin) preparations are needed. Blood transfusions are indicated when the hemoglobin content falls below the critical limit of 25% hematocrit.