Regional vs local drivers of phylogenetic and species diversity in stream fish communities

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A common mechanism for ATP hydrolysis in ABC transporter and helicase superfamilies

ABC (ATP-binding cassette) transporters and helicases are large superfamilies of seemingly unrelated proteins, whose functions depend on the energy provided by ATP hydrolysis. Comparison of the 3D structures of their nucleotide-binding domains reveals that, besides two well-characterized ATP-binding signatures, the folds of their nucleotide-binding sites are similar. Furthermore, there are striking similarities in the positioning of residues thought to be important for ATP binding or hydrolysis. Interestingly, structures have recently been obtained for two ABC proteins that are not involved in transport activities, but that have a function related to DNA modification. These ABC proteins, which contain a nucleotide-binding site akin to those of typical ABC transporters, might constitute the missing link between the two superfamilies.     

The “Weight” of Words on the Forearms During Relaxation

In this paper we examined the influence of repetition of weight-related sentences on the involuntary pressure forces of the forearms, when in a relaxed state. These forces were involuntary oscillations, exerted by muscle movements of the breathing-cycle and muscle movements of the arm on force sensors. We constructed a linguistic bio-mechanical system (Ablasmi), where in each arm of a padded relaxation chair contained special sensors that were specifically designed to detect the pressure forces of each forearm while participants listened to the specific recorded weight-related sentences. In this experiment we used some classic sentences, such as “your right/left arm is heavy,” inspired by Autogenic Training (Schultz in Le training autogene. Paris, PUF, 1974) and some sentences, such as “your right/left arm is made of lead,” inspired by Grossmann’s relaxation technique. We observed that when the recorded sentences were directed to the right arm there was a significant increase of involuntary pressure forces on the right forearm. Additionally, we observed the same effect on the left forearm for the sentences directed to the left forearm. Thus, we believe we have provided experimental evidence of a definite linguistic effect of weight-related sentences on the involuntary pressure forces of the forearms. The implications of these findings are discussed.

Comparison of crystal structures of human androgen receptor ligand-binding domain complexed with various agonists reveals molecular determinants responsible for binding affinity

Androgens exert their effects by binding to the highly specific androgen receptor (AR). In addition to natural potent androgens, AR binds a variety of synthetic agonist or antagonist molecules with different affinities. To identify molecular determinants responsible for this selectivity, we have determined the crystal structure of the human androgen receptor ligand-binding domain (hARLBD) in complex with two natural androgens, testosterone (Testo) and dihydrotestosterone (DHT), and with an androgenic steroid used in sport doping, tetrahydrogestrinone (THG), at 1.64, 1.90, and 1.75 A resolution, respectively. Comparison of these structures first highlights the flexibility of several residues buried in the ligand-binding pocket that can accommodate a variety of ligand structures. As expected, the ligand structure itself (dimension, presence, and position of unsaturated bonds that influence the geometry of the steroidal nucleus or the electronic properties of the neighboring atoms, etc.) determines the number of interactions it can make with the hARLBD. Indeed, THG--which possesses the highest affinity--establishes more van der Waals contacts with the receptor than the other steroids, whereas the geometry of the atoms forming electrostatic interactions at both extremities of the steroid nucleus seems mainly responsible for the higher affinity measured experimentally for DHT over Testo. Moreover, estimation of the ligand-receptor interaction energy through modeling confirms that even minor modifications in ligand structure have a great impact on the strength of these interactions. Our crystallographic data combined with those obtained by modeling will be helpful in the design of novel molecules with stronger affinity for the AR.     

Development of a multimetric approach to assess perturbation of benthic macrofauna in Zostera noltii beds

Biotic indices based on soft-bottom macrozoobenthic communities are currently used throughout Europe to assess the ecological quality of coastal and transitional water bodies according to the European Water Framework Directive. However, the performance of the currently available biotic indices still has to be tested against a variety of different impact sources. In particular, physical perturbations have received much less attention than other kind of disturbances. This study consisted in testing the capacity of currently available uni- (BOPA, AMBI and BENTIX) and multivariate (M-AMBI) Biotic Indices to assess the ecological impact of the destruction of a Zostera noltii seagrass bed in Arcachon Bay (France) following sediment deposits. Changes of habitat after this physical perturbation were hardly assessed by any of these Biotic Indices whereas analysis of the benthic community showed drastic changes of structure following the perturbation and no recovery after 15 months. This study demonstrates that these Biotic Indices must be integrated into a multimetric approach which describes better the biological integrity of the benthic community by including a complementary set of metrics. A new multimetric approach, named MISS (Macrobenthic Index of Sheltered Systems) is proposed. MISS correctly highlighted the destruction of the seagrass beds, by using 16 metrics describing the biological integrity of the macrofauna.     

Novel feeding interactions amplify the impact of species redistribution on an Arctic food web

Species are redistributing globally in response to climate warming, impacting ecosystem functions and services. In the Barents Sea, poleward expansion of boreal species and a decreased abundance of Arctic species are causing a rapid borealization of the Arctic communities. This borealization might have profound consequences on the Arctic food web by creating novel feeding interactions between previously non co‐occurring species. An early identification of new feeding links is crucial to predict their ecological impact. However, detection by traditional approaches, including stomach content and isotope analyses, although fundamental, cannot cope with the speed of change observed in the region, nor with the urgency of understanding the consequences of species redistribution for the marine ecosystem. In this study, we used an extensive food web (metaweb) with nearly 2,500 documented feeding links between 239 taxa coupled with a trait data set to predict novel feeding interactions and to quantify their potential impact on Arctic food web structure. We found that feeding interactions are largely determined by the body size of interacting species, although species foraging habitat and metabolic type are also important predictors. Further, we found that all boreal species will have at least one potential resource in the Arctic region should they redistribute therein. During 2014–2017, 11 boreal species were observed in the Arctic region of the Barents Sea. These incoming species, which are all generalists, change the structural properties of the Arctic food web by increasing connectance and decreasing modularity. In addition, these boreal species are predicted to initiate novel feeding interactions with the Arctic residents, which might amplify their impact on Arctic food web structure affecting ecosystem functioning and vulnerability. Under the ongoing species redistribution caused by environmental change, we propose merging a trait‐based approach with ecological network analysis to efficiently predict the impacts of range‐shifting species on food webs.