Comparative landscape genetics of two frugivorous bats in a biological corridor undergoing agricultural intensification

Agricultural intensification in tropical landscapes poses a new threat to the ability of biological corridors to maintain functional connectivity for native species. We use a landscape genetics approach to evaluate impacts of expanding pineapple plantations on two widespread and abundant frugivorous bats in a biological corridor in Costa Rica. We hypothesize that the larger, more mobile Artibeus jamaicensis will be less impacted by pineapple than the smaller Carollia castanea. In 2012 and 2013, we sampled 735 bats in 26 remnant forest patches surrounded by different proportions of forest, pasture, crops and pineapple. We used 10 microsatellite loci for A. jamaicensis and 16 microsatellite loci for C. castanea to estimate genetic diversity and gene flow. Canonical correspondence analyses indicate that land cover type surrounding patches has no impact on genetic diversity of A. jamaicensis. However, for C. castanea, both percentage forest and pineapple surrounding patches explained a significant proportion of the variation in genetic diversity. Least‐cost transect analyses (LCTA) and pairwise G″st suggest that for A. jamaicensis, pineapple is more permeable to gene flow than expected, while as expected, forest is the most permeable land cover for gene flow of C. castanea. For both species, LCTA indicate that development may play a role in inhibiting gene flow. The current study answers the call for landscape genetic research focused on tropical and agricultural landscapes, highlights the value of comparative landscape genetics in biological corridor design and management and is one of the few studies of biological corridors in any ecosystem to implement a genetic approach to test corridor efficacy.     

Age‐specific infectious period shapes dynamics of pneumonia in bighorn sheep

Superspreading, the phenomenon where a small proportion of individuals contribute disproportionately to new infections, has profound effects on disease dynamics. Superspreading can arise through variation in contacts, infectiousness or infectious periods. The latter has received little attention, yet it drives the dynamics of many diseases of critical public health, livestock health and conservation concern. Here, we present rare evidence of variation in infectious periods underlying a superspreading phenomenon in a free‐ranging wildlife system. We detected persistent infections of Mycoplasma ovipneumoniae, the primary causative agent of pneumonia in bighorn sheep (Ovis canadensis), in a small number of older individuals that were homozygous at an immunologically relevant genetic locus. Interactions among age‐structure, genetic composition and infectious periods may drive feedbacks in disease dynamics that determine the magnitude of population response to infection. Accordingly, variation in initial conditions may explain divergent population responses to infection that range from recovery to catastrophic decline and extirpation.     

Can root trait diversity explain complementarity effects in a grassland biodiversity experiment?

Aims The positive relationship between plant biodiversity and community productivity is well established. However, our knowledge about the mechanisms underlying these positive biodiversity effects is still limited. One of the main hypotheses is that complementarity in resource uptake is responsible for the positive biodiversity effects: plant species differ in resource uptake strategy, which results in a more complete exploitation of the available resources in space and time when plant species are growing together. Recent studies suggest that functional diversity of the community, i.e. the diversity in functional characteristics ('traits') among species, rather than species richness per se, is important for positive biodiversity effects. However, experimental evidence for specific trait combinations underlying resource complementarity is scarce. As the root system is responsible for the uptake of nutrients and water, we hypothesize that diversity in root traits may underlie complementary resource use and contribute to the biodiversity effects.Methods In a common garden experiment, 16 grassland species were grown in monoculture, 4-species mixtures differing in root trait diversity and 16-species mixtures. The 4-species mixtures were designed to cover a gradient in average rooting depth. Above-ground biomass was cut after one growing season and used as a proxy for plant productivity to calculate biodiversity effects.Important findings Overall, plant mixtures showed a significant increase in biomass and complementarity effects, but this varied greatly between communities. However, diversity in root traits (measured in a separate greenhouse experiment and based on literature) could not explain this variation in complementarity effects. Instead, complementarity effects were strongly affected by the presence and competitive interactions of two particular species. The large variation in complementarity effects and significant effect of two species emphasizes the importance of community composition for positive biodiversity effects. Future research should focus on identifying the traits associated with the key role of particular species for complementarity effects. This may increase our understanding of the links between functional trait composition and biodiversity effects as well as the relative importance of resource complementarity and other underlying mechanisms for the positive biodiversity effects.     

Daily activity patterns of coyotes (Canis latrans) in a tropical deciduous forest of western Mexico

We studied the activity patterns of the coyote (Canis latrans) in a tropical deciduous forest in the Mexican Pacific coast over 3 years. Fifteen coyotes (six females, nine males) were fitted with radio-collars equipped with activity sensors to determine the influence of seasonality (dry vs. wet), gender (males vs. females) and diel intervals (dusk, night, dawn, and day) on activity patterns. We found differences in activity patterns between diel intervals, but the only pair of diel intervals that showed significant differences was dawn (more active) vs. day (less active). We found no differences due to sex or season on any of the four studied diel intervals. Coyote activity patterns in this tropical forest could be responding to prey availability, human avoidance or thermoregulation.     

Reduced connectivity in the self-processing network of schizophrenia patients with poor insight

Lack of insight (unawareness of illness) is a common and clinically relevant feature of schizophrenia. Reduced levels of self-referential processing have been proposed as a mechanism underlying poor insight. The default mode network (DMN) has been implicated as a key node in the circuit for self-referential processing. We hypothesized that during resting state the DMN network would show decreased connectivity in schizophrenia patients with poor insight compared to patients with good insight. Patients with schizophrenia were recruited from mental health care centers in the north of the Netherlands and categorized in groups having good insight (n = 25) or poor insight (n = 19). All subjects underwent a resting state fMRI scan. A healthy control group (n = 30) was used as a reference. Functional connectivity of the anterior and posterior part of the DMN, identified using Independent Component Analysis, was compared between groups. Patients with poor insight showed lower connectivity of the ACC within the anterior DMN component and precuneus within the posterior DMN component compared to patients with good insight. Connectivity between the anterior and posterior part of the DMN was lower in patients than controls, and qualitatively different between the good and poor insight patient groups. As predicted, subjects with poor insight in psychosis showed decreased connectivity in DMN regions implicated in self-referential processing, although this concerned only part of the network. This finding is compatible with theories implying a role of reduced self-referential processing as a mechanism contributing to poor insight.     

Proteasome–caspase–cathepsin sequence leading to tau pathology induced by prostaglandin J2 in neuronal cells

Neurofibrillary tangles (NFT) are a hallmark of Alzheimer's disease. The major neurofibrillary tangle component is tau that is truncated at Asp421 (Δtau), hyperphosphorylated and aggregates into insoluble paired helical filaments. Alzheimer's disease brains also exhibit signs of inflammation manifested by activated astrocytes and microglia, which produce cytotoxic agents among them prostaglandins. We show that prostaglandin (PG) J2, an endogenous product of inflammation, induces caspase-mediated cleavage of tau, generating Δtau, an aggregation prone form known to seed tau aggregation prior to neurofibrillary tangle formation. The initial event observed upon PGJ2-treatment of human neuroblastoma SK-N-SH cells was the build-up of ubiquitinated (Ub) proteins indicating an early disruption of the ubiquitin-proteasome pathway. Apoptosis kicked in later, manifested by caspase activation and caspase-mediated cleavage of tau at Asp421 and poly (ADP-ribose) polymerase. Furthermore, cathepsin inhibition stabilized Δtau suggesting its lysosomal clearance. Upon PGJ2-treatment tau accumulated in a large perinuclear aggregate. In rat E18 cortical neuronal cultures PGJ2-treatment also generated Δtau detected in dystrophic neurites. Levels of Δtau were diminished by caspase 3 knockdown using siRNA. PGD2, the precursor of PGJ2, produced some Δtau. PGE2 generated none. Our data suggest a potential sequence of events triggered by the neurotoxic product of inflammation PGJ2 leading to tau pathology. The accumulation of Ub proteins is an early response. If cells fail to overcome the toxic effects induced by PGJ2, including accumulation of Ub proteins, apoptosis kicks in triggering caspase activation and tau cleavage, the clearance of which by cathepsins could be compromised culminating in tau pathology. Our studies are the first to provide a mechanistic link between inflammation and tau pathology.     

DEFINING TAXON BOUNDARIES IN MEMBERS OF THE MORPHOLOGICALLY AND GENETICALLY PLASTIC GENES CAULERPA (CAULERPALES,CHLOROPHYTA)1

Numerous attempts to capture the morphological variability of the genus Caulerpa have resulted in an unstable classification of numerous varieties and formae. In the present study we attempted to test taxon boundaries by investigating morphological and genetic variation within and between seven taxa of Caulerpa, supposedly belonging to four species, sampled at different sites in a Philippine reef system. Using both field and culture observations, we described the relation between the variability of a set of morphological characters and ecological parameters, such as wave exposure, light intensity, and substrate type. Statistical analyses showed that the limits between two (out of three) ecads of the C. racemosa (Forsskål) J. Agardh complex were obscured by the presence of morphological plasticity. Other studied taxa of Caulerpa (i.e. C. cupressoides [Vahl] C. Agardh, C. serrulata [Forsskål] J. Agardh, and two formae of C. sertularioides [S. Gmelin] Howe) could be grouped based on morphology despite the presence of morphological plasticity. Our results indicated a strong association between light intensity and several quantitative morphological variables. Genetic diversity of these taxa was assessed by partial sequencing chloroplast rbcL and tufA genes and the ycf10‐chlB chloroplast spacer. In all phylogenetic analyses, C. serrulata, C. cupressoides, C. sertularioides, and the three ecads of C. racemosa emerged as distinct genetic units. Despite the presence of morphological plasticity and morphological convergence, a subset of morphological characters traditionally used in taxonomic delimitation still had sufficient discriminative power to recognize the terminal phylogenetic clades.     

Damaging UV radiation and invertebrate predation: conflicting selective pressures for zooplankton vertical distribution in the water column of low DOC lakes

In nature most organisms have to manage conflicting demands of food gathering, predator avoidance, and finding a favorable abiotic environment (oxygen, temperature, etc.) in order to maximize their fitness. In the vertical water column of lakes with high solar ultraviolet radiation (UV) and invertebrate predators, zooplankton face two particularly strong and conflicting selective pressures. During daylight hours invertebrate predators often induce an upward vertical migration of zooplankton prey while potentially damaging UV forces a downward migration. We used 2.2 m long columns suspended vertically in a lake to conduct 2×2 factorial experiments to examine patterns of depth selection behavior by zooplankton in the presence and absence of both the invertebrate predator Chaoborus and UV. We hypothesized that Chaoborus and UV both affect the distribution of zooplankton and a combination of both factors would lead to a narrowing of depth distribution. We found that when Chaoborus were present zooplankton tended to be distributed at shallower depths in the columns, while in the presence of UV they exhibited a deeper distribution. Chaoborus themselves were always found near the bottom of the columns regardless of the UV treatment. Simultaneous exposure to predators and UV resulted in a peak of zooplankton (especially Daphnia catawba) distribution at intermediate depths. In a significant number of cases, depth range was narrowed in response to Chaoborus, UV, or both.