Sequestration: causes and consequences

Adhesion of Plasmodium falciparum-infected erythrocytes to endothelial cells and to syncytiotrophoblasts lining the placenta is a key feature of malaria pathogenesis. P. falciparum erythrocyte membrane protein 1, a family of variable proteins, mediates adhesion to CD36 and intercellular adhesion molecule 1 in the systemic vasculature, and to chondroitin sulphate A and hyaluronic acid in the placenta. Recent studies of the pathology of fatal cerebral malaria and of placental malaria that follow such sequestration suggest that coagulation disturbances may have a greater role in pathogenesis than previously realized, and that monocyte infiltrates in response to malaria may initiate some of these changes. Chemokines such as macrophage inflammatory protein 1 alpha and beta and monocyte chemoattractant protein 1 may play a key role in attracting monocytes to the placenta and other organs, but the stimulus to chemokine secretion is not presently known.     

Coral bleaching: causes and consequences

It has been over 10 years since the phenomenon of extensive coral bleaching was first described. In most cases bleaching has been attributed to elevated temperature, but other instances involving high solar irradiance, and sometimes disease, have also been documented. It is timely, in view of our concern about worldwide reef condition, to review knowledge of physical and biological factors involved in bleaching, the mechanisms of zooxanthellae and pigment loss, and the ecological consequences for coral communities. Here we evaluate recently acquired data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment. Cellular mechanisms of bleaching involve a variety of processes that include the degeneration of zooxanthellae in situ, release of zooxanthellae from mesenterial filaments and release of algae within host cells which become detached from the endoderm. Photo-protective defences (particularly carotenoid pigments) in zooxanthellae are likely to play an important role in limiting the bleaching response which is probably elicited by a combination of elevated temperature and irradiance in the field. The ability of corals to respond adaptively to recurrent bleaching episodes is not known, but preliminary evidence suggests that phenotypic responses of both corals and zooxanthellae may be significant.     

Changing distributions of ticks: causes and consequences

Today, we are witnessing changes in the spatial distribution and abundance of many species, including ticks and their associated pathogens. Evidence that these changes are primarily due to climate change, habitat modifications, and the globalisation of human activities are accumulating. Changes in the distribution of ticks and their invasion into new regions can have numerous consequences including modifications in their ecological characteristics and those of endemic species, impacts on the dynamics of local host populations and the emergence of human and livestock disease. Here, we review the principal causes for distributional shifts in tick populations and their consequences in terms of the ecological attributes of the species in question (i.e. phenotypic and genetic responses), pathogen transmission and disease epidemiology. We also describe different methodological approaches currently used to assess and predict such changes and their consequences. We finish with a discussion of new research avenues to develop in order to improve our understanding of these host–vector–pathogen interactions in the context of a changing world.     

Genotyping errors: causes, consequences and solutions

Although genotyping errors affect most data and can markedly influence the biological conclusions of a study, they are too often neglected. Errors have various causes, but their occurrence and effect can be limited by considering these causes in the production and analysis of the data. Procedures that have been developed for dealing with errors in linkage studies, forensic analyses and non-invasive genotyping should be applied more broadly to any genetic study. We propose a protocol for estimating error rates and recommend that these measures be systemically reported to attest the reliability of published genotyping studies.     

Partial migration in fishes: causes and consequences

Partial migration, where only some individuals from a population migrate, has been widely reported in a diverse range of animals. In this paper, what is known about the causes and consequences of partial migration in fishes is reviewed. Firstly, the ultimate and proximate drivers of partial migration are reflected upon: what ecological factors can shape the evolution of migratory dimorphism? How is partial migration maintained over evolutionary timescales? What proximate mechanisms determine whether an individual is migratory or remains resident? Following this, the consequences of partial migration are considered, in an ecological and evolutionary context, and also in an applied sense. Here it is argued that understanding the concept of partial migration is crucial for fisheries and ecosystem managers, and can provide information for conservation strategies. The review concludes with a reflection on the future opportunities in this field, and the avenues of research that are likely to be fruitful to shed light on the enduring puzzle of partial migration in fishes.     

Harmonia axyridis invasions: Deducing evolutionary causes and consequences

I consider evolutionary approaches to deducing factors that have made the ladybird beetle Harmonia axyridis such a successful invader, and the contribution that studies of this species in its native range can make. Work aiming to demonstrate which (pre)adaptations have made the species so successful often fails to compare these putative characters with those of other ladybirds. This has led to a tendency for “argument by design”‐type claims on characters widely shared by non‐invasive coccinellids. There is good evidence from genetic studies that evolutionary change occurred in invasive populations, contributing to their success. There is some evidence for subsequent evolutionary change after the establishment of invasive H. axyridis, primarily in the native organisms with which the ladybird interacts. I show here that there appears to have been little adaptation in H. axyridis, over about 20 generations, to the alkaloids of one North American native intraguild prey, the ladybird Coleomegilla maculata. Studies of H. axyridis in its native range are important, as they provide a snapshot of the ancestral ladybird, unobscured by subsequent evolutionary change related to its invasiveness. They provide baseline data about phenomena such as interactions with natural enemies and intraguild predation, and they also can provide pointers as to how H. axyridis might further adapt in the regions it has colonized. Harmonia axyridis represents an ideal opportunity for greater international co‐operation between scientists studying this species in its native range in Asia and scientists studying it in Europe, America and Africa, where it is an invasive exotic.     

Metabolic consequences of hard work

When an animal has to meet increased demands on its working capacity, for example, for thermoregulation or parental care, two strategies are available. The animal can reallocate energy from costly maintenance processes - such as immunological defence or DNA repair systems (compensation hypothesis) - or it may try to increase the rate of energy intake or efficiency of digestion by increasing the size of the alimentary tract (increased-intake hypothesis). By manipulating brood size, I affected parental effort among marsh tits (Parus palustris) as demonstrated by a significant increase in parental feeding rate with experimental brood size. Basal metabolic rate (BMR) increased both with manipulated brood size and individual feeding rate, supporting the predictions from the increased-intake hypothesis. Furthermore, I found a direct positive relation between BMR and energy expenditure, measured with the help of the doubly labelled water technique. The cost of achieving a higher working capacity is substantial since BMR increases more quickly than the surplus energy available for work. Since the cost of a high sustained workload was not primarily dependent on a reallocation of energy away from maintenance, such a cost should be searched for among the detrimental effects of a high metabolic rate per se, for example, an increased oxidative damage to DNA, proteins and lipids.     

Fragile and unstable chromosomes in cancer: causes and consequences

Cancer cells commonly exhibit various forms of genetic instability, such as changes in chromosome copy number, translocations and point mutations in particular genes. Although transmissible change seems to be an essential part of the neoplastic process, the extent to which DNA instability is a cause rather than a consequence of cancer is unclear. Chromosomal fragile sites have been proposed to be not only susceptible to DNA instability in cancer cells, but also associated with genes that contribute to the neoplastic process. Mutation at fragile site loci might therefore have a causative role in cancer. Recent studies on one class of human chromosomal fragile sites show that instability at fragile site loci can functionally contribute to tumor cell biology.