Natural selection on unpalatable species imposed by state-dependent foraging behaviour

Müllerian mimicry is typically thought to arise as a consequence of defended prey species adopting a similar way of signalling their unprofitability, thereby reducing the costs of predator education. Here we consider subsequent selection on the morphology of prey species, in the potentially lengthy period of time when predators are generally aware of the noxious qualities of their prey (and so no further learning is involved). Using a pair of stochastic dynamic programming equations which describe both the toxin burdens of a predator and its energy level, we identified the optimal state-dependent rules that maximize a predator's long-term survivorship, and examined the implications of this behaviour for the evolution of prey morphologies. When palatable prey are in short supply then those prey species which contain relatively low doses of toxins become profitable to consume by hungry predators. Under these conditions, a weakly defended prey could gain selective advantage in the post educational period by resembling a prey species which contained a higher dose of the same or different toxins, although the precise nature of the ecological relationship between model and mimic could either be mutualistic or parasitic depending on how mimic density increases when favoured by selection. Our work formally demonstrates that one does not always need to invoke educational effects to explain why two or more unpalatable species have evolved a similar appearance, or to explain why mimetic similarity among distasteful species is maintained over time. When two species contain high levels of different toxins then they may gain mutual advantage by resembling one another, not only by educating the predator as to their common unprofitability (classical Müllerian mimicry), but also by increasing predator uncertainty as to the specific kind of toxin a prey item contains.     

Density-dependent effects of multiple predators sharing a common prey in an endophytic habitat

Multiple predator species feeding on a common prey can lead to higher or lower predation than would be expected by simply combining their individual effects. Such emergent multiple predator effects may be especially prevalent if predators share feeding habitat. Despite the prevalence of endophagous insects, no studies have examined how multiple predators sharing an endophytic habitat affect prey or predator reproduction. We investigated density-dependent predation of Thanasimus dubius (Coleoptera: Cleridae) and Platysoma cylindrica (Coleoptera: Histeridae) on a bark beetle prey, Ips pini (Coleoptera: Scolytidae), in a laboratory assay. I. pini utilize aggregation pheromones to group-colonize and reproduce within the stems of conifers. T. dubius and P. cylindrica exploit these aggregation pheromones to arrive simultaneously with the herbivore. Adult T. dubius prey exophytically, while P. cylindrica adults enter and prey within the bark beetle galleries. Larvae of both predators prey endophytically. We used a multiple regression analysis, which avoids confounding predator composition with density, to examine the effects of varying predator densities alone and in combination on herbivore establishment, herbivore reproduction, and predator reproduction. Predators reduced colonization success by both sexes, and decreased I. pini reproduction on a per male and per female basis. The combined effects of these predators did not enhance or reduce prey establishment or reproduction in unexpected manners, and these predators were entirely substitutable. The herbivores net replacement rate was never reduced significantly below one at prey and predator densities emulating field conditions. Similar numbers of each predator species emerged from the logs, but predator reproduction suffered from high intraspecific interference. The net replacement rate of P. cylindrica was not affected by conspecifics or T. dubius. In contrast, the net replacement rate of T. dubius decreased with the presence of conspecifics or P. cylindrica. Combinations of both predators led to an emergent effect, a slightly increased net replacement rate of T. dubius. This may have been due to predation by larval T. dubius on pupal P. cylindrica, as P. cylindrica develops more rapidly than T. dubius within this shared habitat.     

UK patients with primary Sjögren's syndrome are at increased risk from clinical depression

Objective: This study was undertaken to assess the presence and degree of anxiety and depression in a group of UK patients with primary Sjögren's syndrome (1°SS). Design: Cross‐sectional. Setting: Department of Oral Medicine, Liverpool University Dental Hospital. Subjects: Eighty adult patients; 40 diagnosed with 1°SS according to the revised European Criteria and 40 age/gender‐matched controls with no history of chronic illness. Intervention: Hospital Anxiety and Depression Scale (HADS), a self‐administered questionnaire designed to evaluate the presence and degree of anxiety and depression in a clinical setting. Main outcome measures: Age, gender, Hospital Anxiety and Depression Scale (HADS). Results: Forty patients with 1°SS and 40/age/gender‐matched controls completed the HADS. Scores for anxiety in both the 1°SS and control groups showed no statistically significant difference. Patients with 1°SS had statistically significant higher, mean HADS scores for depression than the controls. There was an increased prevalence of ‘definite’ clinical depression in the 1°SS group. Conclusion: Patients with 1°SS appear to be at increased risk from clinical depression. Early recognition and appropriate intervention is therefore essential to reduce the negative impact of depression on the patient's quality of life and outcome of their disease.     

Macrofaunal diversity and habitat structure in intertidal boulder fields

Low-midshore boulder fields in Europe are increasingly subject to degradation related to beach fishing for crabs and abalones. The aim of the study was to better understand the structure and species diversity of macrofaunal assemblages living in a low-midshore boulder field in order to define conservation strategies for this biotope. Sampling strategy involved different spatial scales (macro- and microstrata) relative to the complexity and heterogeneity of the habitat. Assemblages of species and the corresponding habitats were identified by multifactorial analysis and compared by ANOVAs. The results show a hierarchical organization of the macrofauna within the boulder field, corresponding to three spatial levels of habitat structure: (i) eight microhabitats at the lowest level of spatial organization, each defined by a specific assemblage (subcommunity); (ii) three habitats at a middle level combining these microhabitats, each associated with a specific community (open rock, protected rock and sediment); and (iii) three macrohabitats at the uppermost level (corresponding to the scale of the entire boulder field and including the main geomorphological features of the beach), each defined by a specific assemblage of species (boulders on boulders, boulders on bedrock, and boulders on sediment). Two microhabitats with particularly high species diversity were regarded as the most important ecological units of the field in terms of conservation of specific and functional biodiversity. Comparison of habitat/community parameters showed (i) that habitat heterogeneity was not an accurate indicator of faunal diversity, and (ii) that habitat complexity enhanced the species richness of the fauna, but only above a threshold value. This enhancement was due to semi-sheltered microhabitats, which were found only in the most complex areas of the boulder field. It is likely that this complexity affects species richness qualitatively more than by the diversity of microhabitats. In other words, a cross-scale effect is apparent in which high habitat complexity on the middle spatial scale creates microhabitats on the lowest spatial scale that are characterized by stable semi-sheltered environmental conditions conducive to a maximum of species.     

Yeast-like microorganisms in the scale insect Kermes quercus (Insecta,Hemiptera, Coccomorpha: Kermesidae). Newly acquired symbionts?

Scale insects, like other plant sap-consumers, are host to symbiotic microorganisms which provide them with the substances missing from their diet. In contrast to most scale insects, Kermes quercus (Linnaeus) was regarded as asymbiotic. Our histological and ultrastructural observations show that in the body of the feeding stages of K. quercus collected in two locations (Warsaw and Cracow), numerous yeast-like microorganisms occur. These microorganisms were localized in the cytoplasm of fat body cells. The yeast-like microorganisms were observed neither in other organs of the host insect nor in the eggs. These microorganisms did not cause any damage to the structure of the ovaries and the course of oogenesis of the host insect. The females infected by them produced about 1300 larvae. The lack of these microorganisms in the cytoplasm of eggs indicates that they are not transmitted transovarially from mother to offspring. Molecular analyses indicated that the microorganisms which reside in the body of K. quercus are closely related to the entomopathogenic fungi Cordyceps and Ophiocordyceps, which belong to the Sordariomycetes class within the Ascomycota. The role of yeast-like microorganisms to their host insects remains unknown; however, it has been suggested that they may represent newly acquired symbionts.     

Interspecific variation in conspecific negative density dependence can make species less likely to coexist

Conspecific negative density dependence (CNDD) is thought to promote plant species diversity. Theoretical studies showing the importance of CNDD often assumed that all species are equally susceptible to CNDD; however, recent empirical studies have shown species can differ greatly in their susceptibility to CNDD. Using a theoretical model, we show that interspecific variation in CNDD can dramatically alter its impact on diversity. First, if the most common species are the least regulated by CNDD, then the stabilising benefit of CNDD is reduced. Second, when seed dispersal is limited, seedlings that are susceptible to CNDD are at a competitive disadvantage. When parameterised with estimates of CNDD from a tropical tree community in Panama, our model suggests that the competitive inequalities caused by interspecific variation in CNDD may undermine many species’ ability to persist. Thus, our model suggests that variable CNDD may make communities less stable, rather than more stable.     

Stabilizing the Efficiency Beyond 20% with a Mixed Cation Perovskite Solar Cell Fabricated in Ambient Air under Controlled Humidity

Perovskite solar cells have evolved to have compatible high efficiency and stability by employing mixed cation/halide type perovskite crystals as pinhole‐free large grain absorbers. The cesium (Cs)–formamidium–methylammonium triple cation‐based perovskite device fabricated in a glove box enables reproducible high‐voltage performance. This study explores the method to reproduce stable and high power conversion efficiency (PCE) of a triple cation perovskite prepared using a one‐step solution deposition and low‐temperature annealing fully conducted in controlled ambient humidity conditions. Optimizing the perovskite grain size by Cs concentration and solution processes, a route is created to obtain highly uniform, pinhole‐free large grain perovskite films that work with reproducible PCE up to 20.8% and high preservation stability without cell encapsulation for more than 18 weeks. This study further investigates the light intensity characteristics of open‐circuit voltage (V_oc) of small (5 × 5 mm², PCE > 20%) and large (10 × 10 mm², PCE of 18%) devices. Intensity dependence of V_oc shows an ideality factor in the range of 1.7‐1.9 for both devices, implying that the triple cation perovskite involves trap‐assisted recombination loss at the hetero junction interfaces that influences V_oc. Despite relatively high ideality factor, perovskite device is capable of supplying high power conversion efficiency under low light intensity (0.01 Sun) whereas maintaining V_oc over 0.9 V.     

Density‐dependent and density‐independent drivers of population change in Barton Springs salamanders

Understanding population change is essential for conservation of imperiled species, such as amphibians. Worldwide amphibian declines have provided an impetus for investigating their population dynamics, which can involve both extrinsic (density‐independent) and intrinsic (density‐dependent) drivers acting differentially across multiple life stages or age classes. In this study, we examined the population dynamics of the endangered Barton Springs Salamander (Eurycea sosorum) using data from a long‐term monitoring program. We were interested in understanding both the potential environmental drivers (density‐independent factors) and demographic factors (interactions among size classes, negative density dependence) to better inform conservation and management activities. We used data from three different monitoring regimes and multivariate autoregressive state‐space models to quantify environmental effects (seasonality, discharge, algae, and sediment cover), intraspecific interactions among three size classes, and intra‐class density dependence. Results from our primary data set revealed similar patterns among sites and size classes and were corroborated by our out‐of‐sample data. Cross‐correlation analysis showed juvenile abundance was most strongly correlated with a 9‐month lag in aquifer discharge, which we suspect is related to inputs of organic carbon into the aquifer. However, sedimentation limited juvenile abundance at the surface, emphasizing the importance of continued sediment management. Recruitment from juveniles to the sub‐adult size class was evident, but negative density‐dependent feedback ultimately regulated each size class. Negative density dependence may be an encouraging sign for the conservation of E. sosorum because populations that can reach carrying capacity are less likely to go extinct compared to unregulated populations far below their carrying capacity. However, periodic population declines coupled with apparent migration into the aquifer complicate assessments of species status. Although both density‐dependent and density‐independent drivers of population change are not always apparent in time series of animal populations, both have important implications for conservation and management of E. sosorum.