Signatures of an eccentric disc cavity: Dust and gas in IRS 48

We test the hypothesis that the disc cavity in the `transition disc' Oph IRS 48 is carved by an unseen binary companion. We use 3D dust-gas smoothed-particle hydrodynamics simulations to demonstrate that marginally coupled dust grains concentrate in the gas over-density that forms in in the cavity around a low binary mass ratio binary. This produces high contrast ratio dust asymmetries at the cavity edge similar to those observed in the disc around IRS 48 and other transition discs. This structure was previously assumed to be a vortex. However, we show that the observed velocity map of IRS 48 displays a peculiar asymmetry that is not predicted by the vortex hypothesis. We show the unusual kinematics are naturally explained by the non-Keplerian flow of gas in an eccentric circumbinary cavity. We further show that perturbations observed in the isovelocity curves of IRS 48 may be explained as the product of the dynamical interaction between the companion and the disc. The presence of a $\sim$0.4 M$_{\odot}$ companion at a $\sim$10 au separation can qualitatively explain these observations. High spatial resolution line and continuum imaging should be able to confirm this hypothesis.Comment: 9 pages, 7 figures, accepted for publication in MNRA

Swimming capabilities of deep-sea sharks through velocity, anatomical, physiological, and morphological analyses

In marine biology, one of the main objectives is to characterize the ecology of organisms: how they live, move, hunt, reproduce, etc. For that purpose, the study of swimming capabilities remains a feature providing several ecological information, especially for sharks which are mainly active predators. Studies regarding shark swimming capabilities have been initiated a long time ago for shallow-water species. They allowed highlighting differences between species explaining shark distribution, home range but also several internal adaptations related to their locomotor capabilities. While swimming capabilities start to be well known for shallow-water species, information regarding deep-sea sharks is still poorly documented. Indeed, only the speeds of the Greenland shark (Somniosus microcephalus) and the bluntnose sixgills shark (Hexancheus griseus) were measured using satellite telemetry and revealed the slowest velocity recorded for a shark. Other studies have focused on indirect measurements (proxies) of the locomotor muscle metabolism to estimate the swimming capabilities. They have shown that anaerobic metabolism of deep-sea species is lower than their shallow-water counterparts. In contrast, the aerobic metabolism does not show significant difference. Therefore, authors have concluded that deep-sea sharks should have lower swimming capabilities than their shallow-water counterparts. This conclusion is mainly based on two hypotheses: (i) the effect of the cold environment decreasing muscle activity and (ii) the visual interaction hypothesis which suggests that the swimming capabilities of an organism decrease when it lives in a darker environment. However, the low number of deep-sea shark species considered in these studies does not allow to draw this general conclusion for all deep-sea sharks. In this work, we studied the swimming capabilities of several deep-sea sharks from the Squaliformes order. Cruise swimming speed values were obtained using stereo-video analyses. Data analyses have revealed that not all deep-sea sharks swim slowly. Indeed, even if Dalatias licha displayed the lowest speed value ever recorded, and other non-luminous deep-sea sharks intermediate slow cruise swimming speeds, luminous sharks from the Etmopteridae family swim at similar velocities than some shallow-water sharks. This higher cruise swimming speed of Etmopteridae species could be an advantage. Indeed, luminous sharks use their ventral light luminescence to vanish from preys and predators underneath them. It is called couterillumination camouflage. However, their luminescence regulation is under hormonal control which is slow and do not fit with the counterillumination hypothesis which need to modulate quickly its light intensity. In this context, a high velocity might be useful to migrate in the water column in order to match their ventral light with the downwelling light of their environment, this hypothesis is called “isolume follower”. In addition to that, studies of the muscular system were done through red and white muscle fibers quantification and specific enzyme assays. Results highlighted more red muscle in Etmopteridae species with higher aerobic metabolism but lower white muscle and anaerobic metabolism than their non-luminous counterparts and D. licha. These results suggest that Etmotperidae display a muscular system design more for an efficient cruise swimming speed. In contrast, the higher white muscle proportion and anaerobic metabolism of other non-luminous deep-sea sharks suggest higher burst capabilities which might explain why Etmopteridae species are found in stomach contents of these other deep-sea sharks. Study regarding the buoyancy of deep-sea sharks have allowed to confirme that the lift provided by the liver is higher for deep-sea shark species than shallow-water ones. It also provided evidence of relation between the hydrostatic lift and the proportion of red muscle fibers as suggested by Bone in 1979 but never proven. Indeed, sharks with a liver providing more buoyancy display less red muscle fibers across their body. This study is thus the first evidence of the Bone’s hypothesis. Finally studies of morphological features have revealed that Squaliformes sharks displayed different shapes while they were grouped in the same morphotype previously. The spine shape might also have an impact on the velocity but future mechanistic studies should be done on the subject. Also, a new shape of caudal fin was described for D. licha. This caudal fin does not display any fork and should be less efficient for the thrust than heterocercal fins but here again, mechanistic studies should be conducted before obtaining any strong conclusion. This thesis sets up as the first multidisciplinary approach regarding the swimming capabilities of deep-sea sharks revealing differences which give information regarding the ecology of these poorly known species. It also brought new questions, future researches pathways and projects are currently in progress in order to still better understand the ecology of these fascinating animals.(SC - Sciences) -- UCL, 201

Red and white muscle proportions and enzyme activities in mesopelagic sharks

In the last decade, there has been an increase in the study of the ecology of deep-sea organisms. One way to understand an organism's ecology is the study of its metabolism. According to literature, deep-sea sharks possess a lower anaerobic enzyme activity than their shallow-water counterparts, but no difference has been observed regarding their aerobic enzyme activities. These studies have suggested deep-sea sharks should be slow and listless swimmers. However, other studies based on video observations have revealed differences in cruise swimming speed between different species. The present study examined muscles of squaliform sharks, including both luminous and non-luminous species. We combined measurements of the relative amounts of red and white muscle with assays of enzymes that are used as markers for aerobic (citrate synthase, malate dehydrogenase) and anaerobic (lactate dehydrogenase) metabolism, searching for a relationship with cruising speeds. Non-luminous deep-sea species displayed lower aerobic enzyme activities but similar anaerobic enzyme activities than the benthic shallow-water counterpart (Squalus acanthias). Conversely, luminous Etmopteridae species were found to have similar aerobic enzyme activities to S. acanthias but displayed lower anaerobic enzyme activities. Analyses revealed that red muscle proportion and aerobic enzyme activities were positively related to the cruise swimming speed. In contrast, Dalatias licha, which swims at the slowest cruise swimming speed ever recorded, presented a very low aerobic metabolic phenotype (lower aerobic marker enzymes and less red muscle). Finally, the values obtained for white muscle proportion and anaerobic metabolic phenotype suggested a high burst capacity for D. licha and non-luminous sharks

Deep-sea sharks: Relation between the liver's buoyancy and red aerobic muscle volumes, a new approach

Shark's buoyancy depends on two types of force: (i) the hydrostatic force which is mainly provided by their liver filled with low density lipids and (ii) the hydrodynamic force which is provided by the morphology of their body and fins. Shallow-water shark species are usually negatively buoyant, whereas deep-sea shark species have been suggested to display neutral buoyancy. It has been suggested that species that are close to the neutrality would have less red aerobic muscle fibers. Here, we investigated several liver features (the hepatosomatic index, the oil content and the lipid composition) playing a major role regarding the buoyancy of three deep-sea shark species (Etmopterus molleri, Etmopterus spinax and Isistius brasiliensis) and one shallow-water counterpart (Galeus melastomus). We used FT-Raman and FT-MIR spectroscopy to qualify/quantify the lipid composition of their liver. Our results showed that most deep-sea shark species studied have liver features providing more buoyancy than their shallow-water counterparts, appart from E. molleri which shows liver's features that resemble more shallow-water shark species (e.g. G. melastomus). Finally, data regarding liver features of several deep-sea shark species from the literature were added and the red aerobic muscle distribution/proportion of nine species was measured, to reveal how these parameters might be related. Our results showed that sharks characterized by a liver providing more hydrostatic force possess proportionally less red aerobic muscles than sharks having a liver that contributes less to their buoyancy. Therefore, our results i.e. deep-sea shark displaying less red aerobic muscle with a liver providing more buoyancy, support low metabolic rates hence slow swimming speed

Are morphological traits explaining swimming performances of several deep-sea sharks from New Zealand?

Sharks have been present in oceans for more than 400 millions of years and have survived several mass extinctions (Devonian, Permian, Triassic and Cretaceous). Although some morphological features are well preserved between all shark species (cartilaginous skeleton, lack of swim bladder, renewable teeth,...), they show remarkable adaptations to their different lifestyles. Among sharks, data regarding deep-sea species are scares, and especially about their ecology. In this work we focused on deep-sea sharks’ swimming performances. Indeed, as active predators, shark swimming capabilities take part in several essential behaviours such as hunting, escaping, home range, migratory behaviours. While the swimming performances are well studied on shallow-water sharks, only limited data about their deep-sea counterparts are available; at most it is suggested they are slow and lazy swimmers. However, recent study shows significant differences of swimming cruise speed between eight deep-sea sharks from New Zealand. Several studies about the shallow-water species show a high importance of morphological traits related with the swimming performances. Here we investigate what are the morphological traits that could take part in deep-sea sharks swimming cruise speed previously observed. We also measure the traits differences between species and correlate it with their phylogeny. Thirty morphological traits from eight deep-sea species and one surface species (control) were measured. These morphological traits include classical measurements of length from the fins or the body but also geomorphological features and ratios for the rostrum and different fins. First results of the statistical analysis seem to show out that variables like area of the pectoral or caudal fins (which play a major role for locomotion of surface sharks), are not the main factors influencing speed of deep-sea sharks. Conversely, rostrum length, distance between the first and the second dorsal fin with the caudal fin, seem to be factors separating the different speed groups

Etmopteridae bioluminescence: dorsal pattern specificity and aposematic use

Background In the darkness of the ocean, an impressive number of taxa have evolved the capability to emit light. Many mesopelagic organisms emit a dim ventral glow that matches with the residual environmental light in order to camouflage themselves (counterillumination function). Sharks use their luminescence mainly for this purpose. Specific lateral marks have been observed in Etmopteridae sharks (one of the two known luminous shark families) suggesting an inter/intraspecific recognition. Conversely, dorsal luminescence patterns are rare within these deep-sea organisms. Results Here we report evidence that Etmopterus spinax, Etmopterus molleri and Etmopterus splendidus have dorsal luminescence patterns. These dorsal patterns consist of specific lines of luminous organs, called photophores, on the rostrum, dorsal area and at periphery of the spine. This dorsal light seems to be in contrast with the counterilluminating role of ventral photophores. However, skin photophores surrounding the defensive dorsal spines show a precise pattern supporting an aposematism function for this bioluminescence. Using in situ imaging, morphological and histological analysis, we reconstructed the dorsal light emission pattern on these species, with an emphasis on the photogenic skin associated with the spine. Analyses of video footage validated, for the first time, the defensive function of the dorsal spines. Finally, we did not find evidence that Etmopteridae possess venomous spine-associated glands, present in Squalidae and Heterondontidae, via MRI and CT scans. Conclusion This work highlights for the first time a species-specific luminous dorsal pattern in three deep-sea lanternsharks. We suggest an aposematic use of luminescence to reveal the presence of the dorsal spines. Despite the absence of venom apparatus, the defensive use of spines is documented for the first time in situ by video recordings

Étude des transferts de pesticides : site atelier de la baie du Robert 2007-2009

[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAMIt is pertinent to measure hydrological events occurring in a stream and pesticide contents which flow in, as rivers and gutters bring to light events which take place on the related watershed. That's why the Cemagref research unit of Martinique (AEMA), works in partnership with ville du Robert, Ifremer, DIREN and ODE to determine the hydrological polluting flows from Robert bay occupied areas, which generally are small mountain catchments, to coastal zone. Firstly, we took stock of pesticidal molecules. Secondly, we confirmed the influence of seasonal rainfall events on the contents we found. Thirdly, we estimated the annual polluting flow. The novelty is to study occasional gutters and small rivers which were not specially designed as far as hydrological response is concerned.Il est pertinent de mesurer les évènements hydrologiques d'un cours d'eau et les concentrations en pesticides qu'il transporte, car le cours d'eau intègre et révèle les péripéties du bassin versant associé. C'est pourquoi le Cemagref-PRAM, UR Aema, en partenariat avec la ville du Robert, l'Ifremer, la DIREN et l'Office de l'eau de la Martinique a entrepris un programme d'évaluation des flux de molécules à usage phytosanitaire depuis la partie terrestre de la baie du Robert, constituée de versants montagneux de petite dimension, vers la zone littorale. Nous avons tout d'abord dressé un inventaire des molécules présentes. Nous avons ensuite confirmé l'influence de la pluviométrie saisonnière sur les concentrations mesurées. Enfin, nous avons estimé les flux annuels de contaminants. L'originalité de l'étude est de s'intéresser à des cours d'eau intermittents et à des petites rivières dont les réponses hydrologiques ont été peu appréhendées jusqu'à présent

Do Triclosan affect hearing development of Cyprinodon variegatus larvae?

The aquatic environment represents the final sink for many chemicals, including bactericidal agents. Among them Triclosan (TCS) has been shown to affect the thyroid system of teleost. Larval stages are particularly vulnerable to deleterious effects of endocrine disrupters because of potential impairment of fish development and behaviour. Thyroid hormones are critical to the development of the brain and auditory system. Thus, TCS could affect the development of the brain and hearing. The aims of this study were: to investigate hearing development in sheepshead minnows (Cyprinodon variegatus) using the ABR technique (Auditory Brainstem Response) and to investigate the effects of triclosan on hearing development. Exposure to TCS was conducted from fertilization of eggs on at concentrations likely to be found in the environment: 20, 50 and 100 µgl-1. We characterized previously the ontogenic variation of thyroid hormones in embryos and larvae of sheepshead minnows. We observed an increase of thyroid hormones level around the 12th and the 15th day post hatching (dph), that may be associated with the transition from larval to juvenile stage during the development of this species. We concluded, that this period could be defined as a critical exposure window to pollutants. We determined hearing thresholds for sheepshead minnows of different ages. Our sheepshead minnows show ontogenic variations in the hearing ability during their development. At 30 days post hatching, their hearing ability is quite bad, with a narrow bandwidth of detected frequencies. But their hearing ability considerably enhance during their development to reach the adult hearing ability at around 80 days post hatching when this species reach sexual maturity. So we observe during the developmental phase of this fish species clear ontogenic improvements of the hearing ability and they showed an ontogenetic expansion in the frequency bandwidth they were able to detect. The effects of TCS in this development have yet to be determined but will be fully discussed. This study proposes an interesting new endpoint in thyroid disruption research