Can species‐specific prey responses to chemical cues explain prey susceptibility to predation?

The perception of danger represents an essential ability of prey for gaining an informational advantage over their natural enemies. Especially in complex environments or at night, animals strongly rely on chemoreception to avoid predators. The ability to recognize danger by chemical cues and subsequent adaptive responses to predation threats should generally increase prey survival. Recent findings suggest that European catfish (Silurus glanis) introduction induce changes in fish community and we tested whether the direction of change can be attributed to differences in chemical cue perception. We tested behavioral response to chemical cues using three species of freshwater fish common in European water: rudd (Scardinius erythrophthalmus), roach (Rutilus rutilus), and perch (Perca fluviatilis). Further, we conducted a prey selectivity experiment to evaluate the prey preferences of the European catfish. Roach exhibited the strongest reaction to chemical cues, rudd decreased use of refuge and perch did not alter any behavior in the experiment. These findings suggest that chemical cue perception might be behind community data change and we encourage collecting more community data of tested prey species before and after European catfish introduction to test the hypothesis. We conclude that used prey species can be used as a model species to verify whether chemical cue perception enhances prey survival.     

Spontaneous immune responses to sporadic tumors: tumor-promoting, tumor-protective or both?

Cancer cells cannot develop into invasive cancers without interactions with cells and soluble mediators present in the tumor microenvironment. Accumulating evidence indicates that the immune system is a critical determinant of malignant outgrowth; however, the tumor-modulating effects of spontaneous immune responses towards nascent malignancies are rather paradoxical. Both cancer-protective and cancer-promoting features of the immune system have been described. This review will discuss the role of the dynamic inflammatory tumor microenvironment during cancer development and progression, and will focus on the intriguing question: “Do malignancies develop in spite of—or because of—spontaneous immune responses?” Special emphasis will be put on recent progress in our understanding of the immune system’s double-edged sword function during de novo carcinogenesis.     

Vulnerability of black grouse hens to goshawk predation: result of food supply or predation facilitation?

The plant cycle hypothesis says that poor-quality food affects both herbivorous voles (Microtinae spp.) and grouse (Tetraonidae spp.) in vole decline years, leading to increased foraging effort in female grouse and thus a higher risk of predation by the goshawk Accipiter gentilis. Poor-quality food (mainly the bilberry Vaccinium myrtillus) for these herbivores is induced by seed masting failure in the previous year, when the bilberry is able to allocate resources for chemical defence (the mast depression hypothesis; MDH). The predation facilitation hypothesis (PFH) in turn states that increased searching activity of vole-eating predators during or after the decline year of voles disturbs incubating and brooding grouse females. The behaviours used by grouse to avoid these terrestrial predators make them more vulnerable to predation by goshawks. We tested the main predictions of the MDH and PFH by collecting long-term (21-year) data from black grouse Tetrao tetrix hens and cocks killed by breeding goshawks supplemented with indices of bilberry crop, vole abundance and small carnivores in the vicinity of Oulu, northern Finland. We did not find obvious support for the prediction of the MDH that there is a negative correlation of bilberry crop in year t with vole abundance and with predation index of black grouse hens in year t + 1. We did find obvious support for the prediction of the PFH that there is a positive correlation between predator abundance and predation index of grouse hens, because the stoat Mustela erminea abundance index was positively related to the predation index of black grouse hens. We suggest that changes in vulnerability of grouse hens may mainly be caused by the guild of vole-eating predators, who shift to alternative prey in the decline phase of the vole cycle, and thus chase grouse hens and chicks to the talons of goshawks and other avian predators.     

Complex multicellularity in fungi: evolutionary convergence,single origin,or both?

Complex multicellularity represents the most advanced level of biological organization and it has evolved only a few times: in metazoans, green plants, brown and red algae and fungi. Compared to other lineages, the evolution of multicellularity in fungi follows different principles; both simple and complex multicellularity evolved via unique mechanisms not found in other lineages. Herein we review ecological, palaeontological, developmental and genomic aspects of complex multicellularity in fungi and discuss general principles of the evolution of complex multicellularity in light of its fungal manifestations. Fungi represent the only lineage in which complex multicellularity shows signatures of convergent evolution: it appears 8–11 times in distinct fungal lineages, which show a patchy phylogenetic distribution yet share some of the genetic mechanisms underlying complex multicellular development. To explain the patchy distribution of complex multicellularity across the fungal phylogeny we identify four key observations: the large number of apparently independent complex multicellular clades; the lack of documented phenotypic homology between these clades; the conservation of gene circuits regulating the onset of complex multicellular development; and the existence of clades in which the evolution of complex multicellularity is coupled with limited gene family diversification. We discuss how these patterns and known genetic aspects of fungal development can be reconciled with the genetic theory of convergent evolution to explain the pervasive occurrence of complex multicellularity across the fungal tree of life.     

Factors influencing infection patterns of trophically transmitted parasites among a fish community: host diet,host–parasite compatibility or both?

Parasite infection patterns were compared with the occurrence of their intermediate hosts in the diet of nine sympatric fish species in a New Zealand lake. Stomach contents and infection levels of three gastrointestinal helminth species were examined from the entire fish community. The results highlighted some links between fish host diet and the flow of trophically transmitted helminths. Stomach contents indicated that all but one fish species were exposed to these helminths through their diet. Host feeding behaviour best explained infection patterns of the trematode Coitocaecum parvum among the fish community. Infection levels of the nematode Hedruris spinigera and the acanthocephalan Acanthocephalus galaxii, however, were not correlated with host diets. Host specificity is thus likely to modulate parasite infection patterns. The data indicate that host diet and host-parasite compatibility both contribute to the distribution of helminths in the fish community. Furthermore, the relative influence of encounter (trophic interactions between prey and predator hosts) and compatibility (host suitability) filters on infection levels appeared to vary between host-parasite species associations. Therefore, understanding parasite infection patterns and their potential impacts on fish communities requires determining the relative roles of encounter and compatibility filters within and across all potential host-parasite associations.     

Are species adapted to their regeneration niche, adult niche, or both?

Functional traits are important drivers of successional processes and the assembly of plant communities. It is generally assumed that functional traits are closely linked to the regeneration niche because of the high selection pressures in the seedling stage, but recent studies have challenged this view. In this study, I use cross species and phylogenetic correlation analysis between leaf traits and light environment to evaluate whether species are adapted to the regeneration niche, adult niche, or both. Leaf chemistry, morphology, physiology, and crown exposure were quantified for up to 58 Bolivian tropical moist forest tree species that differ in their regeneration and adult light niche. Multiple regression analysis shows that leaf traits of seedlings, saplings, and trees are most strongly related to the regeneration niche, and once this is taken into account, adult niche does not significantly explain any of the remaining variation in leaf traits. This suggests that, although the regeneration phase is short, it has a long-lasting effect on the form and shape of plant species.     

The susceptibility and resilience of corals to thermal stress: adaptation,acclimatization or both?

Coral reefs are threatened with worldwide decline from multiple factors, chief among them climate change ( Hughes et al. 2003 ; Hoegh‐Guldberg et al. 2007 ). The foundation of coral reefs is an endosymbiosis between coral hosts and their resident photosynthetic dinoflagellates (genus Symbiodinium) and this partnership (or holobiont) is exquisitely sensitive to temperature stress. The primary response to hyperthermic stress is coral bleaching, which is the loss of symbionts from coral tissues—the collapse of the symbiosis ( Weis 2008 ). Bleaching can result in increased coral mortality which can ultimately lead to severely compromised reef health ( Hoegh‐Guldberg et al. 2007 ). Despite this grim picture of coral bleaching and reef degradation, coral susceptibility to stress and bleaching is highly variable ( Coles & Brown 2003 ). There is enormous interest in discovering the factors that determine susceptibility in order to help us predict if and how corals will survive a period of rapid global warming. In this issue, Barshis et al. (2010) examine the ecophysiological and genetic basis for differential responses to stress in Porites lobata in American Samoa. They combine a reciprocal transplant experimental design between two neighbouring, but very different reef environments with state‐of‐the‐art physiological biomarkers and molecular genetic markers for both partners to tease apart the contribution of environmental and fixed influences on stress susceptibility. Their results suggest the presence of a fixed, rather than environmental effect on expression of ubiquitin conjugates, one key marker for physiological stress response. In addition, the authors show genetic differentiation in host populations between the two sites suggesting strong selection for physiological adaptation to differing environments across small geographic distances. These conclusions point the study of coral resilience and susceptibility in a new direction.     

Tensile fatigue in bone: are cycles-, or time to failure, or both, important?

In life, bones are subjected to fatigue loading which has different frequency and amplitude components, as well as various kinds of loading modes like tension, compression, shear and combinations of them. Considerable variability is observed in fatigue results of bone, which may be caused by these experimental variables or by the bone itself. In past studies the effect of magnitude and mode of loading have been examined in standard fatigue strength (stress vs. cycles to failure) diagrams. The effect of frequency is not clear, but there is clear evidence (from Carter & co-workers) that, at least in human bone, tension "fatigue" failure was determined solely by time rather than by cycles. We sought to confirm these results in the same and a different species. We cycled human and bovine bone in tension at two frequencies: 0.5 and 5 Hz. There was no cycle number effect; the results from the tests at the two frequencies were different if plotted and analysed as a function of cycles to failure, but were not separable if plotted and analysed as a function of time to failure. In this respect bone differs from tendon, in which failure in tension is a function of both cycles and time.     

The nature of predation: prey dependent, ratio dependent or neither?

To describe a predator-prey relationship, it is necessary to specify the rate of prey consumption by an average predator. This functional response largely determines dynamic stability, responses to environmental influences and the nature of indirect effects in the food web containing the predator-prey pair. Nevertheless, measurements of functional responses in nature are quite rare. Recently, much work has been devoted to comparing two idealized forms of the functional response: prey dependent and ratio dependent. Although we agree that predator abundance often affects the consumption rate of individual predators, this phenomenon requires more attention. Disagreement remains over which of the two idealized responses serves as a better starting point in building models when data on predator dependence are absent.     

Workers, sexuals, or both? Optimal allocation of resources to reproduction and growth in annual insect colonies

Understanding decisions about the allocation of resources into colony growth and reproduction in social insects is one of the challenging issues in sociobiology. In their seminal paper, Macevicz and Oster predicted that, for most annual insect colonies, a bang–bang strategy should be favoured by selection, i.e. a strategy characterised by an “ergonomic phase” with exponential colony growth followed by a “reproductive phase” with all resources invested into the production of sexuals. Yet, there is empirical evidence for the simultaneous investment into the production of workers and sexuals in annual colonies (graded control). We, therefore, re-analyse and extend the original model of Macevicz and Oster. Using basic calculus, we can show that sufficiently strong negative correlation between colony size and worker efficiency or increasing mortality of workers with increasing colony size will favour the evolution of graded allocation strategies. By similar reasoning, graded control is predicted for other factors limiting colony productivity (for example, if queens’ egg laying capacity is limited).     

Territory quality or bird quality? Factors determining breeding success in the Magpie Pica pica

The effects of male, female and territory quality on eight measures of breeding performance in the Magpie Pica pica were examined using repeatability. Comparisons were made for (i) the same male or female on the same territory (ii) the same male or female on different territories during their lifetime and (iii) the same territory occupied by a different male or female. Female quality explained over 60% of the variance in clutch-size and size of eggs laid. Male quality accounted for over 70% of a pair's breeding success within each breeding season. The differential ability of males to provision their female adequately during incubation and their chicks in the nestling period is the most likely explanation for this result. The timing of breeding appeared to be controlled primarily by territory quality, but the effect was relatively weak (19%). Although no effect of female quality on the timing of breeding was detected, this cannot be totally discounted. In addition, it is likely that environmental constraints (i.e. temperature) also exerted some influence on the date of laying. These results contrast with those of Högstedt (1980), who found that 86% of the variance in clutch-size was due to the effects of territory quality, with only 14% of the variance attributable to female effects. Reasons for the differences are examined.     

Human T-cell responses to malaria: mostly forgotten or committed to memory?

T cells have been implicated in both malaria immunity and malaria disease and factors controlling the maintenance of T-cell responses over time may alter the clinical outcome o f infection. Michael Good and Janine Bilsborough have compared the T-cell responses to epitopes from the Plasmodium vivax and P. falciparum circumsporozoite proteins and here discuss the issue of T-cell memory as it applies to malaria.     

The human mandible: Lever,link, or both?

Hylander ('78) recently published important new data on bite force in humans, and showed that the human mandible cannot function purely as a link during incisal biting. He concluded instead that the mandible acts as a lever. Reexamination of Hylander's data suggests that the mandible cannot function purely as a lever either, and in fact it probably functions simultaneously as both lever and link during incisal biting.