Ecological responses to experimental glacier-runoff reduction in alpine rivers

International audienceGlacier retreat is a worldwide phenomenon with important consequences for the hydrological cycle and downstream ecosystem structure and functioning. To determine the effects of glacier retreat on aquatic communities, we conducted a 4-year flow manipulation in a tropical glacier-fed stream. Compared with an adjacent reference stream, meltwater flow reduction induces significant changes in benthic fauna community composition in less than 2 weeks. Also, both algal and herbivore biomass significantly increase in the manipulated stream as a response to flow reduction. After the flow reduction ceased, the system requires 14-16 months to return to its pre-perturbation state. These results are supported by a multi-stream survey of sites varying in glacial influence, showing an abrupt increase in algal and herbivore biomass below 11% glacier cover in the catchment. This study shows that flow reduction strongly affects glacier-fed stream biota, prefiguring profound ecological effects of ongoing glacier retreat on aquatic systems

A mathematical model for mechanotransduction at the early steps of suture formation

Growth and patterning of craniofacial sutures are subjected to the effects of mechanical stress. Mechanotransduction processes occurring at the margins of the sutures are not precisely understood. Here, we propose a simple theoretical model based on the orientation of collagen fibres within the suture in response to local stress. We demonstrate that fibre alignment generates an instability leading to the emergence of interdigitations. We confirm the appearance of this instability both analytically and numerically. To support our model, we use histology and synchrotron x-ray microtomography and reveal the fine structure of fibres within the sutural mesenchyme and their insertion into the bone. Furthermore, using a mouse model with impaired mechanotransduction, we show that the architecture of sutures is disturbed when forces are not interpreted properly. Finally, by studying the structure of sutures in the mouse, the rat, an actinopterygian (\emph{Polypterus bichir}) and a placoderm (\emph{Compagopiscis croucheri}), we show that bone deposition patterns during dermal bone growth are conserved within jawed vertebrates. In total, these results support the role of mechanical constraints in the growth and patterning of craniofacial sutures, a process that was probably effective at the emergence of gnathostomes, and provide new directions for the understanding of normal and pathological suture fusion

Synthesis of Isocoumarin via PTSA-Catalyzed Annulation of Diarylalkynes

International audiencep-Toluenesulfonic acid (PTSA) in EtOH was used as a mild acid-catalyst for the annulation of various functionalized diarylalkynes under microwave irradiation. This free-metal process allowed the synthesis of a range of 3-arylsubstituted isocoumarins in good yields

Influence of substrate types and morphological traits on movement behavior in a toad and newt species

Background Inter-patch movements may lead to genetic mixing, decreasing both inbreeding and population extinction risks, and is hence a crucial aspect of amphibian meta-population dynamics. Traveling through heterogeneous landscapes might be particularly risky for amphibians. Understanding how these species perceive their environment and how they move in heterogeneous habitats is an essential step in explaining metapopulation dynamics and can be important for predicting species’ responses to climate change and for conservation policy and management. Methods Using an experimental approach, the present study focused on the movement behavior (crossing speed and number of stops) on different substrates mimicking landscape components (human-made and natural substrates) in two amphibian species contrasting in locomotion mode: the common toad (Bufo bufo), a hopping and burrowing anuran and the marbled newt (Triturus marmoratus), a walking salamander. We tested the hypothesis that species reaction to substrate is dependent on specific ecological requirements or locomotion modes because of morphological and behavioral differences. Results In both species, substrate type influenced individual crossing speed, with individuals moving faster on soil than on concrete substrate. We also demonstrated that long-legged individuals moved faster than individuals with short legs. In both species, the number of stops was higher in females than in males. In common toads, the number of stops did not vary between substrates tested, whereas in marbled newts the number of stops was higher on concrete than on soil substrate. Discussion We highlighted that concrete substrate (mimicking roads) negatively affect the crossing speed of both studied species, with an effect potentially higher in marbled newts. Our findings corroborate negative effects of such heterogeneous landscapes on movement behavior of two amphibian species, which may have implications for the dynamics of metapopulations

Marking techniques in the Marbled Newt (Triturus marmoratus): PIT-Tag and tracking device implant protocols

Individual marking has become essential for studying population dynamics and ecological requirements. However, marking small-bodied species such as amphibians is becoming a challenge in the last decades. Amphibian surveys may require to mark manually individuals, using toe clipping, polymers and pigments, or passive integrated transponders (PIT-tags). Even if ethics committees have recently recommend avoiding toe clipping in amphibians, the use of PIT-tags led to controversial results because low tag retention reported in some studies. Here, we describe a protocol of potentially life-long PIT-tag marking in a protected species, the marbled newt Triturus marmoratus. In addition, we also detailed a second procedure of surgery for the implantation of transmitters needed in radio-tracking surveys. During both procedures, we found that the newt phase (either aquatic or terrestrial) strongly affected the anesthesia duration. Indeed, newts in aquatic phase were more quickly anesthetized than newts under terrestrial phase. We then recommend to pay attention of this physiological particularity when performing this kind of procedure. Improving our knowledge on ecological requirements and population dynamics of this species is crucial for management and conservation plans, and could be extended to other large newts

Marking techniques in the Marbled Newt (<em>Triturus marmoratus</em>): PIT-Tag and tracking device implant protocols

Individual marking has become essential for studying population dynamics and ecological requirements. However, marking small-bodied species such as amphibians is becoming a challenge in the last decades. Amphibian surveys may require to mark manually individuals, using toe clipping, polymers and pigments, or passive integrated transponders (PIT-tags). Even if ethics committees have recently recommend avoiding toe clipping in amphibians, the use of PIT-tags led to controversial results because low tag retention reported in some studies. Here, we describe a protocol of potentially life-long PIT-tag marking in a protected species, the marbled newt Triturus marmoratus. In addition, we also detailed a second procedure of surgery for the implantation of transmitters needed in radio-tracking surveys. During both procedures, we found that the newt phase (either aquatic or terrestrial) strongly affected the anesthesia duration. Indeed, newts in aquatic phase were more quickly anesthetized than newts under terrestrial phase. We then recommend to pay attention of this physiological particularity when performing this kind of procedure. Improving our knowledge on ecological requirements and population dynamics of this species is crucial for management and conservation plans, and could be extended to other large newts

Multiple glacial refugia and contemporary dispersal shape the genetic structure of an endemic amphibian from the Pyrenees

Historical factors (colonization scenarios, demographic oscillations) and contemporary processes (population connectivity, current population size) largely contribute to shaping species’ present-day genetic diversity and structure. In this study, we use a combination of mitochondrial and nuclear DNA markers to understand the role of Quaternary climatic oscillations and present-day gene flow dynamics in determining the genetic diversity and structure of the newt Calotriton asper (Al. Dugès, 1852), endemic to the Pyrenees. Mitochondrial DNA did not show a clear phylogeographic pattern and presented low levels of variation. In contrast, microsatellites revealed five major genetic lineages with admixture patterns at their boundaries. Approximate Bayesian computation analyses and linear models indicated that the five lineages likely underwent separate evolutionary histories and can be tracked back to distinct glacial refugia. Lineage differentiation started around the Last Glacial Maximum at three focal areas (western, central and eastern Pyrenees) and extended through the end of the Last Glacial Period in the central Pyrenees, where it led to the formation of two more lineages. Our data revealed no evidence of recent dispersal between lineages, whereas borders likely represent zones of secondary contact following expansion from multiple refugia. Finally, we did not find genetic evidence of sex-biased dispersal. This work highlights the importance of integrating past evolutionary processes and present-day gene flow and dispersal dynamics, together with multilocus approaches, to gain insights into what shaped the current genetic attributes of amphibians living in montane habitats.info:eu-repo/semantics/publishedVersio