The resident strikes back: invader-induced switching of resident attractor

The aim of this paper is two-fold: (a) by way of example, we elucidate the phenomenon of invader-induced switches in a resident attractor; (b) we expose in detail how resonance and phase have a strong impact when semelparous organisms (as, e.g. Pacific salmon) with different life-cycle lengths compete in a self-induced periodically fluctuating environment. We analyse a simple model for the competition between annuals and biennials, focusing on the situation that the annual population in isolation converges to a two-cycle. Well-timed biennial mutants sample the periodically varying environment more efficiently than the annual resident. They can invade successfully even when they are inferior to the resident, in the sense that they have lower viability and/or fertility. Successful invasion can lead to resonance-mediated coexistence if the invader is rather inferior to the resident. Remarkably, for mutants that are less inferior to the resident, successful invasion by a mutant strategy will inevitably be followed by the extinction of the former invader and concurrent re-establishment of the resident. The expulsion of the invader is brought about by an invasion-induced phase shift or attractor switch. We call this phenomenon "the resident strikes back" and say that the resident strategy is invasible, yet invincible. After the resident has struck back, other mutants can successfully invade again. On a longer time-scale, this might lead to an intermittent occurrence of ultimately inferior strategies. The results show that even in a deterministic setting, successful invasion does not necessarily lead to establishment and that mutual invasibility is not always sufficient for coexistence.     

The role of cardiac resident macrophage in cardiac aging

Advancements in longevity research have provided insights into the impact of cardiac aging on the structural and functional aspects of the heart. Notable changes include the gradual remodeling of the myocardium, the occurrence of left ventricular hypertrophy, and the decline in both systolic and diastolic functions. Macrophages, a type of immune cell, play a pivotal role in innate immunity by serving as vigilant agents against pathogens, facilitating wound healing, and orchestrating the development of targeted acquired immune responses. Distinct subsets of macrophages are present within the cardiac tissue and demonstrate varied functions in response to myocardial injury. The differentiation of cardiac macrophages according to their developmental origin has proven to be a valuable strategy in identifying reparative macrophage populations, which originate from embryonic cells and reside within the tissue, as well as inflammatory macrophages, which are derived from monocytes and recruited to the heart. These subsets of macrophages possess unique characteristics and perform distinct functions. This review aims to summarize the current understanding of the roles and phenotypes of cardiac macrophages in various conditions, including the steady state, aging, and other pathological conditions. Additionally, it will highlight areas that require further investigation to expand our knowledge in this field.     

The role of climate in limiting European resident bird populations

Abstract Aim To study densities of eight groups of resident forest bird populations across Europe to examine their association with abiotic (temperature, precipitation) factors. Location Europe. Methods Densities of residents (and migrant birds, which were used as a control group) were extracted from published breeding bird censuses. For each census location we obtained geographical co‐ordinates (latitude and longitude), temperature and precipitation variables describing both breeding and non‐breeding seasons. Resident densities were first examined separately in relation to co‐ordinates and principal component axes, which were extracted from temperature and precipitation variables. The relative impact of each explaining factor (co‐ordinates and principal component axis) on resident densities was checked by using residual examination and partial correlation. Results Densities of resident birds were in general negatively correlated with both latitude and longitude and temperature and precipitation factors, but latitude and temperature proved to be the strongest individual factors along which resident densities varied. The higher the latitude or the lower the temperatures, the lower were the densities of most resident birds. Partial correlation analysis suggested that of those two factors, latitude was the dominant one. Both the density of resident and migrant birds decreased towards the north, but the decrease of residents was steeper, and in the north they comprised only a small fraction of breeding bird numbers, whereas further south they commonly comprise half of the breeding bird numbers. Main conclusions The best explanatory factor for resident densities was latitude. For this reason, it was difficult to separate the relative effect of each individual factor, because latitude partly describes all the original variables (temperature and precipitation). The results suggested that precipitation was of less importance and that the interplay between latitude and ambient temperatures was not the sole factor behind the strong effect of latitude. We suggest that the coupled effect of harshening climate and decreasing amount of available energy with increasing latitude is limiting the population sizes of resident birds. We also propose that the effect of those factors is most apparent in northern Fennoscandia, where resident densities are suggested to be lower than would be expected on the basis of summer time carrying capacity.     

The receptor-mediated retention of resident proteins in the endoplasmic reticulum

Conclusion Overwhelming evidence has accumulated to support the bulk flow hypothesis which states that proteins entering the exocytic pathway will follow a default route to the plasma membrane unless they carry specific signals for receptor mediated diversion. The resident soluble and membrane proteins of the ER present a clear example of this signal mediated exception to bulk flow. Their study also provides insights relevant to retention or targetting signals operating later in the secretory pathway.The last few years have seen enormous progress in this field, in the delineation of the retention problem, the identification of the retention signal and recently in the identification of components of the retention machinery itself. The next few years hold the promise of a more complete understanding of the retention machinery and of the enigmatic cellular compartment in which it functions.     

The entry of the Picornaviridae virus family in resident macrophages

For viruses, the following mechanisms of penetration into cells are typical: clathrin- or dinaminmediated endocytosis, the formation of caveolae, local lysis of cell membranes, and macropinocytosis. It is accepted that (those nonenveloped viruses in the Picornaviridae family) enter cells mostly through the local lysis of their membranes. The purpose of the present study is to research the mechanisms of penetration into resident macrophages of viruses of the indicated family, including poliovirus, Echol1 and Coxsackie B1 viruses, and Type 71 enterovirus. It has been detected that, at the adhesion sites of the Coxsackie B1 virus and Type 71 enterovirus on a macrophage surface, invaginations of the plasma membranes of cells appear, followed by the consequent formation of endocytoplasmatic vesicles, i.e., caveolae. The penetration of poliovirus into macrophages occurs both through the formation of caveolae and the local lysis of the plasmolemma of cells; during the later terms (after 45 min), macropinocytosis is observed in the viral particles during the first 15 min after the Echol1 virus penetrated the cytoplasm of macrophages through the local lysis of their plasmolemma. Thereafter, the formation of endocytic vacuolae including viral particles was observed in the cytoplasm of infected macrophages. The exit of the Echol1 virus from endocytic vacuoles was performed by the local lysis of cell membrane.     

The condition for dynamic stability

The well-known condition for standing stability in static situations is that the vertical projection of the centre of mass (CoM) should be within the base of support (BoS). On the basis of a simple inverted pendulum model, an extension of this rule is proposed for dynamical situations: the position of (the vertical projection of) the CoM plus its velocity times a factor (square root l/g) should be within the BoS, l being leg length and g the acceleration of gravity. It is proposed to name this vector quantity 'extrapolated centre of mass position' (XcoM). The definition suggests as a measure of stability the 'margin of stability' b, the minimum distance from XcoM to the boundaries of the BoS. An alternative measure is the temporal stability margin tau, the time in which the boundary of the BoS would be reached without intervention. Some experimental data of subjects standing on one or two feet, flatfoot and tiptoe, are presented to give an idea of the usual ranges of these margins of stability. Example data on walking are also presented.     

The Salton Sea as critical habitat to migratory and resident waterbirds

Concern about the Salton Sea ecosystem, based on potential impacts of increasing salinity, contaminants, disease outbreaks, and large die-offs of birds, is heightened because of tremendous prior loss and degradation of wetland habitat in western North America. In 1999, we used a variety of survey methods to describe patterns of abundance of birds at the Salton Sea and in adjacent habitats. Our results further documented the great importance of the Salton Sea within the Pacific Flyway to wintering, migratory, and breeding waterbirds. Exclusive of Eared Grebes, we estimated about 187000 individual waterbirds at the Salton Sea in January, 88000 in April, 170000 in August, and 261000 in November. Additional surveys of Eared Grebes in November and December suggested the total population of all waterbirds was about 434000 to 583000 in those months, respectively. We also documented breeding by about 14000 pairs of colonial waterbirds. Waterbirds were particularly concentrated along the northern, southwestern, southern, and southeastern shorelines and river deltas. By contrast, some species of wading birds (Cattle Egret, White-faced Ibis, Sandhill Crane) and shorebirds (Mountain Plover, Whimbrel, Long-billed Curlew) were much more numerous in agricultural fields of the Imperial Valley than in wetland habitats at the Sea. Various studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. Important taxa are the Eared Grebe, American White Pelican, Double-crested Cormorant, Cattle Egret, White-faced Ibis, Ruddy Duck, Yuma Clapper Rail, Snowy Plover, Mountain Plover, Gull-billed, Caspian, and Black terns, and Black Skimmer. Proposed restoration projects should be carefully assessed to ensure they do not have unintended impacts and are not placed where large numbers of breeding, roosting, or foraging birds concentrate. Similarly, plans to enhance opportunities for recreation or commerce at the Sea should aim to avoid or minimize disturbance to birds. Future research should focus on filling gaps in knowledge needed to effectively conserve birds at the Salton Sea.     

The spread of apomixis and its effect on resident genetic variation

In a simulation model we investigated how much of the initial genetic variation that is retained in a population after a dominant mutation has brought apomixis to fixation in it. A marker allele associated with the apomixis mutation is generally retained after the fixation of apomixis, particularly if the two alleles are closely linked. The spread of asexuality, however, normally leads to almost no loss of genetic variation, neither with respect to cytotypes nor with respect to genotypes. This holds for large populations and apomixis mutants with strong pollen production. In smaller populations, and with apomicts with reduced pollen production, the outcome is more variable, ranging from no genetic variation retained to only weakly reduced variability compared with the initial state. These results help explain the high genetic variability in many apomicts. They also imply that natural selection will have many genotypes to act on even after the spread of apomixis.     

The critical micelle condition revisited.

Several simple alternatives have been examined as a possible basis for micellar size distributions which are internally consistent with the experimentally required concept of a threshold concentration, the critical micelle condition. Among these are the two-state system, monomer in equilibrium with a single high polymer, indefinite self-association, and continuous self-association with an arbitrary upper limit beyond which all further association is absolutely prohibited. Of these, only the last is a possible choice, although lacking experimental support. This report considers in deeper detail a thermodynamic model for micelle distributions, the so-called shell model of the present author, which is in basic agreement with an earlier statistic-mechanical study [Hoeve CA & Benson GC (1957), Colloid Polym Sci, 252, 56] in predicting the possibility of broad distributions of micellar species. A self-consistent distribution model which predicts a critical micelle condition must also predict a location with respect to degree of polymerization having a minimum concentration. Thus, the molar distribution function for the shell model satisfies this requirement, whereas the equivalent concentration distribution function fails to do so, as would the statistical models for multiple ligand binding. Moreover, the position of this minimum is predicted to change with concentration.     

The nature of iron released by resident and stimulated mouse peritoneal macrophages

Mouse peritoneal macrophages were allowed to ingest ⁵⁹Fe, ¹²⁵I-labelled transferrin-antitransferrin immune complexes, and the release of ⁵⁹Fe and degraded transferrin was studied. Some iron was released as ferritin, but a major portion was bound by bovine transferrin present in the culture medium, which contained fetal calf serum. If the medium was saturated with iron prior to incubation with the cells, little of the released iron was then bound by transferrin but appeared either as a high molecular weight fraction or, if nitrilotriacetate was present in the medium, some also appeared as a low molecular weight fraction. The release of non-ferritin iron was biphasic, the early, rapid phase being more prolonged with resident cells than with stimulated cells. The rate of release in the late phase did not differ significantly between resident and stimulated cells. Incubation at 0°C completely suppressed the release of degraded transferrin, but iron release continued at about 30% of the rate seen in control cultures at 37°C. A model for the intracellular handling of ingested iron is proposed to take account of the different release patterns of resident and stimulated macrophages.     

The influence of resident adults on recruitment: a comparison to settlement

For species recruiting into established sessile communities, the adult colonies and individuals already present form a significant part of the environment and have the potential to alter both larval settlement rates and post-settlement mortality. Settlement rates can be reduced by predation on larvae, by the removal or addition of substratum space, or by stimulation or prohibition of larvae from settling on adjacent substratum. Once attached, the recruiting individual can still be influenced by predation or overgrowth by residents, by the added physical structure for firmer attachment, or by being camouflaged from motile predators. To examine those processes by which residents affect recruitment we exposed experimental substrata with three densities of adults of a single species at a site in eastern Long Island Sound, USA for a 1-wk period. Seven different species of common invertebrates were used in nine separate experiments. The major effect of most resident species was the usurpation of space and the restricting of recruitment to adjacent unoccupied areas. This was particularly true for resident ascidians and bryozoans, but less so for barnacles and oysters. In fact several species recruited in higher densities on or next to oysters and barnacles. Comparison to 1-day settlement experiments indicated that the encrusting ascidian species Diplosoma and possibly Botryllus reduced recruitment relative to settlement, probably by overgrowing newly-settled individuals. However, in the presence of most resident species, recruitment patterns were not greatly different from settlement patterns, indicating that the effects of the attached community on recruitment may result from influences on settlement.     

Kidney regeneration and resident stem cells

Given its complexity, high metabolic activity and excretory functions, the kidney is particularly susceptible to acute ischemic and toxin-mediated injury. Current therapies do not facilitate kidney regeneration, and there is an increasing interest in newer therapies that are based on cellular sources of kidney regeneration, such as stem cell therapy. Our understanding of cellular sources for kidney regeneration and stem cells present in the adult kidney has dramatically evolved over the recent years. Herein, we discuss the current understanding of kidney stem cells present in the adult mammalian kidney and their role in kidney regeneration. We have also summarized the best available evidence supporting the role of stem cells in kidney regeneration.     

Kidney regeneration and resident stem cells

Given its complexity, high metabolic activity and excretory functions, the kidney is particularly susceptible to acute ischemic and toxin-mediated injury. Current therapies do not facilitate kidney regeneration, and there is an increasing interest in newer therapies that are based on cellular sources of kidney regeneration, such as stem cell therapy. Our understanding of cellular sources for kidney regeneration and stem cells present in the adult kidney has dramatically evolved over the recent years. Herein, we discuss the current understanding of kidney stem cells present in the adult mammalian kidney and their role in kidney regeneration. We have also summarized the best available evidence supporting the role of stem cells in kidney regeneration.