MAGNETIC NAVIGATION, MAGNETORECEPTION, AND MIGRATION IN FISHES

As the largest and most diverse vertebrate group on the planet, fishes have evolved an impressive array of sensory abilities to overcome the challenges associated with navigating the aquatic realm. Among these, the ability to detect Earth’s magnetic field, or magnetoreception, is phylogenetically widespread and used by fish to guide movements over a wide range of spatial scales ranging from local movements to transoceanic migrations. During the last half century, considerable evidence has accumulated that fishes use Earth’s magnetic field as a compass for maintaining direction (e.g. toward north or south) as well as a kind of “map” or positional sense that encodes information about their location. Yet, despite significant advances in the field, much about the magnetic navigation in fishes remains enigmatic. How fish detect magnetic fields remains unknown and our understanding of the evolutionary origins of vertebrate magnetoreception would benefit greatly from studies that include a wider array of fish taxa. The research presented in the following six chapters provides new evidence that fishes use Earth’s magnetic field in navigation, insights into the possible underlying mechanisms and functional characteristics of the magnetic sense in fishes, as well as advances in methodology for tracking fish movements.Doctor of Philosoph

A magnetic map leads juvenile European eels to the Gulf Stream

Migration allows animals to track the environmental conditions that maximize growth, survival, and reproduction [ 1–3 ]. Improved understanding of the mechanisms underlying migrations allows for improved management of species and ecosystems [ 1–4 ]. For centuries, the catadromous European eel (Anguilla anguilla) has provided one of Europe’s most important fisheries and has sparked considerable scientific inquiry, most recently owing to the dramatic collapse of juvenile recruitment [ 5 ]. Larval eels are transported by ocean currents associated with the Gulf Stream System from Sargasso Sea breeding grounds to coastal and freshwater habitats from North Africa to Scandinavia [ 6, 7 ]. After a decade or more, maturing adults migrate back to the Sargasso Sea, spawn, and die [ 8 ]. However, the migratory mechanisms that bring juvenile eels to Europe and return adults to the Sargasso Sea remain equivocal [ 9, 10 ]. Here, we used a “magnetic displacement” experiment [ 11, 12 ] to show that the orientation of juvenile eels varies in response to subtle differences in magnetic field intensity and inclination angle along their marine migration route. Simulations using an ocean circulation model revealed that even weakly swimming in the experimentally observed directions at the locations corresponding to the magnetic displacements would increase entrainment of juvenile eels into the Gulf Stream System. These findings provide new insight into the migration ecology and recruitment dynamics of eels and suggest that an adaptive magnetic map, tuned to large-scale features of ocean circulation, facilitates the vast oceanic migrations of the Anguilla genu

Dynamic eye colour as an honest signal of aggression

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordAnimal eyes are some of the most widely recognisable structures in nature. Due to their salience to predators and prey, most research has focussed on how animals hide or camouflage their eyes [1]. However, across all vertebrate Classes many species actually express brightly coloured or conspicuous eyes, suggesting they may have also evolved a signalling function. Nevertheless, perhaps due to the difficulty with experimentally manipulating eye appearance, very few species beyond humans [2] have been experimentally shown to use eyes as signals [3]. Using staged behavioural trials we show that Trinidadian guppies (Poecilia reticulata), which can rapidly change their iris colour, predominantly express conspicuous eye colouration when performing aggressive behaviours towards smaller conspecifics. We then show, using a novel visually-realistic robotic system to create a mismatch between signal and relative competitive ability, that eye colour is used to honestly signal aggressive motivation. Specifically, robotic ‘cheats’, i.e. smaller and thus less-competitive robotic fish that displayed aggressive eye colouration when defending a food patch, attracted greater food competition from larger real fish. Our study suggests that eye colour may be an under-appreciated aspect of signalling in animals, shows the utility of our new biomimetic robotic system for investigations in animal behaviour, and provides rare experimental evidence that socially-mediated costs towards low-quality individuals may maintain the honesty of dynamic colour signals.This work was supported by a research grant from the Leverhulme Trust (RPG-2015-047) awarded to D.P.C. and S.K.D. D.P.C. and S.K.D. also acknowledge funding from the Danish Council for Independent Research (DFF – 1323-00105). We are very grateful to Rajendra Mahabir for assistance in the field, to Fiona Moultrie, Joah Madden, Sam Ellis, Ashley Ward, and John Endler for valuable discussion, and to Tom Houslay for advice on the R code to generate the plots

Response to Durif et al.

Our recent study [1] in Current Biology used a magnetic displacement experiment and simulations in an ocean circulation model to provide evidence that young European eels possess a ‘magnetic map’ that can aid their marine migration. Our results support two major conclusions: first, young eels distinguish among magnetic fields corresponding to locations across their marine range; second, for the fields that elicited significantly non-random orientation, swimming in the experimentally observed direction from the corresponding locations would increase entrainment in the Gulf Stream system. In their critique, Durif et al. [2] seem to conflate the separate and potentially independent ‘map step’ and ‘compass step’ of animal navigation. In the map step, an animal derives positional information to select a direction, whereas in the compass step the animal maintains that heading 3, 4. Our experiment was designed such that differences in eel orientation among treatments would indicate an ability to use the magnetic field as a map; the compass cue(s) used by eels was not investigated

Efficacy and safety of subcutaneous tocilizumab in rheumatoid arthritis over 1 year: a UK real-world, open-label study

Objective. The ACT-MOVE study assessed the real-world efficacy and safety of s.c. tocilizumab (TCZSC), provided as monotherapy or in combination with conventional synthetic DMARDs (csDMARDs) over 1 year, in patients with RA and an inadequate response to csDMARD therapy and/or first TNF inhibitor. Methods. In this UK multicentre, open-label phase IIIb study, patients received TCZ-SC 162 mg once weekly for 52 weeks as monotherapy or with csDMARDs. Efficacy and safety were evaluated at baseline, weeks 2 and 4 and every 4 weeks thereafter up to week 52. Results. Of 161 patients who received at least one dose of TCZ-SC, 21 (13.0%) received TCZ-SC alone and 140 (87.0%) TCZ-SC with a csDMARD(s). From baseline to week 52, there was a mean decrease in DAS28-ESR score among all patients (!3.68), and within monotherapy (!3.75) and combination therapy (!3.67) groups. The proportion of patients who achieved DAS28 clinical remission (DAS28-ESR <2.6) at week 52 was 75.4% (95% CI 66.8, 82.8). At the same time point, "80% of patients who remained on TCZ-SC achieved DAS28 clinical remission or had low disease activity (DAS28-ESR "2.6 and #3.2). Overall, 6.2% of patients had at least one serious adverse event (10.2/ 100 patient-years), and there was one death; 11.2% of patients discontinued owing to adverse events. Conclusion. TCZ-SC was effective and tolerated in a real-world setting over 1 year. The efficacy of TCZ-SC was similar whether given as monotherapy or with csDMARDs; its safety profile was consistent with that previously establishe

Solenoid Insert

Solenoid Inser